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.
Vincent
Robert D
RD
Department of Anesthesiology, University of Alabama School of Medicine, Birmingham, AL 35233, USA. rdv@uab.edu
Brockwell
Russell C
RC
Moreno
Michael C
MC
Adkins
Shannon L
SL
D000328:Adult; D000368:Aged; D000732:Androstanols / Q000008:administration & dosage; D004566:Electrodes; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D018482:Muscle, Skeletal / Q000502:physiology; D009213:Myography / Q000295:instrumentation / Q000379:methods; D019148:Neuromuscular Blockade; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage; D015203:Reproducibility of Results; D000077123:Rocuronium; D012680:Sensitivity and Specificity; D013746:Tetany; D004561:Transcutaneous Electric Nerve Stimulation
D000732:Androstanols; D003473:Neuromuscular Nondepolarizing Agents; D000077123:Rocuronium