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Correspondence |
Balgrist University Hospital, Zurich, Switzerland, E-mail: alain.borgeat{at}balgrist.ch
To the Editor:
Weber et al.1 sought to determine the optimal dose of ropivacaine 0.5% for analgesia injected through a femoral catheter, and as a secondary endpoint the success rate of obturator nerve block. The authors found a very high rate of effective block of the obturator nerve (up to 95%). This is in contrast with the results found by Parkinson et al.2 We have some concerns regarding the observations of Weber et al.1 due to the limitations of their study design. First, threading a femoral catheter up to 12 cm is hazardous. Capdevila et al.3 demonstrated that threading the catheter 16 to 20 cm results in a correct placement close to the lumbar plexus in only 23% of the patients, emphasiz-ing that the course of the catheter was unpredictable. Ritter4 was unable to demonstrate in cadavers, a femo-ral nerve sheath capable of conveying a solution – or a catheter – from the inguinal ligament to the lumbar plexus. Unfortunately, Weber et al.1 did not verify radiologically the position of the catheter tip, leaving some doubt regarding its position.
Bouaziz et al.5 demonstrated that sensory tests (cold and light touch perception) – as used in Weber’s study – are inadequate to assess obturator nerve block. After performing a selective obturator nerve block, supported by a marked decrease of adductor strength, the authors showed an absence of sensory cutaneous contribution in 57% of patients. Without electromyo-gram monitoring or adductor strength assessment, blockade of the obturator nerve is only speculative. In the model used by the authors, sensory assessment of the medial side of the knee is even more complex, since the sciatic nerve may also have sensory branches in this area. Weber et al.1 found that 20 mL ropivacaine 0.5% was the most appropriate dose to block the femoral nerve. On the other hand, evidence of obturator nerve block is speculative, and the design of their study does not fully support this conclusion. We view that there is sufficient evidence in the current literature to doubt the existence of the three-in-one block.
Footnotes
Accepted for publication August 29, 2005.
References
1 Weber A, Fournier R, Riand N, Gamulin Z. Duration of analgesia is similar when 15, 20, 25 and 30 mL of ropivacaine 0.5% are administered via a femoral cath-eter. Can J Anesth 2005; 52: 390–6.
2 Parkinson SK, Mueller JB, Little WL, Bailey SL. Extent of blockade with various approaches to the lumbar plexus. Anesth Analg 1989; 68: 243–8.
3 Capdevila X, Biboulet P, Morau D, et al. Continuous three-in-one block for postoperative pain after lower limb orthopedic surgery: where do the catheters go? Anesth Analg 2002; 94: 1001–6.
4 Ritter JW. Femoral nerve "sheath" for inguinal par-avascular lumbar plexus block is not found in human cadavers. J Clin Anesth 1995; 7: 470–3.[Medline]
5 Bouaziz H, Vial F, Jochum D, et al. An evaluation of the cutaneous distribution after obturator nerve block. Anesth Analg 2002; 94: 445–9.
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