Fascial layers influence the spread of injectate during ultrasound-guided infraclavicular brachial plexus block: a cadaver study

Background: Fascial layers of the neurovascular sheath containing the brachial plexus influence distribution of local anaesthetic, hence increasing the risk of block failure when performing infraclavicular brachial plexus block (ICB). Methods: Ultrasound-guided infraclavicular brachial plexus block was performed on cadavers using a single injection technique with dye (20–30 ml). After injection, we carried out consecutive dissection of the neurovascular bundle to study dye injectate spread and identify the presence of fascial layers. Ultrasound video images (scout scan and injection) and recordings of dissections were evaluated by independent experts (regional anaesthetists and anatomists). Results: Well defined fascial layers were identified at dissection in seven out of 12 infraclavicular spaces studied. These fascial layers impeded the spread of dye injectate substantially in six cases and partially in one case. No fascial layers were identified at dissection in five cases, in each of which the spread of injectate was complete throughout the neurovascular bundle. The sensitivity and specificity of ultrasonography and haptic sensation for detection of fascial layers were poor. Conclusions: When fascial layers are present in the neurovascular sheath, they impede the spread of injectate during infraclavicular brachial plexus block. Ultrasound detection of these fascial layers is unreliable in cadavers. These findings support the use of greater volumes of injectate or a multiple injection technique when performing this block.