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Critical Care Research and Practice
Volume 2014 (2014), Article ID 236520, 7 pages
http://dx.doi.org/10.1155/2014/236520
Research Article

An In Vitro Analysis of the Effects of Intravenous Lipid Emulsion on Free and Total Local Anaesthetic Concentrations in Human Blood and Plasma

1Monash Health Emergency Medicine Program, Monash Medical Centre, Clayton Road, Clayton, VIC 3168, Australia
2Department of Forensic Toxicology, Institute of Forensic Medicine, Kantonsspital St. Gallen, Rorschacher Straße 95, Building 11, 9007 St. Gallen, Switzerland
3Department of Forensic Medicine, Victorian Institute of Forensic Medicine, Monash University, 57-83 Kavanagh Street, Southbank, VIC 3006, Australia
4School of Clinical Sciences at Monash Health, Monash University, Clayton, VIC 3168, Australia

Received 20 June 2014; Revised 26 September 2014; Accepted 10 October 2014; Published 5 November 2014

Academic Editor: Robert Boots

Copyright © 2014 Louise Ann Clark et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background. Intravenous lipid emulsion (ILE) is recommended as a “rescue” treatment for local anaesthetic (LA) toxicity. A purported mechanism of action suggests that lipophilic LAs are sequestered into an intravascular “lipid-sink,” thus reducing free drug concentration. There is limited data available correlating the effects of ILE on LAs. Aims. To compare the in vitro effect of ILE on LA concentrations in human blood/plasma and to correlate this reduction to LA lipophilicity. Method. One of four LAs (bupivacaine-most lipophilic-4 mg/L, ropivacaine-6 mg/L, lignocaine-14 mg/L, and prilocaine-least lipophilic-7 mg/L) was spiked into plasma or whole blood. ILE or control-buffer was added. Plasma was centrifuged to separate ILE and total-LA concentration assayed from the lipid-free fraction. Whole blood underwent equilibrium dialysis and free-LA concentration was measured. Percent reduction in LA concentration from control was compared between the LAs and correlated with lipophilicity. Results. ILE caused a significant reduction in total and free bupivacaine concentration compared with the other LAs. Ropivacaine had the least reduction in concentration, despite a lipophilicity similar to bupivacaine. The reduction in LA concentration correlated to increasing lipophilicity when ropivacaine was excluded from analysis. Conclusion. In this first in vitro model assessing both free- and total-LA concentrations exposed to ILE in human blood/plasma, ILE effect was linearly correlated with increasing lipophilicity for all but ropivacaine.