In Reply:—
We appreciate the opportunity to comment on the case report by Autore et al. 1and the correspondence by Dr. Camann. We also have difficulty with the conclusion that ropivacaine should be the “drug of choice” for cesarean delivery in the setting of hypertrophic cardiomyopathy. The presumed lesser cardiotoxicity of ropivacaine is based on the assumption of equipotency with bupivacaine. Our recent minimum local analgesic concentration (MLAC) study of the relative analgesic potencies of ropivacaine and bupivacaine for epidural analgesia in labor found that ropivacaine was 40% less potent than bupivacaine. 2These results are in agreement with both a recent European study 3and a study comparing intrathecal administration of the two local anesthetics. 4Clearly, the cardiotoxic potential of local anesthetics can only be properly evaluated when comparing equipotent doses. The therapeutic index may favor bupivacaine. That said, we would like to emphasize that our studies determined analgesic potencies, and the results may not be generalizable to anesthetic potencies.
We agree with Dr. Camann that careful fractionated dosing of lidocaine allows for slow block onset and that it is the least toxic of the three local anesthetics. In addition, the shorter duration of lidocaine allows for a quicker return to preblock hemodynamics, which may be advantageous in hypertrophic cardiomyopathy.
