Factors affecting train-of-four fade.

The characteristics of the train-of-four response during neuromuscular blockade with two agents, atracurium and vecuronium, have been compared. During onset of blockade, at 75% depression of the initial twitch, atracurium was associated with significantly more fade than was vecuronium, and larger doses of atracurium were associated with less fade than smaller doses of the same agent. In addition, with both agents, the degree of fade at a given amount of initial twitch depression was significantly less during onset than during spontaneous offset of action. The degree of train-of-four fade bears no fixed relationship to depression of the initial twitch.