Opioid-induced rigidity after intravenous fentanyl.

BACKGROUND: Large doses of intravenous opioids may cause severe rigidity and prevent spontaneous or controlled ventilation. The mechanism of this effect appears to be neuraxis dopamine antagonism. Rigidity after analgesic doses of fentanyl has not been reported previously. CASE: A pregnant woman receiving haloperidol for multiple psychiatric conditions presented for evaluation of vaginal bleeding. Intravenous fentanyl was administered to facilitate vaginal examination. Severe rigidity of the extremities and truncal region occurred, which prevented spontaneous or assisted ventilation. CONCLUSION: Opioid administration may result in rigidity and respiratory embarrassment. Decreased analgesic requirements in pregnancy and concomitant butyrophenone administration may predispose to opioid-induced rigidity.