An algorithmic approach to preoxygenation: Stepwise addition of pressure support and positive end-expiratory pressure when tidal volume breathing is inadequate. A randomised controlled trial

An algorithmic approach to preoxygenation: Stepwise addition of pressure support and positive end-expiratory pressure when tidal volume breathing is inadequate. 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A randomised controlled trial Çağın Tanrıverdi, Selvinaz Yüksel Tanrıverdi, Erkan Tomatır This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6321502/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 15 Oct, 2025 Read the published version in Perioperative Medicine → Version 1 posted 10 You are reading this latest preprint version Abstract Background Preoxygenation is crucial for airway management safety. The standard method for preoxygenation is tidal volume breathing (TVB). This study aimed to determine whether an algorithmic approach which involves stepwise adding pressure support ventilation (PSV) and positive end-expiratory pressure (PEEP) when TVB is inadequate, would improve preoxygenation. Methods 200 patients planned for general anesthesia and having end-tidal oxygen (ETO 2 ) < 90% after 3 min TVB were randomly divided into two: TVB was continued or 6 cmH 2 O PSV was added. After 4 min, PSV patients having ETO 2 < 90% were divided into two again: either PSV was continued or 4 cmH 2 O PEEP was also added to PSV. The time to achieve ETO 2 ≥ 90% and adverse effects were noted. Results After 4 min, patients with adequate preoxygenation was significantly lower with TVB (52%) compared with PSV (76%; P < 0.001). After 5 min, it was 97% and 100%, respectively. The mean durations of adequate preoxygenation with TVB, PSV and PSV-PEEP between 4–5 min were 274.90 ± 18.55, 268.94 ± 12.24 and 252.38 ± 7.46 s, respectively. The differences between TVB and PSV-PEEP (P < 0.001) and between PSV and PSV-PEEP (P = 0.001) were significant. Total time was significantly longer with TVB (237.17 ± 40.31 s) compared with PSV (222.63 ± 27.24 s; P = 0.003). Conclusions An algorithmic approach, stepwise adding PSV and PEEP in patients inadequately preoxygenated with standard TVB, ensures adequate preoxygenation in all patients and reduces the time required. Although this time difference was statistically significant, we considered that it was not clinically significant. No serious adverse effects were observed. Trial registration: NCT06736197 Algorithm Stepwise Tidal volume breathing Positive end expiratory pressure Preoxygenation Pressure support ventilation Figures Figure 1 Figure 2 Figure 3 Background The most common problems in airway management are difficulty, delay or failure to secure the airway. More than 90% of cases of difficult tracheal intubation and difficult mask ventilation cannot be anticipated by preoperative assessment (Nørskov et al. 2015 ). Prolongation of nonhypoxemic apnea time is crucial to provide safe airway management (Artime et al. 2020). Filling the functional residual capacity of the lungs with oxygen is the main way to increase nonhypoxemic apnea time. Preoxygenation is performed before induction of anesthesia and tracheal intubation and routinely recommended for all patients (Bell 2004 ). Adequate preoxygenation is an end-tidal oxygen (ETO 2 ) value of 90% or higher (Berry at al. 1994.) Three minutes of spontaneous tidal volume breathing (TVB) of 100% oxygen with a face mask is the conventional method of preoxygenation (Hamilton and Eastwood 1955 ). Later, techniques such as deep breathing (Gold et al. 1981 ) vital capacity breathing (Russell et al. 1987 ), noninvasive positive pressure ventilation (NIPPV) (Herriger at al. 2004) and high flow nasal oxygen (HFNO) (Ng at al. 2018) have also been described. Deep breathing can reduce ETCO 2 (Nimmagadda at al. 2016) and HFNO requires special equipment. It has been reported that NIPPV techniques such as pressure support ventilation (PSV) and positive end-expiratory pressure (PEEP) can increase the success rate to 100%, (Arab at al. 2016) however adverse effects such as discomfort and gastric distension may be observed in patients (Delay at al. 2008; Bouroche 2015 ; Tianliang 2019). In published studies, a single preoxygenation technique was generally used, determined at the beginning for each patient, and did not change throughout the administration; combining different techniques in a stepwise approach was not encountered. In the present study, to optimize the risk-benefit ratio, it was considered that NIPPV techniques were not need in patients whose target ETO 2 (≥ 90%) was achieved within 3 min with conventional TVB for preoxygenation; it was aimed to test the hypothesis that an algorithmic approach based on adding PSV and PEEP, where adequate preoxygenation cannot be achieved after 3 min with TVB, will both increase the percentage of preoxygenated patients and shorten the preoxygenation time. Methods The study was performed on 200 patients planned for general anesthesia for elective surgery, aged 18–65 years, American Society of Anesthesiologists physical status classification 1–2, without premedication and ETO 2 < 90% at the end of the 3rd minute with spontaneous TVB of 100% oxygen. The exclusion criteria were as follows: patients who were hemodynamically unstable and required oxygen support in the preoperative period; patients undergoing thoracic or emergency surgery; patients with high intracranial or intraocular pressure for whom positive pressure ventilation may be indirectly harmful; patients with a body mass index (BMI) of 35 kg/m² or above; patients who were pregnant; and male patients with beards that may cause leakage in mask ventilation. The recommended check of the anesthesia machine was performed properly. The gas analysis line was connected to the elbow of the Y-connector on the circle system. The system was flushed for 30 seconds by activating the oxygen bypass valve to remove room air. The demographic data, peripheral oxygen saturation (SpO₂), noninvasive systolic (SAP) and diastolic (DAP) arterial pressures and heart rate (HR) values were recorded. Fresh gas flow was started at 12 L/min with 100% oxygen. The adjustable pressure limiting valve was fully opened to allow spontaneous breathing without resistance. All patients were informed that a face mask would be placed to deliver oxygen, and the mask was then placed tightly to prevent leakage. ETO 2 values were monitored continuously. According to a computer-generated randomization table, the patients were randomly assigned to one of two groups (Group TVB and Group PSV). In the patients in Group TVB, the tidal volume breathing was maintained for two more minutes. Group PSV received inspiratory pressure support of 6 cmH 2 O for + 1 min. At the end of four minutes, patients whose ETO₂ value had not reached a minimum of 90% were randomly divided into two