Respiratory effects of trunk inclination in obese and non-obese patients mechanically ventilated for ARDS

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Benites, Shailesh Bihari, Romina Battiato, Alejandro Bruhn, and 11 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7060912/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Oct, 2025 Read the published version in Critical Care → Version 1 posted 9 You are reading this latest preprint version Abstract Background Adjusting trunk inclination in patients with acute respiratory distress syndrome directly affects physiological variables such as respiratory mechanics and PaCO 2 levels. These effects may vary according to the body mass index (BMI) due to differences in lung and chest wall compliance, highlighting the need for further investigation to clarify the clinical relevance of body position across patient subgroups. Methods A secondary analysis compared the physiological effects of increasing trunk inclination angles between mechanically ventilated patients with obesity (BMI ≥ 30 kg/m 2 ) and those without obesity (BMI < 30 kg/m 2 ). Results Data from 159 patients collected across seven individual studies were analyzed. Sixty-five patients with obesity presented a greater decrease in respiratory system compliance (-7.5 [-10; -5] mL/cmH 2 O; p < 0.001) compared to ninety-four patients without obesity (-3.5 [-7; -0.08] mL/cmH 2 O; p = 0.045). Lung compliance decreased in obese patients (-7.8 [-12.4; -3.3] mL/cmH 2 O; p < 0.001), whereas no significant changes were observed in patients without obesity (-5.9 [-14.2; 2.3] mL/cmH 2 O; p = 0.160). Chest wall compliance decreased by -42.9 [-63.2; -22.6] mL/cmH 2 O (p< 0.001) in obese patients and by -47.7 [-95.3; -0.15] mL/cmH 2 O in non-obese patients (p = 0.049). PaCO 2 increased in obese patients by 4.6 [1.4; 7.8] mmHg (p= 0.004) but not in patients without obesity (2.5 [-0.6; 5.6] (p = 0.113). No significant differences were observed in PaO 2 /F I O 2 between phases. Conclusions Increasing the trunk inclination angle in patients during passive ventilation reduces respiratory system, lung, and chest wall compliance. This effect was more pronounced in patients with obesity. Moreover, only this population exhibited an increase in PaCO 2 . These findings highlight the importance of individualized respiratory management strategies, including optimizing bed inclination angles tailored to each patient's condition. ARDS body position supine position compliance of respiratory system obese Figures Figure 1 Figure 2 Figure 3 Background Trunk inclination in the supine position in patients with acute respiratory distress syndrome (ARDS) has generated increasing scientific interest because of its effects on respiratory physiology [1, 2] In many patients with ARDS, controlled mechanical ventilation combined with increased trunk inclination has been linked to decreased respiratory system compliance (C RS ) and increased driving pressure [3, 4]. These positional adjustments were associated with an impairment in ventilatory efficiency for carbon dioxide removal, suggesting lung overdistension in semi-recumbent position [5]. On the other hand, oxygenation may improve in this position, especially in patients with an increase in end-expiratory lung volume (EELV) [6, 7]. Specifically, in mechanically ventilated obese patients with ARDS, transitioning from a supine to a semi-recumbent position has been reported to reduce C RS and the arterial partial pressure of carbon dioxide (PaCO 2 ) compared to patients without obesity [8]. However, this intervention was evaluated in the short term in a single-center study with a small patient cohort, which limits the generalizability of the findings and strength of the conclusions. Moreover, the differential physiological effects of changing trunk inclination between obese and non-obese patients may vary among individuals owing to differences in lung and chest wall mechanics. Therefore, conducting subanalyses of previous studies to assess the effects of increasing the angle of trunk inclination in patients with and without obesity, while integrating data from various physiological variables, could offer a more comprehensive understanding of its impact in an area that remains largely unexplored. We hypothesized that in patients with ARDS, increasing the angle of trunk inclination would result in more pronounced alterations in respiratory system compliance (C RS ) in individuals with obesity (body mass index (BMI) ≥ 30 kg/m²) than in those without obesity (BMI < 30 kg/m²). Accordingly, the primary objective of this study was to analyze the effect of increasing the angle of trunk inclination on C RS in ARDS patients with and without obesity. Secondary objectives were to evaluate the effects of trunk inclination on partitioned respiratory mechanics, arterial oxygen partial pressure to inspired oxygen fraction ratio (PaO 2 /F I O 2 ), PaCO 2 , ventilatory variables, and EELV. Methods A secondary data analysis was conducted based on previously published studies that evaluated the effects of trunk inclination on respiratory variables in patients with ARDS under passive mechanical ventilation. All included studies received approval from their respective local research ethics boards. The studies included in this analysis were identified through a previously conducted scoping review on the topic [1]. The lead and corresponding authors were contacted directly via email and asked to dichotomize their original datasets according to body mass index (BMI), classifying them into two predefined categories: non-obese (BMI < 30 kg/m 2 ) and obese (BMI ≥ 30 kg/m 2 ). After stratification, demographic, clinical, and physiological data were provided for pooled and subgroup analyses. Additionally, data from a study that included only non-obese patients were also included in the analysis [9]. The patients included in the selected studies were adults (≥18 years) with ARDS, invasively mechanically ventilated for fewer than seven days, and under deep sedation or neuromuscular blockade. Each study included in the analysis assessed the respiratory effects of increasing the trunk inclination angle by comparing two different postures in the same patient (Additional file eTable 1). The measured effect corresponded to the transition from the baseline supine position (regardless of the initial inclination angle) to the more elevated trunk position. The effects of trunk inclination were recorded for each patient using the same positive end-expiratory pressure (PEEP) level at each step. The designs and methodological characteristics of the analyzed studies, including population, mechanical ventilation mode, the timing of PEEP setting, the tool used to determine baseline PEEP, body position during PEEP titration, baseline ventilator settings, protocol phases, and data extraction, are provided in the Additional file (eTable 1). Data extraction All studies assessed each variable of interest at the end of each step, which lasted between 10 and 60 minutes. The data analysis included the following variables: respiratory mechanics, oxygenation (PaO 2 /F I O 2 ), EELV, PaCO 2 , ventilatory ratio (VR), and ventilatory inefficiency variables (Bohr dead space (VD Bohr /VT), and the phase III slope of the capnogram (SIII) normalized with fraction of expired CO 2 (F E CO 2 ) (SnIII)). Outcomes Primary outcome: Changes in C RS Secondary outcomes: Changes in partitioned respiratory mechanics (lung and chest wall compliance (C CW )), oxygenation, PaCO 2 , ventilatory ratio (VR), ventilatory inefficiency data, and EELV. Statistical analysis Continuous variables from each study were recorded as means and standard deviations (SD). For each study, the treatment effect was represented by the difference in the means between the two positions and was presented using a forest plot. A weighted measure of variability was calculated by considering the variances and sample sizes to obtain the combined standard deviation. The standard error (SE) indicates the uncertainty of estimating treatment effects. The weight of each study and the calculation of the overall effect were recorded using the fixed-effects model (common) and the random effects model (random). Confidence intervals (CI): Inverse Variance (IV), fixed; 95% confidence interval for the mean difference. A result was considered statistically significant when the confidence interval did not include zero value. Two-tailed Z-test to assess whether the combined mean difference between positions significantly differs from zero. A p <0.05 was considered statistically significant. No imputation for missing data was conducted. Analyses were carried out using complete-case data only, based on the information reported in the original studies. Statistical analyses were conducted using RStudio version 4.4.1. Results Data from 159 patients collected across seven individual studies were analyzed [ 3 – 5 , 8 – 11 ]. Sixty-five patients were included in the group with BMI ≥ 30 kg/m 2 , and 94 patients in the group with BMI < 30 kg/m 2 . The mean BMI was 37.7 ± 4 kg/m 2 and 24.8 ± 2.8 kg/m 2 for obese and non-obese patients, respectively. Changes in C RS were recorded for all the patients. Partitioned respiratory mechanics (lung compliance and C CW ) were assessed in 99 patients (46 obese and 53 non-obese). PaO 2 /F I O 2 was obtained for 114 patients (49 obese and 65 non-obese), and PaCO 2 and VR were obtained for 97 patients (49 obese and 48 non-obese). One study analyzed the effects of EELV [ 10 ], and another analyzed the effects of volumetric capnography on ventilatory efficiency [ 5 ]. The Bohr dead space and SnIII were evaluated in a subset of 12 obese and 10 non-obese patients. The baseline characteristics of the analyzed studies are shown in Table 1 . Table 1 Baseline characteristics of the analyzed studies BMI < 30 kg/m 2 (n = 94) BMI ≥ 30 kg/m 2 (n = 65) P - value Demographics and overall patients’ characteristics Body mass index (kg/m 2 ) mean (SD) 25.2 (2.8) 35.5 (4) < 0.001 Age (years) mean (SD) 63 (10) 62 (11) 0.56 Sex Male / Female (%) 64% / 36% 53% / 47% - Days of mechanical ventilation prior to study onset 3 (2) 3 (2) - Ventilatory settings and mechanics PEEP cmH 2 O mean (SD) 10.5 (1.2) 12.2 (2.3) < 0.001 Peak inspiratory pressure cmH 2 O mean (SD) 29.6 (4.7) 31 (4.4) 0.057 Driving pressure cmH 2 O mean (SD) 13.9 (1.3) 12.3 (1.5) < 0.001 C RS (mL/cmH 2 O) mean (SD) 34.5 (9) 34 (9) 0.731 Respiratory rate (SD) 22.8 (4.8) 20.7 (10.1) 0.122 Gas exchange and ABG parameters PaO 2 /F I O 2 (mm Hg) mean (SD) 148 (54) 163 (43) 0.053 PaO 2 /F I O 2 ≥ 200 mmHg (n) 8 10 - PaO 2 /F I O 2 ≥ 100 - < 200 mmHg (n) 35 31 - PaO 2 /F I O 2 < 100 mmHg (n) 36 15 - PaCO 2 mmHg mean (SD) 47 (7.7) 49 (5.6) 0.059 Aetiology Pulmonary ARDS (%) 91.5% 84.6% - Extrapulmonary ARDS (%) 8.5% 15.4% - PEEP: positive end-expiratory pressure; C RS : Compliance of Respiratory System; PaO 2 /F I O 2 : arterial oxygen partial pressure to inspired oxygen fraction ratio; PaCO 2 : arterial partial pressure of carbon dioxide; ABG: arterial blood gas. The respiratory mechanics and arterial blood gas results are summarized in Tables 2 (obese patients) and 3 (non-obese patients). Grouped data from the included studies are reported in both tables. Each study-level dataset is presented in the supplementary additional file for detailed reference. Table 2 Patients with obesity (BMI ≥ 30 kg/m 2 ). Transition from supine position to a more inclined trunk position. BMI ≥ 30 Kg/m 2 Supine position A more inclined trunk position Mean difference [95% CI] P value PEEP (cmH 2 O) 11.6 (1.8) 11.6 (1.8) 0 [− 0.5; 0.5] 1 Peak inspiratory pressure (cmH 2 O) 30.6 (3.7) 33.4 (3.9) 2.8 [1.5; 4.1] < 0.001 Driving Pressure (cmH 2 O) 10.8 (3) 13.5 (3.7) 2.8 [1.9; 3.7] < 0.001 C RS mL/cmH 2 O 40.2 (9.2) 32.6 (8.6) − 7.5 [− 10; − 5] < 0.001 Lung Compliance 54.4 (17.1) 45.8 (17.5) − 7.8 [− 12.4; − 3.3] < 0.001 Compliance CW mL/cmH 2 O 167.8 (55.7) 120.6 (34.1) − 42.9 [− 63.2; − 22.6] < 0.001 Lung Elastance / Elastance RS 0.77 (0.11) 0.71 (0.11) − 0.06 [− 0.11; − 0.01] 0.011 Elastance CW/ Elastance RS 0.24 (0.11) 0.29 (0.11) 0.05 [0.00; − 0.1] 0.040 Ventilatory ratio (VR) 1.7 (0.36) 1.8 (0.38) 0.1 [− 0.04; − 0.24] 0.150 PaCO 2 (mmHg) 44.9 (5.1) 49 (5.6) 4.6 [ 1.4; 7.8] 0.004 PaO 2 /F I O 2 (mmHg) 146 (41) 158 (43) 11.9 [− 4.3; 28.2] 0.151 Data are expressed as weighted mean differences using a random-effects model and Z-test. PEEP: Positive-end expiratory pressure. C RS : Compliance of respiratory system. C CW : Chest Wall. RS: respiratory system. PaCO 2 : arterial partial pressure of carbon dioxide. PaO 2 /F I O 2 : arterial oxygen partial pressure to inspired oxygen fraction ratio. Table 