Evaluation of needle to nerve interaction for neurological complications in ultrasound-guided interscalene brachial plexus blocks

Background: The use of regional anesthesia techniques carries a well-known risk of perioperative neurological complications. The interscalene approach to brachial plexus block (ISB) is associated with the largest risk of neurological complications of any peripheral nerve block. The reported incidence of nerve injury after ISB varies, with estimates ranging from 0.5 % to 3 % of cases. In this prospective study, we sought to correlate the needle-to-nerve interaction during ISB procedures with the development of post-operative neurological outcomes. Methods: A novel grading system was developed to categorize various needle tip positions during ISB procedures. De-identified ultrasound recordings were graded post-procedure by two independent radiologists. These video grades were correlated with the incidence of post-procedural numbness or paresthesia and post-operative pain scores in the PACU and 24 hours postoperatively. Results: 108 patient videos were included for analysis. Zero videos received grade 1 (intraneural injection), 20 % received grade 2 (injection with needle against nerve root), 68 % received grade 3 (injection inside brachial plexus sheath), and 12 % received grade 4 (injection external to sheath). There was no statistical difference in terms of post-operative neurological complications or pain scores across the grades. Only four patients experienced post-operative neurologic complications on day one, and seven patients had neurological symptoms on day two. All symptoms resolved by post-operative day five. Conclusions: Our scoring system did not reveal relationship between more aggressive needling techniques and adverse post-procedural neurological symptoms. There was also no difference in pain scores across video grades, indicating that injection within the nerve sheath did not lead to better postoperative pain scores compared to injection outside the sheath. Since no procedures were found to be intraneural by the reviewing radiologists, no relationship between intraneural needling and adverse neurological outcomes could be elucidated. Larger studies in diverse settings may be required to capture greater variation in the block grades for more statistical power.