Effect of tetanic stimulation on subsequent train-of-four responses at various levels of vecuronium-induced neuromuscular block.

Tetanic stimulation influences subsequent neuromuscular responses. In addition, the tetanus-induced changes in neuromuscular responses differ according to the level of neuromuscular block at which tetanic stimulation is delivered. We studied the tetanus-induced effect on subsequent train-of-four (TOF) responses at various levels of vecuronium-induced neuromuscular block in 45 anaesthetized patients. Tetanic stimulation was applied when a twitch height of T1 returned to 25%, 50% and 75% of its control twitch height (T0) (groups 1, 2 and 3, respectively) after administration of vecuronium 0.1 mg kg-1. Maximum post-tetanic percentage increases in TOF responses in groups 1, 2 and 3 were 257 (SD 119)%, 107 (75)% and 68 (54)% for T1/T0 (P < 0.001 for group 1 vs 2; P < 0.001 for group 1 vs 3) and 535 (259)%, 421 (213)% and 292 (171)% for T4/T1 (P < 0.01 for group 1 vs 3), respectively. Durations of post-tetanic increases in TOF responses in groups 1, 2, and 3 were 52 (19) s, 37 (14) s and 32 (13) s for T1/T0 (P < 0.05 for group 1 vs 2; P < 0.01 for group 1 vs 3) and 53 (17) s, 46 (15) s and 35 (12) s for T4/T1 (P < 0.05 for group 1 vs 3), respectively. These data suggest that the tetanus-induced effect on subsequent TOF is more apparent and lasts longer at greater degrees than at lesser degrees of neuromuscular block.