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Correspondence |
Zurich, Switzerland
To the Editor:
Mardirosoff et al. describe the occurrence of convulsions after the administration of high dose ropivacaine following an interscalene block.1 This interesting case merits further documentation and comments to increase its educational value. The delay of 20 min between the end of the administration of ropivacaine and the convulsions argues against an iv injection. Therefore, it will be interesting to know if the authors observed premonitory signs (such as dizziness or incoherent speech) before convulsions. Indeed, it seems the sequence of the different phases of central nervous system intoxication are better individualized with ropivacaine,2 which is usually not the case with bupivacaine. Furthermore, did the authors make a second blood drug measurement in order to build a pharmacokinetic model and, by extrapolation, estimate the ropivacaine blood concentration at the time of the convulsions? In a case reported previously with severe cardiac toxicity after sciatic block with ropivacaine,3 we evaluated by extrapolation the total and unbound plasma concentration of ropivacaine to be 8.8 and 1.8 mg•L–1 respectively, at the time of the critical event. Indeed, a "grey" zone remains between the appearance of central nervous system toxicity and slight changes in EEG recordings with venous total plasma concentration of ropivacaine of 2.2 mg•L–1 (range 0.5–3.2) as reported by Knudsen et al.4 and the development of severe cardiac toxicity. The ropivacaine plasma concentrations in Mardirosoff's case together with ours3 and those known in the literature4,5 could add valuable information.
References
1 Mardirosoff C, Dumont L. Convulsions after the administration of high dose ropivacaine following an interscalenic block. Can J Anesth 2000; 47: 1263.[Medline]
2 Klein SM, Benveniste H. Anxiety, vocalization and agitation following peripheral nerve block with ropivacaine. Reg Anesth Pain Med 1999; 24: 175–8.[Medline]
3 Ruetsch YA, Fattinger KE, Borgeat A. Ropivacaine-induced convulsions and severe cardiac dysrhythmia after sciatic block. Anesthesiology 1999; 90: 1784–6.[Medline]
4
Knusden K, Beckman Suurküla M, Blomberg S, Sjövall J, Edvardsson J. Central nervous and cardiovascular effects of i.v. infusions of ropivacaine, bupivacaine and placebo in volunteers. Br J Anaesth 1997; 78: 507–14.
5
Scott DB, Lee A, Fagan D, Bowler GMR, Bloomfiled P, Lundh R. Acute toxicity of ropivacaine compared with that of bupivacaine. Anesth Analg 1989; 69: 563–9.
Annemasse, France
We thank Ekatodramis and Borgeat for their interesting comments.
We did not observe any premonitory signs before the convulsions took place; neither did we perform a second blood drug measurement.
Nevertheless, unlike the case they reported,1 the total venous concentration at the time of convulsions was probably lower than 2.09 mg•L–1 which, in our case, was the concentration measured one hour after the injection. Indeed, studies on ropivacaine pharmacodynamics suggest that 45 to 60 min is the average time to achieve maximal plasma concentrations after a plexus block or a wound infiltration.2,3 The 2.09 mg•L–1 concentration measured in our patient is consistent with concentrations observed in the aforementioned studies, in which such severe central nervous system (CNS) toxicity was not observed.
Moreover, Scott showed that the rate of absorption was better correlated with CNS toxicity than the peak plasma concentration.4 This might also constitute another causal factor in our case, since a faster rate of local anesthetic absorption has been demonstrated in patients with chronic renal failure.5
References
1 Ruetsch YA, Fattinger KE, Borgeat A. Ropivacaine-induced convulsions and severe cardiac dysrythmia after sciatic block. Anesthesiology 1999; 90: 1784–6.
2
Hickey R, Blanchard J, Hoffman J, Sjovall J, Ramamurthy S. Plasma concentrations of ropivacaine given with or without epinephrine for brachial plexus block. Can J Anaesthesia 1990; 37: 878–82.
3 Pettersson N, Emanuelsson B-M, Reventlid H, Hahn RG. High-dose ropivacaine wound infiltration for pain relief after inguinal hernia repair: a clinical and phamacokinetic evaluation. Reg Anesth Pain Med 1998; 23: 189–96.[Medline]
4 Scott DB. Evaluation of clinical tolerance of local anaesthetic agents. Br J Anaesth 1975; 47: 328–31.
5
McEllistrem RF, Schell J, O'Malley K, O'Toole D, Cunningham AJ. Interscalene brachial plexus blockade with lidocaine in chronic renal failure – a pharmacokinetic study. Can J Anaesth 1989; 36: 59–63.
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