Twitch, Tetanus and Posttetanic Potentiation as Indices of Nerve—Muscle Block in Man

Twitch, tetanus and posttetanic potentiation are muscle responses to varying frequencies of indirect stimulation. Responses to tetanic stimulation at various frequencies are a more sensitive index of neuromuscular transmission than twitch or posttetanic potentiation. In lightly anesthetized man, tetanus is maintained at stimulus frequencies from 50 to 200 Hz, and higher. During partial neuromuscular block tetanus is not maintained at the higher frequencies of stimulation even though the magnitude of twitch may have returned to control levels. If neuromuscular transmission is marginally adequate, the tetanic response fails at higher stimulus frequencies. This study demonstrates the use of tetanus at various frequencies to diagnose neuromuscular block not apparent by twitch studies alone. It is suggested that clinical nerve stimulators be modified to provide tetanic stimulation at several fixed frequencies.