Train of Four Responses as Indicies of Onset and Recovery during Pancuronium Induced Neuromuscular Blockade

Shin, Mi Young; Suh, Jae Hyun

Abstract

The train of four (TOF) stimulation is commonly used in animal research and clinical practice to determine the degree of neuromuscular blockade. It has been suggested that relationship existed between the degree of single, or initial twitch depression and the amount of TOF fade responses within train. Although block produced by all non-depolarising muscle relaxants is associated with fade in response to tetanic or TOF stimulation, recent studies have shown quantitative difference in degree of these fade between various agent. However, more recently, the variability of this relationship with the same neuromuscular blocker during onset and spontaneous recovery of neuromuscular blockade has been demonstrated. And so, the degree of fade may be affect the reliability in assessment of degree of block and recovery of block in comparison to single twitch stimulation. In present study, we has assessed the effect of pancuronium 0.04 mg/kg on the pattern of TOF (T(4) ratio) and first twitch response in the train compared with control twitch (T(1) ratio) and, thereafter, the twitch responses of vecuronium 0.02 mg/kg on recovery period from pancuronium induced neuromuscular blockade in 14 rabbits. The changes in neuromuscular transmission were measured by recording the isometric contraction of the left gastrocnemius muscle evoked by supramaximal stimulation of the tibial nerve. The results were as follows: 1) The effect of pancuronium 0.04 mg/kg was variable, ranging from incomplete (64.3%) to complete (35.7%) neuromuscular block. 2) During the onset of action, there was greater reduction associated with T(1) than T(4), ratio in all cases. The changes of T(1) ratio decreased steadily in all cases, but the changes of T(4) ratio in cases of incomplete neuromuscular blockade was biphasic, showing initial decrease to 77.2+/-8.1% followed by increase to 100% of T(4) rato when T(1) ratio was 4.6+/-3.2%. 3) During the recovery period, T(4) ratio was increased linearly with T(1) ratio which reached 25% when T(4) ratio was approximately 22.5+/-18.8% in cases of complete neuromuscular blockade. In cases of incomplete neuromuscular blockade, T(1) ratio was increased linearly depending on time course, but the change of T(4) ratio was biphasic, showing initial decrease to 28.2+/-16.6% when T(1) ratio was 25%, followed by increased linearly with T(1) ratio. 4) The twitch response during the onset of the action and recovery after vecuronium 0.02 mg/kg on 75% recovery period of pancuronium induced neuromscular blokade was similar to that of pancuronium. The results of this study suggest that the TOF ratio and the depression of the single twitch bear no fixed relationship. The clinical use of TOF using the T(4) ratio only, as a monitor of the degree of block and recovery from non-depolarising block has been useful, but we would recommended that T, ratio of TOF should be considered to evaluated the incomplete neuromuscular block of pancuronium and vecuronium in rabbit.