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Crit Care Res Pract. 2014;2014:236520. doi: 10.1155/2014/236520. Epub 2014 Nov 5.

An in vitro analysis of the effects of intravenous lipid emulsion on free and total local anaesthetic concentrations in human blood and plasma.

Author information

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

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.

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