[The respiratory effects of small dose fentanyl associated with controlled hypotension during spontaneous ventilation in anesthetized man (author's transl)].

Deliberately lowering blood pressure facilitates middle ear surgery. However, bleeding can persist in spite of hypotension in some tachypneic patients. Fentanyl is a powerful morphinomimetic which decreases ventilatory frequency. This work studies the respiratory effects of fentanyl during spontaneous ventilation in 16 anesthetized patients. Their systemic blood pressure was decreased 40 per cent by trimetaphan. One single injection of fentanyl (0.0125 mg) reduced minute ventilation by 26 per cent, mean inspiratory flow rate (VT/T1) and T1/TTOT, but did not modify the pulmonary dynamic compliance. The acid-base balance parameters changed little toward respiratory alkalosis by trimetaphan and returned to their control values after the injection of fentanyl. Thus, a small dose of fentanyl can be combined with controlled hypotension during anesthesia and spontaneous ventilation without respiratory risk or an acid-base inbalance. With this dose, it has an efficient central influence to reduce the breathing frequency and can be used to lessen bleeding.