By: 29 May 2012

A new study in Anesthesiology found that the type of lipid emulsion used to reverse toxicity of local anaesthetics may make a difference in effectiveness of the reversal. The study analysed the difference between mixed (medium- and long-chain) and long-chain lipid emulsions, for their ability to extract local anaesthetic from serum.

Local anaesthetics are used to block the pain response during surgery. On rare occasions, toxicity can occur. One way to reverse toxicity of local anaesthetics is through lipid emulsion infusion, a technique commonly used to feed patients intravenously. It is believed to form a “lipid sink” that causes the anaesthetic to be absorbed out of the serum into the lipid and away from target sites like the heart. The use of lipids to treat toxicity has also been used by other physicians, such as in the treatment of drug overdoses in the emergency room.

“Our hope was to further previous research regarding the use of lipid rescue in local anaesthetic toxicity. We used human serum instead of buffer solutions that were used in prior research to produce results as clinically relevant as possible,” said lead study author Deborah French, Ph.D. “The local anaesthetics bupivacaine, ropivacaine and mepivacaine were added to the serum along with a lipid emulsion for testing.”

Findings showed that a lipid emulsion infusion containing both medium- and long-chain triglycerides extracts local anaesthetics from human serum more effectively than an emulsion containing only long-chain triglycerides. These findings are particularly important, because they contrast with past findings that examined local anaesthetic extraction from non-serum solution. Local anaesthetic toxicity often occurs in the setting of high acid in the blood. Importantly, the study also found that lipid emulsion infusion extracts local anaesthetics out of a patient’s serum at an acidic blood pH the same as it would at a normal pH, suggesting that lipid rescue need not be delayed for normalisation of the patient’s acidosis.

The study is part of an ongoing effort to characterise the suitability of lipid administration in the reversal of toxicity from local anaesthetics, as well as other drugs commonly encountered in the setting of a life-threatening overdose. Its findings have implications with respect to current guidelines that call for long-chain triglyceride emulsion instead of mixed emulsion. Nonetheless, additional studies are needed to confirm the clinical applicability of the study’s findings.