Ultrasound-guided popliteal block demonstrates an atypical motor response to nerve stimulation in 2 patients with diabetes mellitus.

Abstract

Nerve stimulation is a useful technique to identify peripheral nerves before blockade. We report 2 cases of the failure of nerve stimulation to accurately localize the sciatic nerve in patients with diabetes mellitus undergoing outpatient foot procedures. We also introduce a novel approach to performing a popliteal fossa block using ultrasound guidance. Ultrasound-guided popliteal fossa blocks were performed in 2 patients with diabetes mellitus. Both patients failed to develop an appropriate motor response or paresthesia to nerve stimulation. The needle positions were confirmed by ultrasound guidance and injections of local anesthesia were made uneventfully. Appropriate surgical anesthesia was established and the procedures were performed uneventfully. Ultrasound facilitated the accurate localization of the sciatic nerve in 2 patients with diabetes mellitus. Neither patient had a paresthesia or muscle twitch below 2.4 mA. There is theoretical concern that patients with underlying neuropathy, such as patients with diabetes mellitus, may have an altered response to either motor or sensory stimulation.