title: Twitch potentiation: a potential source of error during neuromuscular monitoring with acceleromyography in anesthetized dogs.
abstract: OBJECTIVE
  To measure twitch potentiation (the staircase phenomenon) in anesthetized dogs, and assess its relevance during neuromuscular monitoring with acceleromyography (AMG).
  
  
  METHODS
  Randomized, prospective clinical trial.
  
  
  METHODS
  Sixteen dogs undergoing ovariohysterectomy.
  
  
  METHODS
  Under isoflurane anesthesia, neuromuscular function was monitored with train-of-four (TOF) stimuli every 15 seconds and quantified by AMG. Neuromuscular blockade (NMB) was produced with 0.15 mg kg(-1) atracurium IV. Dogs were randomly divided into two groups; a potentiation group (PG) in which TOF stimulation was applied for 20 minutes before atracurium was administered; and a control group (CG) where no such time was allowed. In both groups, the AMG was calibrated (at tCAL) just before atracurium was administered. TOF stimulation continued throughout the experiment in all dogs. The height of the first twitch (T(1)) (expressed as a fraction of T(1) at tCAL) and train-of-four ratio (TOFR) were recorded until TOFR returned to ≥90%.
  
  
  RESULTS
  In PG, T(1) increased significantly (p = 0.0078) from a median of 102% (range, 95, 109) at baseline to 118% (100, 142) at 20 minutes. In PG, no difference was found between T(1) at tCAL (immediately before atracurium administration) and T(1) when neuromuscular transmission returned (p = 0.42). In the CG, T(1) increased significantly between tCAL and the time neuromuscular transmission returned (p = 0.027). TOFR did not increase during twitch potentiation (all p = 0.32).
  
  
  CONCLUSIONS
  T(1) increased significantly during 20 minutes of uninterrupted TOF stimulation in the absence of NMB, establishing that twitch potentiation occurs in anesthetized dogs. With no time for potentiation, T(1) increased during the course of recovery from NMB; this phenomenon introduces a bias in T(1) measurements and could affect studies reporting potency and duration of NMB based on T(1) or single twitches. TOFR was unaltered by potentiation emphasizing its clinical usefulness for excluding post-operative residual NMB.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14850, USA. mm459@cornell.edu
authors.forename: Manuel
authors.initials: M
authors.lastname: Martin-Flores
authors.forename: Eileen J
authors.initials: EJ
authors.lastname: Lau
authors.forename: Luis
authors.initials: L
authors.lastname: Campoy
authors.forename: Hollis N
authors.initials: HN
authors.lastname: Erb
authors.forename: Robin D
authors.initials: RD
authors.lastname: Gleed
mesh_terms: D000769:Anesthesia, Inhalation / Q000662:veterinary*; D000818:Animals; D001279:Atracurium / Q000494:pharmacology*; D004285:Dogs / Q000502:physiology*; D004576:Electromyography / Q000379:methods / Q000662:veterinary*; D005260:Female; D007044:Hysterectomy / Q000662:veterinary; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D019148:Neuromuscular Blockade / Q000379:methods / Q000662:veterinary*; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D010052:Ovariectomy / Q000662:veterinary; D011446:Prospective Studies; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D003473:Neuromuscular Nondepolarizing Agents; D001279:Atracurium