Posttetanic count revisited: are measurements more reliable using the TOF-Watch accelerographic peripheral nerve stimulator?

OBJECTIVE

Measurement of profound neuromuscular block using posttetanic count is among the most subjective measurements made in clinical anesthesia. The TOF-Watch accelerographic peripheral nerve stimulator provides objective measurements of neuromuscular block that may improve our ability to quantitate intense blockade.

METHODS

The TOF-Watch and Digi Stim III peripheral nerve stimulators were used to monitor onset and early recovery of neuromuscular response induced by rocuronium 0.6 mg/kg i.v. in 30 patients anesthetized with general anesthesia. After induction, train-of-four count (when present) was measured at one-min intervals. Subsequently, posttetanic count was measured at three-min intervals until the first response to train-of-four stimulation reappeared.

RESULTS

Posttetanic count and train-of-four count measurements were determined to be consistently unreliable throughout the study in seven (23%) patients with the TOF-Watch stimulator and three (10%) patients with the Digi Stim III stimulator (p = NS). Among stimulators yielding reliable measurements, decreases in train-of-four count to 0/4 were noted earlier with the Digi Stim III monitor (median = 2 min) as compared with the TOF-Watch device (median = 4 min) (p < 0.05). Also, posttetanic count decreased to zero in only 35% of patients with the TOF-Watch stimulator versus 67% of patients with the Digi Stim III stimulator (p < 0.05).

CONCLUSIONS

Both monitors were similar in their ability to predict return to TOFC = 1 as a function of PTC measurements. The TOF-Watch monitor is easy to apply even in inexperienced hands. However, the device yielded erroneous data in 23% of patients.