What is the equation for making a fentanyl (synthetic opioid analgesic) infusion for pediatric patients?

Fentanyl Infusion Preparation in Pediatrics

For pediatric fentanyl infusions, use the standard concentration of 50 mcg/mL (50 micrograms per milliliter), which allows for precise dosing and minimizes volume administration in critically ill children. 1

Standard Concentration Formula

The most practical approach for preparing pediatric fentanyl infusions:

• Standard concentration: 50 mcg/mL 1
• Mix fentanyl (typically from 50 mcg/mL ampules) with normal saline or D5W to achieve desired concentration
• For a 50 mL syringe: Add 2.5 mg (2,500 mcg) fentanyl to 50 mL total volume = 50 mcg/mL 1

Dosing Algorithm for Continuous Infusion

Initial Bolus Dosing

• Opioid-naïve patients: 1-2 mcg/kg IV administered slowly over several minutes 1, 2
• For intubation/RSI: Higher doses of 1-5 mcg/kg are often used, with rapid administration acceptable when muscle relaxants are co-administered 1
• Critical warning: Rapid administration can cause glottic and chest wall rigidity even at doses as low as 1 mcg/kg 1, 2

Starting Infusion Rates

• Begin after achieving initial pain control with boluses 2
• Typical starting range: 1-2 mcg/kg/hour for most pediatric patients 3
• Breakthrough dosing: Provide bolus equal to hourly infusion rate every 5 minutes as needed 4, 2

Titration Protocol

• Double the infusion rate if patient requires two bolus doses within one hour 2
• Reassess after 2-3 days at steady state and adjust based on average daily breakthrough requirements 2
• Expect ten-fold variability in required infusion rates between patients to achieve similar sedation levels 3

Practical Calculation Example

For a 20 kg child requiring 2 mcg/kg/hour:

• Dose needed: 20 kg × 2 mcg/kg/hour = 40 mcg/hour
• Using 50 mcg/mL concentration: 40 mcg/hour ÷ 50 mcg/mL = 0.8 mL/hour infusion rate

Age-Dependent Clearance Considerations

Clearance is highly variable and age-dependent 3:

• Younger infants may require lower infusion rates due to immature hepatic metabolism
• Older children typically have faster clearance
• Always dose to clinical effect rather than using fixed weight-based dosing 3

Pharmacokinetic Warnings for Long-Term Infusions

After prolonged infusions (>24 hours), fentanyl exhibits significantly altered pharmacokinetics 3:

• Volume of distribution increases dramatically: 15.2 L/kg (range 5.1-30.5) vs. 3-5 L/kg with single doses 3
• Terminal elimination half-life is markedly prolonged: 21.1 hours (range 11.2-36.0) vs. 2-4 hours with single doses 3
• Clinical implication: Effects persist much longer after discontinuation of prolonged infusions 3

Conversion from Other Opioids

From IV Morphine to Fentanyl

Use a 60:1 potency ratio (morphine:fentanyl) 2:

1. Calculate 24-hour morphine dose
2. Multiply by 1/60 to get fentanyl dose
3. Divide by 4 to correct for morphine's longer half-life
4. This gives the hourly fentanyl infusion rate 2

Weaning Protocol for Long-Term Use (>7 days)

For patients on continuous fentanyl >7 days, convert to oral methadone 4:

1. Calculate total 24-hour fentanyl dose (mcg)
2. Multiply by 100 to get equipotent methadone dose (mcg)
3. Divide into 4 doses given every 6 hours
4. At second methadone dose: reduce fentanyl to 50%
5. At third methadone dose: reduce fentanyl to 25%
6. After fourth methadone dose: discontinue fentanyl 4

Critical Safety Monitoring

Mandatory monitoring requirements 4, 2:

• Continuous pulse oximetry during infusion
• Assess hourly for first 12 hours after initiation or dose increase
• Every 2 hours for next 12 hours
• Every 4 hours thereafter 4
• Have naloxone 0.1 mg/kg immediately available 2
• Resuscitation equipment must be at bedside 5

High-Risk Combination Warning

Significantly increased apnea risk when combined with benzodiazepines or other sedatives 1, 2:

• This combination requires extreme caution and enhanced monitoring
• Consider reducing doses of both agents when co-administering
• Three apneic episodes occurred in one series of 2,000 pediatric cases, all successfully reversed with naloxone 5

Common Pitfalls to Avoid

• Never use rapid IV push: Always administer boluses slowly over 2-3 minutes to prevent chest wall rigidity 1, 2
• Don't underdose breakthrough pain: Provide adequate bolus doses equal to hourly rate, not arbitrary small amounts 4
• Avoid fixed dosing: Expect wide variability between patients; titrate to clinical effect 3
• Don't forget prolonged effects: After long-term infusions, monitor for at least 24 hours after discontinuation due to prolonged half-life 3