CARBON-DIOXIDE UPTAKE FROM PNEUMOPERITONEUM DURING LAPAROSCOPIC CHOLECYSTECTOMY

Laparoscopic cholecystectomy is claimed to be a minimally invasive pro cedure, 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 investi gated. Methods. In 30 patients (ASA I and II) total intravenous anaest hesia was performed with propofol and fentanyl. Controlled ventilation was started with a tidal volume of 10 ml/kg min, a respiratory rate o f 10/min, and FiO2=0.4 using an Engstrom Erica ventilator. When end-ti dal CO2 (PeCO2) rose to 42 mmHg the respiratory rate was increased. In addition to standard monitoring, intra-abdominal pressure (IAP) was m easured. Minute volume (V(I)), CO2 elimination (VCO2), oxygen uptake ( VO2), and the respiratory quotient (RQ) were registered by indirect ca lorimetry from the Erica Metabolic Monitor. The CO2 resorption (DELTAV CO2) was calculated from the equation: DELTAVCO2(Mi)=VCO2(Mi) -RQ(M1)V O2(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: MI baseline, 30 m in after induction of anaesthesia, M2 10 min after starting CO2 insuff lation, M3 while mobilising the gallbladder from the liver bed, M4 whi le extracting the gall-bladder from the abdominal cavity, and M5 10 mi n after desufflating the CO2-PP (spontaneous breathing). Results. A ty pical pattern of VCO2 was observed (Fig. 1). Baseline VCO2 was 165 (14 5-180) ml/min, PeCO2 was 33 (31-35) mmHg, and V(I) was 6.0 (6.0-7.0) l /min. After insufflation of CO2 to an IAP of between 14 and 20 mmHg, a n 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 observ ed. During extraction of the gallbladder from the abdominal cavity, th e CO2-PP deflated and IAP dropped to 1-5 mmHg. In this phase, maximal VCO2 and DELTAVCO2 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 V(I) was increased to 7.0 (6.0-8.4) l/min (P<0.05). The com plete pattern of VO2 is shown in Fig. 2, the RQ in Fig. 3, and DELTAVC O2 in Fig. 4. The values of P2CO2, IAP, and V(I) 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 ab dominal cavity. Essential CO2 resorption must be assumed during insuff lation of the CO2-PP and immediately after a decrease in IAP. During d issection of the gallbladder no increase in CO2 resorption was observe d, so the experimental finding [19] can be confirmed clinically that a n 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 V(I) must be increased to maintain normocapnia. Therefore, capnography is absolutely necessa ry during laparoscopic cholecystectomy.