3 Patients without obesity (BMI < 30 kg/m 2 ). Transition from supine position to a more inclined trunk position. BMI < 30 Kg/m 2 Supine position A more inclined trunk position Mean difference [95% CI] P value PEEP (cm H 2 O) 10.7 (2.5) 10.7 (2.5) 0 [− 0.45; 045] 1 Peak inspiratory pressure (cmH 2 O) 30.5 (4.1) 32.7 (4.6) 2.2 [-0.1; 4.5] 0.060 Driving Pressure (cm H 2 O) 11.8 (3.5) 14.1 (4.8) 2.4 [0.47; 4.44] 0.023 C RS mL/cmH 2 O 37.4 (11.2) 33 (10) − 3.5 [− 7; − 0.08] 0.045 Lung compliance 50.5 (19) 43.8 (17) − 5.9 [− 14.2; 2.36] 0.160 Compliance CW mL/cmH 2 O 173.9 (90) 127.1 (49.1) − 47.7 [− 95.3; − 0.15] 0.049 Lung Elastance/ Elastance RS 0.78 (0.11) 0.75 (0.11) − 0.02 [− 0.07; 0.03] 0.566 Elastance CW/ Elastance RS 0.22 (0.12) 0.27 (0.12) 0.04 [− 0.01; − 0.09] 0.141 Ventilatory ratio (VR) 1.58 (0.32) 1.63 (0.35) 0.04 [− 0.09; 0.17] 0.512 PaCO 2 (mmHg) 47 (7.7) 49.3 (8.4) 2.5 [− 0.6; 5.6] 0.113 PaO 2 /F I O 2 (mmHg) 142 (48) 142 (54) − 0.76 [− 16.4; 14.9] 0.923 Data are expressed as weighted mean differences using a random-effects model and Z-test. PEEP: Positive-end expiratory pressure. C RS : Compliance of respiratory system. C CW : Chest Wall. RS: respiratory system. PaCO 2 : arterial partial pressure of carbon dioxide. PaO 2 /F I O 2 : arterial oxygen partial pressure to inspired oxygen fraction ratio. Effect of trunk inclination adjustment on respiratory mechanics In patients with a BMI ≥ 30 kg/m 2 , the transition from supine to a more inclined trunk position significantly decreased C RS from 40.2 ± 9.2 to 32.6 ± 8.6 mL/cm H 2 O, with a weighted mean difference of − 7.5 [85% CI − 10; − 5] mL/cm H 2 O (p < 0.001). In patients with a BMI < 30 kg/m 2 ,, the transition from supine to a more inclined trunk position reduced C RS from 37.4 ± 11.2 to 33 ± 10 mL/cm H 2 O, corresponding to a weighted mean difference of − 3.5 [95% CI − 7; − 0.1] mL/cm H 2 O (p = 0.045). In addition, when C RS changes were compared between the two BMI groups, obese patients exhibited a significantly greater reduction than non-obese patients (p = 0.04) (Fig. 1; see Table 1 A-B in the Additional file). Transitioning from supine to a more inclined trunk position. TE (Treatment Effect): Estimated effect for each study, representing the mean difference in Compliance of respiratory system between the obese and non-obese groups. SE (Standard Error): Weight (common/random): IV (Inverse Variance), Fixed; 95% CI, 95% confidence interval (CI) for the estimated effect under a fixed-effects model. Heterogeneity within subgroups: Tau²: An estimate of variance between studies. Chi²: Chi-squared statistic to assess heterogeneity. I²: Percentage of total variation attributable to heterogeneity between studies. A value of 0% indicated low heterogeneity. Each group is represented by a black diamond, indicating the combined effect (meta-analysis) for that subgroup. The endpoints of diamond reflect the 95% confidence interval (CI). The total at the bottom of the group provides a combined result for all studies within that subgroup. Vertical dotted line: This is the weighted average of all included studies. Continuous vertical line at value 0: Null effect. In patients with a BMI ≥ 30 kg/m 2 , the transition from supine to a more inclined trunk position led to a significant decrease in lung compliance, from 54.4 ± 17.1 to 45.8 ± 17.5 mL/cm H 2 O, with a weighted mean difference of − 7.8 [95% CI − 12.4; − 3.3] mL/cm H 2 O (p < 0.001). In contrast, in patients with a BMI < 30 kg/m 2 , lung compliance showed no significant decrease, from 50.5 ± 19 to 43.8 ± 17 mL/cm H 2 O with a weighted mean difference of − 5.9 [95% CI − 14.2; 2.3] (p = 0.160) under the same positional change (Fig. 2A). In patients with a BMI ≥ 30 kg/m 2 , transitioning from supine to a more inclined trunk position significantly decreased C CW from 167.8 ± 55.7 to 120.6 ± 34.1 with a weighted mean difference of − 42.9 [95% CI − 63.2; − 22.6] mL/cm H 2 O (p < 0.001). Similarly, in patients with a BMI < 30 kg/m 2 , transitioning from supine to a more inclined trunk position reduced C CW from 173.9 ± 90 to 127.1 ± 49.1 mL/cm H 2 O, corresponding to a weighted mean difference − 47.7 [95% CI − 95.3; − 0.15] mL/cm H 2 O (p = 0.049) (Fig. 2B). In addition, no significant differences were observed in lung and chest wall compliance between the two BMI groups (p = 0.59 and p = 0.76, respectively). Transitioning from supine to a more inclined trunk position. A- Lung Compliance. B- Chest Wall Compliance. TE (Treatment Effect): Estimated effect for each study, representing the mean difference in Compliance of respiratory system between the obese and non-obese groups. SE (Standard Error): Weight (common/random): IV (Inverse Variance), Fixed; 95% CI, 95% confidence interval (CI) for the estimated effect under a fixed-effects model. Heterogeneity within subgroups: Tau²: An estimate of variance between studies. Chi²: Chi-squared statistic to assess heterogeneity. I²: Percentage of total variation attributable to heterogeneity between studies. A value of 0% indicated low heterogeneity. Each group is represented by a black diamond, indicating the combined effect (meta-analysis) for that subgroup. The endpoints of diamond reflect the 95% confidence interval (CI). The total at the bottom of the group provides a combined result for all studies within that subgroup. Vertical dotted line: This is the weighted average of all included studies. Continuous vertical line at value 0: Null effect. In obese patients, a change in trunk inclination from the supine to a more inclined trunk position resulted in a significant decrease in the ratio between lung elastance and Elastance of respiratory system (E L /E RS ) and a concurrent increase in its counterpart of the ratio between chest wall elastance and elastance of respiratory system (E CW /E RS ) (Table 2 ). In contrast, no significant changes in these variables were observed among the non-obese patients (Table 3 ; see supplementary Figs. 1 and 2 in the Additional file). Effect of trunk inclination adjustment on oxygenation In patients with a BMI ≥ or < 30 kg/m 2 , no significant differences were observed in PaO 2 /F I O 2 between phases (supine vs. a more inclined trunk position) (Tables 2 and 3 ). Additionally, no differences were observed when PaO 2 /F I O 2 changes were compared between the two BMI groups (p = 0.28) (supplementary Fig. 4 in the Additional file). Effects of Trunk Inclination on PaCO 2 and Ventilatory Variables In patients with BMI ≥ 30 kg/m 2 , PaCO 2 increased when transitioning from supine to a more inclined trunk position (Table 2 ). In contrast, among patients with BMI < 30 kg/m 2 , changes in trunk inclination did not result in significant variations in PaCO 2 (Table 3 ). When comparing PaCO 2 changes between the two BMI groups, obese patients exhibited a numerically higher but insignificant increase in PaCO 2 compared to non-obese individuals (p = 0.37; supplementary Fig. 5 in the additional file). The VR remained unchanged across the different trunk inclinations in both BMI subgroups (Tables 2 and 3 ). In the same line with PaCO 2 results, in obese patients, the transition from supine to a more inclined trunk position VD Bohr /V T increased from 0.40 ± 0.06 to 0.49 ± 0.05 [mean difference 0.09; 95% CI: 0.03–0.12; p = 0.0012], whereas in non-obese patients, it changed from 0.42 ± 0.08 to 0.47 ± 0.09 [mean difference 0.05; 95% CI, -0.03–0.13; p = 0.198]. In obese patients, SnIII increased from 0.7 (± 0.39) to 1.3 (± 0.67) [mean difference 0.6; 95% CI: 0.12–1.06] (P = 0.016), whereas in non-obese patients, it changed from 1.00 ± 0.7 to 1.82 ± 1.22 [mean difference 0.81; 95% CI: -0.13–1.76]; (p = 0.088). (Supplementary Fig. 6–9 in the Additional File) Effect of trunk inclination adjustment on EELV One included study assessed the effect of trunk inclination on EELV. No significant changes in EELV were observed in either group (see Table 11 in the Additional File). Discussion The main findings of the present analysis were as follows: 1) a more inclined trunk position led to a reduction in C RS in both obese and non-obese patients; 2) this decrease in C RS was more pronounced in patients with a BMI ≥ 30 kg/m 2 than in those with a BMI < 30 kg/m 2 ; and 3) only obese patients exhibited a significant increase in PaCO 2 following this postural change. These findings provide comparative insights into the effects of body positioning on respiratory mechanics in obese and nonobese patients. Additionally, these findings suggest that patients with obesity may represent a distinct subgroup characterized by greater susceptibility to changes in respiratory mechanics in response to variations in trunk inclination. Accordingly, particular attention should be paid to the physiological impact of this intervention in this population. In obese and non-obese patients, alveolar collapse in dependent lung regions is promoted by gravitational forces, which generate superimposed pressure [12] and a vertical pleural pressure gradient [13]. These two mechanisms operate simultaneously, contributing to alveolar collapse, and their relative impact is likely to vary according to the severity of lung injury and the thoracic positioning [14]. Superimposed pressure describes the pressure exerted by the weight of the overlying tissue on more dependent pulmonary regions due to gravitational forces. This hydrostatic force, generated by lung weight, is considered a determinant of the pleural pressure gradient [14, 15]. Furthermore, increased body weight and fat around the thorax are key factors that influence superimposed pressure, resulting in greater mechanical compression in dependent regions [12, 13]. The pleural pressure gradient refers to the pressure difference within the pleural space along the vertical axis of the lungs [16]. Although lung morphology and elastance of both the lung and chest wall appear similar between obese and non-obese patients, obesity is characterized by a reduced lung apex-to-base length and an increased sternum-to-vertebral diameter [14]. In supine-flat obese patients, this altered thoracic geometry increases the anteroposterior dimension of the lungs, thereby steepening the gravitational pleural pressure gradient. This anatomical configuration likely contributes to a rightward shift of the pressure-volume relationship, reflecting the greater external mechanical load imposed by the chest wall [14]. In addition, obese patients exhibit increased intra-abdominal fat and pressure [17], which may lead to a greater upward displacement of the abdominal contents against the diaphragm. This, in turn, causes distortion of the thoracic compartment structures, contributing to altered respiratory mechanics and reduced lung compliance [18]. Therefore, transitioning from a supine to a more inclined trunk position, owing to the lung's morphological characteristics in obese patients and the effect of superimposed weight [14], should increase the vertical height of the lung and amplify the pleural pressure gradient [19]. Although the volume of the abdominal contents does not change when moving to a semi-recumbent position, the shape of the abdominal cavity is likely distorted. Distortion leads to an increase in intra-abdominal pressure, which is transmitted primarily to the thoracic compartment [20-22]. This positive upward pressure is likely to be concentrated in the dependent juxtadiaphragmatic regions. Consequently, the ventilation distribution in mechanically ventilated obese patients is preferentially directed toward regions with greater compliance, such as non-dependent lung areas. This phenomenon is physiologically translated as a rightward shift of the pressure-volume curve [23], indicating a greater susceptibility to alterations in lung mechanics in obese patients (Figure 3). Our analysis shows that both obese and non-obese patients with ARDS experienced a reduction in C CW when transitioning from supine to a more inclined trunk position. This effect was more pronounced and precise in obese patients (with less variability in data dispersion) than in nonobese individuals. Additionally, we observed a decline in lung compliance, specifically in obese individuals. Although the reduction in C RS and C CW associated with increased trunk inclination could not directly indicate lung injury, the decline in lung compliance observed in obese patients following this postural change likely reflects an increased risk of ventilator-induced lung injury, particularly when the optimal PEEP levels are not appropriately adjusted. Moreover, in patients with obesity, the transition from supine to a more inclined trunk position led to a consistent decrease in E L /E RS and a significant increase in its