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[Pulmonary CO2 elimination in laparoscopic cholecystectomy. A clinical study]
H Wurst1, H Schulte-Steinberg, U Finsterer
1Institut für Anaesthesiologie der Ludwig-Maximilians-Universität München.
Methods:
We measured pulmonary elimination of carbon dioxide (VCO2), end-tidal and arterial CO2 tensions (PETCO2, PaCO2), deadspace ventilation (VD/VT), and arterial oxygen tension (PaO2) using a Siemens 930 CO2 analyzer incorporated into a servoventilator and arterial blood gas analyses, respectively, in 31 patients undergoing laparoscopic cholecystectomy with a median duration of pneumoperitoneum (PP) of 60 min.
Results:
During the first 30 min of PP VCO2 increased significantly by a mean of 30% (Fig. 1). At the same time, with constant minute ventilation PETCO2 und PaCO2 increased by about 8 mm Hg each (Fig. 3, Table 1). In a subgroup of 10 patients who could be observed for up to 75 min of PP, we found a stepwise increase in minute ventilation with no further increase in PETCO2 and PaCO2 after 30 min PP, but a slowly rising VCO2 (Fig. 2). Arterial-to-end-tidal CO2 tension difference (Pa-PETCO2) remained constant at about 4 mm Hg with institution and during the course of PP (Fig. 4), as did VD/VT at a median value of 0.38-0.40 (Fig. 5). PaO2 (FIO2 = 0.5) did not change significantly with PP (Table 1). With desufflation we found a short-term increase in VCO2 (Table 2).
Conclusions:
During PP, CO2 is reabsorbed from the peritoneal cavity. During the initial unstable phase with rising PaCO2, reabsorption of CO2 is the sum of increased pulmonary elimination of CO2 above baseline and uptake of CO2 into gas stores of the body. We estimated CO2 reabsorption to be on the order of 70 ml/min during the first 30 min of PP. During the later, stable phase, reabsorption of CO2 equals increased pulmonary elimination of CO2 above baseline and was estimated to be in the order of 90 ml/min in 10 patients with 30-75 min of PP (hatched area in Fig. 2). PET-CO2 corresponded well with PaCO2 in these patients. VD/VT and arterial oxygenation did not change significantly with institution or during the course of PP. Monitoring VCO2 probably is a useful aid in the early detection of CO2 emphysema (Fig. 6).