Ultrasound guidance showing real-time local anesthetic extravasation during injection of two lateral popliteal sciatic nerve blocks

Objective: The purpose of this case report is to describe an observation of local anesthetic extravasation while performing single-shot lateral sciatic popliteal blocks on two patients using ultrasound guided imaging. This under-reported phenom- enon may have clinical implications and warrants further examination of conventional practice techniques. Case report: We performed lateral sciatic popliteal blocks under ultrasound guidance for post-operative pain in two patients having surgery in the left lower extremity. Both blocks involved sequential, real-time scans during the injection beneath the complex fascial sheath of the sciatic nerve. Observations included extrafascial extravasation of local anesthetic away from the nerve, up the needle path, and also concentrically outside the nerve sheath. Both blocks had 100% sensory block but slower clinical onset than expected. Conclusions: Ultrasound imaging is an evolving technology gaining popularity for performing peripheral nerve blocks. The incidence and volume of local anesthetic extravasation with single shot nerve blocks are unknown. This phenomenon may be common but frequently undetected given the limited resolution and the two-dimensional nature of current ultrasound imaging technology. The clinical consequences of local anesthetic injection into tissues outside of the nerve sheath are unknown, however our observations suggest speed of onset and quality of blocks may be affected. Further investigation evaluating the extravasation of local anesthetics during ultrasound blockade is needed to re-evaluate injection speeds and the use of conventional volumes for injection.