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A4094
October 15, 2013
8:00:00 AM - 9:00:00 AM
Room Room 104-Area C
12 Hour Evaluation of Filters to Prepare an Anesthesia Machine for Malignant Hyperthermia Susceptible Patients
Robert Stoker, M.D., Mathew Romankowski, M.D., Kyle M. Burk, No Degree, Joseph A. Orr, Ph.D.
University of Utah, Salt Lake City, Utah, United States
Introduction: Plastic and rubber components in the anesthesia machine absorb vapor from the previous anesthetic that is desorbed during the subsequent procedure. The concentration of anesthetic released from the machine has been shown to be high enough to trigger malignant hyperthermia in susceptible patients. Activated charcoal filters have been shown effective for preparation of an anesthesia machine for treatment of malignant hyperthermia-susceptible patients. Activated charcoal filters can capture only a finite amount of vapor before they become saturated. Once saturated, the vapor could pass through the filter to the patient. We were concerned that over the course of a long anesthetic, the cumulative amount of vapor released by an anesthesia machine could saturate the charcoal in the filters. We tested the ability of these filters to remove residual anesthetic from an anesthesia machine during a long (12 hour) test period.

Methods: We contaminated an anesthesia machine (Apollo, Draeger) by delivering 1 MAC of anesthetic to a mock patient for one hour followed by a simulated emergence during which the vaporizer was turned off for three minutes and the fresh gas flow was increased to 10 L/min. We then placed activated charcoal filters (Vapor-Clean, Dynasthetics, Salt Lake City, UT) on both the inspired and expired limbs of the contaminated anesthesia machine. We used the contaminated machine to ventilate a test lung for 12 hours and recorded the concentration of anesthetic in the inspired limb of the breathing circuit using a trace gas analyzer (MIRAN SaphIRe, Thermo Electron Environmental Instruments, Franklin, MA). We placed a heated water humidifier in the expired limb of the breathing circuit. We repeated the test at three and 10 L/min fresh gas flow and for each of isoflurane, sevoflurane and desflurane.

Results: The table below shows the final concentration of anesthetic at the end of the 12 hour tests. The activated charcoal filters maintained the concentration of anesthetic below five ppm for all tests at both fresh gas flow rates. The plot shows the results of a typical test. In all of the tests the concentration remained below 5 ppm. In some tests, the concentration of anesthetic with the filter in place was not detectable because the analyzer read zero or a slight negative concentration.

Discussion: When activated charcoal filters are not used, it can take up to 104 minutes of flushing to prepare a machine for use in a MH susceptible patient. Earlier studies have shown that commercially available activated charcoal filters effectively maintain anesthetic concentration below five parts per million (PPM) for up to two hours. This data shows that the active charcoal filters prevent residual anesthetic from reaching the patient for each of the three gases whether even when used with a lower fresh gas flow.

References:

1. Birgenhieir N, Stoker R, Westenskow D, Orr J; Activated charcoal effectively removes inhaled anesthetics from modern anesthesia machines; Anesthesia and Analagesia, June 2011, 112:6, pp 1363-70

2. Gunter JB, Ball J, Than-Win S.; Preparation of the Draeger Fabius anesthesia machine for the malignant hyperthermia susceptible patient; Anesth Analg,2008; 107:1936-1945.

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