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Ankle block success rate: a prospective analysis of 1,000 patients

Adelaide, Australia

To the Editor:

There have been few published studies investigating ankle block success.¹ We therefore conducted a prospective audit of 1,000 ankle blocks for mid or forefoot surgery. Aims were to determine block success rate, risk factors for block failure and length of action of differing combinations of local anesthetic (LA). The choice of LA was either a 50/50 mixture of lidocaine 1.5% plain and ropivacaine 7.5 mg•mL^–1, ropivacaine 7.5 mg•mL^–1 alone, or ropivacaine 7.5 mg•mL^–1 and clonidine 1 µg•kg^–1. A standardized ankle block technique was used using a 40 mL total maximum volume with optional sedation for block and surgery. Using a 25 gauge 35-mm needle, the tibial nerve was blocked with up to 10 mL LA at the medial malleolar level, posterior to the posterior tibial artery pulsation. The saphenous and superficial peroneal nerves were blocked by infiltration of 10 to 15 mL LA along a line joining both malleoli and the sural nerve with up to 10 mL LA infiltrated 1.5 cm distal to the tip of the fibula. The deep peroneal nerve were blocked at the malleolar level, with up to 5 mL LA between bone and skin (both sides of the dorsalis pedis pulsation). A 15-cm wide low-pressure ankle tourniquet (Zimmer, Warsaw, Indiana) was applied at the supramalleolar level and inflated to a pressure of 250 mmHg for surgery. A successful block was defined as one that did not require surgical supplementation, iv sedation or general anesthesia (GA) for surgery.

Overall block success rate was 94.7%, with a 4.4% improvement over the last 700 cases. The failure rate when surgery commenced before 20 min from block insertion was significantly (P < 0.001) greater than for longer waiting periods; there was a sharp drop in failure as waiting periods increased (Figure). Nine patients required GA (3 tourniquet pain, 2 block failures, 3 anxiety, 1 confused). Ropivacaine with clonidine had a significantly longer mean duration of action at 15.9 hr compared to other LA agents (P < 0.001).

View larger version (22K): [in this window] [in a new window]   FIGURE Relationship between waiting time and block failure.

References

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2 Provenzano DA, Viscusi ER, Adams SB Jr, Kerner MB, Torjman MC, Abidi NA. Safety and efficacy of the popliteal fossa nerve block when utilized for foot and ankle surgery. Foot Ankle Int 2002; 23: 394–9.[Medline]

3 Singelyn FJ, Gouverneur JM, Gribomont BF. Popliteal sciatic nerve block aided by a nerve stimulator: a reliable technique for foot and ankle surgery. Reg Anesth 1991; 16: 278–81.[Medline]

4 McLeod DH, Wong DH, Vaghadia H, Claridge RJ, Merrick PM. Lateral popliteal sciatic nerve block compared with ankle block for analgesia following foot surgery. Can J Anaesth 1995; 42: 765–9.[Abstract/Free Full Text]

5 Rudkin GE, Micallef TA. Impediments to the use of ankle block in Australia. Anaesth Intensive Care 2004; 32: 368–71.[Medline]

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