Effects of atracurium and vecuronium on the latency and the duration of the negative deflection of the evoked compound action potential of the adductor pollicis.

The effect of atracurium or vecuronium on the depolarization phase of the evoked compound action potential of the adductor pollicis has been investigated in 30 adult patients. Patients were studied using single supramaximal stimulation of the ulnar nerve at the wrist. The evoked compound action potential was measured over the adductor pollicis muscle. When blockade by atracurium exceeded 80%, a significant decrease in latency was recorded (P less than 0.05). There was no significant change in latency after vecuronium. During the onset of blockade, depression of the amplitude of the evoked compound action potential was associated with a prolongation of its duration (P less than 0.05). The mean maximum increase in the negative deflection time was found to be similar after atracurium and after vecuronium. However, this phase was prolonged to a greater extent for a given degree of amplitude depression during the onset of blockade by atracurium (P less than 0.05).