The superiority of one-day dietary preparation over three-day dietary preparation for high-intensity focused ultrasound treatment: a retrospective study

Objective To compare dietary preparation durations and evaluate optimal diet types before high-intensity focused ultrasound (HIFU) treatment.

Five hundred patients with uterine fibroids or adenomyosis undergoing HIFU were enrolled. Initially, 300 patients were randomized to 3-day, 2-day, or 1-day dietary preparation (n = 100 each) to compare enema frequency, intestinal gas volume, comfort scores, and compliance. Subsequently, the 1-day group (Group A, clear liquid diet) was compared with 200 additional patients assigned to Group B (semiliquid diet) or Group C (low-residue diet) regarding intestinal cleansing efficacy, comfort scores, serum electrolyte changes, and physical recovery.

No significant differences were observed in enema frequency or intestinal gas volume among the three duration groups (p > 0.05); however, the 1-day group demonstrated superior comfort scores (p < 0.05). Within 1-day preparation, the low-residue diet group exhibited higher comfort scores, reduced intestinal gas volume, and better compliance compared to clear liquid and semiliquid diets (p < 0.05).

One-day dietary preparation is superior to three-day preparation for bowel cleansing before HIFU. Low-residue diet effectively meets clinical bowel cleansing requirements while achieving high patient acceptability. We recommend one-day low-residue diet as the preferred bowel preparation protocol for patients undergoing HIFU treatment.

During high-intensity focused ultrasound (HIFU) ablation for abdominal solid tumors, the presence of intraluminal fecal material or gas within the intestinal tract poses a significant risk of bowel perforation. This risk is primarily due to ultrasound-induced thermal effects and cavitation phenomena [Citation1,Citation2]. Therefore, preoperative bowel preparation should be performed to eliminate colonic contents and reduce gas accumulation, as this is critical for ensuring procedural safety and efficacy. The traditional clinical protocol utilizes a three-day preoperative bowel preparation regimen consisting of dietary modification combined with laxatives and/or enemas [Citation3]. The dietary protocol follows a progressively restrictive pattern: low-residue diet on day 1, transitioning to a semi-liquid diet on day 2, and culminating in a clear liquid diet on day 3 [Citation3]. However, prolonged dietary restrictions and nutritionally unbalanced dietary regimens lead to poor patient compliance, and sometimes the bowel preparation is still inadequate, necessitating additional mechanical cleansing procedures. Clinically significant adverse effects such as severe nausea, vomiting, abdominal cramps, hunger-related fatigue, insomnia and neuropsychiatric manifestations are commonly reported. These preparatory challenges can lead to electrolyte imbalances (particularly hypokalemia and hyponatremia) secondary to fluid shifts, which not only compromise patient comfort, but also negatively impact procedural tolerability and postoperative recovery outcomes [Citation4]. Patients undergoing colonoscopy and HIFU therapy share comparable preprocedural bowel preparation requirements. Current clinical guidelines recommend implementing a low-residue dietary regimen for 24 h preceding colonoscopy to optimize bowel cleansing efficacy while reducing procedure-related complications [Citation5,Citation6]. This clinical similarity raises a crucial question: Can strategic modifications to the duration and composition of dietary restrictions achieve adequate bowel preparation for HIFU procedures, potentially optimizing patient compliance and minimizing gastrointestinal discomfort?