counterpart, E CW /E RS , indicating a greater contribution of the elastic load on chest wall to overall respiratory mechanics. In contrast, non-obese patients exhibited no significant changes in the relative distribution of elastic loads between the lungs and the chest wall. To understand the relationship between trunk angle and changes in the pressure–volume curve in obese and non-obese patients, it is essential to consider the results obtained from optimizing PEEP in various body positions. Marrazzo et al. demonstrated that optimized PEEP requires adjustments to be made for each change in the chest position. In the supine-flat position, the optimal PEEP levels are, on average, 5 cmH 2 O higher than in the semi-recumbent position. Therefore, when the optimal PEEP is set in the supine-flat position, transitioning to a semi-recumbent position may require reducing the PEEP to avoid alveolar overdistension [24]. Therefore, maintaining the same PEEP levels after transitioning from a supine flat to a semi-recumbent position may contribute to excessive EELV and regional hyperinflation, particularly in patients with low lung recruitment ability. In this context, it is plausible that trunk elevation produces physiological effects similar to those induced by increasing PEEP in non-recruitable lung regions, leading to increased pulmonary vascular resistance and deleterious effects on the right ventricle [2, 25, 26]. Regarding gas exchange, we observed that PaCO 2 levels worsened when patients were transitioned from supine to a more inclined trunk position, with this effect being more pronounced in the obese subgroup. To explain this phenomenon, one study employed volumetric capnography to evaluate the impact of trunk inclination on ventilatory inefficiency [5]. Under pressure-controlled ventilation, transitioning to a more inclined trunk position resulted in a significant reduction in tidal volume, suggesting impairment in lung mechanics associated with postural changes. This was accompanied by increased VD Bohr /VT and PaCO 2 , which likely reflected alveolar overdistension. Moreover, the slope of phase III of the capnogram, normalized to the fraction of expired CO 2 (F E CO 2 ), also increased significantly, suggesting that postural changes in obese individuals may exacerbate ventilation-perfusion mismatch [5]. Collectively, these observations reinforce the link between reduced lung compliance and impaired CO 2 clearance in obesity, indicating that greater trunk inclination may predispose to alveolar overdistension and compromised gas exchange. Regarding the effects of changes in trunk inclination on oxygenation, it is known that improvements in oxygenation with trunk inclination have only been observed in certain patients with ARDS, particularly those who experience a notable increase in EELV [6, 7]. This effect is believed to result from reduced dorsal atelectasis due to less compression of the dependent lung regions by the cephalad displacement of the abdomen and diaphragm [27] and from a decrease in apical and mid-apical pleural pressures, which increases transpulmonary pressure, the principal determinant of lung distension [28]. Another study demonstrated that when PEEP was titrated in the semi-recumbent position (30°) and remained unchanged during changes in trunk inclination, transitioning patients from the 30° to the flat supine position (0°) resulted in a decline in oxygenation and EELV. This deterioration likely reflects alveolar derecruitment induced by postural shift without PEEP readjustment. Re-elevation to 30° reversed these effects, suggesting recruitment of previously collapsed lung regions. However, further increases in inclination to 60° and 90° did not yield additional improvements and were associated with a decline in oxygenation and EELV [2]. Therefore, an excessively upright posture without adequate PEEP adjustment may promote overdistension. In our analysis, the transition from supine to a more inclined trunk position did not result in statistically significant changes in PaO₂/F I O₂ or EELV in the obese or non-obese subgroups. However, the consistent trend toward improved oxygenation in obese patients with increased trunk inclination may reflect an underlying physiological effect that warrants confirmation in larger cohorts, particularly regarding the trunk angle at which the optimal PEEP is set. Final comments and clinical implications This is the first multicenter analysis to identify obesity as a clinical condition associated with heightened respiratory physiological response to increased trunk inclination during passive mechanical ventilation. These findings strengthen the external validity and provide clinically relevant insights into the interplay between body positioning, respiratory mechanics, and patient phenotypes. Therefore, accurate documentation of bed inclination and comprehensive respiratory assessment are essential for objectively evaluating positioning strategies in each patient with ARDS. Grounded in the principles of precision medicine, this personalized strategy is gaining recognition as a critical element of effective clinical care and underscores the need for mechanical ventilation approaches tailored to individual patient characteristics. Limitations The limitations of these analyzed results include several considerations. While the study stratified patients according to BMI status, the analysis included heterogeneous forms of ARDS, including C-ARDS, pulmonary ARDS, and extrapulmonary ARDS. Each of these entities may exhibit distinct pathophysiological profiles, potentially influencing respiratory mechanics and response to postural changes, thereby introducing variability in the observed outcomes. BMI was dichotomized, and a definitive cut-off value could not be established to identify accurately which patients might benefit most from this intervention. These subpopulations may exhibit different responses to changes in trunk inclination, depending on the body position in which PEEP was optimized in each study. Likewise, in many of the included studies, the calculation of airway opening pressure was lacking, which may have influenced the accuracy of the reported outcomes. Additionally, the evaluation time for each posture across all included studies did not exceed 60 minutes, leaving the long-term persistence of these effects unknown. Conclusions Increasing the trunk inclination angle in patients during passive ventilation reduces respiratory system, lung, and chest wall compliance. This effect was more pronounced in patients with obesity. Moreover, only this population exhibited an increase in PaCO 2 . These findings highlight the importance of individualized respiratory management strategies, including optimizing bed inclination angles tailored to each patient's condition. Abbreviations ARDS Acute respiratory distress syndrome C RS Respiratory system compliance EELV End-expiratory lung volume PaCO 2 Pressure of carbon dioxide BMI Body mass index PaO 2 /F I O 2 PaO 2 over the fraction of inspired oxygen PEEP Positive end-expiratory pressure C CW Chest Wall Compliance VR Ventilatory ratio VD Bohr /VT Bohr dead space fraction SnIII the phase III slope of the capnogram (SIII) normalized with fraction of expired CO2 Declarations Supplementary Information The online version contains supplementary material Acknowledgments None. Funding None. Availability of data and materials The data sets used and analyzed during the current study are available from the corresponding author on reasonable request. Contributions MHB, GB, AB, and JR contributed to the conception and design of the study. All authors performed the title and abstract screening. MHB, RB, TL, FM, JJM, JS, CG, MM, SB, UW, JD, and JR performed the data extraction. MHB, RB, TL, FM, JJM, JS, CG, MM, SB, UW, ELVC, and JR organized the data and created the characteristic tables. MHB and RB performed the data analysis. MHB, TL, FM, JJM, JS, CG, MM, SB, UW, JD, AB, GB, ELVC, JD, and JR wrote the first draft of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version. Ethics declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests Dr. Costa received funding from Magnamed and Timpel. Dr. Mehdi Mezidi reports receiving congress fees from Pfizer, unrelated to the present work. The other authors declare that they have no competing interests. ORCID IDs: 0000-0001-6366-534X (MHB) References Benites MH, Zapata-Canivilo M, Poblete F, Labbe F, Battiato R, Ferre A, et al. Physiological and clinical effects of trunk inclination adjustment in patients with respiratory failure: a scoping review and narrative synthesis. Crit Care. 2024;28(1):228. Bouchant L, Godet T, Arpajou G, Aupetitgendre L, Cayot S, Guerin R, et al. Physiological effects and safety of bed verticalization in patients with acute respiratory distress syndrome. Crit Care. 2024;28(1):262. Marrazzo F, Spina S, Zadek F, Forlini C, Bassi G, Giudici R, et al. Ventilation distribution during changes in trunk inclination in ARDS patients. Respir Care. 2023;22:11175. Marrazzo F, Spina S, Forlini C, Guarnieri M, Giudici R, Bassi G, et al. Effects of trunk inclination on respiratory mechanics in patients with COVID-19-associated acute respiratory distress syndrome: let’s always report the angle!. Am J Respir Crit Care Med. 2022;205:582–4. Benites MH, Torres D, Poblete F, Labbe F, Bachmann MC, Regueira TE, et al. Effects of changes in trunk inclination on ventilatory efficiency in ARDS patients: quasi-experimental study. Intensive Care Med Exp. 2023;11(1):65. Dellamonica J, Lerolle N, Sargentini C, Hubert S, Beduneau G, Di Marco F, et al. Effect of different seated positions on lung volume and oxygenation in acute respiratory distress syndrome. Intensive Care Med. 2013;39:1121–7. Richard JC, Maggiore SM, Mancebo J, Lemaire F, Jonson B, Brochard L. Effects of vertical positioning on gas exchange and lung volumes in acute respiratory distress syndrome. Intensive Care Med. 2006;32:1623–6. Bihari S, Wiersema UF. Changes in respiratory mechanics with trunk inclination differs between obese and non-obese ARDS patients. Chest. 2024;165(3):583–9. Chen X, Xiong R, Zhang M, Guan C, Feng L, Yao Z, et al. Effects of sitting position on ventilation distribution determined by electrical impedance tomography in ventilated ARDS patients. Intensive Crit Care Nurs. 2024;85:103782. Mezidi M, Guérin C. Effect of body position and inclination in supine and prone position on respiratory mechanics in acute respiratory distress syndrome. Intensive Care Med. 2019;45(2):292–294. Selickman J, Crooke PS, Tawfik P, Dries DJ, Gattinoni L, Marini JJ. Paradoxical Positioning: Does "Head Up" Always Improve Mechanics and Lung Protection?. Crit Care Med. 2022;50(11):1599–1606. Spina S, Mantz L, Xin Y, Moscho DC, Ribeiro De Santis Santiago R, Grassi L, et al. The pleural gradient does not reflect the superimposed pressure in patients with class III obesity. Crit Care. 2024;28(1):306. Pelosi P, D'Andrea L, Vitale G, Pesenti A, Gattinoni L. Vertical gradient of regional lung inflation in adult respiratory distress syndrome. Am J Respir Crit Care Med. 1994;149(1):8–13. Chiumello D, Colombo A, Algieri I, Mietto C, Carlesso E, Crimella F, et al. Effect of body mass index in acute respiratory distress syndrome. Br J Anaesth. 2016;116(1):113–21. Gattinoni L, Pesenti A. The concept of "baby lung". Intensive Care Med. 2005;31(6):776–84. Pelosi P, D'Andrea L, Vitale G, Pesenti A, Gattinoni L. Vertical gradient of regional lung inflation in adult respiratory distress syndrome. Am J Respir Crit Care Med. 1994;149(1):8–13. Smit M, Werner MJM, Lansink-Hartgring AO, Dieperink W, Zijlstra JG, van Meurs M. How central obesity influences intra-abdominal pressure: a prospective, observational study in cardiothoracic surgical patients. Ann Intensive Care. 2016;6(1):99. Pirrone M, Fisher D, Chipman D, Imber DAE, Corona J, Mietto C, et al. Recruitment maneuvers and positive end-expiratory pressure titration in morbidly obese ICU patients. Crit Care Med. 2016;44:300–7. West JB, Matthews FL. Stresses, strains, and surface pressures in the lung caused by its weight. J Appl Physiol. 1972;32(3):332–-45. Zhou Y, He H, Cui N, Wang X, Long Y, Liu D, et al. Elevation of the head of bed reduces splanchnic blood flow in patients with intra-abdominal hypertension. BMC Anesthesiol. 2023;23(1):133. McBeth PBZD, Widder S, Cheatham M, Zengerink I, Glowa J, Kirkpatrick AW. Effect of patient postioining on intraabdominal pressure monitoring. Am J Surg. 2007;193:644–7. Vasquez DG, Berg-Copas GM, WettaHall R, Berg-Copas GM, Wetta-Hall R. Influence of semirecumbent position on intra-abdominal pressure as measured by bladder pressure. J Surg Res. 2007;139:280–5. Pelosi P, Croci M, Ravagnan I, Cerisara M, Vicardi P, Lissoni A, et al. Respiratory system mechanics in sedated, paralyzed, morbidly obese patients. J Appl Physiol (1985). 