BACKGROUND:Carbon dioxide insufflation during laparoscopic surgery results in an acid-base imbalance. The purpose of this study was to investigate the effect of pneumoperitoneum on the acid-base status using Stewart's approach. METHODS:Thirty patients undergoing abdominal surgery were allocated to the laparotomy group (n=15) or the laparoscopy group (n=15). The acid-base parameters were measured 10 min after the induction (T1), 40 min after opening the peritoneum or pneumoperitoneum according to the group (T2), at the end of the surgery (T3), and 1 h after the surgery (T4). RESULTS:There were no significant differences in the standard base excess (SBE), strong ion gap, or anion gap between the two groups. In both groups, the SBE decreased at T2, T3, and T4 compared with baseline value. At T3 and T4 in the laparotomy group, the apparent strong ion difference (SIDa) and pH were decreased whereas the lactate and chloride were increased compared with their baseline values. At T2 in the laparoscopy group, the pH was decreased whereas Pa(CO(2)) was increased compared with their baseline values. CONCLUSIONS:The decrease in the pH during the pneumoperitoneum was affected by the increase in Pa(CO(2)), which promptly returned to a normal value after the desufflation. On the other hand, the decrease in the pH after laparotomy was affected by the metabolic factors, which persisted an hour after the surgery.