An ultrasonographic assessment of nerve stimulation-guided median nerve block at the elbow: a local anesthetic spread, nerve size, and clinical efficacy study.
BACKGROUND
Nerve stimulation is an effective technique for peripheral nerve blockade. However, the local anesthetic (LA) distribution pattern obtained with this blind approach is unknown and may explain its clinical effects.


METHODS
One hundred patients received a median nerve block at the elbow using a nerve stimulator approach. After correct needle placement defined by a minimal stimulating current < or = 0.5 mA (2 Hz, 0.1 millisecond), 6 mL lidocaine 1.5%with epinephrine 1:200,000 was injected. A linear 5- to 13-MHz probe (12L-RS) was used to assess a cross-section area of median nerve, which was calculated by 3 consecutive measurements before and after injection, and LA circumferential spread around the nerve during static and longitudinal examination. Intraneural injection defined as an increase in nerve area was detected using an iterative method for outlier detection. Results of sensory tests (cold and light touch) on 3 nerve territories and of motor blockade were compared with the imaging aspects. We performed clinical neurological examination at 3 days and 1 month after block.


RESULTS
Nerve swelling, considered significant when an increase in cross-sectional area was > or = 75%, was observed in 43 patients. Nerve swelling associated with a circumferential LA spread image, present in 37 patients, was associated with a sensory success rate of 86%. The success rate was 34% for 32 patients in whom none of these signs was visualized. A circumferential spread around a nonswollen nerve, present in 25 patients, was followed by a sensory success rate of 76% within the 30-minute evaluation period. No major early neurological complications were observed.


CONCLUSIONS
Nerve stimulation does not prevent intraneural injection. In the absence of intraneural injection, the presence of circumferential LA spread image seemed predictive of successful sensory block in almost 75% of the cases within the 30-minute evaluation period.
Dufour
Eric
E
Department of Anesthesiology, Hôpital Privé de l'Ouest Parisien, Trappes, France.
Cymerman
Alexandre
A
Nourry
Gérard
G
Balland
Nicolas
N
Couturier
Christian
C
Liu
Ngai
N
Dreyfus
Jean-François
JF
Fischler
Marc
M
D000328:Adult; D000556:Ambulatory Surgical Procedures; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000009:adverse effects; D004550:Elbow / Q000294:innervation*; D017558:Elective Surgical Procedures; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007267:Injections; D008012:Lidocaine / Q000008:administration & dosage* / Q000009:adverse effects; D008297:Male; D008475:Median Nerve / Q000000981:diagnostic imaging* / Q000187:drug effects*; D008875:Middle Aged; D009043:Motor Activity / Q000187:drug effects; D009407:Nerve Block / Q000009:adverse effects / Q000379:methods*; D011446:Prospective Studies; D012677:Sensation / Q000187:drug effects; D013997:Time Factors; D014463:Ultrasonography
D000779:Anesthetics, Local; D008012:Lidocaine