Preoxygenation with deep breathing plus pressure support and positive end-expiratory pressure in obese patients and ultrasound assessment of gastric distension: a randomized controlled trial

Abstract Background It is known that anatomical and physiological differences in obese patients make preoxygenation difficult and limit its success. This study aimed to investigate the effects of adding pressure support ventilation (PSV) and positive end expiratory pressure (PEEP), to the deep breathing (DB) technique, utilized as the primary ventilation method, on time required to achieve adequate preoxygenation. The secondary objective was to quantitatively evaluate gastric distension using ultrasonography. Methods Seventy-five adult patients for elective surgery with a body mass index (BMI) ≥ 30 kg/m² and ASA physical status II–III were randomized into three groups: DB alone, DB with PSV (DB + PSV), and DB with PSV plus PEEP (DB + PSV + PEEP). Preoxygenation continued until end-tidal oxygen (EtO₂) reached 90%. The primary outcome was time to EtO₂ ≥90%. Gastric antrum area was ultrasonographically measured before and after preoxygenation to assess gastric distension. Results The time to achieve EtO₂ ≥90% was similar among groups (DB: 96.4 ± 33.1 s; DB + PSV: 82.2 ± 15.1 s; DB + PSV + PEEP: 91.7 ± 22.6 s; P = 0.261). After preoxygenation, the gastric antrum area was significantly increased in all groups compared to baseline ( P < 0.050). These differences in increase were statistically significant among the three groups ( P = 0.025). Antral area increased over time ( P < 0.001). Conclusion In conclusion, adding PSV or PSV+PEEP to DB preoxygenation in obese patients was not shown to shorten the time required to reach target EtO₂ levels. Although gastric antral area increased with an overall group-dependent pattern, no significant baseline-adjusted pairwise differences were observed between groups. Trial registration ClinicalTrials.gov Identifier: NCT07380425 (first submitted date: 11/01/2026; retrospectively registered).