groups again. One group continued with PSV, while the other was administered 4 cmH₂O PEEP in addition to PSV (Group PSV-PEEP). When adequate preoxygenation was achieved, the duration of preoxygenation, SpO 2 , end-tidal carbon dioxide (ETCO 2 ), arterial blood pressure, and heart rate values were recorded. Any adverse effects, such as discomfort or gastric distension, were noted. Statistical methods A power analysis was performed based on the rates of patients who could not achieve adequate preoxygenation with tidal volume ventilation and positive pressure support ventilation in a similar study (Hanouz at al. 2015). This analysis calculated that 198 participants (at least 99 per group) would be required to achieve 80% power at a 95% confidence level. Data were analyzed using SPSS (Statistical Package for the Social Sciences: IBM SPSS Statistics 25 software; Armonk, NY: IBM Corp.). Continuous variables were presented as mean ± standard deviation, while categorical variables were presented as frequency and percentage. Before proceeding with the relevant analyses, normality assumptions for continuous variables were assessed by comparing the Kolmogorov-Smirnov and Shapiro-Wilk statistical values, evaluating skewness and kurtosis values, and interpreting Q-Q plots. Since the data showed a normal distribution, parametric tests were used. The difference between independent groups was analyzed using an independent samples t-test and One-Way Anova, and the difference between dependent groups was analyzed with paired samples t-test. If normality assumptions were not met, non-parametric tests were used. The difference between independent groups was analyzed using the Mann-Whitney U test, while the Wilcoxon signed-rank test was used for dependent groups. A χ 2 test was used to determine the differences between categorical variables. Statistical significance was considered at P < 0.05. Results Of the 378 patients preoxygenated with spontaneous tidal volume breathing, 178 (47%) with ETO 2 ≥ 90 at the end of the 3rd minute were excluded. The study included 200 patients (53%) with ETO 2 < 90 (Fig. 1). This study was conducted in a single tertiary hospital, from March 2020 to March 2021. The groups were similar regarding patient characteristics (Table 1 ). Table 1 Patient characteristics (Mean ± SD) Group TVB ( n = 100) Group PSV ( n = 100) P Age (years) 44 ± 14 45 ± 15 0,445 Sex Male/Female 53/47 71/29 0,013 BMI (kg/m 2 ) 25,9 ± 3,8 26,0 ± 4,3 0,919 ASA 1 70 (%70) 57 (%57) 0,078 2 30 (%30) 43 (%43) BMI, body mass index; ASA, The American Society of Anesthesiologists Physical Status Classification System At the end of the 4th min, the percentage of patients with adequate preoxygenation was significantly lower in Group TVB (52%) compared with Group PSV (76%; P < 0.001). At the end of the 5th min, adequate preoxygenation was not achieved in 3 patients in Group TVB, whereas it was completed in all patients in Group PSV (Fig. 2). In patients who achieved adequate preoxygenation at the end of the 4th minute, the mean time was significantly shorter in the Group TVB (202.35 ± 16.14 s) ( n = 52/100) compared with Group PSV (209.75 ± 14.98 s; P = 0.009) ( n = 76/100). In patients who achieved adequate preoxygenation at the end of the 5th minute, the mean durations were 274.90 ± 18.55 s in Group TVB, 268.94 ± 12.24 s in Group PSV and 252.38 ± 7.46 s in Group PSV-PEEP. The differences between Group TVB and Group PSV-PEEP and between Group PSV and Group PSV-PEEP were significant (P < 0.001 and P = 0.001, respectively). The total duration of preoxygenation was significantly longer in Group TVB (237.17 ± 40.31 s) compared with Group PSV (222.63 ± 27.24 s; P = 0.003) (Fig. 3). SpO 2 values were significantly higher in both groups after preoxygenation (P < 0.001). No significant difference was found between the groups regarding arterial pressure, heart rate and ETCO 2 values (Table 2 ). Adverse effects observed in the study were epigastric distension in only 1 patient in Group PSV-PEEP and discomfort in 1 patient in Group TVB and 2 patients in Group PSV. No patient required termination of the procedure. Table 2 SpO 2 , ETCO 2 , systolic/diastolic arterial pressures and heart rate (Mean ± SD) Group TVB Group PSV Before-PO After-PO P Before-PO After-PO P SpO 2 (%) 98,87 ± 1,14 99,89 ± 0,37 0,000 97,99 ± 1,82 99,88 ± 0,38 0,000 ETCO 2 (mmHg) 36,70 ± 2,43 36,67 ± 2,55 0,932 SAP (mmHg) 133,50 ± 20,29 131,79 ± 20,97 0,194 140,52 ± 22,25 139,70 ± 22,37 0,524 DAP (mmHg) 76,59 ± 11,11 76,18 ± 11,83 0,605 79,71 ± 12,97 80,13 ± 13,55 0,641 HR (bpm) 81,34 ± 12,84 81,39 ± 13,93 0,953 77,03 ± 12,48 76,10 ± 12,95 0,216 PO, Preoxygenation; SpO 2 , peripheral oxygen saturation; ETCO 2 , end-tidal carbon dioxide; SAP, systolic arterial pressure; DAP, diastolic arterial pressure; HR, heart rate (beats per minute) Discussion Most anesthesia malpractice claims, including death and brain damage, arise from difficult airway management during the induction period (Peterson at al. 2005). Routine preoxygenation of all patients is an effective measure that prolongs the safe apnea time (Bell 2004 ). It can be considered like the ‘safety belt’ of airway management. In the present study, which focused on an algorithmic approach, the rate of inadequate preoxygenation with 3 min TVB was 53%. This is comparable to the 50% and 56% rates reported in previous studies (Baillard at al. 2019; Baillard at al. 2014). The standard preoxygenation technique is inadequate in approximately half of the patients. In patients who could not achieve adequate preoxygenation at the end of the third minute with the standard technique in the present study, when TVB was continued for another minute, approximately half (52%) of these patients achieved adequate preoxygenation, while when PSV was added for one minute, this rate increased to approximately three-quarters (76%; P < 0.001). Although this time difference was statistically significant, we considered that it was not clinically significant. By the end of the five minutes, the proportion of patients in TVB group who had reached adequate preoxygenation was 97%, while in PSV group, this rate was 100%. Hanouz et al.( Hanouz et al.2015) reported in their study, in which they used one of three methods from the beginning that the rates of inadequacy at 250th seconds were 27% with TVB, 15% with PSV, and 10% with PSV-PEEP, and all patients achieved an adequate preoxygenation with all three methods by the end of the fifth minute. Despite notable methodological differences between the two studies, the rates can be regarded as similar once the necessary adaptations are made. Baillard et al.