Labour analgesia Drug volume
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Labour Analgesia - Drug Volumes & Concentrations
1. Epidural Analgesia
Initial (Loading) Dose - First Stage of Labour
The goal is a T10-L1 sensory level. The initial bolus is given as 10 mL in 5 mL increments, waiting 1-2 minutes between doses.
| Solution | Concentration | Volume | Opioid Added |
|---|---|---|---|
| Bupivacaine | 0.125% | ~10 mL | Fentanyl 50-100 mcg OR Sufentanil 5-10 mcg |
| Bupivacaine | 0.0625-0.125% | 10 mL | Fentanyl 50-100 mcg OR Sufentanil 10-20 mcg |
| Ropivacaine | 0.1-0.2% | 10 mL | Fentanyl 50-100 mcg OR Sufentanil 5-10 mcg |
- Barash Clinical Anesthesia 9e, p. 3490
- Morgan & Mikhail's Clinical Anesthesiology 7e, p. 1618
Note: Lower volumes (6-10 mL) are generally adequate for obstetric analgesia compared to surgical epidural procedures (10-20 mL).
Maintenance of Labour Epidural Analgesia
Three options exist: continuous infusion, PCEA, or PIEB.
Option A - Continuous Epidural Infusion (CEI)
| Agent | Concentration | Rate |
|---|---|---|
| Bupivacaine | 0.0625-0.1% | 10-12 mL/h |
| Ropivacaine | 0.08-0.15% | 10-12 mL/h |
| + Fentanyl | 1-3 mcg/mL | added to above |
| + Sufentanil | 0.1-0.5 mcg/mL | added to above |
Option B - Patient-Controlled Epidural Analgesia (PCEA)
| Parameter | Setting |
|---|---|
| Bolus dose | 5-10 mL |
| Lockout interval | 10-20 minutes |
| Background infusion | 0-10 mL/h (typically 30-50% of hourly dose) |
| Hourly limit | 15-25 mL |
| Solution | Same dilute bupivacaine/ropivacaine + opioid as above |
Option C - Programmed Intermittent Epidural Bolus (PIEB)
| Parameter | Setting |
|---|---|
| Bolus dose | 5-10 mL |
| Bolus interval | Every 30-60 minutes |
| Example regimen | 6 mL bupivacaine 0.0625% every 30 min (without baseline) |
PIEB provides better distribution in the epidural space, greater patient satisfaction, lower drug consumption, and less motor block than CEI alone. It is often combined with PCEA.
- Barash Clinical Anesthesia 9e, p. 3490-3491
- Miller's Anesthesia 10e, p. 8858
- Morgan & Mikhail 7e, p. 1618
Second Stage / Operative Vaginal Delivery
To extend block to S2-S4 dermatomes:
| Agent | Concentration | Volume |
|---|---|---|
| Bupivacaine | 0.25-0.5% | 10 mL |
| Lidocaine | 1% | 10-15 mL |
| 2-Chloroprocaine | 2-3% | 10-15 mL |
For urgent conversion to cesarean delivery, 3% 2-chloroprocaine or lidocaine 2% with epinephrine (+ bicarbonate 1 mEq/10 mL) is used for rapid epidural top-up.
2. Intrathecal Analgesia (Spinal / CSE - First Stage)
For Combined Spinal-Epidural (CSE) or pure spinal analgesia during the first stage:
| Agent | Dose | Notes |
|---|---|---|
| Bupivacaine (preservative-free) | 1.25-2.5 mg | Combined with opioid |
| Ropivacaine | 3-4 mg | Alternative to bupivacaine |
| Fentanyl | 10-25 mcg | Alone or with local anesthetic |
| Sufentanil | 2-5 mcg | Alone or with local anesthetic |
| Morphine | May be added to prolong duration |
The intrathecal combination of bupivacaine 1.25-2.5 mg + fentanyl 10-25 mcg produces profound analgesia lasting 90-120 minutes, after which the epidural catheter is activated.
- Barash Clinical Anesthesia 9e, p. 3491-3492
- Morgan & Mikhail 7e, p. 1623
3. Saddle Block (Spinal just before Delivery)
For operative vaginal delivery or terminal delivery analgesia:
| Agent | Dose |
|---|---|
| Hyperbaric bupivacaine | 2.5-5 mg |
| Hyperbaric tetracaine | 3-4 mg |
| Lidocaine (hyperbaric) | 20-40 mg |
| + Fentanyl | 12.5-25 mcg |
| + Sufentanil | 5-7.5 mcg |
Achieves excellent perineal anesthesia (S2-S5 saddle distribution). A T10 level requires slightly larger doses.
- Morgan & Mikhail 7e, p. 1623
4. Bupivacaine Concentration Summary (Quick Reference)
| Concentration | Volume | Opioid | Effect |
|---|---|---|---|
| 0.5% | 5-10 mL | None | Sensory + motor block (surgical) |
| 0.25% | 10-15 mL | None | Sensory + partial motor block |
| 0.125% | 10-15 mL | Fentanyl 1-3 mcg/mL | Sensory, minimal motor block |
| 0.0625% | 10-20 mL | Fentanyl 2-3 mcg/mL | Sensory only (walking epidural) |
- Pfenninger & Fowler's Procedures for Primary Care, p. 44
5. Adjuvants
- Epinephrine: 1:400,000 to 1:800,000 (dilute - reduces vascular uptake, adds α2 analgesia; avoid higher doses due to uterine artery vasoconstriction)
- Clonidine: Effective but FDA label warns against routine obstetric use (risk of hypotension/bradycardia)
- Dexmedetomidine: Efficacious adjunct with bupivacaine/ropivacaine; not FDA-approved for neuraxial use in US
- Neostigmine (epidural): Reduces LA requirements without nausea (unlike intrathecal neostigmine, which was abandoned)
Key principle: Labour analgesia uses the highest volume + lowest concentration strategy to maximize spread and minimize motor block. The trend is toward higher-volume, more-dilute local anesthetic solutions combined with lipophilic opioids - allowing the parturient to ambulate ("walking epidural" with ≤0.0625% bupivacaine).
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