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IS THE END-TIDAL PARTIAL PRESSURE OF ISOFLURANE A GOOD PREDICTOR OF ITS ARTERIAL PARTIAL PRESSURE?

FREI, F. J. ; ZBINDEN, A. M. ; THOMSON, D. A. ; RIEDER, H. U.

In: BJA: British Journal of Anaesthesia, 1991, vol. 66, no. 3, p. 331-339

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    Title
    • IS THE END-TIDAL PARTIAL PRESSURE OF ISOFLURANE A GOOD PREDICTOR OF ITS ARTERIAL PARTIAL PRESSURE?
    Author
    • FREI, F. J.. Department of Anaesthesia, University of Basel/Kantonsspital CH-4031 Basel, Switzerland
    • ZBINDEN, A. M.. Institute for Anaesthesiology and Intensive Care, Inselspital, University of Bern CH-3010 Bern, Switzerland
    • THOMSON, D. A.. Institute for Anaesthesiology and Intensive Care, Inselspital, University of Bern CH-3010 Bern, Switzerland
    • RIEDER, H. U.. Institute for Anaesthesiology and Intensive Care, Inselspital, University of Bern CH-3010 Bern, Switzerland
    Document Type
    • Postprint
    Language
    • English
    Published in
    • BJA: British Journal of Anaesthesia, 1991, vol. 66, no. 3, p. 331-339. Oxford University Press
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:299974
    Summary
    End-tidal partial pressure of isoflurane (PE′iso) may be used as a measure of anaesthetic depth. During uptake, an arterial partial pressure (Paiso) which is considerably less than PE′iso(Paiso/PE′iso<<1) leads to underestimation of depth of anaesthesia and, during elimination, PE′iso/Paiso<<1 will lead to an overestimation of anaesthetic depth. We measured Paiso/PE′iso during a 60-min uptake period of 1% isoflurane and PE′iso/Paiso during the subsequent 60-min elimination period in 26 patients (age 13-88 yr, ASA I-III) undergoing various surgical procedures. After 15 min of isoflurane uptake, Paiso/PE′iso of 26 patients was mean 0.78 (SD 0.10) and this increased only marginally at 60 min (0.79 (0.09)), whereas during elimination, PE′iso/Paiso was in the range 0.79 (0.14)-0.83 (0.11). Predictability of Paiso in a given patient is hindered by the high SD of Paiso/PE′iso and PE′iso/Paiso, but it may be improved by taking into account age, ASA physical status category, vital capacity, inspired minus end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during uptake; and obesity, end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during elimination. However, even with multiple regression analysis (to account for the various possible variables), clinically useful prediction of Paiso/PE′iso and PE′iso/Paiso in a particular patient is not possible (residual SD 0.084 and 0.113, respectively)