Fentanyl Dosing for Induction of Anesthesia
For induction of anesthesia in adults, administer fentanyl 1-2 micrograms/kg intravenously, with higher doses (3-5 micrograms/kg) reserved for patients requiring greater hemodynamic stability during cardiac or high-risk surgery. 1, 2, 3
Standard Induction Dosing
The recommended dose for routine anesthetic induction is 1-2 micrograms/kg administered intravenously. 1, 2, 3 This dosing applies across age groups when adjusted for weight, though specific considerations exist for pediatric and geriatric populations. 2
Dose Selection Based on Surgical Context
- Minor or ambulatory procedures: Use 1 microgram/kg at the lower end of the dosing range 3
- Major or painful procedures: Use 2 micrograms/kg or higher within the recommended range 2, 3
- Cardiac or high-risk patients: Doses of 3-5 micrograms/kg provide superior hemodynamic stability during induction and intubation 1, 4, 5
Combination Induction Strategies
When combining fentanyl with other induction agents, lower fentanyl doses are effective and reduce side effects:
- Fentanyl + Propofol: 5 micrograms/kg fentanyl with propofol 2 mg/kg provides reliable induction 1
- Fentanyl + Etomidate: 3-5 micrograms/kg fentanyl administered 5 minutes before etomidate 0.3-0.4 mg/kg minimizes etomidate-related myoclonus and pain on injection while maintaining hemodynamic stability 4, 6
- Fentanyl + Ketamine adjunct: Adding ketamine 0.5 mg/kg (or 0.25-0.5 mg/kg for S-ketamine) as an adjunct allows reduction of total fentanyl requirements 1, 2, 3
High-Dose Fentanyl Technique
For patients with severely limited cardiovascular reserve requiring complete hemodynamic stability:
- Anesthetic induction dose: 15-60 micrograms/kg administered at 1.2 micrograms/kg/second 5, 7
- Note: Research demonstrates that 15 micrograms/kg achieves adequate anesthesia for induction and intubation with cardiovascular responses similar to 60 micrograms/kg, making the higher dose unnecessary in most cases 5
- Age consideration: Patients over 60 years have higher success rates with lower doses (30 micrograms/kg achieves anesthesia in 100% of patients >60 years) 8
Critical Dosing Considerations
Timing and administration technique significantly impact efficacy:
- Administer fentanyl 3-5 minutes before other induction agents to allow peak effect during laryngoscopy and intubation 1, 6
- Rapid administration (1.2 micrograms/kg/second) achieves faster onset but increases risk of chest wall rigidity 5
Side effect profile varies with dose:
- Chest wall rigidity: Occurs more frequently with doses >30 micrograms/kg, particularly without muscle relaxant pretreatment 4, 8
- Apnea: Incidence increases proportionally with dose (53% with no fentanyl pretreatment vs 100% with 500 micrograms pretreatment before etomidate) 6
- Respiratory depression: May persist postoperatively, requiring monitoring; occurs in approximately 10% of patients receiving high doses 2
Muscle Relaxation and Rigidity Prevention
To prevent fentanyl-induced rigidity during induction:
- Administer neuromuscular blocking agents (rocuronium 0.6 mg/kg or succinylcholine 1 mg/kg) immediately after loss of consciousness 1
- Pancuronium pretreatment significantly reduces rigidity incidence and severity 8
- Combined pancuronium plus benzodiazepine pretreatment provides superior rigidity prevention compared to either agent alone 8
Hemodynamic Management
Expected cardiovascular responses:
- Standard induction doses (1-5 micrograms/kg) produce minimal hemodynamic changes with small decreases in heart rate and blood pressure 4, 5
- Higher doses provide greater attenuation of the hypertensive and tachycardic response to laryngoscopy and intubation 6, 5
- Concomitant nitroglycerin infusion (0.3 micrograms/kg/minute) helps maintain hemodynamic stability in cardiac patients 5
Essential Monitoring Requirements
During fentanyl administration for induction, continuously monitor: