ABSTRACT
Twenty-four patients of both sexes, physical status ASA I and II, were submitted to laparoscopic cholecystectomy. Patients were premedicated with 10 mg of diazepam and the anesthesia was induced with droperidol (0,03 mg.kg(-1)), alfentanil (40 mg.kg(-1)), propofol (2 mg.kg(-1) ) and atracurium (0,5 mg.kg(-1)). After tracheal intubation, pulmonary ventilation was maintained with a Takaoka 676 ventilator with a tidal volume of 7 ml.kg(-1), FiO2 of 0.33-0.35, intracheal pressure of 10-12 cmH2 O and respiratory rate adjusted to maintain ETCO2 36-38 mmHg and Sp)2 97-98 por cent. The patients were allocated into two groups. Group air: ventilated eith room air enriched with oxygen to a FiO2 of 0.35 and group N20: ventilated with 67 por cent N2O in O2. Maintenance of anesthesia was done with 10 mg.kg(-1).h(-1) of propofol in the first 20 min and with 5 mg.kg(-1).h(-1) afterwards until the end of the surgical procedure, plus intermittent doses of alfentanil. Changes in pulmonary ventilation rate and in the intratracheal pressures were record at nine moments. Carbon dioxide was administered until intrabdominal pressure reached 12-14 mm Hg; the initial and final volumes administered were recorded. The intracavitary concentration of N2O was evoluated by an Ohmeda 5250 Gas Multianalyser at the end of the procedure. Systolic and dystolic blood pressure and heart rate were evaluated every 5 min, at the same moments as the pulmonary ventilation parameters. There was no difference in the minute volumes at moment 1, but they were significantly higher at the subsequent moments (p major then 0,05), in the group which was ventilated with air. There were significant differences in intratracheal pressures before and the after the insuflation of CO2 and after the deflation within each group, but not between the groups. Nitrous oxide was detected in the abdominal cavity in remarkable concentrations. There were significant differences between the groups regarding systolic arterial pressure after insuflation and deflation of CO2, during maintenance and after extubation. The authors conclued that N2O diffuses to the abdominal cavity in significant concentrations and that it is able to minimize the respiratory changes associated with high intrabdominal pressure and with CO2 absorption. There were no differences in CO2 volumes required during the laparoscopic procedure