Zur Frage der CO2-Speicherung bei laparoskopischer Cholezystektomie mit CO2-Pneumoperitoneum

Methods. Two groups of 22 patients each were studied in a prospective, randomised fashion during laparoscopic cholecystectomy (LCh) and CO₂ pneumoperitoneum (PP) with regard to end-tidal and arterial PCO₂ and pulmonary elimination of CO₂ (ECO₂, Servoventilator with integrated CO₂-analyser 930, Siemens). In group 1 minute ventilation was kept constant, resulting in moderate hypercapnia during PP. paCO₂ increased by about 10?mmHg during up to 50?min PP. In group 2 paCO₂ was kept constant by a stepwise increase in minute ventilation (Fig.?1, Table?2). Results. Compared to values just before PP, ECO₂ increased in group 1 rather rapidly up to 20?min of PP and more slowly thereafter, reaching a mean value 35% above control at 45?min PP. In group 2 ECO₂ was significantly higher than in group 1 between 15 and 35?min PP. At 45?min PP, however, ECO₂ was identical in both observation groups (Fig.?2). Conclusions. Assuming a stable metabolic CO₂ production rate during the observation period and no differences in CO₂ absorption from the PP between the two study groups, differences in ECO₂ between groups would be a measure of CO₂ stored in group 1 patients during the increase in paCO₂ with PP (Fig.?3, Table?3). CO₂ storage rapidly increased between 0 and 15?min PP, more or less reached a plateau between 15 and 35?min PP, and ceased at 45?min PP. Storing capacity for CO₂ during the first 45?min PP amounted to a mean value of 1.20?ml CO₂/kg body weight and mmHg paCO₂, which agrees favourably with data from the literature and a computer model from Fahri and Rahn published in 1960 (Fig.?4, Table?4). If during LCh with CO₂-PP patients are ventilated with a constant minute ventilation, a moderate increase in paCO₂ of about 10?mm Hg can be expected. In this case, during the first 45?min PP a 70-kg patient will retain about 1000?ml CO₂ in blood and tissues, which must be eliminated after cessation of PP. If the paCO₂ is to be held constant during PP, minute ventilation has to be progressively increased by about 40%.