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

Background. We compared pressure and volume-controlled ventilation (PCV and VCV) in morbidly obese patients undergoing laparoscopic gastric banding surgery. Methods. Thirty-six patients, BMI. 35 kg m 22, no major obstructive or restrictive respiratory disorder, and Pa-CO2 < 6.0 kPa, were randomized to receive either VCV or PCV during the surgery. Ventilation settings followed two distinct algorithms aiming to maintain end-tidal CO2 (E'(CO2)) between 4.40 and 4.66 kPa and plateau pressure (P-plateau) as low as possible. Primary outcome variable was peroperative P-plateau. Secondary outcomes were Pa-O2 (F-IO2 at 0.6 in each group) and Pa-CO2 during surgery and 2h after extubation. Pressure, flow, and volume time curves were recorded. Results. There were no significant differences in patient characteristics and co-morbidity in the two groups. Mean pH, Pa-O2, Sa(O2), and the Pa-O2/F-IO2 ratio were higher in the PCV group, whereas Pa-CO2 and 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 cardiovascular variables, blood gases, and morphine requirements after the operation were similar. Conclusions. The changes in oxygenation can only be explained by an improvement in the lungs ventilation/perfusion ratio. The decelerating inspiratory flow used in PCV generates higher instantaneous flow peaks and may allow a better alveolar recruitment. PCV improves oxygenation without any side-effects.