• T J Sanford, M B Weinger, N T Smith, J L Benthuysen, N Head, H Silver, and T A Blasco.
• Department of Anesthesiology, University of California, San Diego, School of Medicine.
• J Clin Anesth. 1994 Nov 1; 6 (6): 473-80.

Study ObjectiveTo evaluate and compare the efficacy of various pretreatment agents to attenuate or prevent opioid-induced muscle rigidity using a well-established, previously described clinical protocol.DesignProspective, controlled, single-blind, partially randomized study.SettingLarge medical center.PatientsASA physical status I-III patients undergoing elective surgical procedures of at least 3 hours' duration.InterventionsThe effect of pretreatment with nondepolarizing muscle relaxants (atracurium 40 micrograms/kg or metocurine 50 micrograms/kg), benzodiazepine agonists (diazepam 5 mg or midazolam 2.5 mg), or thiopental sodium 1 mg/kg on the increased muscle tone produced by alfentanil 175 micrograms/kg was compared with a control group (given no pretreatment).Measurements And Main ResultsRigidity was assessed quantitatively by measuring the electromyographic activity of five muscle groups (biceps, intercostals, abdominals, quadriceps, and gastrocnemius). Rigidity also was rated qualitatively by attempts to initiate and maintain mask ventilation, attempts to flex an extremity, and the occurrence of myoclonic movements. Pretreatment with the two nondepolarizing muscle relaxants had no effect on the severe muscle rigidity produced by high-dose alfentanil. Whereas thiopental was only mildly effective, the benzodiazepines midazolam and diazepam significantly attenuated alfentanil rigidity (p < 0.05).ConclusionThis study suggests that benzodiazepine pretreatment is frequently, but not always, effective in preventing opioid-induced muscle rigidity.

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