|
|
October 16-20, 2010 San Diego, CA Home Abstract Archive Search Abstracts 2010 Session Grid 2010 Meeting Website Policy Statements ASA Website Feedback 
Visit Anesthesiology.org |
| Previous Abstract | Next Abstract |
| Printable Version |
|
A514
October 18, 2009 1:00 PM - 2:30 PM Room Room 357 |
| Empirical General Anesthetic Equation: Desflurane in O 2 – Part II. Derivation in Broader Population |
|
**
Christine Lescrenier, M.D., Eugene Vandermeersch, M.D., Ph.D., Jan F.A. Hendrickx, M.D., Ph.D., Luc Foubert, M.D., Ph.D., Andre M. De Wolf, M.D. Anesthesiology, KUL University/OLV Hospital, Leuven/Aalst, Belgium |
|
Introduction
While the fundamentals of the administration of potent inhaled agents have been described well in the seminal work by Eger (1), comprehensive empirical data that describe the course of vaporizer settings (F D ) that maintain a constant end-expired agent concentration (F A ) across the entire fresh gas flow (FGF) spectrum are few (2). A better understanding of the relationship between F D , FGF, and time could facilitate the development of administration schedules that strike a good between rapidly achieving the desired F A , simplicity, and reducing agent usage. We therefore sought to develop an empirical model that describes this relationship for desflurane in O 2 . An initial model that proved promising in a small number of patients (see Part I) is now extended to a larger population with covariate analysis for age, height, and weight. Methods After IRB approval, 30 patients undergoing general surgery lasting > 40 min were enrolled. After IV induction and endotracheal intubation, ventilation was controlled mechanically with the ADU® anesthesia machine (General Electric, Helsinki, Finland). All patients received desflurane in O 2 . Using Excel as a randomization tool, the FGF in each patient was changed randomly every 6 min with the F D being adjusted to maintain desflurane F A at 5.0%. The FGF and F D data were used to build a model based on the following premises: (1) circuit wash-in plus patient uptake can be mathematically described by a two-exponential decay function; (2) the degree of rebreathing is inversely proportional to FGF; and (3) for any given FGF, F D gradually declines to a constant value. This mathematically translates into F D = A1+ (B1*e -time/B2 + C1*e -time/C2 )/FGF. The parameters of the model (A1,B1,B2,C1,C2) were derived by having Excel's solver function minimize the sum of the squared differences between the measured and predicted F D . Age, height, and weight were used as covariates. Results See figures 1 and 2. The resulting model was: F D = 5.93 + (24.6*e -time/1.81 + 1.93*e -time/124.2 )/FGF (figure 1). Incorporating age, height, and weight did not improve the model.[figure1][figure2] Discussion. We empirically derived a formula that describes the F D -FGF combinations that could be used to maintain a constant desflurane F A in O 2 with the ADU® anesthesia machine. Data collection and modeling efforts continue at the time of reporting. Patient demographics did not improve the model. Further fine-tuning of the model may require the inclusion of more patients and an alternate rebreathing function. References : (1) Eger EI II: Anesthetic Uptake and Action. Williams & Wilkins, 1974. (2) Lowe HJ, Ernst EA: The Quantitative Practice of Anesthesia. Williams & Wilkins, 1981. From Proceedings of the 2009 Annual Meeting of the American Society Anesthesiologists. |
Figure 1
 Figure 2  |