Lipid emulsion-mediated reversal of toxic-dose aminoamide local anesthetic-induced vasodilation in isolated rat aorta

BACKGROUND: Intravenous lipid emulsion has been used to treat systemic toxicity of local anesthetics. The goals of this in vitro study were to determine the ability of two lipid emulsions (Intralipid® and Lipofundin® MCT/LCT) to reverse toxic dose local anesthetic-induced vasodilation in isolated rat aortas. METHODS: Isolated endothelium-denuded aortas were suspended for isometric tension recording. Vasodilation was induced by bupivacaine (3 × 10(-4) M), ropivacaine (10(-3) M), lidocaine (3 × 10(-3) M), or mepivacaine (7 × 10(-3) M) after precontraction with 60 mM KCl. Intralipid® and Lipofundin® MCT/LCT were then added to generate concentration-response curves. We also assessed vasoconstriction induced by 60 mM KCl, 60 mM KCl with 3 × 10(-4) M bupivacaine, and 60 mM KCl with 3 × 10(-4) M bupivacaine plus 1.39% lipid emulsion (Intralipid® or Lipofundin® MCT/LCT). RESULTS: The two lipid emulsions reversed vasodilation induced by bupivacaine, ropivacaine, and lidocaine but had no effect on vasodilation induced by mepivacaine. Lipofundin® MCT/LCT was more effective than Intralipid® in reversing bupivacaine-induced vasodilation. The magnitude of lipid emulsion-mediated reversal of vasodilation induced by high-dose local anesthetics was as follows (from highest to lowest): 3 × 10(-4) M bupivacaine-induced vasodilation, 10(-3) M ropivacaine-induced vasodilation, and 3 × 10(-3) M lidocaine-induced vasodilation. CONCLUSIONS: Lipofundin® MCT/LCT-mediated reversal of bupivacaine-induced vasodilation was greater than that of Intralipid®; however, the two lipid emulsions equally reversed vasodilation induced by ropivacaine and lidocaine. The magnitude of lipid emulsion-mediated reversal of vasodilation appears to be correlated with the lipid solubility of the local anesthetic.