1997;82(3):811–8. Marrazzo F, Spina S, Zadek F, Forlini C, Bassi G, Giudici R, et al. PEEP titration is markedly affected by trunk inclination in mechanically ventilated patients with COVID-19 ARDS: a physiologic, cross-over study. J Clin Med. 2023;12(12):3914. Benites MH, Retamal J. Effect of trunk upward verticalization on pulmonary vascular resistance in ARDS. Crit Care. 2025;29(1):93. Cappio Borlino S, Hagry J, Lai C, Rocca E, Fouqué G, Rosalba D, et al. The Effect of Positive End-Expiratory Pressure on Pulmonary Vascular Resistance Depends on Lung Recruitability in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2024;210(7):900–907. Rezoagli E, Bastia L, Brochard L, Bellani G. Physical manoeuvres in patients with ARDS and low compliance: bedside approaches to detect lung hyperinflation and optimise mechanical ventilation. Eur Respir J. 2023;61(5):2202169. D’Angelo E, Bonanni MV, Michelini S, et al. Topography of the pleural surface pressure in rabbits and dogs. Respir Physiol. 1970;8: 204–229. Additional Declarations Competing interest reported. Dr. Costa received funding from Magnamed and Timpel. Dr. Mehdi Mezidi reports receiving congress fees from Pfizer, unrelated to the present work. The other authors declare that they have no competing interests. Supplementary Files AdditionalFile.docx Cite Share Download PDF Status: Published Journal Publication published 28 Oct, 2025 Read the published version in Critical Care → Version 1 posted Editorial decision: Revision requested 07 Aug, 2025 Reviews received at journal 04 Aug, 2025 Reviews received at journal 01 Aug, 2025 Reviewers agreed at journal 11 Jul, 2025 Reviewers agreed at journal 11 Jul, 2025 Reviewers invited by journal 11 Jul, 2025 Editor assigned by journal 08 Jul, 2025 Submission checks completed at journal 07 Jul, 2025 First submitted to journal 06 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7060912","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":484179594,"identity":"e6588ed5-9a15-4172-8c33-967dca8d2dae","order_by":0,"name":"Martín H. 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Dr. Costa received funding from Magnamed and Timpel.\nDr. Mehdi Mezidi reports receiving congress fees from Pfizer, unrelated to the present work.\nThe other authors declare that they have no competing interests.","formattedTitle":"Respiratory effects of trunk inclination in obese and non-obese patients mechanically ventilated for ARDS","fulltext":[{"header":"Background","content":"\u003cp\u003eTrunk inclination in the supine position in patients with acute respiratory distress syndrome (ARDS) has generated increasing scientific interest because of its effects on respiratory physiology [1, 2] In many patients with ARDS, controlled mechanical ventilation combined with increased trunk inclination has been linked to decreased respiratory system compliance (C\u003csub\u003eRS\u003c/sub\u003e) and increased driving pressure [3, 4]. These positional adjustments were associated with an impairment in ventilatory efficiency for carbon dioxide removal, suggesting lung overdistension in semi-recumbent position [5]. On the other hand, oxygenation may improve in this position, especially in patients with an increase in end-expiratory lung volume (EELV) [6, 7]. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSpecifically, in mechanically ventilated obese patients with ARDS, transitioning from a supine to a semi-recumbent position has been reported to reduce C\u003csub\u003eRS\u003c/sub\u003e and the arterial partial pressure of carbon dioxide (PaCO\u003csub\u003e2\u003c/sub\u003e) compared to patients without obesity [8]. However, this intervention was evaluated in the short term in a single-center study with a small patient cohort, which limits the generalizability of the findings and strength of the conclusions. Moreover, the differential physiological effects of changing trunk inclination between obese and non-obese patients may vary among individuals owing to differences in lung and chest wall mechanics. Therefore, conducting subanalyses of previous studies to assess the effects of increasing the angle of trunk inclination in patients with and without obesity, while integrating data from various physiological variables, could offer a more comprehensive understanding of its impact in an area that remains largely unexplored.\u003c/p\u003e\n\u003cp\u003eWe hypothesized that in patients with ARDS, increasing the angle of trunk inclination would result in more pronounced alterations in respiratory system compliance (C\u003csub\u003eRS\u003c/sub\u003e) in individuals with obesity (body mass index (BMI) ≥ 30 kg/m²) than in those without obesity (BMI \u0026lt; 30 kg/m²). Accordingly, the primary objective of this study was to analyze the effect of increasing the angle of trunk inclination on C\u003csub\u003eRS\u003c/sub\u003e in ARDS patients with and without obesity. Secondary objectives were to evaluate the effects of trunk inclination on partitioned respiratory mechanics, arterial oxygen partial pressure to inspired oxygen fraction ratio (PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e), PaCO\u003csub\u003e2\u003c/sub\u003e, ventilatory variables, and EELV.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eA secondary data analysis was conducted based on previously published studies that evaluated the effects of trunk inclination on respiratory variables in patients with ARDS under passive mechanical ventilation. All included studies received approval from their respective local research ethics boards.\u003c/p\u003e\n\u003cp\u003eThe studies included in this analysis were identified through a previously conducted scoping review on the topic [1]. The lead and corresponding authors were contacted directly via email and asked to dichotomize their original datasets according to body mass index (BMI), classifying them into two predefined categories: non-obese (BMI \u0026lt; 30 kg/m\u003csup\u003e2\u003c/sup\u003e) and obese (BMI ≥ 30 kg/m\u003csup\u003e2\u003c/sup\u003e). After stratification, demographic, clinical, and physiological data were provided for pooled and subgroup analyses. Additionally, data from a study that included only non-obese patients were also included in the analysis [9].\u003c/p\u003e\n\u003cp\u003eThe patients included in the selected studies were adults (≥18 years) with ARDS, invasively mechanically ventilated for fewer than seven days, and under deep sedation or neuromuscular blockade. Each study included in the analysis assessed the respiratory effects of increasing the trunk inclination angle by comparing two different postures in the same patient (Additional file eTable 1). The measured effect corresponded to the transition from the baseline supine position (regardless of the initial inclination angle) to the more elevated trunk position.\u003c/p\u003e\n\u003cp\u003eThe effects of trunk inclination were recorded for each patient using the same positive end-expiratory pressure (PEEP) level at each step. The designs and methodological characteristics of the analyzed studies, including population, mechanical ventilation mode, the timing of PEEP setting, the tool used to determine baseline PEEP, body position during PEEP titration, baseline ventilator settings, protocol phases, and data extraction, are provided in the Additional file (eTable 1).\u003c/p\u003e\n\u003cp\u003eData extraction\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll studies assessed each variable of interest at the end of each step, which lasted between 10 and 60 minutes. The data analysis included the following variables: respiratory mechanics, oxygenation (PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e), EELV, PaCO\u003csub\u003e2\u003c/sub\u003e, ventilatory ratio (VR), and ventilatory inefficiency variables (Bohr dead space (VD\u003csub\u003eBohr\u003c/sub\u003e/VT), and the phase III slope of the capnogram (SIII) normalized with fraction of expired CO\u003csub\u003e2\u003c/sub\u003e\u0026nbsp; (F\u003csub\u003eE\u003c/sub\u003eCO\u003csub\u003e2\u003c/sub\u003e) (SnIII)).\u003c/p\u003e\n\u003cp\u003eOutcomes\u003c/p\u003e\n\u003cp\u003ePrimary outcome: Changes in C\u003csub\u003eRS\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSecondary outcomes: Changes in partitioned respiratory mechanics (lung and chest wall compliance (C\u003csub\u003eCW\u003c/sub\u003e)), oxygenation, PaCO\u003csub\u003e2\u003c/sub\u003e, ventilatory ratio (VR), ventilatory inefficiency data, and EELV.\u003c/p\u003e\n\u003cp\u003eStatistical analysis\u003c/p\u003e\n\u003cp\u003eContinuous variables from each study were recorded as means and standard deviations (SD). For each study, the treatment effect was represented by the difference in the means between the two positions and was presented using a forest plot. A weighted measure of variability was calculated by considering the variances and sample sizes to obtain the combined standard deviation. The standard error (SE) indicates the uncertainty of estimating treatment effects. The weight of each study and the calculation of the overall effect were recorded using the fixed-effects model (common) and the random effects model (random). Confidence intervals (CI): Inverse Variance (IV), fixed; 95% confidence interval for the mean difference. \u0026nbsp;A result was considered statistically significant when the confidence interval did not include zero value. Two-tailed Z-test to assess whether the combined mean difference between positions significantly differs from zero. A p \u0026lt;0.05 was considered statistically significant. No imputation for missing data was conducted. Analyses were carried out using complete-case data only, based on the information reported in the original studies. Statistical analyses were conducted using RStudio version 4.4.1.\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eData from 159 patients collected across seven individual studies were analyzed [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e]. Sixty-five patients were included in the group with BMI\u0026thinsp;\u0026ge;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, and 94 patients in the group with BMI\u0026thinsp;\u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e. The mean BMI was 37.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4 kg/m\u003csup\u003e2\u003c/sup\u003e and 24.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8 kg/m\u003csup\u003e2\u003c/sup\u003e for obese and non-obese patients, respectively. Changes in C\u003csub\u003eRS\u003c/sub\u003e were recorded for all the patients. Partitioned respiratory mechanics (lung compliance and C\u003csub\u003eCW\u003c/sub\u003e) were assessed in 99 patients (46 obese and 53 non-obese). PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was obtained for 114 patients (49 obese and 65 non-obese), and PaCO\u003csub\u003e2\u003c/sub\u003e and VR were obtained for 97 patients (49 obese and 48 non-obese). One study analyzed the effects of EELV [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e], and another analyzed the effects of volumetric capnography on ventilatory efficiency [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e]. The Bohr dead space and SnIII were evaluated in a subset of 12 obese and 10 non-obese patients. The baseline characteristics of the analyzed studies are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eBaseline characteristics of the analyzed studies\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBMI\u0026thinsp;\u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;94)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBMI\u0026thinsp;\u0026ge;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;65)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e- value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDemographics and overall patients\u0026rsquo; characteristics\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBody mass index (kg/m\u003csup\u003e2\u003c/sup\u003e) mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25.2 (2.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35.5 (4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAge (years) mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e63 (10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e62 (11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSex Male / Female (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e64% / 36%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e53% / 47%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDays of mechanical ventilation prior to study onset\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVentilatory settings and mechanics\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePEEP cmH\u003csub\u003e2\u003c/sub\u003eO mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.5 (1.