(Baillard et al. 2019 ) reported that the rate of inadequate preoxygenation with 5 minutes of TVB was 30% in their studies investigating the risk factors for difficult preoxygenation. This rate is much higher than the rate in the present study, and the possible reason is that patients at risk of difficult preoxygenation were excluded in the present study. When different methods were compared in terms of the time to reach adequate preoxygenation, it was shown that the order was PSV-PEEP < PSV < TVB(Hanouz et al. 2015 ; Taxak et al. 2023 ), the findings in the present study are also similar. Additionally, in another study conducted by Hanouz et al.( Hanouz et al. 2018 ) it was emphasized that the PSV-PEEP application can also prevent air leakage, which may occur due to mask-face incompatibility. Different pressure values have been used for NIPPV in preoxygenation; Delay et al. (Delay et al. 2008 ) reported a pressure of 6 cmH 2 O for PSV and 4 cmH 2 O for PEEP, while Hanouz et al. (Hanouz at al. 2015) preferred higher pressures (12 and 6 cmH 2 O respectively). In the present study low pressure levels were chosen as 6 cmH 2 O PSV and 4 cmH 2 O PEEP. Especially at high pressure levels, NIPPV and PEEP can affect hemodynamics by decreasing venous return and cardiac output (Kallet et al. 2009). Hemodynamics did not change significantly in the present study; previous studies have also reported no significant change in hemodynamics when applying NIPPV with PEEP for preoxygenation (Delay et al. 2008 ; Taxak et al. 2023 ). It can be considered that the choice of low pressures and short processing time may have played a role in this. The adverse effects that may be observed due to NIPPV include discomfort and gastric distension. In the present study, discomfort and epigastric distension were rare, and none of the patients required discontinuation of the procedure. In the study conducted by Delay et al (Delay et al. 2008 ). gastric distension was scored from 0-100 during laparoscopy by a surgeon blinded to the preoxygenation method, and it was reported a modest, although significant, increase in gastric distension and no adverse effects with NIPPV techniques compared with TVB. Georgescu et al. (Georgescu et al. 2012 ) reported that they stopped the procedure in one (6%) of 15 patients undergoing NIPPV for preoxygenation because of discomfort. It seems that the adverse effects, such as discomfort and epigastric distension due to NIPPV for preoxygenation, are rare and clinically insignificant. It should be noted that the present study has some limitations. The study focused on the percentage and duration of patients in whom algorithmically applied preoxygenation was successful, but the duration of nonhypoxemic apnea was not examined due to ethical concerns. Since the method is unsuitable for a blind study, the risk of bias could not be completely excluded. Epigastric distension due to positive pressure was evaluated by observation only; a reliable measurement method could not be used. In addition, since patients in special risk groups such as the elderly, pregnant women, children, and the morbidly obese were not included in the study, possible differences regarding these groups could not be analyzed. Further, well-designed studies are needed to determine whether the algorithmic approach is effective in patients in special risk groups. Conclusion In conclusion, the hypothesis that an algorithmic approach based on the stepwise addition of PSV and PEEP in patients who cannot be adequately preoxygenated with TVB will provide adequate preoxygenation in a shorter time and in all patients has been confirmed. Abbreviations TVB Tidal volume breathing PSV pressure support ventilation PEEP positive end-expiratory pressure ETO 2 end-tidal oxygen NIPPV noninvasive positive pressure ventilation HFNO high flow nasal oxygen BMI body mass index SpO₂ peripheral oxygen saturation SAP systolic arterial pressure DAP diastolic arterial pressure HR heart rate ASA The American Society of Anesthesiologists Physical Status Classification System PO Preoxygenation ETCO 2 end-tidal carbon dioxide Declarations Acknowledgements: None . Authors’s contributions: Study conception, design, validation: Ç.T. and E.T.; data acquisition: Ç.T., S.Y.T.; analysis: Ç.T., S.Y.T., E.T.; data interpretation: Ç.T., S.Y.T., E.T.; draf-ing of the manuscript: Ç.T., E.T.; review of the manuscript: Ç.T., S.Y.T., E.T. All authors read and approved the submission and publication of this manuscript. Funding support: None. Data availability: No datasets were generated or analysed during the current study. Ethics approval and consent to participate: This study was conducted with the approval of the Pamukkale University (Denizli, Türkiye) Ethics Committee dated 18.02.2020 and number 60116787-020/15624 and with the informed written consent of the patients. Consent for publication: All authors approved the version of the manuscript to be published. Competing interests: The authors declare no competing interests. References Arab OA, Guinot PG, Dimov E, et al. Low-positive pressure ventilation improves non-hypoxaemic apnoea tolerance during ear, nose and throat pan-endoscopy. Eur J Anaesthesiol 2016; 33: 269–274. https://doi.org/10.1097/EJA.0000000000000394 Artime CA, Hagberg CA. Airway management in the adult. In: Miller’s Anesthesia. Gropper MA editor. Philadelphia, Elsevier; 2020. p. 1373–1412. Baillard C, Boubaya M, Statescu E, et al. Incidence and risk factors of hypoxaemia after preoxygenation at induction of anaesthesia. 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Cite Share Download PDF Status: Published Journal Publication published 15 Oct, 2025 Read the published version in Perioperative Medicine → Version 1 posted Editorial decision: Revision requested 15 Jun, 2025 Reviewers agreed at journal 12 Jun, 2025 Reviews received at journal 11 Jun, 2025 Reviewers agreed at journal 10 Jun, 2025 Reviews received at journal 02 Jun, 2025 Reviewers agreed at journal 19 May, 2025 Reviewers invited by journal 19 May, 2025 Editor assigned by journal 27 Mar, 2025 Submission checks completed at journal 27 Mar, 2025 First submitted to journal 27 Mar, 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. 