THE INFLUENCE OF THE DURATION OF CONTROL STIMULATION ON THE ONSET ANDRECOVERY OF NEUROMUSCULAR BLOCK

The onset of action of atracurium 450 mu g/kg, mivacurium 160 mu g/kg, and vecuronium 80 mu g/kg was measured after train-of-four (TOF) stim ulation had been applied for 1, 5, 10, 15, or 20 min in groups of 10 p atients each during anesthesia with thiopental, nitrous oxide-oxygen, and fentanyl. TOF stimulation was applied to the ulnar nerve at 2 Hz e very 12 s and the force of contraction of the adductor pollicis muscle recorded. There was a progressive and significant reduction in the ti me to onset of maximum block with increasing times of control stimulat ion with all three relaxants (P < 0.0001). The mean +/- SD times to on set of maximum block decreased from 224 +/- 103 to 73 +/- 28 s with at racurium, 239 +/- 81 to 101 +/- 33 s with vecuronium, and 198 +/- 72 t o 106 +/- 23 s with mivacurium as the period of control stimulation in creased from 1 to 20 min. The time to recovery of T1 (first response i n the TOF stimulation) to 25% of control (duration of clinical relaxat ion) increased from 33 +/- 5.7 to 52 +/- 13.4 min with atracurium, 25 +/- 7.6 to 38 +/- 9.4 min with vecuronium, and 13 +/- 2.5 to 18 +/- 3. 5 min with mivacurium with the period of control stimulation increasin g from 1 to 20 min. The differences were significant for atracurium an d vecuronium (P < 0.05-0.0001). We conclude that increasing periods of control stimulation are associated with decreasing time to onset of n euromuscular block with atracurium, vecuronium, and mivacurium at the adductor pollicis muscle. The duration of clinical relaxation of atrac urium and vecuronium, but not mivacurium, are also prolonged with incr easing periods of stimulation.