Train-of-four fade and edrophonium antagonism of neuromuscular block by succinylcholine in man.

Thumb twitch in response to train-of-four stimulation (2 Hz for 2 sec) of the ulnar nerve was measured in 36 patients anesthetized with halothane and N2O and paralyzed with succinylcholine chloride (SCC). Train-of-four fade was detected whenever a block was produced. The train-of-four ratio decreased with continued exposure to SCC. Edrophonium effect was predictable by the train-of-four ratio in a semiquantitative manner, a high ratio predicting block enhancement and a low ratio, antagonism. When calculated at 30 to 50 percent recovery (from complete block), a train-of-four ratio of 0.4 or less reliably predicts antagonism. The magnitude of antagonism is also predictable in a semiquantitative manner, although complete antagonism cannot be ascertained. The lower the ratio, the more effective the antagonism becomes. Train-of-four fade, therefore, appears to be a consistent and sensitive quantitative sign of phase II neuromuscular block by SCC in man.