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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-6321502","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":458831843,"identity":"2ae12df6-9a5b-4049-9c87-a6bfcda32604","order_by":0,"name":"Çağın Tanrıverdi","email":"","orcid":"","institution":"Denizli State Hospital","correspondingAuthor":false,"prefix":"","firstName":"Çağın","middleName":"","lastName":"Tanrıverdi","suffix":""},{"id":458831844,"identity":"32266a54-b9bc-4e24-9e89-9f62fe59c317","order_by":1,"name":"Selvinaz Yüksel Tanrıverdi","email":"","orcid":"","institution":"Denizli State Hospital","correspondingAuthor":false,"prefix":"","firstName":"Selvinaz","middleName":"Yüksel","lastName":"Tanrıverdi","suffix":""},{"id":458831845,"identity":"b7596f45-433b-4599-933a-fbbf53e1da84","order_by":2,"name":"Erkan Tomatır","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA10lEQVRIiWNgGAWjYPACCQZ+CIOZCMVsICJBgkGyAaaFjTgtDAwGB4jVwi/ffHTDzx8W+ca3m59JMFRYJzbI9z7Aq0WyjS3tZk+ChOW2O8fMJBjOpCc2sLEb4NVicIzH7AZPgoSB2Y0EMwnGtsNALQRcZg/UcvMPUIvxjPRvEoz/iNBiwMZjdhtki4FEDtCWBiK0SBxLS7stkyZhIHHnTLFFwrF0Y6Dn8Gvhbz587OYbmzoD/tntG298qLGW7Wc+hl8Lkn0M4PghHJOoWkbBKBgFo2AUYAMAxzk9dWv6X/IAAAAASUVORK5CYII=","orcid":"","institution":"Pamukkale University","correspondingAuthor":true,"prefix":"","firstName":"Erkan","middleName":"","lastName":"Tomatır","suffix":""}],"badges":[],"createdAt":"2025-03-27 14:38:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6321502/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6321502/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s13741-025-00575-z","type":"published","date":"2025-10-15T15:58:28+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83294401,"identity":"8f803bfe-a7d3-4be0-bc91-939acfecd60c","added_by":"auto","created_at":"2025-05-22 13:32:45","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":360134,"visible":true,"origin":"","legend":"\u003cp\u003eStudy flow diagram.\u003c/p\u003e\n\u003cp\u003e(TVB, tidal volume breathing; PSV, pressure support ventilation; ETO\u003csub\u003e2\u003c/sub\u003e, end-tidal oxygen; PEEP, positive end-expiratory pressure)\u003c/p\u003e","description":"","filename":"1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6321502/v1/8188caeec6e16785c2e0ffa8.jpeg"},{"id":83294402,"identity":"fe16107f-9695-4163-85ec-b8fe0277b2c6","added_by":"auto","created_at":"2025-05-22 13:32:45","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":91324,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of patients achieving adequate preoxygenation\u003c/p\u003e\n\u003cp\u003e(\u003csup\u003e*\u003c/sup\u003e) P \u0026lt; 0,001: between Group TVB and Group PSV.\u003c/p\u003e","description":"","filename":"2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6321502/v1/7c14f0df1c8327654b79d36f.jpeg"},{"id":83293741,"identity":"cad36046-fbd2-4c9d-b739-30feeca96ae8","added_by":"auto","created_at":"2025-05-22 13:24:45","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":9549,"visible":true,"origin":"","legend":"\u003cp\u003eTime to achieve adequate preoxygenation\u003c/p\u003e\n\u003cp\u003e(\u003csup\u003e*\u003c/sup\u003e) P = 0,009: between Group TVB and Group PSV\u003c/p\u003e\n\u003cp\u003e(\u003csup\u003e†\u003c/sup\u003e) P \u0026lt; 0,001: between Group TVB and Group PSV-PEEP\u003c/p\u003e\n\u003cp\u003e(\u003csup\u003e‡\u003c/sup\u003e) P = 0,001: between Group PSV and Group PSV-PEEP\u003c/p\u003e\n\u003cp\u003e(\u003csup\u003e§\u003c/sup\u003e) P = 0,003: between Group TVB and Group PSV\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6321502/v1/7f6dd8e4c2b78c28c62cbfc2.png"},{"id":93956240,"identity":"f0afc70e-3906-4545-ba63-87ae2647f812","added_by":"auto","created_at":"2025-10-20 16:11:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1076137,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6321502/v1/f16c137a-f25e-404f-87ec-14c63db415d1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eAn algorithmic approach to preoxygenation: Stepwise addition of pressure support and positive end-expiratory pressure when tidal volume breathing is inadequate. A randomised controlled trial\u003c/p\u003e","fulltext":[{"header":"Background","content":"\u003cp\u003eThe most common problems in airway management are difficulty, delay or failure to secure the airway. More than 90% of cases of difficult tracheal intubation and difficult mask ventilation cannot be anticipated by preoperative assessment (N\u0026oslash;rskov et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Prolongation of nonhypoxemic apnea time is crucial to provide safe airway management (Artime et al. 2020). Filling the functional residual capacity of the lungs with oxygen is the main way to increase nonhypoxemic apnea time. Preoxygenation is performed before induction of anesthesia and tracheal intubation and routinely recommended for all patients (Bell \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Adequate preoxygenation is an end-tidal oxygen (ETO\u003csub\u003e2\u003c/sub\u003e) value of 90% or higher (Berry at al. 1994.)\u003c/p\u003e \u003cp\u003eThree minutes of spontaneous tidal volume breathing (TVB) of 100% oxygen with a face mask is the conventional method of preoxygenation (Hamilton and Eastwood \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1955\u003c/span\u003e). Later, techniques such as deep breathing (Gold et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1981\u003c/span\u003e) vital capacity breathing (Russell et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1987\u003c/span\u003e), noninvasive positive pressure ventilation (NIPPV) (Herriger at al. 2004) and high flow nasal oxygen (HFNO) (Ng at al. 2018) have also been described. Deep breathing can reduce ETCO\u003csub\u003e2\u003c/sub\u003e (Nimmagadda at al. 2016) and HFNO requires special equipment. It has been reported that NIPPV techniques such as pressure support ventilation (PSV) and positive end-expiratory pressure (PEEP) can increase the success rate to 100%, (Arab at al. 2016) however adverse effects such as discomfort and gastric distension may be observed in patients (Delay at al. 2008; Bouroche \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Tianliang 2019). In published studies, a single preoxygenation technique was generally used, determined at the beginning for each patient, and did not change throughout the administration; combining different techniques in a stepwise approach was not encountered.\u003c/p\u003e \u003cp\u003eIn the present study, to optimize the risk-benefit ratio, it was considered that NIPPV techniques were not need in patients whose target ETO\u003csub\u003e2\u003c/sub\u003e (\u0026ge; 90%) was achieved within 3 min with conventional TVB for preoxygenation; it was aimed to test the hypothesis that an algorithmic approach based on adding PSV and PEEP, where adequate preoxygenation cannot be achieved after 3 min with TVB, will both increase the percentage of preoxygenated patients and shorten the preoxygenation time.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThe study was performed on 200 patients planned for general anesthesia for elective surgery, aged 18\u0026ndash;65 years, American Society of Anesthesiologists physical status classification 1\u0026ndash;2, without premedication and ETO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;90% at the end of the 3rd minute with spontaneous TVB of 100% oxygen.\u003c/p\u003e \u003cp\u003eThe exclusion criteria were as follows: patients who were hemodynamically unstable and required oxygen support in the preoperative period; patients undergoing thoracic or emergency surgery; patients with high intracranial or intraocular pressure for whom positive pressure ventilation may be indirectly harmful; patients with a body mass index (BMI) of 35 kg/m\u0026sup2; or above; patients who were pregnant; and male patients with beards that may cause leakage in mask ventilation.