[Influence of neuromuscular blockade on motor evoked potential of forearm muscles]

To investigate the influence of different degrees of neuromuscular blockade on motor evoked potential (MEP) of forearm muscles under the same condition of anesthesia depth and analgesia.

Forty ASA I - II patients aged 20 - 60 underwent general anesthesia via intravenous injection of propofol, fentanyl, and vecuronium to achieve the bispectral index (BIS) at the level of (50 + 10) during neurosurgical operation. The patients were all given fentanyl infusion at a rate of 2 microg/kg/h during the operation and continuous vecuronium injection while the value of train of four stimulations (TOF) was monitored under 3 different levels: TOF = 4 (TOF(4)), TOF = 2 (TOF(2)), and TOF = 0 (TOF(0)). The values of amplitude and latency at the 3 forearm muscles, forearm flexors (FF), abductor pollicis brevis (APB), and abductor digiti minimi (ADM) were monitored and compared under stable hemodynamic status.

There was no significant differences in the latency of compound muscle action potential (CMAP) between the anesthesia status TOF(4) and anesthesia status TOF(2) in FF, APB, and ADM (all P > 0.05). The amplitude of CMAP deceased gradually as the degree of neuromuscular blockade increased in FF, APB, and ADM (all P < 0.05). CMAP could not be recorded when the value of TOF was 0 (P < 0.01).

Neuromuscular blocking drugs significantly depress the MEP in a dose-dependent manner. Intra-operatively it may be preferable to maintain the value of TOF not less than 2 during the critical periods of MEP monitoring.