Postoperative Apnea Induced by Fentanyl and Other Multiple Respiratory-Modulating Factors

Abstract

Purpose: Opioids are concerned as a major cause of postoperative respiratory depression. In the immediate postoperative period, however, other factors can produce instability of breathing such as pain, agitation, and residual effects of anesthetics. Such factors might be overlooked masked by the fear for opioid-induced respiratory depression. We report a case who presented apnea immediately after emergence from anesthesia that we considered was produced by an interaction among such factors accompanied with fentanyl-induced respiratory depression. Clinical Features: A 31-year-old woman underwent ovarian cystectomy under general anesthesia with continuous infusions of propofol and remifentanil, and bolus doses of fentanyl. Transversus abdominis plane blocks with ropivacaine were given upon completion of surgery. She complained of severe wound pain and was agitated at the emergence from anesthesia. Fentanyl 50 µg was administered intravenously. In several minutes, she developed apnea, unconsciousness, and difficulty of mechanical ventilation via a face mask. The estimated effect site concentration at the onset of the episode (2.9 ng•ml −1 ) was approximately the same (3.0 ng•ml −1 ) as after 30 min when she regained consciousness and spontaneous breathing. It indicated that not only direct inhibition of the respiratory center by fentanyl but also other stimulatory and inhibitory factors contributed to respiratory arrest. Conclusion: In the immediate postoperative period, transient factors, such as pain, mental instability and anesthetic residues, which are indirectly-related with breathing, can interact each other and with opioids. The interaction would induce apnea through mechanisms combined among direct inhibition of the respiratory center, and modulation of chemical and cortical controls of breathing.