\u003c/p\u003e \u003cp\u003eThe recommended check of the anesthesia machine was performed properly. The gas analysis line was connected to the elbow of the Y-connector on the circle system. The system was flushed for 30 seconds by activating the oxygen bypass valve to remove room air.\u003c/p\u003e \u003cp\u003eThe demographic data, peripheral oxygen saturation (SpO₂), noninvasive systolic (SAP) and diastolic (DAP) arterial pressures and heart rate (HR) values were recorded. Fresh gas flow was started at 12 L/min with 100% oxygen. The adjustable pressure limiting valve was fully opened to allow spontaneous breathing without resistance. All patients were informed that a face mask would be placed to deliver oxygen, and the mask was then placed tightly to prevent leakage. ETO\u003csub\u003e2\u003c/sub\u003e values were monitored continuously.\u003c/p\u003e \u003cp\u003eAccording to a computer-generated randomization table, the patients were randomly assigned to one of two groups (Group TVB and Group PSV). In the patients in Group TVB, the tidal volume breathing was maintained for two more minutes. Group PSV received inspiratory pressure support of 6 cmH\u003csub\u003e2\u003c/sub\u003eO for +\u0026thinsp;1 min. At the end of four minutes, patients whose ETO₂ value had not reached a minimum of 90% were randomly divided into two groups again. One group continued with PSV, while the other was administered 4 cmH₂O PEEP in addition to PSV (Group PSV-PEEP).\u003c/p\u003e \u003cp\u003eWhen adequate preoxygenation was achieved, the duration of preoxygenation, SpO\u003csub\u003e2\u003c/sub\u003e, end-tidal carbon dioxide (ETCO\u003csub\u003e2\u003c/sub\u003e), arterial blood pressure, and heart rate values were recorded. Any adverse effects, such as discomfort or gastric distension, were noted.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical methods\u003c/h2\u003e \u003cp\u003eA power analysis was performed based on the rates of patients who could not achieve adequate preoxygenation with tidal volume ventilation and positive pressure support ventilation in a similar study (Hanouz at al. 2015). This analysis calculated that 198 participants (at least 99 per group) would be required to achieve 80% power at a 95% confidence level.\u003c/p\u003e \u003cp\u003eData were analyzed using SPSS (Statistical Package for the Social Sciences: IBM SPSS Statistics 25 software; Armonk, NY: IBM Corp.). Continuous variables were presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation, while categorical variables were presented as frequency and percentage. Before proceeding with the relevant analyses, normality assumptions for continuous variables were assessed by comparing the Kolmogorov-Smirnov and Shapiro-Wilk statistical values, evaluating skewness and kurtosis values, and interpreting Q-Q plots. Since the data showed a normal distribution, parametric tests were used. The difference between independent groups was analyzed using an independent samples t-test and One-Way Anova, and the difference between dependent groups was analyzed with paired samples t-test. If normality assumptions were not met, non-parametric tests were used. The difference between independent groups was analyzed using the Mann-Whitney U test, while the Wilcoxon signed-rank test was used for dependent groups. A χ\u003csup\u003e2\u003c/sup\u003e test was used to determine the differences between categorical variables. Statistical significance was considered at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eOf the 378 patients preoxygenated with spontaneous tidal volume breathing, 178 (47%) with ETO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026ge;\u0026thinsp;90 at the end of the 3rd minute were excluded. The study included 200 patients (53%) with ETO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;90 (Fig. 1). This study was conducted in a single tertiary hospital, from March 2020 to March 2021.\u003c/p\u003e\n\u003cp\u003eThe groups were similar regarding patient characteristics (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"char\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\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\u003ePatient characteristics (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGroup TVB\u003c/p\u003e\n \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;100)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGroup PSV\u003c/p\u003e\n \u003cp\u003e(\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;100)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP\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\u003e\u003cstrong\u003eAge (years)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45\u0026thinsp;\u0026plusmn;\u0026thinsp;15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,445\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSex\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eMale/Female\u003c/strong\u003e\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\u003e71/29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,013\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBMI (kg/m\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25,9\u0026thinsp;\u0026plusmn;\u0026thinsp;3,8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26,0\u0026thinsp;\u0026plusmn;\u0026thinsp;4,3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,919\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eASA 1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70 (%70)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e57 (%57)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" rowspan=\"2\"\u003e\n \u003cp\u003e0,078\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30 (%30)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43 (%43)\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\u003eBMI, body mass index; ASA, The American Society of Anesthesiologists Physical Status Classification System\u003c/p\u003e\n\u003cp\u003eAt the end of the 4th min, the percentage of patients with adequate preoxygenation was significantly lower in Group TVB (52%) compared with Group PSV (76%; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). At the end of the 5th min, adequate preoxygenation was not achieved in 3 patients in Group TVB, whereas it was completed in all patients in Group PSV (Fig. 2).