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Canadian Journal of Anesthesia 51:851 (2004)
© Canadian Anesthesiologists' Society, 2004

Correspondence

Ropivacaine plasma concentrations are similar during continuous lumbar plexus blockade using two techniques: pharmacokinetics or pharmacodynamics?

Stephan Blumenthal, MD, Georgios Ekatodramis, MD and Alain Borgeat, MD

Zurich, Switzerland

To the Editor:

We read with interest the recent article published by Kaloul et al.1 We would like to congratulate the authors for having performed this study looking more closely for the pharmacokinetics of a perineural continuous infusion of ropivacaine. However, we disagree with their final conclusion stating that a continuous infusion of ropivacaine 0.2% at 12 mL·hr–1 results in a local anesthetic accumulation and may result in a dangerous blood concentration if maintained at that rate for 48 hr. The results of their study do not allow the authors to state that, since the free concentration of ropivacaine, responsible for the pharmacodynamic effects, has not been measured. In a quite similar condition it has been shown that the plasma concentration of unbound ropivacaine and unbound 2.6-pipecoloxylidide (the major active metabolite of ropivacaine) added together, does not increase and remains well below threshold levels for systemic toxicity after a continuous infusion of ropivacaine of either 6 or 9 mL·hr–1 after 48 hr.2 Surgery is responsible for the release of {alpha}1-acid glycoprotein which is buffering the free fraction of ropivacaine preventing any dangerous increase in blood concentration. The increase in the total ropivacaine blood concentration observed in both studies is explained by an infusion rate greater than the liver metabolism.3 Under these conditions1,2 the danger of systemic toxicity is most likely after the initial bolus, not after a continuous infusion as long as the liver continues to release {alpha}1-acid glycoprotein.

References

1 Kaloul I, Guay J, Côté C, Halwagi A, Varin F. Ropivacaine plasma concentrations are similar during continuous lumbar plexus blockade using the anterior three-in-one and the posterior psoas compartment techniques. Can J Anesth 2004; 51: 52–6.[Abstract/Free Full Text]

2 Ekatodramis G, Borgeat A, Huledal G, Jeppsson L, Westman L, Sjövall J. Continuous interscalene analgesia with ropivacaine 2 mg/ml after major shoulder surgery. Anesthesiology 2003; 98: 143–50.[Medline]

3 Erichsen CJ, Sjövall J, Kehlet H, Hedlund C, Arvidsson T. Pharmacokinetics and analgesic effect of ropivacaine during continuous epidural infusion for postoperative pain relief. Anesthesiology 1996; 84: 834–42.[Medline]


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CJA 2004 51: 851-852. [Full Text]  




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