Impossible mask ventilation after an unusually low dose fentanyl-induced muscle rigidity in a patient with essential tremor: a case report and review of the literature.

: Although opioid-induced muscle rigidity occurs more commonly with large doses and rapid administration of the drugs, there is a number of cases reported, where muscle rigidity was experienced with lower doses of opioids. We present and discuss a case of muscle rigidity induced by an unusually low dose of fentanyl as primary agent during induction of anesthesia. A 79 year old male patient, scheduled for hernia repair, and with a preoperative physical examination of slight hand tremor, received a bolus of 100 mcg (1.2 mcg/kg) fentanyl as primary agent for induction. About 40 sec later he stopped responding, lost consciousness and developed neck and masseter muscle spasm with jaw closure and thoracoabdominal rigidity. Blood pressure was increased significantly. Ventilation was impossible. Rapid oxygen desaturation led us to proceed with IV propofol 150 mg and suxamethonium 100 mg. Opioid-induced muscle rigidity may cause life-threatening respiratory compromise and should be readily recognized and treated by anesthesiologists.