CHANGES IN CARBON-DIOXIDE (CO2) STORES DURING LAPAROSCOPIC CHOLECYSTECTOMY WITH 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 p ulmonary elimination of CO2 (EGO(2), Servoventilator with integrated C O2-analyser 930, Siemens). In group 1 minute ventilation was kept cons tant, resulting in moderate hypercapnia during PP. paCO(2) increased b y about 10 mmHg during up to 50 min PP. In group 2 paCO(2) was kept co nstant by a stepwise increase in minute ventilation (Fig. 1, Table 2). Results. Compared to values just before PP, EGO(2) increased in group 1 rather rapidly up to 20 min of PP and more slowly thereafter, reach ing a mean value 35% above control at 45 min PP. In group 2 EGO(2) was significantly higher than in group 1 between 15 and 35 min PP. At 45 min PP, however, EGO(2) was identical in both observation groups (Fig, 2). Conclusions. Assuming a stable metabolic CO2 production rate duri ng the observation period and no differences in CO2 absorption from th e PP between the two study groups, differences in EGO(2) between group s would be a measure of CO2 stored in group 1 patients during the incr ease in paCO(2) with PP (Fig. 3, Table 3). CO2 storage rapidly increas ed 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 durin g the first 45 min PP amounted to a mean Value of 1.20 ml CO2/kg body weight and mmHg paCO(2), which agrees favourably with data from the li terature and a computer model from Fahri and Rahn published in 1960 (F ig. 4, Table 4). If during LCh with CO2-PP patients are ventilated wit h a constant minute ventilation, a moderate increase in paCO(2) of abo ut 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, wh ich must be eliminated after cessation of PP. If the paCO(2) is to be held constant during PP, minute ventilation has to be progressively in creased by about 40%.