This research was approved by the ethics committee at Deyang People’s Hospital (the approved protocol number: 2025-04-111-K01). The requirement for informed consent was waived. Initially, we planned a prospective study to investigate the bowel cleansing effects of different preoperative dietary restriction periods and nutritional components before HIFU treatment. However, the study failed due to improper grouping methods and failure to complete clinical trial registration in a timely manner. Nevertheless, the collected data still provided valuable insights for improving the dietary protocols and offered clues for future research, we have shifted to a retrospective analysis. The retrospective study enrolled 500 consecutive gynecological patients who underwent HIFU ablation at Deyang People’s Hospital between January 1, 2022 and January 1, 2024, all of whom were from the Chinese population. The inclusion criteria were as follows: 1) radiologically confirmed target localization in accordance with HIFU treatment principles [Citation7]; 2) provision of written informed consent as approved by the Institutional Review Board. The exclusion criteria included: 1) decompensated systemic comorbidities contraindicating HIFU therapy; 2) preexisting diabetes mellitus (fasting glucose ≥ 7.0 mmol/L); 3) age ≥ 60 years or body mass index (BMI) ≥ 30 kg/m2 (WHO obesity class I) or < 18.5 kg/m2; 4) history of chronic bowel dysfunction (≥ 3 constipation episodes/week) or abdominopelvic surgery; 5) baseline malnutrition (serum albumin < 35 g/L) or uncorrected electrolyte abnormalities (potassium < 3.5 mmol/L, sodium < 135 mmol/L). For gynecological patients with fibroids and adenomyosis who met these exclusion criteria, the usual course was traditional treatment options such as medical management, myomectomy, or hysterectomy. To explore the optimal preoperative dietary preparation protocol, a total of 500 cases were retrospectively included in this study after exclusion. According to the sample size calculation, these cases were divided into multiple groups with 100 participants in each group, and the efficacy of different preparation durations among three of these groups was first compared in the first phase. The control group (3-day group) followed a standardized 3-day bowel preparation protocol: on day 1, a low-residue diet (rice, noodles, and controlled portions of meat, vegetables, and fruits compliant with American Society of Anesthesiologists [ASA] guidelines) [Citation8]; on day 2, a semi-liquid regimen comprising cereal porridges and starch-based supplements; on day 3, a clear liquid diet limited to strained soups, broth, and glucose solution. The first experimental group underwent a modified 2-day preparation (2-day group): on day 1, a semi-liquid diet identical to that of the 3-day group; on day 2, the same clear liquid protocol as the final day of the 3-day group. The second experimental group received an accelerated 1-day preparation (1-day group) consisting solely of clear liquids on the day before intervention. Based on preliminary results showing that 1-day dietary preparation achieved equivalent bowel cleanliness and superior patient comfort, the second phase of this study further added two more groups (100 participants in each group) on the basis of the 1-day dietary second experimental group from the first phase, to compare the efficacy of different 1-day dietary structures: Group A (clear liquid diet, i.e. the original second experimental group), Group B (semi-liquid diet), and Group C (low-residue diet). All patients across all groups received a standardized polyethylene glycol electrolyte (PEG) solution regimen as part of bowel preparation: an initial 2-L oral dose was administered starting at 16:00 on the preoperative day, with consumption evenly distributed over 2 h; a subsequent 1-L oral dose was administered at 06:00 on the morning of surgery, to be completed within 1 h. Patients with adequate bowel preparation (Grade 1 or 2 on the semi-objective assessment scale) proceeded directly to surgical intervention without additional preparation, while those with suboptimal preparation (Grade > 2) were additionally administered a standardized 500-ml warm normal saline enema (37 °C) until the Grade 2 standard was achieved. The efficacy of bowel preparation, as the primary outcome measure, was evaluated by assessing intestinal residual stool volume and intraluminal gas content after the completion of all preparatory procedures; residual stool was graded on a 3-point scale as follows: Grade 1 (Satisfactory; ): No solid stool or fecal residue present, with clear intraluminal fluid; Grade 2 (Partially effective; ): No formed stool identified, with turbid fecal liquid present; Grade 3 (Inadequate; ): Persistent solid fecal matter or residual sludge associated with opaque yellowish-brown liquid stool. Transabdominal ultrasonography was performed using a B-mode probe (Ca430, MyLab 70, Esaote, Genova, Italy) that constituted a component of the HIFU system subsequently utilized for uterine ablation; this imaging modality was used to assess intraluminal gas surrounding the uterus, which was categorized as: none (no obvious gas-containing intestinal segments; ), sparse (gas present in 1–2 bowel segments; ), moderate (gas present in 3–5 bowel segments; ), and abundant (gas present in more than 5 bowel segments; ). The grading of residual stool volume was jointly evaluated by two HIFU-specialized physicians and one HIFU-specialized nurse. Secondary outcome measures included laboratory tests, physical measurements, and patient comfort evaluation: 3 ml of venous blood was collected from all enrolled patients by venipuncture before and after bowel preparation to detect serum potassium and sodium concentrations, with the numerical variations of these indices calculated and analyzed; fasting body weight (measured with patients wearing thin, form-fitting clothing) was recorded pre- and post-preparation with an accuracy of 0.1 kg, and the weight differences were documented; patient comfort was assessed using the National Institutes of Health Visual Analogue Scale (VAS) with scores ranging from 0 (no discomfort at all) to 10 (severe discomfort); postoperatively, patients were instructed to record the time required for the complete recovery of dietary patterns and physical strength to preoperative baseline levels. Statistical analyses were conducted using SPSS 23.0 software. Continuous and ordinal variables were presented as median [interquartile range, IQR], and categorical variables as n (%). The Kruskal-Wallis H test was used to compare medians of continuous and ordinal variables across multiple independent groups; for indices with a significant overall result, nonparametric pairwise comparisons were further performed to identify specific intergroup differences. Fisher’s exact test with simulated p-values (2000 replicates) was applied for intergroup comparisons of categorical variables. A two-tailed p < 0.05 was considered statistically significant for all analyses.

