Preanesthetic train-of-four fade predicts the atracurium requirement of myasthenia gravis patients.
BACKGROUND
The most sensitive diagnostic criterion of myasthenia gravis is a decrement in the muscular response to repetitive stimulation. The authors hypothesized that myasthenia gravis patients who show a train-of-four ratio (T4/T1) < 0.9 in the preanesthetic period will have increased sensitivity to nondepolarizing neuromuscular blocking agents compared with myasthenia gravis patients with preanesthetic T4/T1 > or = 0.9.


METHODS
After institutional review board approval was obtained, 20 electrophysiologically documented myasthenia gravis patients were studied. Current pyridostigmine therapy was continued until the morning of surgery. Before induction of anesthesia, neuromuscular transmission was recorded from the hypothenar muscles using electromyography with train-of-four stimulation of the ulnar nerve. According to the T4/T1 ratio, patients were assigned to the "normal" group (T4/T1 > or = 0.9) or the "decrement" group (T4/T1 < 0.9). After induction of intravenous anesthesia, the effective dose to achieve a 95% neuromuscular blockade (ED95) for atracurium was assessed with a cumulative bolus technique. Postoperatively, pyridostigmine was titrated to obtain a T4/T1 > 0.75 and to treat residual myasthenic symptoms.


RESULTS
In 14 patients, preanesthetic T4/T1 was > or = 0.9 (normal), whereas 6 patients presented with T4/T1 < 0.9 (decrement). Decrement patients had a lower ED95 of 0.07 +/- 0.03 mg/kg atracurium (mean +/- SD) compared with normal patients with an ED95 of 0.24 +/- 0.11 mg/kg atracurium (P = 0.002). All patients were extubated within 30 min after surgery. Postoperative pyridostigmine infusion did not differ significantly between groups.


CONCLUSIONS
The requirement for atracurium is significantly reduced in myasthenia gravis patients with a T4/T1 ratio < 0.9 before anesthesia. This study indicates that routine neuromuscular monitoring in myasthenia gravis patients should be extended into the preinduction period to identify patients who require less atracurium.
Mann
R
R
Klinik für Anaesthesiologie der Technischen Universität München, Klinikum rechts der Isar, Munich, Germany.
Blobner
M
M
Jelen-Esselborn
S
S
Busley
R
R
Werner
C
C
D000328:Adult; D001279:Atracurium / Q000008:administration & dosage / Q000494:pharmacology*; D002800:Cholinesterase Inhibitors / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004576:Electromyography; D004594:Electrophysiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology*; D019148:Neuromuscular Blockade; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage / Q000494:pharmacology*; D011229:Preanesthetic Medication; D011237:Predictive Value of Tests; D011729:Pyridostigmine Bromide / Q000627:therapeutic use; D012044:Regression Analysis; D009435:Synaptic Transmission / Q000187:drug effects; D014459:Ulnar Nerve / Q000187:drug effects*
D002800:Cholinesterase Inhibitors; D003473:Neuromuscular Nondepolarizing Agents; D001279:Atracurium; D011729:Pyridostigmine Bromide