Ultrasound predictors of peripheral nerve block failure after blast injury: a prospective cohort study

High-energy blast injuries produce severe anatomical distortion that may compromise ultrasound-guided peripheral nerve blocks (PNBs). However, large-scale data identifying predictors of block failure in this population remain limited.

To determine the incidence and independent predictors of PNB failure in patients with blast-related limb trauma.

Prospective observational cohort study conducted between March 2023 and February 2026 at a tertiary war trauma center. Adult patients undergoing ultrasound-guided PNB for blast-related limb injuries were included. Primary block failure was defined as failure to achieve ≥50% reduction in Numeric Rating Scale (NRS) pain score within 30 min together with incomplete sensory blockade in the expected dermatomal distribution. Rescue opioid requirement within 6 h was analyzed separately as a secondary indicator of analgesic burden. Anatomical distortion variables and injury severity were analyzed. Multivariable logistic regression identified independent predictors of failure.

A total of 774 patients were analyzed. Overall block failure rate was 27.8%. Anatomical distortion was present in 64% of cases. Independent predictors of failure included vascular reconstruction (aOR 2.43, 95% CI 1.65-3.58), large hematoma (aOR 1.91, 95% CI 1.43-2.55), scar tissue/adhesions (aOR 1.74, 95% CI 1.29-2.33), fracture displacement (aOR 1.68, 95% CI 1.25-2.24), and Injury Severity Score > 25 (aOR 1.56, 95% CI 1.14-2.13).

Anatomical distortion following blast injury significantly increases the risk of PNB failure. Recognition of trauma-specific anatomical predictors is essential for optimizing regional anesthesia strategies in high-energy injury populations.