Bupivacaine Dosing in Combined Spinal-Epidural Anesthesia
For labor analgesia using CSE, administer 1.75-2.5 mg intrathecal bupivacaine combined with 15-25 µg fentanyl as the initial spinal dose, followed by epidural maintenance with 0.0417-0.1% bupivacaine plus 2-2.5 µg/mL fentanyl at 1-3 mL/hour. 1
Initial Intrathecal Dosing for Labor Analgesia
Standard Dosing Regimen
- Administer 1.0-2.5 mg bupivacaine (0.1%, 0.125%, or 0.25% concentration) in 1-2.5 mL volume as the initial intrathecal bolus 1
- Add fentanyl 12.5-25 µg or sufentanil 1-5 µg to the local anesthetic for reliable analgesia 1
- The ED95 for effective labor analgesia is 1.75 mg bupivacaine with 15 µg fentanyl 1
- The minimum effective dose (ED50) for bupivacaine alone is 2.37 mg, which decreases to 0.69-0.85 mg when combined with fentanyl 1
Key Dosing Considerations
- CSE requires approximately 20% less bupivacaine than single-shot spinal to achieve equivalent sensory levels 2
- The median effective dose is 9.18 mg for CSE versus 11.37 mg for single-shot spinal under similar conditions 2
- Bupivacaine is more potent than levobupivacaine (potency ratio 0.8) and ropivacaine (potency ratio 0.65) 1
- At least 15 µg fentanyl is required for reliable analgesia when combined with 2.5 mg bupivacaine 1
Epidural Maintenance Following Spinal Dose
Continuous Infusion Protocol
- Use 0.0417-0.1% bupivacaine combined with fentanyl 2-2.5 µg/mL 1
- Infusion rate: 1-3 mL/hour 1
- Alternative: 0.175-0.2% ropivacaine with sufentanil 0.75-1 µg/mL at the same rate 1
Breakthrough Pain Management
- Administer 1-2 mL boluses of the maintenance solution by trained personnel 1
- Patient-controlled epidural analgesia (PCEA) option: 0.5-1 mL every 20-30 minutes 1
Conversion to Surgical Anesthesia (Cesarean Section)
Incremental Dosing via Intrathecal Catheter
- Give 2.5 mg bupivacaine increments every 3 minutes until T4 sensory level achieved 1, 3
- Use hyperbaric bupivacaine 0.5% for more predictable spread 1, 3
- Mean total dose required: 15 mg (range 10-25 mg) 1
- Initial opioid administration: 15-20 µg fentanyl plus 0.25-0.3 mg morphine before local anesthetic increments 3
Alternative Dosing for High-Risk Cardiac Patients
- Administer 1.25 mg increments of hyperbaric bupivacaine 0.5% every 3 minutes following initial diamorphine 300 µg 1, 3
- This controlled titration minimizes hemodynamic instability 1, 3
Critical Safety Protocols
Test Dosing Requirements
- Maximum test dose: 10 mg bupivacaine (or equivalent) to detect intrathecal placement while minimizing high/total spinal risk 1
- This dose produces clinically evident sensory, motor, or autonomic effects if intrathecal 1
- Administer epidural doses in 3-5 mL increments with sufficient time between doses to detect intravascular or intrathecal injection 4
Maximum Dosing Limits
- Do not exceed 175 mg bupivacaine without epinephrine or 225 mg with epinephrine 1:200,000 in a single administration 4
- Total daily dose should not exceed 400 mg 4
- Doses may be repeated every 3 hours 4
- Reduce doses for elderly, debilitated patients, and those with cardiac/hepatic disease 4
Common Pitfalls and How to Avoid Them
Volume vs. Dose Effects in Epidural Top-Ups
- Both 5 mL and 10 mL volumes produce similar increases in sensory level through compression of the dural sac 5
- At least 25 mg bupivacaine is required to produce an additional local anesthetic effect beyond the volume effect 5
- Smaller volumes (5 mL) are therefore preferable to minimize total drug exposure while achieving the same volume effect 5
Motor Block Considerations
- Ropivacaine 2.5 mg produces significantly less motor block than bupivacaine 2.5 mg (5% vs 40%) while providing equivalent analgesia 6
- 0.25% bupivacaine concentrations produce incomplete motor block suitable for labor 4
- Monitor for straight-leg raising ability as a screening method for motor block 7
Monitoring Requirements
- Standard ASA monitoring throughout (non-invasive blood pressure, ECG, pulse oximetry) 3
- Assess sensory level every 5 minutes until no further extension observed 3
- Alert anesthetist if patient cannot perform straight-leg raising at 4 hours from last epidural dose 7
- Maintain IV access with running fluids during major regional blocks 4