Voluntary respiratory effects of butorphanol and fentanyl following barbiturate induction: a double-blind study.

Thirty-one healthy women undergoing outpatient gynecologic surgery were given either butorphanol or fentanyl following barbiturate induction, and various respiratory parameters were measured at intervals after administration of the study drugs. Both fentanyl and butorphanol caused comparable decrements in tidal volume and other respiratory parameters. However, seven of the 15 patients receiving fentanyl had significant respiratory depression that required assisted ventilation. One of the butorphanol patients experienced a 45-second self-limited respiratory depression. One of three butorphanol patients experiencing side effects required treatment for these effects, compared with seven of nine fentanyl patients who experienced adverse effects. It is concluded that butorphanol and fentanyl have comparable anesthetic effects, but butorphanol is safer in terms of respiratory and adverse effects.