summarizes the demographic characteristics of the study population, with no statistically significant intergroup differences observed in baseline variables. The median age was comparable across the 3-Day, 2-Day and 1-Day Groups, at 44 years (interquartile range [IQR]: 38–48), 45 years (IQR: 41–47) and 44 years (IQR: 39–47), respectively (p = 0.69 for mean age). Consistent homogeneity was also noted in median body weight across the three groups (58 kg [IQR: 53–63], 55 kg [IQR: 50.5–60.5] and 55 kg [IQR: 50.5–60], respectively), with no significant difference in mean weight (p = 0.06). The mean body mass index (BMI) values for the 3-Day, 2-Day and 1-Day Groups were 23.07 kg/m2, 23.10 kg/m2 and 22.68 kg/m2, respectively. Additional analyses of perioperative clinical indices in revealed no statistically significant differences in the number of enemas (p = 0.300) or intestinal gas volume (p = 0.825) among the three groups. While patients in the 1-Day Group reported significantly lower comfort scores compared with those in the 2-Day and 3-Day Groups (p < 0.001), compliance rates were comparable across all groups (p = 0.260). Most importantly, perioperative ultrasound monitoring confirmed that the 1-day preoperative dietary regimen achieved equivalent bowel preparation adequacy for high-intensity focused ultrasound (HIFU) procedures, meeting all predefined clinical requirements. These findings indicated that condensing the preoperative dietary preparation period to 24 h maintained procedural readiness for HIFU while optimizing clinical feasibility. To further refine this optimized 1-day preoperative protocol, we subsequently investigated the impact of different dietary formulations (clear liquid, semi-liquid and low-residue diets) on HIFU treatment outcomes. As shown in , comparative analyses of the three dietary formulations within the 1-day preparation window identified a statistically significant difference in intestinal gas volume between the semi-liquid and low-residue diet subgroups (p = 0.010). In contrast, no significant differences were observed in stool frequency (p = 0.561) or the number of enemas (p = 0.050) across the clear liquid, semi-liquid and low-residue diet subgroups. Notable intergroup differences (all p < 0.05) were also detected in patient-reported comfort scores, self-assessed compliance ratings, serum potassium fluctuations, time to resumption of regular diet and perioperative weight fluctuations among the three dietary subgroups (). Specifically, the low-residue diet subgroup exhibited superior gastrointestinal tolerance, whereas the semi-liquid diet subgroup demonstrated more favorable outcomes in dietary and physical recovery. In contrast, serum sodium concentrations and key physical recovery timelines remained comparable across all three subgroups (all p > 0.05), suggesting that these physiological and recovery parameters were independent of the preoperative dietary interventions examined in the present study.

