Effects of pneumoperitoneum on intraoperative pulmonary mechanics and gas exchange during laparoscopic gastric bypass

Background: Hypercarbia and elevated intraabdominal pressure resulting from carbon dioxide (CO₂) pneumoperitoneum can adversely affect respiratory mechanics. This study examined the changes in mechanical ventilation, CO₂ homeostasis, and pulmonary gas exchange in morbidly obese patients undergoing a laparoscopic or open gastric bypass (GBP) procedure. Methods: In this study, 58 patients with a body mass index (BMI) of 40 to 60 kg/m² were randomly allocated to laparoscopic (n = 31) or open (n = 27) GBP. Minute ventilation was adjusted to maintain a low normal arterial partial pressure of CO₂ (PaCO₂), low normal end-tidal partial pressure of CO₂ (ETCO₂), and low airway pressure. Respiratory compliance, ETCO₂, peak inspiratory pressure (PIP), total exhaled CO₂ per minute (VCO₂), and pulse oximetry (SO₂) were measured at 30-min intervals. The acid–base balance was determined by arterial blood gas analysis at 1-h intervals. The pulmonary gas exchange was evaluated by calculation of the alveolar dead space–to–tidal volume ratio (V_Dalv/V_T) and alveolar–arterial oxygen gradient (PAO₂–PaO₂). Results: The two groups were similar in age, gender, and BMI. As compared with open GBP, laparoscopic GBP resulted in higher ETCO₂, PIP, and VCO₂, and a lower respiratory compliance. Arterial blood gas analysis demonstrated higher PaCO₂ and lower pH during laparoscopic GBP than during open GBP (p < 0.05). The V_Dalv/V_T ratio and PAO₂–PaO₂ gradient did not change significantly during laparoscopic GBP. Intraoperative oxygen desaturation (SO₂ < 90%) did not develop in any of the patients in either group. Conclusions: Laparoscopic GBP alters intraoperative pulmonary mechanics and acid–base balance but does not significantly affect pulmonary oxygen exchange. Changes in pulmonary mechanics are well tolerated in morbidly obese patients when proper ventilator adjustments are maintained.