Ventilatory effects of laparoscopic cholecystectomy

Background: During laparoscopic cholecystectomy the arterial-end-tidal CO2 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 CO2 insufflation limited to 12 mmHg, 15 degrees 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 CO2. VA was calculated as the alveolar fraction of expired VT multiplied by the respiratory frequency. Results: During pneumoperitoneum it is shown that: 1) FaETCO(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 CO2 loading, and not VA, can explain such increase in FETCO(2) and FaCO(2), in cases of limited CO2 insufflating pressure in ASA 1-2 patients.