Background and objective: To evaluate the temporal changes in respiratory physiological dead space and dynamic compliance of the respiratory system during non-abdominal, upper abdominal and lower abdominal surgery under general anaesthesia with intermittent positive pressure ventilation.
Methods: Thirty-four adult patients were studied (non-abdominal surgery, n = 8; upper abdominal surgery, n = 13 and lower abdominal surgery in lithotomy position, n = 13). Physiological dead space was measured using the single breath carbon dioxide test. The physiological dead space to tidal volume ratio (VD/VT), dynamic compliance of respiratory system, expiratory tidal volume and respiratory rate were measured 10 min after tracheal intubation, and 30, 60 and 120 min later.
Results: In lower abdominal surgery group, VD/VT was significantly increased at 120 min compared with 0 min (P = 0.005) and 30 min (P = 0.009). There were no significant differences in VD/VT between the three groups at any time point. Compliance decreased significantly in patients with upper abdominal (120 min) and lower abdominal surgery (60 and 120 min), but there were no significant changes during non-abdominal surgery.
Conclusions: We found that the VD/VT increased in patients undergoing lower abdominal surgery in lithotomy and head down tilt, and compliance decreased in those undergoing upper abdominal and lower abdominal surgery over time.