Acceleromyography at the Flexor Hallucis Brevis Muscle Underestimates Residual Neuromuscular Blockade

Purpose: Recovery of the train-of-four ratio (TOFR) to > 0.9 in the upper limb is commonly used to determine that neuromuscular function has returned to the preoperative level. It is not known whether recovery of neuromuscular function can be determined in the same way using lower limb acceleromyography. We compared measurements of recov- ery from neuromuscular blockade using upper limb electromyography and lower limb acceleromyography. Methods: Twenty-nine patients who were scheduled for elective surgery were enrolled in this study. Patients were ex- cluded if they had neuromuscular disease or contraindications to neuromuscular blockade. General anesthesia was induced and maintained with propofol and fentanyl. Patients were monitored using electromyography at the first dorsal interosse- ous muscle of the upper limb and acceleromyography at the flexor hallucis brevis muscle of the lower limb. Vecuronium 0.1 mg/kg was administered for neuromuscular blockade, and the profile of the blockade was recorded, including onset time and recovery times to TOFR 0.7 and 0.9. Results were compared between the upper and lower limbs. Results: The first dorsal interosseous muscle of the upper limb was slower to recover to TOFR 0.7 and 0.9 than the flexor hallucis brevis muscle. When the TOFR at the flexor hallucis brevis muscle had recovered to 0.9, the TOFR at the first dorsal interosseous muscle was 0.44 ± 0.23. Conclusion: Monitoring the flexor hallucis brevis muscle using acceleromyography underestimates the residual neuro- muscular blockade.