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REGIONAL ANESTHESIA

The Long Term Myotoxic Effects of Bupivacaine and Ropivacaine After Continuous Peripheral Nerve Blocks

Wolfgang Zink, MD, DEAA^*, Jürgen R. E. Bohl, MD, Nicola Hacke, MD, Barbara Sinner, MD^*, Eike Martin, MD^*, and Bernhard M. Graf, MD, PhD^*

Departments of *Anesthesiology and Vascular Surgery, University of Heidelberg, Heidelberg; and Department of Neuropathology, University of Mainz, Mainz, Germany

Address correspondence and reprint requests to Bernhard M. Graf, MD, PhD, Department of Anesthesiology, University of Heidelberg, Im Neuenheimer Feld 110, D-69120 Heidelberg, Germany. Address e-mail to bernhard_graf{at}med.uni-heidelberg.de.

Compared with bupivacaine, acute myotoxicity of ropivacaine is less severe. Thus, in this study we compared the long term myotoxic effects of both drugs in a clinically relevant setting. Femoral nerve catheters were inserted in anesthetized pigs, and either 20 mL of bupivacaine (5 mg/mL) or ropivacaine (7.5 mg/mL) was injected. Subsequently, bupivacaine (2.5 mg/mL) and ropivacaine (3.75 mg/mL) were continuously infused (8 mL/h) over 6 h. Control animals were treated with corresponding volumes of normal saline. After 7 and 28 days, respectively, muscle samples were dissected at the former injection sites, and histological patterns of muscle damage were blindly scored (0 = no damage to 3 = marked lesions/myonecrosis) and compared. No morphological tissue changes were detected in control animals. In the observed period, both local anesthetics induced morphologically identical patterns of calcific myonecrosis, formation of scar tissue, and a marked rate of fiber regeneration. However, bupivacaine’s effects were constantly more pronounced than those of ropivacaine. These data show that both drugs induce irreversible skeletal muscle damage in a clinically relevant model, and confirm the exceeding rate of myotoxicity of bupivacaine. However, the clinical impact of these long term myotoxic effects still has to be assessed.