Volume 10, No. 4 • Winter 1995

New Anesthetic Requires New Vaporizers for Safety

William Clayton Petty, M.D.

Sevoflurane (ULTANE) has been approved by the FDA as an inhalation anesthetic. Tandem with the FDA drug approval process was the development of new single-agent vaporizers for the safe delivery of sevoflurane. Three temperature compensated, pressure compensated, flow compensated sevoflurane vaporizers have been designed and manufactured:

  1. Penlon, sevoflurane series Sigma Elite vaporizer,
  2. Ohmeda, sevoflurane series TEC 5 vaporizer, and
  3. North American Drager, sevoflurane series 19.1 vaporizer.

Sevoflurane is a liquid anesthetic at room temperature with a vapor pressure of 157 mmHg at 20 C. In the capped bottle, the gaseous space above the liquid has a concentration of approximately 21% at 20 C. Using this potent drug without a precision vaporizer created specifically for this volatile anesthetic would be difficult, dangerous, and foolhardy.

The total liquid capacity, wick holding capacity, filling time, and drain time of the three vaporizers are similar. The output curves for sevoflurane for each of the three vaporizers with oxygen as the carrier gas (1 LPM to 15 LPM) through the vaporizer with the vaporizer dial settings from 0.2% to 8.0% shows the three vaporizers to be dependable and accurate. Delivered sevoflurane concentration was virtually independent of oxygen gas flow. The substitution of air as the carrier gas decreased the output approximately 4 to 5% below the dial concentration (e.g. dial set at 4.0%, output was 3.8%). Excellent accuracy was maintained for all three vaporizers in the middle flow ranges. The MAC for sevoflurane in humans is approximately 2%. Output concentrations in the range of MAC are consistent with dependable accurate delivery of the potent agent, sevoflurane.

The Penlon, Ohmeda, and North American Drager vaporizers for sevoflurane are very similar to the traditional vaporizers for halothane, enflurane, and isoflurane. External and internal components are similar in appearance and function. The same reliability can be expected with any of the three vaporizers as has been known from the vaporizers now in service for halothane, enflurane, and isoflurane.

Sevoflurane (CFH2-O-CH[CF3]2) is a new potent inhalation anesthetic agent to be added to our armamentarium. Three single-agent vaporizers allow us to safely deliver sevoflurane to our patients. Research in pharmacology and technology have combined again to benefit the patient and the specialty of anesthesia. Dr. Petty is Professor and Vice Chairman, Department of Anesthesiology, Uniformed Services University of the Health Sciences, Bethesda, MD.