Intravenous Lipid Emulsion Does Not Augment Blood Pressure Recovery in A Rabbit Model of Metoprolol Toxicity

Abstract

Intravenous lipid emulsion (ILE) has been demonstrated to be an effective treatment for systemic toxicity associated with local anaesthetics and increasingly non-local anaesthetic agents of high lipophilicity. Effect for ILE has been demonstrated in animal models of propranolol poisoning; however, any benefit for ILE in more hydrophilic β-blockers remains uncertain. We determined to examine the effect of ILE on haemodynamic recovery following induction of hypotension with the relatively hydrophilic β-blocker, metoprolol. Twenty sedated, invasively monitored and mechanically ventilated adult New Zealand white rabbits underwent metoprolol infusion to mean arterial pressure (MAP) 60% baseline. Intravenous rescue was given according to the following groups: 6mL/kg 20% lipid emulsion or 6mL/kg 0.9% saline solution over 4min. Haemodynamic parameters were obtained in 15min. MAP was 70 (interquartile range (IQR), 58-82) mmHg saline group and 79 (IQR, 72-89) mmHg ILE group at baseline, and 38 (IQR, 33-40) mmHg saline group and 41 (IQR, 40-43) mmHg ILE group, respectively, following metoprolol infusion. No statistically significant difference between ILE and saline-treated groups was observed in MAP, or pulse rate, at any time point following rescue therapy. ILE was not effective in reversal of metoprolol-induced hypotension in this rabbit model. These findings lend inferential support for the 'lipid sink' as principal mechanism for the beneficial effect observed with ILE administration in other models of lipophilic β-blocker-induced toxicity.