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Anesth Analg 2005;101:1023-1028
© 2005 International Anesthesia Research Society
doi: 10.1213/01.ane.0000168337.88469.9c

ANESTHETIC PHARMACOLOGY

The Effect of Using Different Values for the Effect-Site Equilibrium Half-Time on the Prediction of Effect-Site Sevoflurane Concentration: A Simulation Study

R. Ross Kennedy, MB, ChB, PhD FANZCA

Department of Anaesthesia, Christchurch Hospital & Christchurch School of Medicine and Health Sciences, Christchurch, New Zealand

Address correspondence to R. Ross Kennedy, MB, ChB, PhD, FANZCA, Department of Anaesthesia, Christchurch Hospital & Christchurch School of Medicine and Health Sciences, Rolleston Ave., Christchurch, New Zealand. Address e-mail to ross.kennedy{at}chmeds.ac.nz.

We have developed a predictive display that allows effect-site concentration (Ceff) to be used as a target for administration of inhaled anesthesia. Ceff is dependent on the half-time for plasma effect-site equilibrium [t1/21/2(ke0)]. The t1/2(ke0) used in the predictive display is fixed and may differ from that in the patient. We wished to explore the effect of this difference on predictions of Ceff. In a computer simulation, fresh gas flow and vaporizer settings required to achieve a predefined time profile for Ceff were determined for t1/2(ke0) of 2.5, 3.5, and 5 min. The end-tidal values for each simulation were used to recalculate Ceff with each t1/2(ke0). The maximal deviation at predetermined points, measures of global fit, and the delay in "recovery" were calculated. With a predictive display t1/2(ke0) of 3.5 min, the maximal error in Ceff was 0.18 vol%, occurring during the wash-in phase and disappearing within 2–3 min. The difference in time for Ceff to decrease from 1.0 to 0.7 vol% was 1.3 min. Results with a display t1/2(ke0) of 2.5 min or 5 min and simulated patient t1/2(ke0) of 5 min or 2.5 min were approximately twice as large. These results suggest that Ceff is relatively insensitive to large (50%–100%) variations in t1/2(ke0).




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press
Copyright © 2005 by the International Anesthesia Research Society.