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 PAO ₂-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.