CARBON-DIOXIDE OUTPUT IN LAPAROSCOPIC CHOLECYSTECTOMY

In pneumoperitoneum, carbon dioxide eliminated in expired gas (carbon dioxide output) contains both metabolic and absorbed carbon dioxide fr om the peritoneal cavity. When elimination of carbon dioxide is much h igher than carbon dioxide output, storage of tissue carbon dioxide and arterial carbon dioxide concentrations change. Finally, the rate of c arbon dioxide eliminated in expired gas is not a match for the real ra te of metabolic production and absorbed carbon dioxide from the perito neal cavity. During and after insufflation of carbon dioxide, changes in carbon dioxide output were elucidated under constant arterial carbo n dioxide pressure (Pa-CO2), the same as the preinduction level. We st udied patients undergoing elective laparoscopic cholecystectomy. Carbo n dioxide output, oxygen uptake, respiratory exchange ratio (RER), exp ired minute ventilation (VE), deadspace to tidal volume ratio (VD/VT r atio) and arterial to end-tidal carbon dioxide partial pressure differ ence (Pa-CO2-PE'(CO2)) were determined before induction, and during an aesthesia, pneumoperitoneum and recovery. By controlling ventilatory f requency (f) every 1 min, Pa-CO2 was adjusted to concentrations before induction. Constant monitoring of end-tidal carbon dioxide partial pr essure (PE'(CO2)) and intermittent measurement of (Pa-CO2-PE'(CO2)) (1 5-min intervals) were conducted to predict Pa-CO2). Carbon dioxide out put and oxygen uptake decreased significantly from mean values of 83.5 (SEM 5.2), 101.6 (5.1) to 68.5 (4.2), 81.1 (4.6) ml min(-1) m(-2) (AT PS, P < 0.05) with sevoflurane anaesthesia, and RER did not change. Du ring carbon dioxide pneumoperitoneum (intra-abdominal pressure 8 mm Hg ), carbon dioxide output increased by 49% (102.4 (5.0) ml min(-1) m(-2 )) (P < 0.05) while oxygen uptake remained stable and RER increased fr om 0.84 (0.02) to 1.16 (0.03) (P < 0.05). It was necessary to increase VE during pneumoperitoneum by 1.54 times that during anaesthesia to m aintain individual Pa-CO2 values constant. After removal of carbon dio xide from the abdominal cavity, the regression equation of excess carb on dioxide output/BSA best fitted a two-compartment model. The time co nstants of the rapid and slow compartments were 8.2 and 990 min, respe ctively. Excess carbon dioxide output/BSA was still 5.5 ml min(-1) m(- 2), 30 min after pneumoperitoneum.