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

Louise Ann Clark, Jochen Beyer & Andis Graudins

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.
   
citation Clark L A, Beyer J, Graudins A. An in vitro analysis of the effects of intravenous lipid emulsion on free and total local anaesthetic concentrations in human blood and plasma. Crit Care Res Pract 2014; 2014:236520.
   
type journal paper/review (English)
date of publishing 05-11-2014
journal title Crit Care Res Pract (2014)
ISSN print 2090-1305
pages 236520
PubMed 25538850
DOI 10.1155/2014/236520