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A841
October 14, 2007 2:00 PM - 4:00 PM Room Hall D, Area K, |
| Evaluation of a Remifentanil Sevoflurane Response Surface in Patients Undergoing Elective Surgery |
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Ken B. Johnson, M.D., Noah D. Syroid, M.S., Sandeep C. Manyam, Ph.D., Dhanesh K. Gupta, M.D., Talmage D. Egan, M.D. Anesthesiology, University of Utah, Salt Lake City, Utah |
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Introduction: We previously reported response surface models that characterized the synergistic interaction between remifentanil and sevoflurane in blunting responses to verbal and painful stimuli.(1) The models were built from data collected in volunteers that received target controlled infusions of remifentanil and target end-tidal sevoflurane levels using a Logit model construct. As an update to the models, sevoflurane effect-site concentrations were subsequently estimated from measured end tidal levels using a pharmacokinetic model.(2) We hypothesized that the loss of responsiveness (LOR) response surface model based on sevoflurane effect site concentrations would predict return of responsiveness at the end of surgery better than our original end tidal based model. Methods: After institutional review board approval, 20 ASA I-III patients scheduled for elective surgery were enrolled. Each patient was induced with propofol, remifentanil, and succinylcholine. Anesthesia was maintained with sevoflurane and remifentanil, and fentanyl was administered at the discretion of the attending anesthesiologist. Assessments of responsiveness were made every 20 seconds from the termination of the anesthetic until emergence. For analysis, fentanyl was converted to remifentanil equivalents by a potency factor. Model performance (accuracy, bias, and root mean squared error) was assessed between the predicted and observed return of responsiveness. Results: The revsied and original LOR models predicted a mean probability of 56 ± 26% and 23 ± 37% respectively that patients would be unresponsive when patients began to respond during emergence. Estimates of accuracy, bias, and root mean squared error analysis were 7.9%, 7.9% and 21.9% for the revised model and 4808%, -4808%, and 9932% for the original model. In Figure 1, the solid and open circles represent the revised and original model predictions respectively. Discussion: The revised LOR model improved accuracy, bias, and root mean squared error analysis when compared to the original model. Using sevoflurane effect site in place of end tidal concentrations to construct sevolfurane-remifetnanil LOR interaction models improve model performance during non steady state conditions such as emergence from anesthesia. References: (1) Manyam et. al. Anesthesiology. 2006 Aug;105(2):267-78. (2) Lerou JG and Booij LH. Br J Anaesth. 2001 Jan;86(1):12-28.[figure1] Anesthesiology 2007; 107: A841 |
Figure 1
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