Given its noninvasive nature, HIFU has gained increasing clinical adoption for ablating solid abdominal tumors. However, precise targeting during HIFU therapy mandates rigorous bowel preparation protocols, as intestinal gas-containing structures may cause acoustic interference and pose risks of thermal injury. This necessitates standardized bowel cleansing regimens to ensure procedural safety while maintaining therapeutic efficacy. The traditional 3 - day preoperative dietary protocol, despite requiring strict compliance with medical guidelines, often clashes with patients’ customary dietary patterns, leading to subpar adherence [Citation5]. This restrictive diet gives rise to discernible physiological repercussions, such as diminished physical endurance, unintentional weight loss, and intense hunger-related discomfort [Citation9]. Clinical evidence demonstrates that approximately 20% of suboptimal bowel preparation cases are directly associated with patients’ limited tolerance for protracted dietary alterations [Citation10,Citation11]. Moreover, metabolic analyses disclose that a 48-h dietary restriction results in inadequate energy intake (in < 59% of cases) and protein intake (in < 45% of cases) when compared to the recommended thresholds [Citation12]. These findings underscore the substantial physiological and psychological burdens imposed by the conventional three-day dietary protocols prior to HIFU procedures. Our comparative analysis demonstrated that the 1-day bowel preparation regimen achieved comparable clinical efficacy to traditional 2- and 3-day protocols, with a 99% successful cleansing rate and minimal re-enema requirement. Notably, patient-reported outcomes measured by validated questionnaires revealed significantly lower comfort scores in the 1-day group, indicating enhanced compliance and procedural tolerance. Serum electrolyte tests showed that there were no differences in sodium ion fluctuations among the groups, while the changes in potassium ions demonstrated greater dispersion in the cohort with a one-day (bowel preparation) period. Importantly, no clinically significant hypokalemia (< 3.5 mmol/L) or hyponatremia (< 135 mmol/L) occurred across groups. Systematic monitoring of adverse events identified higher incidence rates of dietary restriction-related complications in extended regimens, primarily manifesting as unintentional weight loss, decreased physical endurance, and transient appetite disturbances. These findings suggest the 1-day protocol optimizes the risk-benefit ratio by maintaining bowel preparation adequacy while minimizing physiological stress and patient burden. Dietary composition critically influences bowel preparation outcomes. Comparative studies in pre-colonoscopy protocols demonstrate that clear liquid and semi-liquid regimens, despite rapid gastrointestinal absorption, frequently induce adverse symptoms including hunger-related discomfort, abdominal pain, and sleep disruption [Citation13,Citation14]. In contrast, low-residue diets exhibit dual physiological advantages: enhanced satiety through delayed gastric emptying and improved fecal clearance via augmented colonic motility [Citation15,Citation16]. While maintaining equivalent bowel cleansing efficacy to traditional liquid-based preparations [Citation17,Citation18], low-residue protocols demonstrate superior tolerability profiles, with significantly lower incidence rates of nausea, vomiting, and dizziness [Citation4,Citation12]. These mechanistic advantages have positioned low-residue diets as the preferred preoperative nutritional strategy in endoscopic practice, as evidenced by the American Gastroenterological Association’s 24-h pre-procedural recommendation [Citation19]. This consensus aligns with our clinical findings regarding optimized dietary protocols for HIFU pretreatment bowel preparation. This study has several limitations. First, we did not systematically assess potential confounders that may influence bowel preparation quality, including variability in oral polyethylene glycol (PEG) administration schedules, inter-individual differences in habitual dietary patterns, and nutritional disparities associated with two-day versus other preparation regimens. Second, the evaluation of intestinal gas relied on a semi-subjective ultrasonographic approach, which may be prone to measurement bias. In addition, the retrospective, non-blinded study design, together with our preliminary observation of a potentially optimal dietary protocol, introduces the possibility of inadvertent observer bias. Finally, the non-randomized, time-sequential allocation of participants into groups may have resulted in selection bias and limited the generalizability of our findings. Further well-designed, prospective, randomized controlled trials are needed to address these methodological limitations.

Our findings suggest that a one-day regimen of a low-residue diet combined with oral polyethylene glycol (PEG) administration is an effective bowel preparation protocol for abdominal high-intensity focused ultrasound (HIFU) procedures. Compared with traditional preparation methods, this approach achieves adequate bowel cleansing while improving patient tolerability and adherence. Notably, it alleviates adverse effects associated with prolonged fasting and physical deconditioning and further facilitates accelerated postoperative recovery. This combined dietary-PEG bowel preparation strategy thus shows great promise as a standardized preoperative protocol for patients undergoing abdominal HIFU therapy [Citation20]; however, given the inherent limitations of the present study, its clinical value and applicability warrant further validation through well-designed prospective investigations. Disclosure statement No potential conflict of interest was reported by the author(s). Data availability statement The data that support the findings of this study are available from the corresponding author, YW Zhang, upon reasonable request. Additional information Funding

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