END-TIDAL OXYGEN MEASUREMENT COMPARED WITH PATIENT FACTOR ASSESSMENT FOR DETERMINING PREOXYGENATION TIME

Time to adequate preoxygenation was assessed in 200 elective surgical patients, using measurement of end-tidal oxygen concentration. A varie ty of patient factors were assessed as to their ability to predict the time required to preoxygenate a patient. Of the 200 patients, 23 (11. 5%) were unable to be adequately preoxygenated; most of these cases we re due to a poor mask fit. The average time for preoxygenation was 154 seconds (range 43-364 seconds). Of those patients who could be preoxy genated, 46 (23%) required more than three minutes. Although a regress ion equation could be constructed to calculate time required for preox ygenation, the wide standard errors of the coefficients preclude a cli nically useful predictive equation. We thus found that we could not ac curately predict time required for preoxygenation and that a routine t hree minutes preoxygenation may not be sufficient for many patients. H owever, the measurement of end-tidal oxygen concentration is a very us eful method of determining the end-point for preoxygenation.