Respiratory effects of epidural fentanyl. Changes in end-tidal CO2 and respiratory rate following single doses and continuous infusions of epidural fentanyl.

Respiratory function following single bolus doses as well as continuous infusions of epidural fentanyl were studied in 21 patients. Respiratory rate decreased significantly and end-tidal CO2 showed a non-significant increase following single doses of epidural fentanyl (1.5 micrograms/kg). These changes occurred within minutes of injection, but could not be attributed solely to rapid systemic absorption of fentanyl from the epidural space. Prior administration of parenteral morphine resulted in significantly higher end-tidal CO2 concentrations and lower respiratory rates following epidural fentanyl. Continuous epidural fentanyl infusion (0.5 micrograms/kg/hour) started 60 minutes after the bolus dose had no effect on end-tidal CO2 concentration or respiratory rate for up to 18 hours. Infusions were continued after the study terminated for up to 9 days, during which there was no clinically significant respiratory depression.