Development and performance of a two-step desflurane-O2/N2O fresh gas flow sequence

Study Objective: To determine if the previously described single-step O-2/N2O fresh gas flow (FGF) sequence could be combined with a simple desflurane vaporizer(F-D) sequence to maintain the end-expired desflurane (F(A)des) at 4.5% with the anesthesia delivery unit machine (ADU Anesthesia Machine(R); General Electric, Helsinki, Finland). Design: prospective randomized clinical study. Setting: Onze Lieve Vrouw Hospital, Aalst, Belgium, a large teaching hospital. Patients:42 ASA physical status I and II patients requiring general endotracheal anesthesia and controlled mechanical ventilation. Interventions: In 18 patients undergoing general anesthesia with controlled mechanical ventilation, F-D was determined to maintain FAdes at 4.5% with O-2/N2O FGF of two and 4 L per minute for three minutes and 0.3 and 0.4 L per minute thereafter. Using the same FGF sequence, we prospectively tested the FD schedule that approached this observed F-D pattern with the fewest possible adjustments in another 24 patients. Main Results: F-D of 6.5% for 15 Minutes followed by 5.5% thereafter approximated the observed FD course well. When it was prospectively tested, the median (25th, 75th percentiles) performance error was -1% (-5.1%,5.2%); absolute pertlorniance error, 7.1% (3.9%,9.5%); divergence, -6.6% per hour (23.1%, 3.1%/h); and wobble, 2.2% (1.8%, 3.2%). Because F(A)des increased above 4.9%, F-D) was decreased in 5 patients after 23 minutes (0.5% decrement once or twice); in two patients, F-D was temporarily increased. In one patient, FGF was temporarily increased because the bellows volume became insufficient.