The post-tetanic count during vecuronium-induced neuromuscular blockade in halothane-anaesthetized dogs.
OBJECTIVE
To evaluate the post-tetanic count (PTC) for predicting the return of reversible neuromuscular blockade at the n. facialis-m. nasolabialis (nF-mNL) and n. ulnaris-mm. carpi flexorii (nU-mCF) nerve-muscle units (NMUs) during profound vecuronium neuromuscular blockade in halothane-anaesthetized dogs.


METHODS
Randomized, prospective, experimental study.


METHODS
Twenty-five dogs (seven male 18 female) undergoing surgery; mean age: 4.8 years; mean body weight 22 kg.


METHODS
Thirty minutes after acepromazine (0.05 mg kg(-1)) and morphine (0.5 mg kg(-1)) pre-medication, anaesthesia was induced with intravenous (IV) thiopental and maintained with halothane, N(2)O and O(2). The lungs were mechanically ventilated and end-tidal halothane concentration (Fe'(HAL)) maintained at 1.04%. Neuromuscular transmission was monitored using the train-of-four count (TOFC) at one nF-mNL and both nU-mCF units. Vecuronium (50 microg kg(-1) IV) was injected after 15 minutes constant Fe'(HAL). When the first twitch (T1) at both nU-mCF units had disappeared (t = 0) one (randomly allocated) ulnar nerve was stimulated every 5 minutes using PTC; TOF stimulation continued at the other sites. The PTC was plotted against the interval between recording time and T1's reappearance at the other NMUs.


RESULTS
At t = 0, the mean PTC in the contralateral nU-mCF unit was 18 (range 0-20). Mean PTC was a minimum at t = 5, rising to the maximum (20) at 25 minutes. Six dogs were vecuronium-resistant as monitored by PTC. Excluding data from these revealed a strong negative relationship between ulnar PTC and the time taken for T1's return at the facial (r = -0.7018; p < 0.00001) and contralateral ulnar (r = -0.8409; p < 0.00001) NMUs.


CONCLUSIONS
Post-tetanic count monitoring beginning >5 minutes after the TOFC at nU-mCF = 0 provided a reliable estimate of T1's return at ulnar and facial NMUs.
Sarrafzadeh-Rezaei
Farshid
F
Department of Clinical Sciences, University of Urmia, Western Azerbaijan, Iran.
Eddie Clutton
R
R
D000769:Anesthesia, Inhalation / Q000662:veterinary; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D004285:Dogs; D005260:Female; D006221:Halothane / Q000494:pharmacology*; D008297:Male; D019148:Neuromuscular Blockade / Q000662:veterinary*; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D014673:Vecuronium Bromide / Q000494:pharmacology*
D018685:Anesthetics, Inhalation; D003473:Neuromuscular Nondepolarizing Agents; D014673:Vecuronium Bromide; D006221:Halothane