Pretreatment with sedative-hypnotics, but not with nondepolarizing muscle relaxants, attenuates alfentanil-induced muscle rigidity.

STUDY OBJECTIVE To 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. DESIGN Prospective, controlled, single-blind, partially randomized study. SETTING Large medical center. PATIENTS ASA physical status I-III patients undergoing elective surgical procedures of at least 3 hours' duration. INTERVENTIONS The 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 RESULTS Rigidity 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). CONCLUSION This study suggests that benzodiazepine pretreatment is frequently, but not always, effective in preventing opioid-induced muscle rigidity.