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.2 (2.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeak inspiratory pressure cmH\u003csub\u003e2\u003c/sub\u003eO mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29.6 (4.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31 (4.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.057\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDriving pressure cmH\u003csub\u003e2\u003c/sub\u003eO mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.9 (1.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.3 (1.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003eRS\u003c/sub\u003e (mL/cmH\u003csub\u003e2\u003c/sub\u003eO) mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.5 (9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34 (9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.731\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRespiratory rate (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.8 (4.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20.7 (10.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.122\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGas exchange and ABG parameters\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (mm Hg) mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e148 (54)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e163 (43)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.053\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026ge; 200 mmHg (n)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026ge; 100 - \u0026lt; 200 mmHg (n)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026lt; 100 mmHg (n)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e mmHg mean (SD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47 (7.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e49 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.059\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAetiology\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePulmonary ARDS (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e91.5%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.6%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eExtrapulmonary ARDS (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.5%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.4%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003ePEEP: positive end-expiratory pressure; C\u003csub\u003eRS\u003c/sub\u003e: Compliance of Respiratory System; PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e: arterial oxygen partial pressure to inspired oxygen fraction ratio; PaCO\u003csub\u003e2\u003c/sub\u003e: arterial partial pressure of carbon dioxide; ABG: arterial blood gas.\u003c/p\u003e\n\u003cp\u003eThe respiratory mechanics and arterial blood gas results are summarized in Tables\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e (obese patients) and 3 (non-obese patients). Grouped data from the included studies are reported in both tables. Each study-level dataset is presented in the supplementary additional file for detailed reference.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePatients with obesity (BMI\u0026thinsp;\u0026ge;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e). Transition from supine position to a more inclined trunk position.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBMI\u0026thinsp;\u0026ge;\u0026thinsp;30 Kg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSupine\u003c/p\u003e\n \u003cp\u003eposition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eA more inclined trunk position\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean difference [95% CI]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePEEP (cmH\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.6 (1.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.6 (1.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 [\u0026minus;\u0026thinsp;0.5; 0.5]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeak inspiratory pressure (cmH\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.6 (3.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33.4 (3.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.8 [1.5; 4.1]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDriving Pressure\u003c/p\u003e\n \u003cp\u003e(cmH\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.8 (3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.5 (3.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.8 [1.9; 3.7]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003eRS\u003c/sub\u003e mL/cmH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40.2 (9.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.6 (8.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;7.5 [\u0026minus;\u0026thinsp;10; \u0026minus;\u0026thinsp;5]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLung Compliance\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e54.4 (17.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45.8 (17.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;7.8 [\u0026minus;\u0026thinsp;12.4; \u0026minus;\u0026thinsp;3.3]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCompliance CW mL/cmH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e167.8 (55.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e120.6 (34.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;42.9 [\u0026minus;\u0026thinsp;63.2; \u0026minus;\u0026thinsp;22.6]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLung Elastance / Elastance RS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.77 (0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.71 (0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;0.06 [\u0026minus;\u0026thinsp;0.11; \u0026minus;\u0026thinsp;0.01]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eElastance CW/ Elastance RS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.24 (0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.29 (0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.05 [0.00; \u0026minus;\u0026thinsp;0.1]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVentilatory ratio (VR)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.7 (0.36)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.8 (0.38)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1 [\u0026minus;\u0026thinsp;0.04; \u0026minus;\u0026thinsp;0.24]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.150\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.9 (5.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e49 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.6 [ 1.4; 7.8]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e146 (41)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e158 (43)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.9 [\u0026minus;\u0026thinsp;4.3; 28.2]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.151\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eData are expressed as weighted mean differences using a random-effects model and Z-test. PEEP: Positive-end expiratory pressure. C\u003csub\u003eRS\u003c/sub\u003e: Compliance of respiratory system. C\u003csub\u003eCW\u003c/sub\u003e: Chest Wall. RS: respiratory system. PaCO\u003csub\u003e2\u003c/sub\u003e: arterial partial pressure of carbon dioxide. PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e: arterial oxygen partial pressure to inspired oxygen fraction ratio.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePatients without obesity (BMI\u0026thinsp;\u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e). Transition from supine position to a more inclined trunk position.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBMI\u0026thinsp;\u0026lt;\u0026thinsp;30 Kg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSupine\u003c/p\u003e\n \u003cp\u003eposition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eA more inclined trunk position\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean difference\u003c/p\u003e\n \u003cp\u003e[95% CI]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePEEP (cm H\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.7 (2.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.7 (2.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 [\u0026minus;\u0026thinsp;0.45; 045]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeak inspiratory pressure (cmH\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.5 (4.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.7 (4.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.2 [-0.1; 4.5]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.060\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDriving Pressure\u003c/p\u003e\n \u003cp\u003e(cm H\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.8 (3.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.1 (4.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4 [0.47; 4.44]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.023\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003eRS\u003c/sub\u003e mL/cmH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.4 (11.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33 (10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;3.5 [\u0026minus;\u0026thinsp;7; \u0026minus;\u0026thinsp;0.08]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.045\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLung compliance\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50.5 (19)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.8 (17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;5.9 [\u0026minus;\u0026thinsp;14.2; 2.36]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.160\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCompliance CW mL/cmH\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e173.9 (90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e127.1 (49.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;47.7 [\u0026minus;\u0026thinsp;95.3; \u0026minus;\u0026thinsp;0.15]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.049\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLung Elastance/ Elastance RS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.78 (0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75 (0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;0.02 [\u0026minus;\u0026thinsp;0.07; 0.03]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.566\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eElastance CW/ Elastance RS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.22 (0.12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.27 (0.12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.04 [\u0026minus;\u0026thinsp;0.01; \u0026minus;\u0026thinsp;0.09]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.141\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVentilatory ratio (VR)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.58 (0.32)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.63 (0.35)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.04 [\u0026minus;\u0026thinsp;0.09; 0.17]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.512\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47 (7.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e49.3 (8.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5 [\u0026minus;\u0026thinsp;0.6; 5.6]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.113\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e142 (48)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e142 (54)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;0.76 [\u0026minus;\u0026thinsp;16.4; 14.9]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.923\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eData are expressed as weighted mean differences using a random-effects model and Z-test. PEEP: Positive-end expiratory pressure. C\u003csub\u003eRS\u003c/sub\u003e: Compliance of respiratory system. C\u003csub\u003eCW\u003c/sub\u003e: Chest Wall. RS: respiratory system. PaCO\u003csub\u003e2\u003c/sub\u003e: arterial partial pressure of carbon dioxide. PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e: arterial oxygen partial pressure to inspired oxygen fraction ratio.