Authors’ reply to ‘Plasma clearance and lipaemic index of lipid emulsion used for lipid emulsion treatment’

Dear Editor,

We thank Professor Sohn Ju-Tae for his interest in our article and his comment regarding the need to consider in vivo clearance. ¹ Indeed, we have accounted for the clearance of lipaemia for physiological doses of total parenteral nutrition in our article. ²

We agree that lipid rescue therapy is effective in the management of cardiovascular collapse from overdose of lipophilic drugs (e.g. calcium channel blockers, tricyclic antidepressants) and local anaesthetic systemic toxicity (LAST), which was one of our motivations for performing the interference experiments.

In our article, we considered the first 5 min of a lipid rescue therapy as proposed by Association of Anaesthetists of Great Britain and Ireland (AAGBI). ³ We used a bolus of 1.5 mL/kg and 5 min infusion at rate of 15 mL/kg/h (equivalent to 0.25 mL/kg/min). The resultant total infusion is 2.75 mL/kg, far below the maximum cumulative dose of 12 mL/kg; yet, there was significant interference at L-index of 1220 mg/dL.

The study by Schlotzer and Kanning, ⁴ which found the half-life of SMOFlipid to be 34 ± 11 min, was performed at a lower infusion rate of 0.625 mL/kg/h, compared with the much larger rates of 15 mL/kg/h (equivalent 0.25 mL/kg/min) used in lipid rescue therapy. Hence, the pharmacokinetics parameter established in that study may not accurately reflect the clearance when a much larger dose is administered at higher rates in the setting of lipid rescue therapy. However, we agree that given a sufficient time interval between phlebotomy and the discontinuation of lipid rescue therapy, exogenous triglycerides concentrations in plasma and risk of interference will be reduced.

Furthermore, the maintenance of 1% plasma triglyceride (1000 mg/dL, lipaemic index: 1000) for lipid emulsion treatment of toxicity induced by non-local anaesthetic drugs as suggested by Fettiplace et al. also exceeds the interference thresholds for common analytes such as aspartate aminotransferase and alanine aminotransferase. ⁵ , ⁶

Professor Sohn has suggested the use of Lipoclear, but Lipoclear also has its limitations and could interfere with the measurement of electrolytes, albumin, total protein, GGT and CRP.^7–9

Nonetheless, we feel that analytical interference should not preclude the potentially life-saving use of lipid resuscitation therapy. Clinical samples may still be sent. Laboratories may verify their own analytical interference limits, perform appropriate removal of lipaemia and release results of these samples with appropriate comments. This clinical scenario of lipid rescue therapy further emphasizes the need for close collaboration between clinicians and laboratories to optimize patient outcomes.