Ventilatory effects of laparoscopic cholecystectomy

Background : During laparoscopic cholecystectomy the arterial-end-tidal CO 2 gradient (Fa-ETCO 2 ) has been variously shown to be unchanged, increased, decreased or even negative. The goal of this study was to evaluate Fa-ETCO 2 , and to determine the proper contribution of VECO 2 and VA in regard to the increase of FETCO 2 . Methods : Ventilatory patterns were studied in 15 ASA 1-2 patients (mean age±SD : 48.5±15.0) undergoing laparoscopic cholecystectomy, with intraperitoneal CO 2 insufflation limited to 12 mmHg, 15° head-up position, during general anaesthesia and controlled ventilation. The following were studied before, during, and after the pneumoperitoneum : FaCO 2 , FETCO 2 , nasopharyngeal temperature ; dead space ventilation, and expired volumes using the Single Breath Test for CO 2 . VA was calculated as the alveolar fraction of expired VT multiplied by the respiratory frequency. Results : During pneumoperitoneum it is shown that : 1) Fa-ETCO 2 either decreases and becomes even negative (n=8) (P<0.01), or stays unchanged (n=7), but never elevates ; 2) VECO 2 increases (peak value : + 22.6%) (P<0.01) ; 3) VA is unchanged, and 4) dead space ventilation, determined in 7 patients, remains unchanged. Conclusion : We conclude that only exogenous CO 2 loading, and not VA, can explain such increase in FETCO 2 and FaCO 2 , in cases of limited CO 2 insufflating pressure in ASA 1-2 patients.