Ventilatory requirements during laparoscopic cholecystectomy

The purpose of this clinical study was to determine: (1) the increase in minute ventilation required to maintain preinsufflation arterial carbon dioxide tension (PaCO2) during laparoscopic cholecystectomy, and (2) whether end-tidal PCO2 (PETCO2) can be used as an index of PaCO2 and, therefore, of the adequacy of minute ventilation during the pneumoperitoneum. We measured PaCO2, PETCO2, expired minute volume (Vexp) standardized for body surface area (SA), airway and intra-abdominal pressure (P(aw), Pabd) during general anaesthesia for laparoscopic cholecystectomy just before and 30 min after the creation of a CO2 pneumoperitoneum in 28 healthy (ASA class 1 and 2) consenting adults. They were in the reverse Trendlenburg position (20 degrees) with a 5 degrees lateral tilt. Expired minute volume was increased from 3.75 (SEM +/- 0.12) to 4.19 (0.15) L.min-1 x m-2 to maintain PaCO2 close to control levels: 38.9 (0.8) vs 40.1 (0.6) mmHg 5.19 (0.1) vs 5.35 (0.08) kPa). In most of the patients (23/28), PETCO2 was less than 41 mmHg with a correlation between PaCO2 and PETCO2. In ten of these patients, (Pa-PET)CO2 was greater than the normal range. In 5/28, (Pa-PET)CO2 was negative. The "driving pressure" (P(aw)-Pabd) increased from 8.7 (1.0) to 10.4 (1.1) cm H2O, without any correlation between the increase in P(aw)-Pabd and that in Vexp. The results indicate the need for extra ventilatory requirement during laparoscopy and that PETCO2 is an imperfect index of PaCO2 under these circumstances.