Fentanyl-induced rigidity during emergence from general anesthesia potentiated by venlafexine

Purpose: To present and discuss a case of opioid-induced rigidity with low-dose fentanyl during recovery from anesthesia. Clinical features: A 41-yr-old woman underwent laparotomy for total abdominal hysterectomy and bilateral salpingooophorectomy under general anesthesia. She received a total of 500 μg of fentanyl by iv intermittent boluses during the three-hour anesthetic. During emergence from anesthesia, while intubated, the patient presented with rigidity. No changes in ventilatory parameters were measured during the episode. The only notable predisposing factor was treatment with venlafexine, an antidepressant that modifies serotonin and norepinephrine levels. She was successfully treated with iv naloxone 20 μg. The rest of the postoperative period was uneventful. Conclusion: We observed an atypical case of opioid-induced rigidity in contrast to the classical syndrome, which presents at induction with high-dose opioids. This syndrome has many clinical presentations with neurologic and ventilatory signs of varying intensity. Early recognition of the syndrome and adequate treatment is crucial. If treated adequately, opioid-induced rigidity is self-limited with few complications.