\u003c/p\u003e\n\u003cp\u003eEffect of trunk inclination adjustment on respiratory mechanics\u003c/p\u003e\n\u003cp\u003eIn patients with a BMI\u0026thinsp;\u0026ge;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, the transition from supine to a more inclined trunk position significantly decreased C\u003csub\u003eRS\u003c/sub\u003e from 40.2\u0026thinsp;\u0026plusmn;\u0026thinsp;9.2 to 32.6\u0026thinsp;\u0026plusmn;\u0026thinsp;8.6 mL/cm H\u003csub\u003e2\u003c/sub\u003eO, with a weighted mean difference of \u0026minus;\u0026thinsp;7.5 [85% CI \u0026minus;\u0026thinsp;10; \u0026minus;\u0026thinsp;5] mL/cm H\u003csub\u003e2\u003c/sub\u003eO (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In patients with a BMI\u0026thinsp;\u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e,, the transition from supine to a more inclined trunk position reduced C\u003csub\u003eRS\u003c/sub\u003e from 37.4\u0026thinsp;\u0026plusmn;\u0026thinsp;11.2 to 33\u0026thinsp;\u0026plusmn;\u0026thinsp;10 mL/cm H\u003csub\u003e2\u003c/sub\u003eO, corresponding to a weighted mean difference of \u0026minus;\u0026thinsp;3.5 [95% CI \u0026minus;\u0026thinsp;7; \u0026minus;\u0026thinsp;0.1] mL/cm H\u003csub\u003e2\u003c/sub\u003eO (p\u0026thinsp;=\u0026thinsp;0.045). In addition, when C\u003csub\u003eRS\u003c/sub\u003e changes were compared between the two BMI groups, obese patients exhibited a significantly greater reduction than non-obese patients (p\u0026thinsp;=\u0026thinsp;0.04) (Fig. 1; see Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA-B in the Additional file).\u003c/p\u003e\n\u003cp\u003eTransitioning from supine to a more inclined trunk position. TE (Treatment Effect): Estimated effect for each study, representing the mean difference in Compliance of respiratory system between the obese and non-obese groups. SE (Standard Error): Weight (common/random): IV (Inverse Variance), Fixed; 95% CI, 95% confidence interval (CI) for the estimated effect under a fixed-effects model. Heterogeneity within subgroups: Tau\u0026sup2;: An estimate of variance between studies. Chi\u0026sup2;: Chi-squared statistic to assess heterogeneity. I\u0026sup2;: Percentage of total variation attributable to heterogeneity between studies. A value of 0% indicated low heterogeneity. Each group is represented by a black diamond, indicating the combined effect (meta-analysis) for that subgroup. The endpoints of diamond reflect the 95% confidence interval (CI). The total at the bottom of the group provides a combined result for all studies within that subgroup. Vertical dotted line: This is the weighted average of all included studies. Continuous vertical line at value 0: Null effect.\u003c/p\u003e\n\u003cp\u003eIn patients with a BMI\u0026thinsp;\u0026ge;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, the transition from supine to a more inclined trunk position led to a significant decrease in lung compliance, from 54.4\u0026thinsp;\u0026plusmn;\u0026thinsp;17.1 to 45.8\u0026thinsp;\u0026plusmn;\u0026thinsp;17.5 mL/cm H\u003csub\u003e2\u003c/sub\u003eO, with a weighted mean difference of \u0026minus;\u0026thinsp;7.8 [95% CI \u0026minus;\u0026thinsp;12.4; \u0026minus;\u0026thinsp;3.3] mL/cm H\u003csub\u003e2\u003c/sub\u003eO (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In contrast, in patients with a BMI\u0026thinsp;\u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, lung compliance showed no significant decrease, from 50.5\u0026thinsp;\u0026plusmn;\u0026thinsp;19 to 43.8\u0026thinsp;\u0026plusmn;\u0026thinsp;17 mL/cm H\u003csub\u003e2\u003c/sub\u003eO with a weighted mean difference of \u0026minus;\u0026thinsp;5.9 [95% CI \u0026minus;\u0026thinsp;14.2; 2.3] (p\u0026thinsp;=\u0026thinsp;0.160) under the same positional change (Fig.\u0026nbsp;2A). In patients with a BMI\u0026thinsp;\u0026ge;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, transitioning from supine to a more inclined trunk position significantly decreased C\u003csub\u003eCW\u003c/sub\u003e from 167.8\u0026thinsp;\u0026plusmn;\u0026thinsp;55.7 to 120.6\u0026thinsp;\u0026plusmn;\u0026thinsp;34.1 with a weighted mean difference of \u0026minus;\u0026thinsp;42.9 [95% CI \u0026minus;\u0026thinsp;63.2; \u0026minus;\u0026thinsp;22.6] mL/cm H\u003csub\u003e2\u003c/sub\u003eO (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Similarly, in patients with a BMI\u0026thinsp;\u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, transitioning from supine to a more inclined trunk position reduced C\u003csub\u003eCW\u003c/sub\u003e from 173.9\u0026thinsp;\u0026plusmn;\u0026thinsp;90 to 127.1\u0026thinsp;\u0026plusmn;\u0026thinsp;49.1 mL/cm H\u003csub\u003e2\u003c/sub\u003eO, corresponding to a weighted mean difference \u0026minus;\u0026thinsp;47.7 [95% CI \u0026minus;\u0026thinsp;95.3; \u0026minus;\u0026thinsp;0.15] mL/cm H\u003csub\u003e2\u003c/sub\u003eO (p\u0026thinsp;=\u0026thinsp;0.049) (Fig. 2B). In addition, no significant differences were observed in lung and chest wall compliance between the two BMI groups (p\u0026thinsp;=\u0026thinsp;0.59 and p\u0026thinsp;=\u0026thinsp;0.76, respectively).\u003c/p\u003e\n\u003cp\u003eTransitioning from supine to a more inclined trunk position. \u003cstrong\u003eA-\u003c/strong\u003e Lung Compliance. \u003cstrong\u003eB-\u003c/strong\u003e Chest Wall Compliance. TE (Treatment Effect): Estimated effect for each study, representing the mean difference in Compliance of respiratory system between the obese and non-obese groups. SE (Standard Error): Weight (common/random): IV (Inverse Variance), Fixed; 95% CI, 95% confidence interval (CI) for the estimated effect under a fixed-effects model. Heterogeneity within subgroups: Tau\u0026sup2;: An estimate of variance between studies. Chi\u0026sup2;: Chi-squared statistic to assess heterogeneity. I\u0026sup2;: Percentage of total variation attributable to heterogeneity between studies. A value of 0% indicated low heterogeneity. Each group is represented by a black diamond, indicating the combined effect (meta-analysis) for that subgroup. The endpoints of diamond reflect the 95% confidence interval (CI). The total at the bottom of the group provides a combined result for all studies within that subgroup. Vertical dotted line: This is the weighted average of all included studies. Continuous vertical line at value 0: Null effect.\u003c/p\u003e\n\u003cp\u003eIn obese patients, a change in trunk inclination from the supine to a more inclined trunk position resulted in a significant decrease in the ratio between lung elastance and Elastance of respiratory system (E\u003csub\u003eL\u003c/sub\u003e/E\u003csub\u003eRS\u003c/sub\u003e) and a concurrent increase in its counterpart of the ratio between chest wall elastance and elastance of respiratory system (E\u003csub\u003eCW\u003c/sub\u003e/E\u003csub\u003eRS\u003c/sub\u003e) (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). In contrast, no significant changes in these variables were observed among the non-obese patients (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e; see supplementary Figs.\u0026nbsp;1 and 2 in the Additional file).\u003c/p\u003e\n\u003cp\u003eEffect of trunk inclination adjustment on oxygenation\u003c/p\u003e\n\u003cp\u003eIn patients with a BMI\u0026thinsp;\u0026ge;\u0026thinsp;or \u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, no significant differences were observed in PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e between phases (supine vs. a more inclined trunk position) (Tables \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). Additionally, no differences were observed when PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e changes were compared between the two BMI groups (p\u0026thinsp;=\u0026thinsp;0.28) (supplementary Fig. 4 in the Additional file).\u003c/p\u003e\n\u003cp\u003eEffects of Trunk Inclination on PaCO\u003csub\u003e2\u003c/sub\u003e and Ventilatory Variables\u003c/p\u003e\n\u003cp\u003eIn patients with BMI\u0026thinsp;\u0026ge;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, PaCO\u003csub\u003e2\u003c/sub\u003e increased when transitioning from supine to a more inclined trunk position (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). In contrast, among patients with BMI\u0026thinsp;\u0026lt;\u0026thinsp;30 kg/m\u003csup\u003e2\u003c/sup\u003e, changes in trunk inclination did not result in significant variations in PaCO\u003csub\u003e2\u003c/sub\u003e (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). When comparing PaCO\u003csub\u003e2\u003c/sub\u003e changes between the two BMI groups, obese patients exhibited a numerically higher but insignificant increase in PaCO\u003csub\u003e2\u003c/sub\u003e compared to non-obese individuals (p\u0026thinsp;=\u0026thinsp;0.37; supplementary Fig. 5 in the additional file). The VR remained unchanged across the different trunk inclinations in both BMI subgroups (Tables \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eIn the same line with PaCO\u003csub\u003e2\u003c/sub\u003e results, in obese patients, the transition from supine to a more inclined trunk position VD\u003csub\u003eBohr\u003c/sub\u003e/V\u003csub\u003eT\u003c/sub\u003e increased from 0.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 to 0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05 [mean difference 0.09; 95% CI: 0.03\u0026ndash;0.12; p\u0026thinsp;=\u0026thinsp;0.0012], whereas in non-obese patients, it changed from 0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 to 0.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09 [mean difference 0.05; 95% CI, -0.03\u0026ndash;0.13; p\u0026thinsp;=\u0026thinsp;0.198]. In obese patients, SnIII increased from 0.7 (\u0026plusmn;\u0026thinsp;0.39) to 1.3 (\u0026plusmn;\u0026thinsp;0.67) [mean difference 0.6; 95% CI: 0.12\u0026ndash;1.06] (P\u0026thinsp;=\u0026thinsp;0.016), whereas in non-obese patients, it changed from 1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 to 1.82\u0026thinsp;\u0026plusmn;\u0026thinsp;1.22 [mean difference 0.81; 95% CI: -0.13\u0026ndash;1.76]; (p\u0026thinsp;=\u0026thinsp;0.088). (Supplementary Fig. 6\u0026ndash;9 in the Additional File)\u003c/p\u003e\n\u003cp\u003eEffect of trunk inclination adjustment on EELV\u003c/p\u003e\n\u003cp\u003eOne included study assessed the effect of trunk inclination on EELV. No significant changes in EELV were observed in either group (see Table\u0026nbsp;11 in the Additional File).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe main findings of the present analysis were as follows: 1)\u0026nbsp;a more inclined trunk position led to a reduction in C\u003csub\u003eRS\u003c/sub\u003e in both obese and non-obese patients; 2) this decrease in C\u003csub\u003eRS\u003c/sub\u003e was more pronounced in patients with a BMI ≥ 30 kg/m\u003csup\u003e2\u003c/sup\u003e than in those with a BMI \u0026lt; 30 kg/m\u003csup\u003e2\u003c/sup\u003e; and 3) only obese patients exhibited a significant increase in PaCO\u003csub\u003e2\u003c/sub\u003e following this postural change.\u003c/p\u003e\n\u003cp\u003eThese findings provide comparative insights into the effects of body positioning on respiratory mechanics in obese and nonobese patients. Additionally, these findings suggest that patients with obesity may represent a distinct subgroup characterized by greater susceptibility to changes in respiratory mechanics in response to variations in trunk inclination. Accordingly, particular attention should be paid to the physiological impact of this intervention in this population.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn obese and non-obese patients, alveolar collapse in dependent lung regions is promoted by gravitational forces, which generate superimposed pressure [12] and a vertical pleural pressure gradient [13]. These two mechanisms operate simultaneously, contributing to alveolar collapse, and their relative impact is likely to vary according to the severity of lung injury and the thoracic positioning [14]. Superimposed pressure describes the pressure exerted by the weight of the overlying tissue on more dependent pulmonary regions due to gravitational forces. This hydrostatic force, generated by lung weight, is considered a determinant of the pleural pressure gradient [14, 15]. Furthermore, increased body weight and fat around the thorax are key factors that influence superimposed pressure, resulting in greater mechanical compression in dependent regions [12, 13]. The pleural pressure gradient refers to the pressure difference within the pleural space along the vertical axis of the lungs [16]. Although lung morphology and elastance of both the lung and chest wall appear similar between obese and non-obese patients, obesity is characterized by a reduced lung apex-to-base length and an increased sternum-to-vertebral diameter [14]. In supine-flat obese patients, this altered thoracic geometry increases the anteroposterior dimension of the lungs, thereby steepening the gravitational pleural pressure gradient. This anatomical configuration likely contributes to a rightward shift of the pressure-volume relationship, reflecting the greater external mechanical load imposed by the chest wall [14].