\u003c/p\u003e\n\u003cp\u003eIn patients who achieved adequate preoxygenation at the end of the 4th minute, the mean time was significantly shorter in the Group TVB (202.35\u0026thinsp;\u0026plusmn;\u0026thinsp;16.14 s) (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;52/100) compared with Group PSV (209.75\u0026thinsp;\u0026plusmn;\u0026thinsp;14.98 s; P\u0026thinsp;=\u0026thinsp;0.009) (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;76/100). In patients who achieved adequate preoxygenation at the end of the 5th minute, the mean durations were 274.90\u0026thinsp;\u0026plusmn;\u0026thinsp;18.55 s in Group TVB, 268.94\u0026thinsp;\u0026plusmn;\u0026thinsp;12.24 s in Group PSV and 252.38\u0026thinsp;\u0026plusmn;\u0026thinsp;7.46 s in Group PSV-PEEP. The differences between Group TVB and Group PSV-PEEP and between Group PSV and Group PSV-PEEP were significant (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001 and P\u0026thinsp;=\u0026thinsp;0.001, respectively). The total duration of preoxygenation was significantly longer in Group TVB (237.17\u0026thinsp;\u0026plusmn;\u0026thinsp;40.31 s) compared with Group PSV (222.63\u0026thinsp;\u0026plusmn;\u0026thinsp;27.24 s; P\u0026thinsp;=\u0026thinsp;0.003) (Fig. 3).\u003c/p\u003e\n\u003cp\u003eSpO\u003csub\u003e2\u003c/sub\u003e values were significantly higher in both groups after preoxygenation (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). No significant difference was found between the groups regarding arterial pressure, heart rate and ETCO\u003csub\u003e2\u003c/sub\u003e values (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eAdverse effects observed in the study were epigastric distension in only 1 patient in Group PSV-PEEP and discomfort in 1 patient in Group TVB and 2 patients in Group PSV. No patient required termination of the procedure.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"char\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\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\u003eSpO\u003csub\u003e2\u003c/sub\u003e, ETCO\u003csub\u003e2\u003c/sub\u003e, systolic/diastolic arterial pressures and heart rate (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"7\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eGroup TVB\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eGroup PSV\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBefore-PO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAfter-PO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBefore-PO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAfter-PO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP\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\u003e\u003cstrong\u003eSpO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003e(%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e98,87\u0026thinsp;\u0026plusmn;\u0026thinsp;1,14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e99,89\u0026thinsp;\u0026plusmn;\u0026thinsp;0,37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e97,99\u0026thinsp;\u0026plusmn;\u0026thinsp;1,82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e99,88\u0026thinsp;\u0026plusmn;\u0026thinsp;0,38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eETCO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003e(mmHg)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36,70\u0026thinsp;\u0026plusmn;\u0026thinsp;2,43\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=\"char\"\u003e\n \u003cp\u003e36,67\u0026thinsp;\u0026plusmn;\u0026thinsp;2,55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,932\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSAP (mmHg)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e133,50\u0026thinsp;\u0026plusmn;\u0026thinsp;20,29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e131,79\u0026thinsp;\u0026plusmn;\u0026thinsp;20,97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,194\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e140,52\u0026thinsp;\u0026plusmn;\u0026thinsp;22,25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e139,70\u0026thinsp;\u0026plusmn;\u0026thinsp;22,37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,524\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eDAP (mmHg)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e76,59\u0026thinsp;\u0026plusmn;\u0026thinsp;11,11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e76,18\u0026thinsp;\u0026plusmn;\u0026thinsp;11,83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,605\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79,71\u0026thinsp;\u0026plusmn;\u0026thinsp;12,97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e80,13\u0026thinsp;\u0026plusmn;\u0026thinsp;13,55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,641\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eHR (bpm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81,34\u0026thinsp;\u0026plusmn;\u0026thinsp;12,84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81,39\u0026thinsp;\u0026plusmn;\u0026thinsp;13,93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,953\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e77,03\u0026thinsp;\u0026plusmn;\u0026thinsp;12,48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e76,10\u0026thinsp;\u0026plusmn;\u0026thinsp;12,95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0,216\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\u003ePO, Preoxygenation; SpO\u003csub\u003e2\u003c/sub\u003e, peripheral oxygen saturation; ETCO\u003csub\u003e2\u003c/sub\u003e, end-tidal carbon dioxide; SAP, systolic arterial pressure; DAP, diastolic arterial pressure; HR, heart rate (beats per minute)\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eMost anesthesia malpractice claims, including death and brain damage, arise from difficult airway management during the induction period (Peterson at al. 2005). Routine preoxygenation of all patients is an effective measure that prolongs the safe apnea time (Bell \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). It can be considered like the \u0026lsquo;safety belt\u0026rsquo; of airway management.\u003c/p\u003e \u003cp\u003eIn the present study, which focused on an algorithmic approach, the rate of inadequate preoxygenation with 3 min TVB was 53%. This is comparable to the 50% and 56% rates reported in previous studies (Baillard at al. 2019; Baillard at al. 2014). The standard preoxygenation technique is inadequate in approximately half of the patients.\u003c/p\u003e \u003cp\u003eIn patients who could not achieve adequate preoxygenation at the end of the third minute with the standard technique in the present study, when TVB was continued for another minute, approximately half (52%) of these patients achieved adequate preoxygenation, while when PSV was added for one minute, this rate increased to approximately three-quarters (76%; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Although this time difference was statistically significant, we considered that it was not clinically significant. By the end of the five minutes, the proportion of patients in TVB group who had reached adequate preoxygenation was 97%, while in PSV group, this rate was 100%. Hanouz et al.