Pressure-controlled ventilation improves oxygenation during laparoscopic obesity surgery compared with volume-controlled ventilation

Background: We compared pressure and volume-controlled ventilation (PCVand VCV) in morbidly obese patients undergoing laparoscopicgastric banding surgery. Methods: Thirty-six patients, BMI>35 kg m^–2, no major obstructiveor restrictive respiratory disorder, and Pa_CO2<6.0 kPa, wererandomized to receive either VCV or PCV during the surgery.Ventilation settings followed two distinct algorithms aimingto maintain end-tidal CO₂ (E'_CO2) between 4.40 and 4.66 kPaand plateau pressure (P_plateau) as low as possible. Primaryoutcome variable was peroperative P_plateau. Secondary outcomeswere Pa_O2 (FI_O2 at 0.6 in each group) and Pa_CO2 during surgeryand 2 h after extubation. Pressure, flow, and volume time curveswere recorded. Results: There were no significant differences in patient characteristicsand co-morbidity in the two groups. Mean pH, Pa_O2, Sa_O2, andthe Pa_O2/FI_O2 ratio were higher in the PCV group, whereas Pa_CO2and the E'_CO2–Pa_CO2 gradient were lower (all P<0.05).Ventilation variables, including plateau and mean airway pressures,anaesthesia-related variables, and postoperative cardiovascularvariables, blood gases, and morphine requirements after theoperation were similar. Conclusions: The changes in oxygenation can only be explained by an improvementin the lungs ventilation/perfusion ratio. The decelerating inspiratoryflow used in PCV generates higher instantaneous flow peaks andmay allow a better alveolar recruitment. PCV improves oxygenationwithout any side-effects.