Obesity is associated with decreased lung compliance and hypercapnia during robotic assisted surgery

Robotic assisted surgery (RAS) represents a great challenge for anesthesiology due to the increased intraabdomial pressures required for surgical optimal approach. The changes in lung physiology are difficult to predict and require fast decision making in order to prevent altered gas exchange. The aim of this study was to document the combined effect of patient physical status, medical history and intraoperative position during RAS on lung physiology and to determine perioperative risk factors for hypercapnia. We prospectively analyzed 62 patients who underwent elective RAS. Age, co-morbidities and body mass index (BMI) were recorded before surgery. Ventilatory parameters and arterial blood gas analysis were determined before induction of anesthesia, after tracheal intubation and on an hourly basis until the end of surgery. In RAS, the induction of pneumoperitoneum was associated with a significant decrease in lung compliance from a mean of 42.5-26.7 ml cm H₂O^-1 (p = 0.001) and an increase in plateau pressure from a mean of 16.1 mmHg to a mean of 23.6 mmHg (p = 0.001). Obesity, demonstrated by a BMI over 30, significantly correlates with a decrease in lung compliance after induction of anesthesia (p = 0.001). A significant higher increase in arterial CO₂ tension was registered in patients undergoing RAS in steep Trendelenburg position (p = 0.05), but no significant changes in end-tidal CO₂ were recorded. A higher arterial to end-tidal CO₂ tension gradient was observed in patients with a BMI > 30 (p < 0.001). In conclusion, patients' physical status, especially obesity, represents the main risk factor for decreased lung compliance during RAS and patient positioning in either Trendelenburg or steep Trendelenburg during surgery has limited effects on respiratory physiology.