Clinical evaluation of the Datex 221 neuromuscular transmission monitor for recording posttetanic electromyographic responses.

The assessment of deep neuromuscular blockade produced by nondepolarizing neuromuscular blocking agents is not possible with the conventional use of the Datex NMT-221 "relaxograph" (Datex NMT-221 monitor, Datex Instrumentarium, Helsinki, Finland), an otherwise useful electromyographic (EMG) monitoring device. A method whereby the relaxograph can be adapted to quantitatively measure posttetanic responses is described here. In anesthetized adult patients, neuromuscular blockade was monitored simultaneously on both hands with two relaxographs. On one hand, EMG responses of hypothenar muscles to the built-in 1/20-second sequence of train-of-four stimuli of the monitor were used. On the other hand, similar recordings were made with the addition of periodically superimposed supramaximal tetanic stimuli of 100 Hz to the ulnar nerve. Neuromuscular block was provided with pancuronium. The time courses of the spontaneous recovery of the first of the train-of-four EMG responses were compared in the stimulated and control arms. At the end of the surgery, the neuromuscular block was pharmacologically reversed with atropine and neostigmine. If no tetanic stimuli were applied, the EMG responses were identical in both arms during the spontaneous recovery from the neuromuscular blockade. If tetanic stimuli were applied every 4 or 7 minutes, the rate of recovery in the stimulated hand usually exceeded that of the control hand. However, no significant difference was observed in the recovery rate when the tetanic stimuli were spaced at 15-minute intervals. Pharmacologic reversal by atropine and neostigmine was found to be identical in all patient groups. The author concludes that the Datex relaxograph is suitable for the quantitative assessment of profound surgical neuromuscular blockade with the described modification.