There have been reports of monitoring LSR during MVD surgery helps predicting the clinical outcome of MVD. However, there have been no evidence of which degree of partial neuromuscular blockade should be performed during LSR monitoring under sevoflurane anesthesia. Therefore, the investigators performed a randomized controlled trial to evaluate the effect of different degree of partial neuromuscular blockade on the LSR monitoring for MVD surgery.

Hemifacial spasm develops by vascular compression of facial nerve at the root exit zone from brain stem. Microvascular decompression (MVD) is known for its curative treatment. Lateral spread response (LSR) is a kind of pathologic electromyographic (EMG) wave form which develops when facial nerve is compressed by vessel. There have been reports of monitoring LSR during MVD surgery helps predicting the clinical outcome of MVD.

As neuromuscular blockade during LSR monitoring decreases the amplitude of EMG, partial neuromuscular blockade is usually maintained during general anesthesia for MVD. However, there have been no evidence of which degree of partial neuromuscular blockade should be performed during LSR monitoring under sevoflurane anesthesia. Therefore, the investigators performed a randomized controlled trial to evaluate the effect of different degree of partial neuromuscular blockade on the LSR monitoring for MVD surgery.

Inclusion Criteria:

• Those who undergo microvascular decompression with sevoflurane anesthesia by diagnosis of hemifacial spasm in our institution

Exclusion Criteria:

• Patients were excluded from the study if they had any of following: severe cardiopulmonary disorder with hemodynamic unstability (pulmonary hypertension, cardiomyopathy, mechanical ventilation, American Society of Anesthesiologists physical status III or more), severe hepatic or renal disease.
• Those who can not undergo MEP monitoring due to central or peripheral neuromuscular disease, e.g. cerebral palsy, myasthenia gravis, acute spinal injury, neurologic shock