Anesth Analg 2004;99:1159-1163
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000131507.65132.7F
TECHNOLOGY, COMPUTING, AND SIMULATION
The Effect of a Model-Based Predictive Display on the Control of End-Tidal Sevoflurane Concentrations During Low-Flow Anesthesia
R. Ross Kennedy, MB ChB, PhD, FANZCA,
Richard A. French, MB BS, FANZCA, and
Sandra Gilles, BAgSci
Department of Anaesthesia, Christchurch Hospital and 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 and Christchurch School of Medicine and Health Sciences, Rolleston Ave., Christchurch, New Zealand. Address e-mail to ross.kennedy{at}chmeds.ac.nz Reprints will not be available from the authors.
We have shown that a multicompartment model accurately predicts end-tidal (ET) sevoflurane (sevo) and isoflurane concentrations. The model has been adapted to use real-time fresh gas flow and vaporizer settings to display a 10-min prediction of ET sevo concentrations. In this study, we evaluated the effect of the predictive display on the speed and accuracy of changes in ET sevo by the anesthesiologist. Fifteen patients were studied in whom sevo-based anesthesia was expected to last more than 2 h. Four step changes of target ET concentration (+0.5, +1.0, –1.0, and –0.5 vol%) were made either unaided or with the prediction display. Fresh gas flow was 1 L/min. Response time, maximum overshoot, and stability in the 5 min after the target was achieved were compared by using two-tailed paired Student’s t-tests. Changes were made on average 1.5–2.3 times faster with the predictive display than without it. These differences were statistically significant (P < 0.05) for the +0.5, +1.0, and –0.5 vol% step changes but not for the –1.0 vol% change. There were no differences in the degree of overshoot or stability. These differences are comparable to those seen with an automatic feedback control system. This system may simplify the administration of volatile anesthesia and the use of low-flow anesthesia.
IMPLICATIONS: A model-based system that uses anesthesia machine settings to predict and display future end-tidal (ET) sevoflurane concentrations was tested. Anesthesiologists made step changes in ET sevoflurane 1.5–2.3 times faster when using the system. This display may simplify the administration of volatile anesthesia, especially at low gas flows.
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