Joel B. Gunter, MD, John Ball, AS, BMET, Sean Than-Win, BMET
BACKGROUND: Anesthesia machines must be flushed of halogenated anesthetics before use in patients susceptible to malignant hyperthermia. We studied the kinetics of sevoflurane clearance in the Draeger Fabius anesthesia machine and compared them to a conventional anesthesia machine (Draeger Narkomed GS).
METHODS: Before each trial, the anesthesia machine was contaminated for 2 h with 3% sevoflurane and then prepared by changing the CO2 absorbent, removing the vaporizer(s), and mounting a clean circuit and artificial lung. The basic flush procedure consisted of oxygen 10 L/min with the ventilator set to a tidal volume of 600 mL at a rate of 10/min. Residual sevoflurane in the inspiratory limb of the circuit was measured using an ambient air analyzer capable of measuring sevoflurane to _1 ppm. Results were analyzed using log-linear regression of residual concentration as a function of time. This model was used to estimate the time required to achieve a desired residual anesthetic concentration.
RESULTS: Times to achieve 10 and 5 ppm in the Draeger Narkomed GS were 11 and 18 min, respectively. For the Draeger Fabius anesthesia machine, times to 10 and 5 ppm were 75 and 104 min, respectively. Several maneuvers to accelerate clearance of residual sevoflurane from the Draeger Fabius resulted in only modest reductions in these times (10 and 5 ppm times 40–50 min and 60–80 min, respectively). Insertion of an activated charcoal filter (QED_, Anecare Laboratories, Salt Lake City, UT) into the inspiratory limb of the Draeger Fabius circuit reduced the residual anesthetic concentration to _5 ppm within 10 min; this concentration was maintained for _6 h despite a fresh gas flow of only 2 L/min after the first 15 min.
DISCUSSION: Preparation of the Draeger Fabius anesthesia machine using conventional flushing techniques required almost 10 times as long as an older, conventional anesthesia machine. If a prolonged flush is impractical or impossible, we describe a procedure using an activated charcoal filter inserted on the inspiratory limb of the breathing circuit which can effectively scrub residual sevoflurane to a concentration _5 ppm within 10 min. This procedure includes an initial 5 min flush without the activated charcoal filter followed by a 5 min flush with the charcoal filter, after which the machine is ready for use in the malignant hyperthermia susceptible patient. The charcoal filter must remain on the machine for the remainder of the anesthetic, and the fresh gas flow should be maintained _10 L/min for the first 5 min, and _2 L/min thereafter.
(Anesth Analg 2008;107:1936 –45)