( Hanouz et al.2015) reported in their study, in which they used one of three methods from the beginning that the rates of inadequacy at 250th seconds were 27% with TVB, 15% with PSV, and 10% with PSV-PEEP, and all patients achieved an adequate preoxygenation with all three methods by the end of the fifth minute. Despite notable methodological differences between the two studies, the rates can be regarded as similar once the necessary adaptations are made. Baillard et al.(Baillard et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) reported that the rate of inadequate preoxygenation with 5 minutes of TVB was 30% in their studies investigating the risk factors for difficult preoxygenation. This rate is much higher than the rate in the present study, and the possible reason is that patients at risk of difficult preoxygenation were excluded in the present study. When different methods were compared in terms of the time to reach adequate preoxygenation, it was shown that the order was PSV-PEEP\u0026thinsp;\u0026lt;\u0026thinsp;PSV\u0026thinsp;\u0026lt;\u0026thinsp;TVB(Hanouz et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Taxak et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), the findings in the present study are also similar. Additionally, in another study conducted by Hanouz et al.( Hanouz et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) it was emphasized that the PSV-PEEP application can also prevent air leakage, which may occur due to mask-face incompatibility.\u003c/p\u003e \u003cp\u003eDifferent pressure values have been used for NIPPV in preoxygenation; Delay et al. (Delay et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) reported a pressure of 6 cmH\u003csub\u003e2\u003c/sub\u003eO for PSV and 4 cmH\u003csub\u003e2\u003c/sub\u003eO for PEEP, while Hanouz et al. (Hanouz at al. 2015) preferred higher pressures (12 and 6 cmH\u003csub\u003e2\u003c/sub\u003eO respectively). In the present study low pressure levels were chosen as 6 cmH\u003csub\u003e2\u003c/sub\u003eO PSV and 4 cmH\u003csub\u003e2\u003c/sub\u003eO PEEP. Especially at high pressure levels, NIPPV and PEEP can affect hemodynamics by decreasing venous return and cardiac output (Kallet et al. 2009). Hemodynamics did not change significantly in the present study; previous studies have also reported no significant change in hemodynamics when applying NIPPV with PEEP for preoxygenation (Delay et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Taxak et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). It can be considered that the choice of low pressures and short processing time may have played a role in this.\u003c/p\u003e \u003cp\u003eThe adverse effects that may be observed due to NIPPV include discomfort and gastric distension. In the present study, discomfort and epigastric distension were rare, and none of the patients required discontinuation of the procedure. In the study conducted by Delay et al (Delay et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). gastric distension was scored from 0-100 during laparoscopy by a surgeon blinded to the preoxygenation method, and it was reported a modest, although significant, increase in gastric distension and no adverse effects with NIPPV techniques compared with TVB. Georgescu et al. (Georgescu et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) reported that they stopped the procedure in one (6%) of 15 patients undergoing NIPPV for preoxygenation because of discomfort. It seems that the adverse effects, such as discomfort and epigastric distension due to NIPPV for preoxygenation, are rare and clinically insignificant.\u003c/p\u003e \u003cp\u003eIt should be noted that the present study has some limitations. The study focused on the percentage and duration of patients in whom algorithmically applied preoxygenation was successful, but the duration of nonhypoxemic apnea was not examined due to ethical concerns. Since the method is unsuitable for a blind study, the risk of bias could not be completely excluded. Epigastric distension due to positive pressure was evaluated by observation only; a reliable measurement method could not be used. In addition, since patients in special risk groups such as the elderly, pregnant women, children, and the morbidly obese were not included in the study, possible differences regarding these groups could not be analyzed. Further, well-designed studies are needed to determine whether the algorithmic approach is effective in patients in special risk groups.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, the hypothesis that an algorithmic approach based on the stepwise addition of PSV and PEEP in patients who cannot be adequately preoxygenated with TVB will provide adequate preoxygenation in a shorter time and in all patients has been confirmed.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eTVB\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eTidal volume breathing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePSV\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003epressure support ventilation\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePEEP\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\"\u003eETO\u003csub\u003e2\u003c/sub\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eend-tidal oxygen\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNIPPV\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003enoninvasive positive pressure ventilation\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eHFNO\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ehigh flow nasal oxygen\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBMI\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\"\u003eSpO₂\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eperipheral oxygen saturation\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eSAP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003esystolic arterial pressure\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDAP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ediastolic arterial pressure\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eHR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eheart rate\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eASA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eThe American Society of Anesthesiologists Physical Status Classification System\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePO\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePreoxygenation\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eETCO\u003csub\u003e2\u003c/sub\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eend-tidal carbon dioxide\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u003c/strong\u003e None\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo;s contributions:\u0026nbsp;\u003c/strong\u003eStudy conception, design, validation: \u0026Ccedil;.T. and E.T.; data acquisition: \u0026Ccedil;.T., S.Y.T.; analysis: \u0026Ccedil;.T., S.Y.T., E.T.; data interpretation: \u0026Ccedil;.T., S.Y.T., E.T.; draf-ing of the manuscript: \u0026Ccedil;.T., E.T.; review of the manuscript: \u0026Ccedil;.T., S.Y.T., E.T. All authors read and approved the submission and publication of this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding support:\u0026nbsp;\u003c/strong\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u0026nbsp;\u003c/strong\u003eNo datasets were generated or analysed during the current study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate:\u0026nbsp;\u003c/strong\u003eThis study was conducted with the approval of the Pamukkale University (Denizli, T\u0026uuml;rkiye) Ethics Committee dated 18.02.2020 and number 60116787-020/15624 and with the informed written consent of the patients.