[The resorption of carbon dioxide from the pneumoperitoneum in laparoscopic cholecystectomy]

Laparoscopic cholecystectomy is claimed to be a minimally invasive procedure, but uptake of carbon dioxide (CO2) from the pneumoperitoneum (CO2-PP) can cause clinically relevant hypercapnia. In this prospective study, CO2 resorption during laparoscopic cholecystectomy was investigated. METHODS. In 30 patients (ASA I and II) total intravenous anesthesia was performed with propofol and fentanyl. Controlled ventilation was started with a tidal volume of 10 ml/kg min, a respiratory rate of 10/min, and FiO2 = 0.4 using an Engström Erica ventilator. When end-tidal CO2 (PeCO2) rose to 42 mmHg the respiratory rate was increased. In addition to standard monitoring, intra-abdominal pressure (IAP) was measured. Minute volume (VI), CO2 elimination (VCO2), oxygen uptake (VO2), and the respiratory quotient (RQ) were registered by indirect calorimetry from the Erica Metabolic Monitor. The CO2 resorption (delta VCO2) was calculated from the equation: delta VCO2(Mi) = VCO2(Mi) RQ(M1)VO2(Mi). (i = 1; 2; ...;5) All values are medians (interquartile range) or ranges. All parameters were compared at five measuring points that are characteristic for laparoscopic cholecystectomy: M1 baseline, 30 min after induction of anaesthesia, M2 10 min after starting CO2 insufflation, M3 while mobilising the gallbladder from the liver bed, M4 while extracting the gallbladder from the abdominal cavity, and M5 10 min after desufflating the CO2-PP (spontaneous breathing). RESULTS. A typical pattern of VCO2 was observed (Fig. 1). Baseline VCO2 was 165 (145-180) ml/min, PeCO2 was 33 (31-35) mmHg, and VI was 6.0 (6.0-7.0) l/min. After insufflation of CO2 to an IAP of between 14 and 20 mmHg, an increase in VCO2 to 201 (179-222) ml/min was registered (P < 0.05). During mobilisation of the gallbladder, the IAP was between 12 and 18 mmHg and no further increase in VCO2 (200 (179-229) ml/min) was observed. During extraction of the gallbladder from the abdominal cavity, the CO2-PP deflated and IAP dropped to 1-5 mmHg. In this phase, maximal VCO2 and delta VCO2 were measured at 232 (206-245) ml/min and 43 (30-57) ml/min (P < 0.05), respectively. PeCO2 rose to 40 (37-42) mmHg (P < 0.05) although VI was increased to 7.0 (6.0-8.4) l/min (P < 0.05). The complete pattern of VO2 is shown in Fig. 2, the RQ in Fig. 3, and delta VCO2 in Fig. 4. The values of PeCO2, IAP, and VI are listed in Table 2. DISCUSSION. The combination of increased VCO2 and stable VO2 during CO2-PP must be interpreted as indicating resorption of CO2 from the abdominal cavity. Essential CO2 resorption must be assumed during insufflation of the CO2-PP and immediately after a decrease in IAP. During dissection of the gallbladder no increase in CO2 resorption was observed, so the experimental finding [19] can be confirmed clinically that an IAP higher than the venous capillary pressure protects from further CO2 resorption by compressing the venous capillaries of the peritoneum. CO2 resorption is clinically relevant because VI must be increased to maintain normocapnia. Therefore, capnography is absolutely necessary during laparoscopic cholecystectomy.