Lipid emulsion infusion and its effect on anaesthetic drugs

Lipid emulsion has several established clinical uses, including parenteral nutrition, treatment of local anaesthetic systemic toxicity and as an energy source in metabolic crises, such as maple syrup urine disease. In toxicological settings, it acts via a 'lipid sink' mechanism, sequestering lipophilic drugs and reducing their bioavailability. This raises the possibility that the pharmacokinetics of commonly used anaesthetic agents may be affected in patients with a high intravascular lipid load. We report the peri-operative management of a 14-year-old child with maple syrup urine disease receiving a high-dose lipid emulsion infusion during a metabolic crisis, who required general anaesthesia and intubation to facilitate transfer to a specialist paediatric centre. During induction of anaesthesia, fentanyl appeared to have a minimal sedating effect. Ketamine was avoided due to concerns regarding unpredictable efficacy in the setting of lipid loading. The patient also developed significant hypotension during maintenance with sevoflurane at one minimum alveolar concentration, raising the possibility of altered anaesthetic potency. A review of the literature revealed a lack of evidence examining the pharmacodynamics of anaesthetic drugs in lipid-loaded patients. As the use of lipid emulsion increases, further research is required to guide safe and effective anaesthetic practice in this setting.