Pressure-controlled ventilation does not improve gas exchange in morbidly obese patients undergoing abdominal surgery

Background Morbid obesity results in marked respiratory pathophysiologic changes that may lead to impaired intra-operative gas exchange. The decelerating inspiratory flow and constant inspiratory airway pressure resulting from pressure-controlled ventilation (PCV) may be more adapted to these changes and improve gas exchanges compared with volume-controlled ventilation (VCV). Methods Forty morbidly obese patients scheduled for gastric bypass were included in this study. Total intravenous anesthesia was given using the target-controlled infusion technique. During the first intraoperative hour, VCV was used and the tidal volume was adjusted to keep end-tidal PCO2 around 35 mmHg. After 1 h, patients were randomly allocated to 30-min VCV followed by 30-min PCV or the opposite sequence using a Siemens (R) Servo 300. FiO(2) was 0.6. During PCV, airway pressure was adjusted to provide the same tidal volume as during VCV. Arterial blood was sampled for gas analysis every 15 min. Ventilatory parameters were also recorded. Results Peak inspiratory airway pressures were significantly lower during PCV than during VCV (P<0.0001). The other ventilatory parameters were similar during the two periods of ventilation. PaO2 and PaCO2 were not significantly different during PCV and VCV. Conclusion PCV does not improve gas exchange in morbidly obese patients undergoing gastric bypass compared to VCV.