The impact of two different inspiratory to expiratory ratios (1:1 and 1:2) on respiratory mechanics and oxygenation during volume-controlled ventilation in robot-assisted laparoscopic radical prostatectomy: a randomized controlled trial

Background: Volume-controlled ventilation with a prolonged inspiratory to expiratory ratio (I:E ratio) has been used to optimize gas exchange and respiratory mechanics in various surgical settings. We hypothesized that, when compared with an I:E ratio of 1:2, a prolonged I:E ratio of 1:1 would improve respiratory mechanics without reducing cardiac output (CO) during pneumoperitoneum and steep Trendelenburg positioning, both of which can impair respiratory function in robot-assisted laparoscopic radical prostatectomy. Furthermore, we evaluated its effect on oxygenation during robot-assisted laparoscopic radical prostatectomy. Methods: Eighty patients undergoing robot-assisted laparoscopic radical prostatectomy were randomly allocated to receive an I:E ratio of either 1:1 (group 1:1) or 1:2 (group 1:2). The primary endpoint, peak airway pressure (Ppeak), as well as hemodynamic data, including cardiac output (CO) and arterial oxygen tension (PaO₂), were compared between groups at four time points: ten minutes after anesthesia induction (T1), 30 and 60 min after pneumoperitoneum with steep Trendelenburg positioning (T2 and T3), and ten minutes after supine positioning (T4). Overall comparisons were made between groups using linear mixed model analysis with post hoc testing of individual time points adjusted using a Bonferroni correction. Results: Linear mixed model analysis showed a significant overall difference in Ppeak between the two groups (P < 0.001). Post hoc analysis showed a significantly lower mean (SD) Ppeak in group 1:1 than in group 1:2 at T2 [28.4 (4.0) cm H₂O vs 32.8 (5.2) cm H₂O, respectively; mean difference, 4.3 cm H₂O; 95% confidence interval (CI), 2.3 to 6.4; P < 0.001] and T3 [27.8 (3.9) cm H₂O vs 32.6 (5.0) cm H₂O, respectively; mean difference, 4.7 cm H₂O; 95% CI, 2.7 to 6.7; P < 0.001]. The CO assessed over these time points was comparable in both groups (P = 0.784). In addition, there were no significant differences in PaO₂ between the two groups (P = 0.521). Conclusions: Compared with an I:E ratio of 1:2, a ratio of 1:1 lowered Ppeak without reducing CO during pneumoperitoneum and steep Trendelenburg positioning. Nevertheless, our results did not support its use solely for improving oxygenation. This trial was registered at http://clinicaltrials.gov/ (NCT01892449).