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.