Pressure-Controlled versus Volume-Controlled Ventilation in Low-Flow Anesthesia; Intraoperative Respiratory Mechanics and Postoperative Pulmonary Function: A Randomized Controlled Trial

Abstract Background Pressure-controlled ventilation (PCV) and volume-controlled ventilation (VCV) differ in their effects on airway pressure and lung compliance; however, comparative evidence of their effects during low-flow anesthesia is limited. This study aimed to compare the intraoperative respiratory mechanics and early postoperative pulmonary function between PCV and VCV during low-flow anesthesia in ASA I–II adult patients. Methods In this single-center, prospective, randomized controlled trial, 40 ASA I–II adult patients scheduled for elective surgery were randomized to receive PCV (n = 20) or VCV (n = 20) under low-flow anesthesia. After induction, the fresh gas flow was reduced to 1 L/min. The primary outcome was the peak inspiratory pressure (Ppeak). Secondary outcomes included mean airway pressure (Pmean), dynamic lung compliance (Cdyn), and pre- versus postoperative pulmonary function measured using Triflo incentive spirometry. Data were analyzed using t-tests, Mann–Whitney U tests, repeated-measures ANOVA, or Friedman tests as appropriate, with significance set at p < 0.05. Results Demographic and perioperative variables were comparable between the groups. Ppeak was consistently lower in the PCV group than in the VCV group at all time points (p < 0.001). Pmean values were similar, although VCV demonstrated a significant reduction after transition to low flow (p = 0.004). Cdyn was significantly higher in the PCV group at baseline (62.6 ± 8.5 vs. 48.0 ± 7.4 mL/cmH₂O, p = 0.001), but intergroup differences resolved after low-flow initiation. Postoperatively, inspiratory Triflo performance declined significantly in both groups (PCV: p = 0.025; VCV: p = 0.002), whereas expiratory capacity significantly decreased only in the VCV group (p = 0.014). The between-group differences in postoperative spirometry were not significant. Subgroup analyses showed lower Ppeak with PCV in male patients and in both younger and older subgroups, but no significant sex-by-mode or age-by-mode interactions were observed. Conclusions Under low-flow anesthesia, PCV provided a significantly lower Ppeak than VCV without compromising mean airway pressure, intraoperative compliance, or early postoperative pulmonary function. These findings support PCV as a preferred strategy when minimizing airway pressure is a clinical priority, while confirming that both modes remain safe and effective options for low-risk patients undergoing low-flow anesthesia. Clinical Trial Registry: https://clinicaltrials.gov/study/NCT07305129. Registry identifier : NCT07305129. Retrospectively registered and first submitted date 11.27.2025.