Bilateral loss of neural function after interscalene plexus blockade may be caused by epidural spread of local anesthetics: a cadaveric study

Interscalene brachial plexus blockade is widely used in surgical procedures of the upper limb. Recently, we experienced the complication of a contralateral blockade after ultrasound-guided interscalene block. The clinical appearance was a blockade of both the ipsilateral and the contralateral cervical segments 6 to 8. We hypothesized that epidural spread of local anesthetics could be cause for this phenomenon. We conducted a cadaveric study using ultrasound for needle guidance of interscalene blocks in 5 cadavers by a single investigator using contrast agent. Injections were made either ventral (extrafascial) or dorsal (subfascial) to the prevertebral lamina of the deep cervical fascia. Computed tomography was obtained following each injection with contrast agent immediately after incremental injections of progressively higher volumes. Subsequently, contrast spread to anatomic landmarks was investigated by a radiologist. After ultrasound-controlled injection of contrast agent beneath the prevertebral layer of the deep cervical fascia, 4 of the 5 investigated specimens showed contrast enhancement in the epidural space in the consecutive computed tomography scans. After extrafascial injection, none of the investigated specimens showed contrast enhancement in the epidural space. Contralateral blockade after ultrasound-guided interscalene injection of local anesthetics is very likely to be the effect of epidural spread. Future in vivo studies are needed to understand the implications of needle location and volume on epidural spread in interscalene blockade.