[The effects of the carbon dioxide pneumoperitoneum in laparoscopic cholecystectomy on postoperative spontaneous respiration].

Laparoscopic cholecystectomy (LSC) is being performed increasingly often. The carbon dioxide cavity increases end-expiratory carbon dioxide (exCO2), which can be regulated by mechanical ventilation. Because about 20-40% carbon dioxide remains in the patient at the end of surgery, we were interested in its influence on spontaneous respiration. PATIENTS AND METHODS. Fifteen patients classed as ASA 1-2 and undergoing LSC were compared with 15 patients (also ASA 1-2) undergoing laparotomy for cholecystectomy (LAP). All patients had balanced anaesthesia with fentanyl, enflurane, nitrous oxide and vecuronium. After surgery they were extubated when spontaneous respiration and vigilance were adequate. In the next 3 h we continuously determined exCO2 in the expired air through an intranasal catheter, and oxygen saturation (SAT), respiratory rate (RR) and heart rate (HR) using Oscar (Datex) and Ohmeda (Braun) apparatus while the patients were breathing room air. The blood pressure (BP) was determined intermittently. Postoperative pain treatment was standardized. RESULTS. The groups were reduced comparable with respect of the anthropometric data, because the weight was significantly higher in the LAP group. Fentanyl consumption was also significantly higher in the LAP group, reflecting the more pronounced trauma than with LSC. Mean exCO2 was 46 mmHg after LSC and 36 mmHg after LAP (P less than or equal to 0.05), continuously decreasing in the LSC group and increasing in the LAP group to 40 mmHg after 3 h. Mean RR was 18-20.min-1 after LSC and 12-15.min-1 after LAP during this period (P less than or equal to 0.05). There were no differences in SAT (94-96%), HR (75.min-1) and BP (130/80 mmHg). DISCUSSION AND CONCLUSIONS. The remaining carbon dioxide after LSC has important implications for postoperative spontaneous respiration. Probably due to an activation of carbon dioxide receptors, RR is increased to eliminate residual carbon dioxide. This is confirmed by a significantly increased exCO2 compared with that in the LAP group. This effect lasts at least 3 h, exCO2 being comparable in both groups, but RR is still increased after LSC. This different respiratory pattern does not affect SAT, being normal without hypoxic episodes. Cardiovascular parameters were also normal without group differences. We conclude that the carbon dioxide peritoneal cavity has important consequences for postoperative ventilation. Using our anaesthetic technique and postoperative treatment exCO2 reaches normal values after about 3 h due to an increased RR. If other methods, e.g., stronger opioids, which decrease carbon dioxide response are used, this effect may even be prolonged and more pronounced. We are now performing an investigation to evaluate this effect.