A 3-dimensional ultrasound study of local anesthetic spread during lateral popliteal nerve block: what is the ideal end point for needle tip position?
OBJECTIVE
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.
Department of Anesthesiology and Acute Pain, University Miami-Miller School of Medicine, Miami, FL 33141, USA. amissair@med.miami.edu
Andres
A
Missair
Robyn S
RS
Weisman
Maria Rene
MR
Suarez
Relin
R
Yang
Ralf E
RE
Gebhard
D000577:Amides / Q000008:administration & dosage; D000779:Anesthetics, Local / Q000008:administration & dosage*; D005205:Fascia / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007267:Injections / Q000379:methods; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D010147:Pain Measurement; D010149:Postoperative Pain / Q000517:prevention & control; D011446:Prospective Studies; D000077212:Ropivacaine; D012584:Sciatic Nerve / Q000000981:diagnostic imaging*; D016037:Single-Blind Method; D018084:Ultrasonography, Interventional
D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine