Ventilatory effects of laparoscopic cholecystectomy

During laparoscopic cholecystectomy the arterial-end-tidal CO2 gradient (Fa-ETCO2) has been variously shown to be unchanged, increased, decreased or even negative. The goal of this study was to evaluate Fa-ETCO2, and to determine the proper contribution of VECO2 and VA in regard to the increase of FETCO2.

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: FaCO2, FETCO2, 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 multipled by the respiratory frequency.

During pneumoperitoneum it is shown that: 1) Fa-ETCO2 either decreases and becomes even negative (n = 8) (P < 0.01), or stays unchanged (n = 7), but never elevates; 2) VECO2 increases (peak value: +22.6%) (P < 0.01); 3) VA is unchanged, and 4) dead space ventilation, determined in 7 patients, remains unchanged.

We conclude that only exogenous CO2 loading, and not VA, can explain such increase in FETCO2 and FaCO2, in cases of limited CO2 insufflating pressure in ASA 1-2 patients.