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn addition, obese patients exhibit increased intra-abdominal fat and pressure [17], which may lead to a greater upward displacement of the abdominal contents against the diaphragm. This, in turn, causes distortion of the thoracic compartment structures, contributing to altered respiratory mechanics and reduced lung compliance [18]. Therefore, transitioning from a supine to a more inclined trunk position, owing to the lung's morphological characteristics in obese patients and the effect of superimposed weight [14], should increase the vertical height of the lung and amplify the pleural pressure gradient [19]. Although the volume of the abdominal contents does not change when moving to a semi-recumbent position, the shape of the abdominal cavity is likely distorted. Distortion leads to an increase in intra-abdominal pressure, which is transmitted primarily to the thoracic compartment [20-22]. This positive upward pressure is likely to be concentrated in the dependent juxtadiaphragmatic regions. Consequently, the ventilation distribution in mechanically ventilated obese patients is preferentially directed toward regions with greater compliance, such as non-dependent lung areas. This phenomenon is physiologically translated as a rightward shift of the pressure-volume curve [23], indicating a greater susceptibility to alterations in lung mechanics in obese patients (Figure 3).\u003c/p\u003e\n\u003cp\u003eOur analysis shows that both obese and non-obese patients with ARDS experienced a reduction in C\u003csub\u003eCW\u003c/sub\u003e when transitioning from supine to a more inclined trunk position. This effect was more pronounced and precise in obese patients (with less variability in data dispersion) than in nonobese individuals. Additionally, we observed a decline in lung compliance, specifically in obese individuals.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAlthough the reduction in C\u003csub\u003eRS\u003c/sub\u003e and C\u003csub\u003eCW\u003c/sub\u003e associated with increased trunk inclination could not directly indicate lung injury, the decline in lung compliance observed in obese patients following this postural change likely reflects an increased risk of ventilator-induced lung injury, particularly when the optimal PEEP levels are not appropriately adjusted. Moreover, in patients with obesity, the transition from supine to a more inclined trunk position led to a consistent decrease in E\u003csub\u003eL\u003c/sub\u003e/E\u003csub\u003eRS\u003c/sub\u003e and a significant increase in its counterpart, E\u003csub\u003eCW\u003c/sub\u003e/E\u003csub\u003eRS\u003c/sub\u003e, indicating a greater contribution of the elastic load on chest wall to overall respiratory mechanics. In contrast, non-obese patients exhibited no significant changes in the relative distribution of elastic loads between the lungs and the chest wall.\u003c/p\u003e\n\u003cp\u003eTo understand the relationship between trunk angle and changes in the pressure–volume curve in obese and non-obese patients, it is essential to consider the results obtained from optimizing PEEP in various body positions. Marrazzo et al. demonstrated that optimized PEEP requires adjustments to be made for each change in the chest position. In the supine-flat position, the optimal PEEP levels are, on average, 5 cmH\u003csub\u003e2\u003c/sub\u003eO higher than in the semi-recumbent position. Therefore, when the optimal PEEP is set in the supine-flat position, transitioning to a semi-recumbent position may require reducing the PEEP to avoid alveolar overdistension [24]. Therefore, maintaining the same PEEP levels after transitioning from a supine flat to a semi-recumbent position may contribute to excessive EELV and regional hyperinflation, particularly in patients with low lung recruitment ability.\u0026nbsp;In this context, it is plausible that trunk elevation produces physiological effects similar to those induced by increasing PEEP in non-recruitable lung regions, leading to increased pulmonary vascular resistance and deleterious effects on the right ventricle [2, 25, 26].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRegarding gas exchange, we observed that PaCO\u003csub\u003e2\u003c/sub\u003e levels worsened when patients were transitioned from supine to a more inclined trunk position, with this effect being more pronounced in the obese subgroup. To explain this phenomenon, one study employed volumetric capnography to evaluate the impact of trunk inclination on ventilatory inefficiency [5]. Under pressure-controlled ventilation, transitioning to a more inclined trunk position resulted in a significant reduction in tidal volume, suggesting impairment in lung mechanics associated with postural changes. This was accompanied by increased VD\u003csub\u003eBohr\u003c/sub\u003e/VT and PaCO\u003csub\u003e2\u003c/sub\u003e, which likely reflected alveolar overdistension. Moreover, the slope of phase III of the capnogram, normalized to the fraction of expired CO\u003csub\u003e2\u003c/sub\u003e (F\u003csub\u003eE\u003c/sub\u003eCO\u003csub\u003e2\u003c/sub\u003e), also increased significantly, suggesting that postural changes in obese individuals may exacerbate ventilation-perfusion mismatch [5]. Collectively, these observations reinforce the link between reduced lung compliance and impaired CO\u003csub\u003e2\u003c/sub\u003e clearance in obesity, indicating that greater trunk inclination may predispose to alveolar overdistension and compromised gas exchange.\u003c/p\u003e\n\u003cp\u003eRegarding the effects of changes in trunk inclination on oxygenation, it is known that improvements in oxygenation with trunk inclination have only been observed in certain patients with ARDS, particularly those who experience a notable increase in EELV [6, 7]. This effect is believed to result from reduced dorsal atelectasis due to less compression of the dependent lung regions by the cephalad displacement of the abdomen and diaphragm [27] and from a decrease in apical and mid-apical pleural pressures, which increases transpulmonary pressure, the principal determinant of lung distension [28]. Another study demonstrated that when PEEP was titrated in the semi-recumbent position (30°) and remained unchanged during changes in trunk inclination, transitioning patients from the 30° to the flat supine position (0°) resulted in a decline in oxygenation and EELV. This deterioration likely reflects alveolar derecruitment induced by postural shift without PEEP readjustment. Re-elevation to 30° reversed these effects, suggesting recruitment of previously collapsed lung regions. However, further increases in inclination to 60° and 90° did not yield additional improvements and were associated with a decline in oxygenation and EELV [2]. Therefore, an excessively upright posture without adequate PEEP adjustment may promote overdistension. \u0026nbsp;In our analysis, the transition from supine to a more inclined trunk position did not result in statistically significant changes in PaO₂/F\u003csub\u003eI\u003c/sub\u003eO₂ or EELV in the obese or non-obese subgroups. However, the consistent trend toward improved oxygenation in obese patients with increased trunk inclination may reflect an underlying physiological effect that warrants confirmation in larger cohorts, particularly regarding the trunk angle at which the optimal PEEP is set.\u003c/p\u003e\n\u003cp\u003eFinal comments and clinical implications\u003c/p\u003e\n\u003cp\u003eThis is the first multicenter analysis to identify obesity as a clinical condition associated with heightened respiratory physiological response to increased trunk inclination during passive mechanical ventilation. These findings strengthen the external validity and provide clinically relevant insights into the interplay between body positioning, respiratory mechanics, and patient phenotypes. Therefore, accurate documentation of bed inclination and comprehensive respiratory assessment are essential for objectively evaluating positioning strategies in each patient with ARDS. Grounded in the principles of precision medicine, this personalized strategy is gaining recognition as a critical element of effective clinical care and underscores the need for mechanical ventilation approaches tailored to individual patient characteristics.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLimitations\u003c/p\u003e\n\u003cp\u003eThe limitations of these analyzed results include several considerations. While the study stratified patients according to BMI status, the analysis included heterogeneous forms of ARDS, including C-ARDS, pulmonary ARDS, and extrapulmonary ARDS. Each of these entities may exhibit distinct pathophysiological profiles, potentially influencing respiratory mechanics and response to postural changes, thereby introducing variability in the observed outcomes. BMI was dichotomized, and a definitive cut-off value could not be established to identify accurately which patients might benefit most from this intervention. These subpopulations may exhibit different responses to changes in trunk inclination, depending on the body position in which PEEP was optimized in each study. Likewise, in many of the included studies, the calculation of airway opening pressure was lacking, which may have influenced the accuracy of the reported outcomes. Additionally, the evaluation time for each posture across all included studies did not exceed 60 minutes, leaving the long-term persistence of these effects unknown.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIncreasing the trunk inclination angle in patients during passive ventilation reduces respiratory system, lung, and chest wall compliance. This effect was more pronounced in patients with obesity. Moreover, only this population exhibited an increase in PaCO\u003csub\u003e2\u003c/sub\u003e. These findings highlight the importance of individualized respiratory management strategies, including optimizing bed inclination angles tailored to each patient's condition.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eARDS\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eAcute respiratory distress syndrome\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eC\u003c/b\u003e\u003csub\u003e\u003cb\u003eRS\u003c/b\u003e\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eRespiratory system compliance\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eEELV\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eEnd-expiratory lung volume\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003ePaCO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003ePressure of carbon dioxide\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eBMI\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eBody mass index\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003ePaO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e/F\u003c/b\u003e\u003csub\u003e\u003cb\u003eI\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e over the fraction of inspired oxygen\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003ePEEP\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003ePositive end-expiratory pressure\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eC\u003c/b\u003e\u003csub\u003e\u003cb\u003eCW\u003c/b\u003e\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eChest Wall Compliance\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eVR\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eVentilatory ratio\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eVD\u003c/b\u003e\u003csub\u003e\u003cb\u003eBohr\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e/VT\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eBohr dead space fraction\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eSnIII\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003ethe phase III slope of the capnogram (SIII) normalized with fraction of expired CO2\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupplementary Information\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe online version contains supplementary material\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data sets used and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMHB, GB, AB, and JR contributed to the conception and design of the study. All authors performed the title and abstract screening. MHB, RB, TL, FM, JJM, JS, CG, MM, SB, UW, JD, and JR performed the data extraction. MHB, RB, TL, FM, JJM, JS, CG, MM, SB, UW, ELVC, and JR organized the data and created the characteristic tables. MHB and RB performed the data analysis. MHB, TL, FM, JJM, JS, CG, MM, SB, UW, JD, AB, GB, ELVC, JD, and JR wrote the first draft of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDr. Costa received funding from Magnamed and Timpel.