To the Editor:
After institutional review board approval and informed consent, onset of neuromuscular block by succinylcholine (1.5 mg/kg body weight) was measured at the adductor pollicis (AP) and stapedius muscles during ketamine/midazolam anesthesia in four patients (20-41 yr old) scheduled for elective nasal surgery. Relaxometry of the AP muscle (train-of-four stimulation of the ulnar nerve, 2 Hz every 15 s; Accelograph Registered Trademark; Biometer, Denmark) was performed simultaneously with acoustic reflex threshold measurement (110 dB hearing threshold level, 1000 Hz; CIM 85 Registered Trademark; Hortmann, Germany) .
Responses in both muscles disappeared completely during succinylcholine-induced paralysis. Onset to complete neuromuscular block in the stapedius muscle (range: 23 to 38 s) invariably preceded that in the AP muscle (range: 60 to 90 s).
In humans, various types of measurement have shown that onset of succinylcholine relaxation is slower at the AP muscle than at the diaphragm (transdiaphragmatic pressure measurement) , the vocal cords (pressure measurement) , or the masseter (mechanomyography) . The finding that the stapedius muscle response is lost more quickly than the response of the AP muscle demonstrates that the relaxation of the stapedius muscle is similar to that of the respiratory muscles; this may indicate a difference in the sensitivities to succinylcholine between the stapedius and AP muscles or a difference in the kinetics of drug delivery, based on differences in perfusion of the two muscles by the circulation.
U. Bissinger, MD
Department of Anesthesiology, Eberhard Karls University, Tubingen, Germany
1. Northern JL. Clinical measurement procedures in impedance audiometry. In: Jerger JJ, Northern JL, eds. Clinical impedance audiometry. 2nd ed. Stuttgart: Georg Thieme Verlag, 1980:19-39.
2. Pansard JL, Chauvin M, Lebrault C, et al. Effect of an intubating dose of succinylcholine and atracurium on the diaphragm and the adductor pollicis muscle in humans. Anesthesiology 1987;67:326-30.
3. Wright PMC, Caldwell JE, Miller RD. Onset and duration of rocuronium and succinylcholine at the adductor pollicis and laryngeal adductor muscles in anesthetized humans. Anesthesiology 1994;81:1110-5.
4. Smith CE, Donati F, Bevan DR. Effects of succinylcholine at the masseter and adductor pollicis muscles in adults. Anesth Analg 1989;69:158-62.