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LETTER TO THE EDITOR

Plasma Bupivacaine Concentrations Are Too Low to Explain Reduced Vecuronium Requirement with an Epidural

Department of Anesthesia; Sanjay Gandhi Post Graduate Institute of Medical Sciences; Lucknow, India; aagarwal{at}sgpgi.ac.in

In Response:

We would like to thank Drs. Donati and Fortier for their interest in our article and their valuable comments. We agree that the marked reduction in the requirement of muscle relaxants that we observed with an epidural local anesthetic is in sharp contrast with the earlier reports (1–5). But do these observations really apply to our study? All the studies quoted by Drs. Donati and Fortier have observed the interaction of muscle relaxants and local anesthetics at the neuromuscular junction. However, the clinical practice of anesthesia is a polypharmacy; wherein the anesthetic state is the net result of the action of different drugs and their interactions. Propofol enhances both the presynaptic and postsynaptic effects of the vecuronium in the rat diaphragm (6). Marked reduction in the requirement of vecuronium in our study could have been the result of either additive or synergistic action of bupivacaine and propofol on the requirement of vecuronium (7).

References

1. Matsuo S, Rao DB, Chaudry I, Foldes FF. Interaction of muscle relaxants and local anesthetics at neuromuscular junction. Anesth Analg 1978;57:580–7.[Web of Science][Medline]
2. Burm AG, Vermeulen AP, van Kleef JW et al. Pharmacokinetics of lidocaine and bupivacaine in surgical patients following epidural administration: simultaneous investigation of absorption and disposition kinetics using stable inotropes. Clin Pharmacokinet 1987;13:191–203.[Web of Science][Medline]
3. Teliveo L, Katz RL. The effect of modern intravenous local analgesics on respiration during partial neuromuscular block in man. Anaesthesia 1970;25:30–5.[Web of Science][Medline]
4. Toft P, Kirkegaard NH, Severinsen I, Heblo-Hasan HS. Effect of epidurally administered bupivacaine on atracurium induced neuromuscular blockade. Acta Anaesthesiol Scand 1990;34:649–52.[Web of Science][Medline]
5. Taivainen T, Meretoja OA, Rosenberg PH. The effect of epidural bupivacaine on vecuronium induced neuromuscular blockade in children. Acta Anaesthesiol Scand 1994;38:453–6.[Web of Science][Medline]
6. Lebeda MD, Wegezynowicz ES, Wachtel RE. Propofol potentiates both pre and postsynaptic effects of vacuronium in the rat hemidiaphragm. Br J Anaesth 1992;68:282–5.[Abstract/Free Full Text]
7. Agarwal A, Pandey R, Dhiraaj S et al. Effect of epidural bupivacaine on induction and maintenance doses of propofol (evaluated by bispectral index) and maintenance doses of fentanyl and vecuronium. Anesth Analg 2004;99:1684–8.[Abstract/Free Full Text]

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