[Accuracy and dose dependency of the train-of-four count].
The estimation of a nondepolarizing neuromuscular block using the train-of-four (TOF) count shows wide differences compared to the mechanomyographic measurement. The purpose of this study was to evaluate the clinical significance of these differences.


METHODS
89 patients (ASA I-II) in 6 groups received general anesthesia with fentanyl, propofol and a single dose atracurium (150, 200, 250, 300, 450 and 600 microg/kg). Neuromuscular transmission was monitored by stimulation of the ulnar nerve at the wrist with supramaximal TOF stimuli repeated every 15 s using a peripheral nerve stimulator. The isometric force contraction of the m. adductor pollicis was recorded. The height of T1 at reappearance of the second (T2) and fourth (T4) twitch was noted. Also noted was the time difference between the first reappearance of T4 and the 25% recovery of T1. Statistical significance of the results was calculated by the h-test of Kruskal and Wallis. Testing the reliability of the TOF count, a 95% interval of confidence was calculated


RESULTS
There were no significant differences between the mean ages, heights and weights of the six groups. T2 and T4 re-appeared at 11+/-2% and 24+/-6% recovery of T1, respectively. Again, there were no significant differences between the six dose groups (Fig. 1). The time difference between the re-appearance of T4 and the 25% recovery was -1.0+/-2 (range: -5-3) minutes. The calculation of a 95% interval of confidence indicated a recovery between 14% and 33% at reappearance of T4, 25% recovery can be expected 5 min before to 3 min after reappearance of T4, respectively.


CONCLUSIONS
At reappearance of T4, a recovery of neuromuscular block of 25% is missed only by 3 to 5 min during relaxation with atracurium. We consider this margin of error as unimportant for clinical use. More-over we were able to show that the TOF-count is not dose dependent.
Krombach
J
J
Klinik für Anästhesiologie und operativem Intensivmedizin der Universität zu Köln.
Krieg
N
N
Diefenbach
C
C
D000328:Adult; D000758:Anesthesia; D000768:Anesthesia, General; D018686:Anesthetics, Intravenous; D001279:Atracurium; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D005283:Fentanyl; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation; D009213:Myography; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage; D009435:Synaptic Transmission / Q000187:drug effects*; D014459:Ulnar Nerve
D018686:Anesthetics, Intravenous; D003473:Neuromuscular Nondepolarizing Agents; D001279:Atracurium; D005283:Fentanyl