Adjuvant Dosing in Spinal and Epidural Anesthesia
Clonidine (Alpha-2 Agonist)
Clonidine is the most evidence-based non-narcotic adjuvant for neuraxial blocks, with preservative-free formulations at 1-2 micrograms/kg providing prolonged analgesia and enhanced block duration. 1
Spinal (Intrathecal) Dosing
- 1-2 micrograms/kg (or 30-75 micrograms in adults) as first-line additive for subarachnoid blocks requiring prolonged analgesia 1
- Must use preservative-free formulations for neuraxial administration 1
- Provides significantly longer two-segment regression time and prolonged effective analgesia compared to fentanyl 2
Epidural Dosing
- Pediatric caudal/epidural blocks: Use as adjunct with long-acting local anesthetics 3
- Continuous epidural infusions: Combined with local anesthetic for postoperative analgesia 3
- Improves block quality and duration in pediatric regional anesthesia 4
Fentanyl (Opioid)
Spinal (Intrathecal) Dosing
For labor analgesia:
- 12.5-15 micrograms combined with 2.5 mg bupivacaine 5
- Provides effective analgesia with faster onset compared to other adjuvants 6
For surgical anesthesia:
- 15-20 micrograms (0.35 micrograms/kg) combined with hyperbaric bupivacaine 7, 2
- Improves quality and duration of sensory anesthesia by 181% compared to plain lidocaine 8
- Does not prolong motor block or time to void 8
- Provides faster onset of T10 sensory blockade (5.5±1.27 minutes) compared to dexmedetomidine 6
Epidural Dosing
For postoperative analgesia (adults):
- 2-4 micrograms/ml in continuous infusion with local anesthetic 9
- Lower concentration (0.1% ropivacaine with 2 micrograms/ml fentanyl) provides comparable analgesia with less motor block than higher concentrations 9
For intraoperative/postoperative use (pediatrics):
- Epidural anesthetic bolus: 0.7 micrograms/kg combined with 0.25% bupivacaine 7
- Epidural analgesic bolus: 0.7 micrograms/kg combined with 0.125% bupivacaine 7
- Continuous infusion: 2-2.5 micrograms/ml with bupivacaine 0.0417-0.1% at 1-3 ml/hr 5
Morphine (Opioid)
Spinal (Intrathecal) Dosing
- 2.85 micrograms/kg combined with bupivacaine for surgical anesthesia 7
- Provides significantly prolonged postoperative analgesia compared to fentanyl (6.9±1.5 hours vs 5.5±0.63 hours to rescue analgesia) 7
- Lower mean pain scores and requires fewer epidural boluses in 24 hours 7
Epidural Dosing (Pediatrics)
- Caudal block adjunct: May be used for prolonged postoperative analgesia 4
- Epidural anesthetic bolus: 0.04 mg/kg combined with 0.25% bupivacaine 7
- Epidural analgesic bolus: 0.04 mg/kg combined with 0.125% bupivacaine 7
Dexmedetomidine (Alpha-2 Agonist)
Spinal (Intrathecal) Dosing
- 10 micrograms combined with hyperbaric bupivacaine 2
- Provides longest duration of analgesia and significantly longer two-segment regression time (141.8±23.5 minutes) compared to fentanyl (94.33±13.6 minutes) 6
- Produces higher sedation scores, particularly in early postanesthesia period 6
- Comparable effectiveness to clonidine for adequate anesthesia and postoperative analgesia 2
Critical Considerations
Preservative-free formulations are mandatory for all neuraxial adjuvants to prevent neurotoxicity 1
Concentration matters more than total dose for epidural infusions—lower concentrations (0.1% vs 0.2% ropivacaine) provide equivalent analgesia with significantly less motor block 9
Choice algorithm:
- For prolonged postoperative analgesia: Use clonidine (1-2 mcg/kg) or dexmedetomidine (10 mcg) intrathecally 1, 2
- For faster onset with shorter duration: Use fentanyl (15-20 mcg) intrathecally 6, 8
- For pediatric regional blocks: Clonidine is preferred adjunct with long-acting local anesthetics 3, 4
- For epidural patient-controlled analgesia: Fentanyl 2 mcg/ml with 0.1% ropivacaine minimizes motor block 9
Common pitfall: Using morphine intrathecally requires monitoring for delayed respiratory depression, though this was not observed in the combined spinal-epidural study at 2.85 mcg/kg 7