To the Editor:--Keifer and Stirt describe an alternative to standard preoxygenation in which they dispense with the anesthesia mask and place the elbow piece of the anesthesia tubing in the patient's mouth.
We attempted to copy this technique in a trial preoxygenation of five male adult volunteers, employing a circle absorber system with a fresh gas flow of 8 l/min. The expired and inspired gases were monitored at the elbow piece using an Ohmeda Rascal II monitor. Inspired and end-expired fractions of oxygen and nitrogen were measured. It was found that, after 90 s of preoxygenation, the end-tidal oxygen fraction, which equates to alveolar fraction, had reached a plateau at a mean value of 0.622 (range 0.59–0.67).
We know from previous work that efficient preoxygenation using a circle system and mask should result in an end-tidal oxygen plateau approaching 0.9. The failure of the Keifer and Stirt technique to attain full preoxygenation probably is due to air inhalation through the nose. Use of a nose clip would eliminate this problem but may be as unpleasant for patients as the application of an anesthesia mask.
We recognize that efficient preoxygenation is not always easy because of lack of patient compliance but advise caution in the use of the Keifer and Stirt technique in situations that mandate full preoxygenation. The difference between an alveolar oxygen fraction of 0.9 and 0.6 could prevent desaturation for a significant period during a difficult intubation.
Patrick Butler, M.B., Ch.B., F.R.C.A., Clinical Instructor.
Mark Kenny, B.A., M.B., B.S., F.R.C.A., Clinical Instructor, Section of Pediatric Anesthesiology, University of Michigan Medical Center, C. S. Mott Children's Hospital, Room F3900, Box 0211, Ann Arbor, Michigan 48109–0211.