SHOULD NITROUS-OXIDE BE DISCONTINUED BEFORE DESFLURANE AFTER ANESTHESIA WITH DESFLURANE N2O/

Background: The appearance of hypoxaemia immediately after anaesthesia with nitrous oxide may be partially explained by diffusion hypoxia. T his study was undertaken to evaluate circulatory and respiratory varia bles during emergence after desflurane/nitrous oxide anaesthesia, and whether there are any differences depending on which gas is discontinu ed first. Methods: 20 patients were studied after gynaecological lapar oscopic surgery. The depth of anaesthesia was reduced 10 min prior to the emergence by stopping the administration of one of the two inhalat ional agents. Desflurane was discontinued first in Group 1, nitrous ox ide in Group 2. Ventilation was controlled with E'CO2 maintained at 5% until the administration of the second anaesthetic gas was discontinu ed. Thereafter, the patients breathed spontaneously. Results: The PaCO 2 at which the respiratory drive reappeared after controlled normovent ilation was similar in both groups, 6.1-6.5 kPa, and extubation was pe rformed after 10-11 min. At extubation, the end-tidal CO2 and total MA C were similar in the groups, about 6.2 vol% and 0.16, respectively. M ean arterial blood pressure was significantly higher in Group 1. The c ardiac output increased in both groups from about 6 l/min at the concl usion of anesthesia to 9.0 and 7.6 l/min at 15 min in the recovery per iod. End-tidal O-2 decreased and CO2 increased in both groups during t he first 10 min in the recovery period, pH was reduced at 15 and 30 mi n in both groups. Conclusion: Irrespective of which agent was disconti nued first, there was an increase in cardiac output, decrease in oxyge nation and a modest acidosis in the first 30-min recovery period. The only significant difference between the groups was in mean arterial bl ood pressure in the early emergence phase with a greater MAP when N2O had been used until the conclusion of anaesthesia.