What is the recommended Fentanyl (opioid analgesic) infusion dose range in mcg/kg/min for a 62-year-old female patient weighing 55 kilograms undergoing spine decompression surgery under Total Intravenous Anesthesia (TIVA)?

Fentanyl Infusion Dosing for TIVA in Spine Surgery

For a 62-year-old female undergoing spine decompression surgery with TIVA, administer fentanyl 1-2 mcg/kg (55-110 mcg) as an induction bolus, followed by maintenance boluses of 0.5-1 mcg/kg (27.5-55 mcg) every 15-30 minutes, with dose reduction of 20-50% due to her age. 1

Induction Phase

• Administer fentanyl 55-82.5 mcg (reduced from standard 1-2 mcg/kg due to age >60 years) as an induction bolus 3-5 minutes before propofol or other induction agents to achieve peak effect-site concentration during laryngoscopy, intubation, and surgical positioning. 1

• The 20-50% dose reduction for elderly patients (>60 years) is critical to prevent excessive respiratory depression and hemodynamic instability. 1

• Administer neuromuscular blocking agents immediately after loss of consciousness to prevent fentanyl-induced rigidity during induction. 1

Maintenance Phase Dosing

• Standard maintenance boluses of 27.5-55 mcg (0.5-1 mcg/kg) should be administered every 15-30 minutes, titrated to hemodynamic response and surgical stimulation. 1

• For breakthrough pain during surgery, administer 27.5-55 mcg and reassess within 5 minutes for adequacy of analgesia. 1

• Continuous infusion is NOT recommended for intraoperative fentanyl during TIVA for spine surgery; intermittent bolus dosing provides better titratability and reduces risk of accumulation. 2

Critical Dosing Adjustments for This Patient

• Age-related reduction (62 years old): Initial bolus should be reduced by 20-50% to 27.5-82.5 mcg, as elderly patients demonstrate increased sensitivity to opioids and higher risk of respiratory depression. 1

• Weight consideration (55 kg): No additional dose reduction needed beyond age adjustment, as this weight falls within normal adult parameters. 1

• Renal function: Fentanyl is safer than morphine in renal dysfunction and does not require dose adjustment for single-dose or short-term intraoperative use. 1

Adjuvant Strategies to Reduce Total Fentanyl Requirements

• Consider ketamine 0.5 mg/kg (27.5 mg for this patient) as an adjunct to reduce total fentanyl dose by 25-30% and provide anti-hyperalgesic effects. 1

• Dexmedetomidine loading dose of 1-3 mcg/kg followed by 0.2-0.7 mcg/kg/hour infusion can further reduce fentanyl requirements during maintenance. 1

• Combining fentanyl with non-opioid analgesics such as acetaminophen or NSAIDs (if not contraindicated) reduces total opioid consumption. 1

Monitoring Requirements

• Continuous monitoring of oxygen saturation, blood pressure, heart rate, and respiratory rate is mandatory throughout fentanyl administration. 1

• Approximately 10% of patients receiving higher doses (>1.5 mcg/kg total) may develop respiratory depression that persists postoperatively, requiring vigilant monitoring for at least 2 hours after surgery. 1

• Respiratory depression may last longer than the analgesic effect, necessitating extended postoperative observation. 1

Common Pitfalls to Avoid

• Inadequate pre-intubation dosing (administering fentanyl <3 minutes before laryngoscopy) results in inadequate analgesia during intubation and increased hemodynamic instability. 1

• Excessive dosing in elderly patients without age-appropriate reduction leads to prolonged respiratory depression and delayed emergence. 1

• Naloxone 0.2-0.4 mg (0.5-1 mcg/kg) should be immediately available to reverse opioid effects, though it does not reverse propofol or benzodiazepines. 1