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u0026nbsp;\u003c/strong\u003eAll authors approved the version of the manuscript to be published.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eArab OA, Guinot PG, Dimov E, et al. 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Saudi Med J 2019; 40: 989\u0026ndash;995. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.15537/smj.2019.10.24306\u003c/span\u003e\u003cspan address=\"10.15537/smj.2019.10.24306\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\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":"perioperative-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"peri","sideBox":"Learn more about [Perioperative Medicine](http://perioperativemedicinejournal.biomedcentral.com)","snPcode":"13741","submissionUrl":"https://submission.nature.com/new-submission/13741/3","title":"Perioperative Medicine","twitterHandle":"@EMSurgeryBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Algorithm, Stepwise, Tidal volume breathing, Positive end expiratory pressure, Preoxygenation, Pressure support ventilation","lastPublishedDoi":"10.21203/rs.3.rs-6321502/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6321502/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003ePreoxygenation is crucial for airway management safety. The standard method for preoxygenation is tidal volume breathing (TVB). This study aimed to determine whether an algorithmic approach which involves stepwise adding pressure support ventilation (PSV) and positive end-expiratory pressure (PEEP) when TVB is inadequate, would improve preoxygenation.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003e200 patients planned for general anesthesia and having end-tidal oxygen (ETO\u003csub\u003e2\u003c/sub\u003e)\u0026thinsp;\u0026lt;\u0026thinsp;90% after 3 min TVB were randomly divided into two: TVB was continued or 6 cmH\u003csub\u003e2\u003c/sub\u003eO PSV was added. After 4 min, PSV patients having ETO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;90% were divided into two again: either PSV was continued or 4 cmH\u003csub\u003e2\u003c/sub\u003eO PEEP was also added to PSV. The time to achieve ETO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026ge;\u0026thinsp;90% and adverse effects were noted.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eAfter 4 min, patients with adequate preoxygenation was significantly lower with TVB (52%) compared with PSV (76%; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). After 5 min, it was 97% and 100%, respectively. The mean durations of adequate preoxygenation with TVB, PSV and PSV-PEEP between 4\u0026ndash;5 min were 274.90\u0026thinsp;\u0026plusmn;\u0026thinsp;18.55, 268.94\u0026thinsp;\u0026plusmn;\u0026thinsp;12.24 and 252.38\u0026thinsp;\u0026plusmn;\u0026thinsp;7.46 s, respectively. The differences between TVB and PSV-PEEP (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and between PSV and PSV-PEEP (P\u0026thinsp;=\u0026thinsp;0.001) were significant. Total time was significantly longer with TVB (237.17\u0026thinsp;\u0026plusmn;\u0026thinsp;40.31 s) compared with PSV (222.63\u0026thinsp;\u0026plusmn;\u0026thinsp;27.24 s; P\u0026thinsp;=\u0026thinsp;0.003).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eAn algorithmic approach, stepwise adding PSV and PEEP in patients inadequately preoxygenated with standard TVB, ensures adequate preoxygenation in all patients and reduces the time required. Although this time difference was statistically significant, we considered that it was not clinically significant. No serious adverse effects were observed.\u003c/p\u003e\u003ch2\u003eTrial registration:\u003c/h2\u003e \u003cp\u003eNCT06736197\u003c/p\u003e","manuscriptTitle":"An algorithmic approach to preoxygenation: Stepwise addition of pressure support and positive end-expiratory pressure when tidal volume breathing is inadequate. A randomised controlled trial","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-22 13:24:40","doi":"10.21203/rs.3.rs-6321502/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-15T05:43:16+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"136961418321443009514947646176476340964","date":"2025-06-12T14:44:53+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-11T15:46:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"109823070778316089508933052526456985643","date":"2025-06-10T14:35:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-03T00:28:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"4118164979605868565275195438371228156","date":"2025-05-19T15:15:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-19T14:43:47+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-27T23:03:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-27T23:03:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Perioperative Medicine","date":"2025-03-27T14:36:09+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"perioperative-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"peri","sideBox":"Learn more about [Perioperative Medicine](http://perioperativemedicinejournal.biomedcentral.com)","snPcode":"13741","submissionUrl":"https://submission.nature.com/new-submission/13741/3","title":"Perioperative Medicine","twitterHandle":"@EMSurgeryBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"69a40003-2578-4f63-9507-839390be8208","owner":[],"postedDate":"May 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T16:07:58+00:00","versionOfRecord":{"articleIdentity":"rs-6321502","link":"https://doi.org/10.1186/s13741-025-00575-z","journal":{"identity":"perioperative-medicine","isVorOnly":false,"title":"Perioperative Medicine"},"publishedOn":"2025-10-15 15:58:28","publishedOnDateReadable":"October 15th, 2025"},"versionCreatedAt":"2025-05-22 13:24:40","video":"","vorDoi":"10.1186/s13741-025-00575-z","vorDoiUrl":"https://doi.org/10.1186/s13741-025-00575-z","workflowStages":[]},"version":"v1","identity":"rs-6321502","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6321502","identity":"rs-6321502","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}