Time course of acid-base regulation following intraperitoneal CO2 administration in man

Chronological changes in acid-base status during laparoscopic CO2 insufflation were studied for 2 h in 10 patients who underwent laparoscopic cholecystectomy. Carbon dioxide pressure in alveolar air as well as arterial blood promptly and significantly increased within 5 min whereas amount of pulmonary CO2 elimination significantly increased after 15 min. Pulmonary gas exchange ratio (R) exceeded the level of unity at 10 min and progressively increased toward the end of 2 h observation. These results indicated that CO2 equilibrium process between different body compartments with different time constant took place and apparent equilibrium was not completed during observation. In vivo buffer value of the arterial blood started to decrease after 5 min and decreased to about one-third the in vitro buffer value until the end of observation. This indicated that CO2 equilibrium between blood and interstitial fluids took place slowly during entire period of study and no significant contribution of cellular buffering was developed. We conclude that slower development of acid-base regulation in the present study than those reported in the previous studies may have been derived from small diffusion area and blood perfusion for CO2.