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Reg Anesth Pain Med. 2012 Nov-Dec;37(6):627-32. doi: 10.1097/AAP.0b013e31826af511.

A 3-dimensional ultrasound study of local anesthetic spread during lateral popliteal nerve block: what is the ideal end point for needle tip position?

Author information

1
Department of Anesthesiology and Acute Pain, University Miami-Miller School of Medicine, Miami, FL 33141, USA. amissair@med.miami.edu

Abstract

BACKGROUND AND OBJECTIVES:

Recent clinical trials suggest that subfascial (sometimes termed subepineural) injections result in faster block onset and success compared with conventional techniques. This prospective, randomized, observer-blinded study measured and compared the 3-dimensional spread pattern and volume of perineural local anesthetic (LA) in contact with the sciatic nerve after subfascial versus extrafascial lateral popliteal injections.

METHODS:

Sixty patients were randomly assigned to either the subfascial or the extrafascial injection group. All patients received a single-injection, US-guided lateral popliteal sciatic nerve block for postoperative pain. Depending on group assignment, the needle tip was placed outside or beneath the sciatic fascial sheath for a single injection of 30 mL of ropivacaine 0.5%. Using 3-dimensional ultrasound imaging, postblock scans were acquired to quantify the volume and spread pattern of perineural LA around the sciatic nerve in each group.

RESULTS:

The mean LA perineural volume for the extrafascial group was 1.48 (SD, 0.50) mL versus a mean of 5.57 (SD, 1.68) mL for the subfascial group, P < 0.05. The mean distance of longitudinal perineural LA spread (along the length of the nerve) for the subfascial group was 66% greater than that observed using the conventional technique (9.3 vs 5.6 cm, P < 0.01). Complete sensory block to pinprick for the extrafascial group was 63% versus 90% (P < 0.05) for the subfascial group.

CONCLUSIONS:

Placement of the needle tip beneath the complex fascial sheath of the sciatic nerve resulted in significantly greater perineural local anesthetic volume following a single-injection lateral popliteal approach at the nerve bifurcation and was associated with greater sensory blockade and a characteristic laminar LA spread pattern.

PMID:
23080350
DOI:
10.1097/AAP.0b013e31826af511
[Indexed for MEDLINE]

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