Effect of tetanus on subsequent neuromuscular monitoring in patients receiving vecuronium.

The current study evaluated the effects of tetanic stimulation on neuromuscular responses to serial train-of-four (TOF) and double-burst stimulation (DBS). For TOF monitoring (n = 13), a degree of neuromuscular blockade was achieved with an intravenous vecuronium infusion such that the ratio of fourth twitch (T4) to first twitch (T1), T4/T1, was stable at a value between 0.1 and 0.7. Four seconds after a 5-s, 50-Hz tetanic stimulus was delivered, TOF monitoring was resumed at 10-s intervals. Significant changes were noted for T1, T4, and T4/T1, with median increases of 38, 250, and 93%, respectively. The median times for T1, T4, and T4/T1 to return to within 10% of their pretetanic (baseline) values were 34, 43, and 34 s, respectively (P = nonsignificant [NS] among times to recovery). A 100-Hz tetanic stimulus induced 50, 300, and 178% median increases of T1, T4, and T4/T1, while corresponding values for recovery times were 53, 73, and 54 s. For DBS monitoring (n = 14), tetanic stimulation (50-Hz, 5-s) induced 38, 300, and 153% median increases of the DBS3,3 parameters (first response [D1], second response [D2], and their ratio [D2 not equal to D1], respectively). The posttetanic effects on D1, D2, and D2/D1 persisted for 43, 66, and 46 s, respectively. For DBS3,2, median posttetanic (50-Hz, 5-s) increases were 41, 275, and 176%, while corresponding times to recovery were 43, 43, and 43 s. Although the data indicate that the posttetanic percent increase was at least 10 times larger at greater degrees of blockade (T4/T1 = 0.1) than at lesser degrees (T4/T1 = 0.7), all T4/T1 and D2/D1 ratios returned to within 10% of baseline in 125 s or less after 5-s tetanic stimulation.