What is the recommended dose of intrathecal (in the spinal canal) fentanyl?

Intrathecal Fentanyl Dosing Recommendations

For labor analgesia, use 15 µg intrathecal fentanyl combined with local anesthetic as the initial bolus dose, which represents the ED95 (effective in 95% of patients) and provides reliable analgesia without exceeding the safety threshold. 1

Context-Specific Dosing

Labor Analgesia (Most Common Indication)

Initial Bolus:

• The optimal dose is 15 µg fentanyl with 1.75 mg bupivacaine, which achieves reliable analgesia in 95% of patients 1
• The acceptable range is 12.5-25 µg, but 15 µg is most commonly recommended by the American Society of Anesthesiologists 1
• Doses below 15 µg frequently provide inadequate analgesia 1
• Do not exceed 25 µg for initial dosing—higher doses provide no additional benefit for duration or quality of analgesia 1, 2

Continuous Infusion (via intrathecal catheter):

• Use fentanyl concentration of 2-2.5 µg/mL combined with bupivacaine 0.0417-0.1% 1
• Infusion rate: 1-3 mL/hour 1
• Patient-controlled boluses: 0.5-1 mL every 20-30 minutes as adjunct 1

Cesarean Section

Intraoperative Analgesia:

• Use 12.5-15 µg fentanyl added to hyperbaric bupivacaine (10-15 mg) for cesarean delivery 3
• 12.5 µg appears to reach a clinical ceiling effect—higher doses (15 µg) provide no significant additional benefit 4
• Both 12.5 µg and 15 µg provide excellent intraoperative analgesia in nearly 100% of patients, compared to only 33% with bupivacaine alone 4
• Complete analgesia duration: approximately 200-210 minutes with either 12.5 or 15 µg 4

Non-Obstetric Surgery

Postoperative Analgesia:

• 40 µg intrathecal fentanyl provides satisfactory analgesia for approximately 5 hours in elderly patients undergoing lower extremity procedures 5
• 20 µg produces onset of satisfactory analgesia within 4 minutes 5
• 40-50 µg produces excellent analgesia within 10 minutes 5
• Doses below 20 µg provide minimal analgesia 5

Day Surgery:

• 12.5 µg fentanyl with 5 mg bupivacaine provides better surgical anesthesia and increased reliability compared to 7.5 or 10 µg 6
• Lower doses (7.5 µg) have significantly higher failure rates 6

Critical Safety Distinction: Intrathecal vs. Epidural

Never confuse intrathecal and epidural dosing—this is a potentially fatal error:

• Maximum intrathecal dose: 15 µg for labor analgesia (per Obstetric Anaesthetists' Association) 7
• Epidural doses are 50-100 µg (3-7 times higher) 7
• Administering epidural doses intrathecally causes severe respiratory depression and life-threatening complications 7

Monitoring Requirements

Mandatory monitoring after intrathecal fentanyl administration:

• Non-invasive blood pressure every 5 minutes for 30 minutes 1
• Continuous fetal heart rate monitoring for 30 minutes in obstetric patients 1
• Standard institutional monitoring thereafter 1

Common Pitfalls and Side Effects

Dose-Related Considerations:

• Pruritus is the most common side effect, occurring in approximately 50% of patients at 50 µg doses 5, 4
• Pruritus is mild at recommended doses (12.5-15 µg) 4
• No respiratory depression, hypoxemia, or significant hemodynamic changes occur at doses up to 50 µg 5
• Potential for acute spinal opioid tolerance: 25 µg intrathecal fentanyl may increase postoperative IV morphine requirements by 63% between 6-23 hours after delivery 8

Duration Ceiling Effect:

• Doses above 25 µg do not prolong duration of labor analgesia—there is no advantage to exceeding this dose 2
• All doses from 5-25 µg reduce local anesthetic requirements similarly 1