Effects of propofol vs isoflurane on respiratory gas exchange during laparoscopic cholecystectomy

Respiratory function and pulmonary gas exchange are affected in laparoscopic procedures where a pneumoperitoneum is introduced using CO2. Previous studies have shown differing results concerning pulmonary gas exchange during laparoscopic procedures: Whereas in patients undergoing isoflurane anaesthesia decreases in PaO2 are demonstrated, this factor remains unchanged in patients undergoing propofol anaesthesia. In the present study, the effects of propofol on pulmonary gas exchange were compared with those of isoflurane in patients undergoing elective laparoscopic cholecystectomy in a prospective randomised manner.

Twenty ASA patients with physical status I and II were divided randomly between isoflurane (IG) and propofol groups (PG). After induction of anaesthesia patients were moderately hyperventilated. Respirator settings remained unchanged during pneumoperitoneum (PP) until 10 min after deflation of the peritoneal cavity. Blood gas analyses were performed at 5 time points: 15 min after induction of anaesthesia (giving pre-PP values), immediately before carbon dioxide insufflation (0 min PP), after both 30 and 60 min of PP and 10 min post PP. Inspiration plateau pressure (Pplat), compliance of the respiratory system, and both ins- and expiratory gas concentrations were continuously recorded by an Ultima V monitor (Datex Corp., Helsinki, Finland). The difference between arterial and end-tidal CO2 partial pressure (P(a-et)CO2) was calculated so as to allow assessment of physiological dead space by the modified Bohr equation.

Pulmonary gas exchange differed significantly after 30 min of PP between the IG and the PG. At this time, PaO2 was 19.5 +/- 2.9 kPa (mean +/- SD) in the IG and 23.1 +/- 1.8 kPa in the PG (P < 0.01), whereas PaCO2 was 5.5 +/- 0.37 kPa in the IG and 4.9 +/- 0.27 kPa in the PG (P < 0.01). These discrepancies remained until after carbon dioxide desufflation. At 10 min post PP, PaO2 was 18.3 +/- 2.6 kPa in the isoflurane group and 21.9 +/- 2.2 kPa in the propofol group (P < 0.01), whereas PaCO2 was 5.4 +/- 0.46 kPa in the IG and 4.8 +/- 0.22 kPa in the PG (P < 0.01). During carbon dioxide insufflation the P(a-et)CO2 increased significantly in the IG from 0.47 +/- 0.13 kPa to 0.76 +/- 0.37 kPa (P < 0.05), while the values in the PG remained constant.

This study demonstrates that pulmonary gas exchange in patients with laparoscopic cholecystectomy is affected by the choice of anaesthetic procedure. During and after laparoscopic cholecystectomy using isoflurane as the anaesthetic, the PaCO2 is significantly higher and the PaO2 significantly lower than they are with propofol.