\u003c/p\u003e\n\u003cp\u003eDr. Mehdi Mezidi reports receiving congress fees from Pfizer, unrelated to the present work.\u003c/p\u003e\n\u003cp\u003eThe other authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003eORCID IDs: 0000-0001-6366-534X (MHB)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBenites MH, Zapata-Canivilo M, Poblete F, Labbe F, Battiato R, Ferre A, et al. Physiological and clinical effects of trunk inclination adjustment in patients with respiratory failure: a scoping review and narrative synthesis. Crit Care. 2024;28(1):228.\u003c/li\u003e\n \u003cli\u003eBouchant L, Godet T, Arpajou G, Aupetitgendre L, Cayot S, Guerin R, et al. Physiological effects and safety of bed verticalization in patients with acute respiratory distress syndrome. Crit Care. 2024;28(1):262.\u003c/li\u003e\n \u003cli\u003eMarrazzo F, Spina S, Zadek F, Forlini C, Bassi G, Giudici R, et al. Ventilation distribution during changes in trunk inclination in ARDS patients. Respir Care. 2023;22:11175.\u003c/li\u003e\n \u003cli\u003eMarrazzo F, Spina S, Forlini C, Guarnieri M, Giudici R, Bassi G, et al. Effects of trunk inclination on respiratory mechanics in patients with COVID-19-associated acute respiratory distress syndrome: let\u0026rsquo;s always report the angle!. Am J Respir Crit Care Med. 2022;205:582\u0026ndash;4.\u003c/li\u003e\n \u003cli\u003eBenites MH, Torres D, Poblete F, Labbe F, Bachmann MC, Regueira TE, et al. Effects of changes in trunk inclination on ventilatory efficiency in ARDS patients: quasi-experimental study. Intensive Care Med Exp. 2023;11(1):65.\u003c/li\u003e\n \u003cli\u003eDellamonica J, Lerolle N, Sargentini C, Hubert S, Beduneau G, Di Marco F, et al. Effect of different seated positions on lung volume and oxygenation in acute respiratory distress syndrome. Intensive Care Med. 2013;39:1121\u0026ndash;7.\u003c/li\u003e\n \u003cli\u003eRichard JC, Maggiore SM, Mancebo J, Lemaire F, Jonson B, Brochard L. Effects of vertical positioning on gas exchange and lung volumes in acute respiratory distress syndrome. Intensive Care Med. 2006;32:1623\u0026ndash;6.\u003c/li\u003e\n \u003cli\u003eBihari S, Wiersema UF. Changes in respiratory mechanics with trunk inclination differs between obese and non-obese ARDS patients. Chest. 2024;165(3):583\u0026ndash;9.\u003c/li\u003e\n \u003cli\u003eChen X, Xiong R, Zhang M, Guan C, Feng L, Yao Z, et al. Effects of sitting position on ventilation distribution determined by electrical impedance tomography in ventilated ARDS patients. Intensive Crit Care Nurs. 2024;85:103782.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eMezidi M, Gu\u0026eacute;rin C. Effect of body position and inclination in supine and prone position on respiratory mechanics in acute respiratory distress syndrome. Intensive Care Med. 2019;45(2):292\u0026ndash;294.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eSelickman J, Crooke PS, Tawfik P, Dries DJ, Gattinoni L, Marini JJ. Paradoxical Positioning: Does \u0026quot;Head Up\u0026quot; Always Improve Mechanics and Lung Protection?. Crit Care Med. 2022;50(11):1599\u0026ndash;1606.\u003c/li\u003e\n \u003cli\u003eSpina S, Mantz L, Xin Y, Moscho DC, Ribeiro De Santis Santiago R, Grassi L, et al. The pleural gradient does not reflect the superimposed pressure in patients with class III obesity. Crit Care. 2024;28(1):306.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003ePelosi P, D\u0026apos;Andrea L, Vitale G, Pesenti A, Gattinoni L. Vertical gradient of regional lung inflation in adult respiratory distress syndrome. Am J Respir Crit Care Med. 1994;149(1):8\u0026ndash;13.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eChiumello D, Colombo A, Algieri I, Mietto C, Carlesso E, Crimella F, et al. Effect of body mass index in acute respiratory distress syndrome. Br J Anaesth. 2016;116(1):113\u0026ndash;21.\u003c/li\u003e\n \u003cli\u003eGattinoni L, Pesenti A. The concept of \u0026quot;baby lung\u0026quot;. Intensive Care Med. 2005;31(6):776\u0026ndash;84.\u003c/li\u003e\n \u003cli\u003ePelosi P, D\u0026apos;Andrea L, Vitale G, Pesenti A, Gattinoni L. Vertical gradient of regional lung inflation in adult respiratory distress syndrome. Am J Respir Crit Care Med. 1994;149(1):8\u0026ndash;13. \u0026nbsp;\u003c/li\u003e\n \u003cli\u003eSmit M, Werner MJM, Lansink-Hartgring AO, Dieperink W, Zijlstra JG, van Meurs M. How central obesity influences intra-abdominal pressure: a prospective, observational study in cardiothoracic surgical patients. Ann Intensive Care. 2016;6(1):99.\u003c/li\u003e\n \u003cli\u003ePirrone M, Fisher D, Chipman D, Imber DAE, Corona J, Mietto C, et al. Recruitment maneuvers and positive end-expiratory pressure titration in morbidly obese ICU patients. Crit Care Med. 2016;44:300\u0026ndash;7.\u003c/li\u003e\n \u003cli\u003eWest JB, Matthews FL. Stresses, strains, and surface pressures in the lung caused by its weight. J Appl Physiol. 1972;32(3):332\u0026ndash;-45.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eZhou Y, He H, Cui N, Wang X, Long Y, Liu D, et al. Elevation of the head of bed reduces splanchnic blood flow in patients with intra-abdominal hypertension. BMC Anesthesiol. 2023;23(1):133.\u003c/li\u003e\n \u003cli\u003eMcBeth PBZD, Widder S, Cheatham M, Zengerink I, Glowa J, Kirkpatrick AW. Effect of patient postioining on intraabdominal pressure monitoring. Am J Surg. 2007;193:644\u0026ndash;7.\u003c/li\u003e\n \u003cli\u003eVasquez DG, Berg-Copas GM, WettaHall R, Berg-Copas GM, Wetta-Hall R. Influence of semirecumbent position on intra-abdominal pressure as measured by bladder pressure. J Surg Res. 2007;139:280\u0026ndash;5.\u003c/li\u003e\n \u003cli\u003ePelosi P, Croci M, Ravagnan I, Cerisara M, Vicardi P, Lissoni A, et al. Respiratory system mechanics in sedated, paralyzed, morbidly obese patients. J Appl Physiol (1985). 1997;82(3):811\u0026ndash;8. \u0026nbsp;\u003c/li\u003e\n \u003cli\u003eMarrazzo F, Spina S, Zadek F, Forlini C, Bassi G, Giudici R, et al. PEEP titration is markedly affected by trunk inclination in mechanically ventilated patients with COVID-19 ARDS: a physiologic, cross-over study. J Clin Med. 2023;12(12):3914.\u003c/li\u003e\n \u003cli\u003eBenites MH, Retamal J. Effect of trunk upward verticalization on pulmonary vascular resistance in ARDS. Crit Care. 2025;29(1):93. \u0026nbsp;\u003c/li\u003e\n \u003cli\u003eCappio Borlino S, Hagry J, Lai C, Rocca E, Fouqu\u0026eacute; G, Rosalba D, et al. The Effect of Positive End-Expiratory Pressure on Pulmonary Vascular Resistance Depends on Lung Recruitability in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2024;210(7):900\u0026ndash;907. \u0026nbsp;\u003c/li\u003e\n \u003cli\u003eRezoagli E, Bastia L, Brochard L, Bellani G. Physical manoeuvres in patients with ARDS and low compliance: bedside approaches to detect lung hyperinflation and optimise mechanical ventilation.\u0026nbsp;Eur Respir J. 2023;61(5):2202169.\u003c/li\u003e\n \u003cli\u003eD\u0026rsquo;Angelo E, Bonanni MV, Michelini S, et al. Topography of the pleural surface pressure in rabbits and dogs. Respir Physiol. 1970;8: 204\u0026ndash;229.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"critical-care","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cric","sideBox":"Learn more about [Critical Care](http://ccforum.biomedcentral.com/)","snPcode":"13054","submissionUrl":"https://submission.nature.com/new-submission/13054/3","title":"Critical Care","twitterHandle":"@Crit_Care","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"ARDS, body position, supine position, compliance of respiratory system, obese","lastPublishedDoi":"10.21203/rs.3.rs-7060912/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7060912/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Adjusting trunk inclination in patients with acute respiratory distress syndrome directly affects physiological variables such as respiratory mechanics and PaCO\u003csub\u003e2\u003c/sub\u003e levels. These effects may vary according to the body mass index (BMI) due to differences in lung and chest wall compliance, highlighting the need for further investigation to clarify the clinical relevance of body position across patient subgroups.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA secondary analysis compared the physiological effects of increasing trunk inclination angles between mechanically ventilated patients with obesity (BMI ≥ 30 kg/m\u003csup\u003e2\u003c/sup\u003e) and those without obesity (BMI \u0026lt; 30 kg/m\u003csup\u003e2\u003c/sup\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData from 159 patients collected across seven individual studies were analyzed. Sixty-five patients with obesity presented a greater decrease in respiratory system compliance (-7.5 [-10; -5] mL/cmH\u003csub\u003e2\u003c/sub\u003eO; p \u0026lt; 0.001) compared to ninety-four patients without obesity (-3.5 [-7; -0.08] mL/cmH\u003csub\u003e2\u003c/sub\u003eO; p = 0.045). Lung compliance decreased in obese patients (-7.8 [-12.4; -3.3] mL/cmH\u003csub\u003e2\u003c/sub\u003eO; p \u0026lt; 0.001), whereas no significant changes were observed in patients without obesity (-5.9 [-14.2; 2.3] mL/cmH\u003csub\u003e2\u003c/sub\u003eO; p = 0.160). Chest wall compliance decreased by -42.9 [-63.2; -22.6] mL/cmH\u003csub\u003e2\u003c/sub\u003eO (p\u0026lt; 0.001) in obese patients and by -47.7 [-95.3; -0.15] mL/cmH\u003csub\u003e2\u003c/sub\u003eO in non-obese patients (p = 0.049). PaCO\u003csub\u003e2\u003c/sub\u003e increased in obese patients by 4.6 [1.4; 7.8] mmHg (p= 0.004) but not in patients without obesity (2.5 [-0.6; 5.6] (p = 0.113). No significant differences were observed in PaO\u003csub\u003e2\u003c/sub\u003e/F\u003csub\u003eI\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e between phases.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIncreasing the trunk inclination angle in patients during passive ventilation reduces respiratory system, lung, and chest wall compliance. This effect was more pronounced in patients with obesity. Moreover, only this population exhibited an increase in PaCO\u003csub\u003e2\u003c/sub\u003e. These findings highlight the importance of individualized respiratory management strategies, including optimizing bed inclination angles tailored to each patient's condition.\u003c/p\u003e","manuscriptTitle":"Respiratory effects of trunk inclination in obese and non-obese patients mechanically ventilated for ARDS","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-15 13:57:08","doi":"10.21203/rs.3.rs-7060912/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-07T08:08:59+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-04T17:54:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-01T21:38:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"193459169223153002628482881919968858706","date":"2025-07-11T16:33:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"68673651594798376321871982785971451633","date":"2025-07-11T07:22:12+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-11T05:40:55+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-08T05:40:21+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-08T03:55:08+00:00","index":"","fulltext":""},{"type":"submitted","content":"Critical Care","date":"2025-07-07T03:30:43+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"critical-care","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cric","sideBox":"Learn more about [Critical Care](http://ccforum.biomedcentral.com/)","snPcode":"13054","submissionUrl":"https://submission.nature.com/new-submission/13054/3","title":"Critical Care","twitterHandle":"@Crit_Care","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"dd83a3df-c2ea-4376-bae7-72ca3407a75d","owner":[],"postedDate":"July 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-11-03T16:04:34+00:00","versionOfRecord":{"articleIdentity":"rs-7060912","link":"https://doi.org/10.1186/s13054-025-05694-z","journal":{"identity":"critical-care","isVorOnly":false,"title":"Critical Care"},"publishedOn":"2025-10-28 15:57:42","publishedOnDateReadable":"October 28th, 2025"},"versionCreatedAt":"2025-07-15 13:57:08","video":"","vorDoi":"10.1186/s13054-025-05694-z","vorDoiUrl":"https://doi.org/10.1186/s13054-025-05694-z","workflowStages":[]},"version":"v1","identity":"rs-7060912","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7060912","identity":"rs-7060912","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}