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.

Autore C, Brauneis S, Apponi F, Commisso C, Pinto G, Fedele F: Section in patients with hypertrophic cardiomyopathy: A report of three cases. A NESTHESIOLOGY 1999; 90:1205–7
Polley LS, Columb MO, Naughton NN, Wagner DS, van de Ven CJM: Relative analgesic potencies of ropivacaine and bupivacaine for epidural analgesia in labor: Implications for therapeutic indexes. A NESTHESIOLOGY 1999; 90:944–50
Capogna G, Celleno D, Fusco P, Lyons G, Columb M: Relative potencies of bupivacaine and ropivacaine for analgesia in labour. Br J Anaesth 1999; 82:371–3
McDonald SB, Liu SS, Kopacz DJ, Stephenson CA: Hyperbaric spinal ropivacaine: A comparison to bupivacaine in volunteers. A NESTHESIOLOGY 1999; 90:971–7