Regional Anesthesia in Obstetrics

Physiology & RA Choices - Bump & Block Basics

• Physiological Changes (Pregnancy & RA):
  • CV: ↑CO, ↓SVR. Aortocaval compression (LUD vital!).
  • Resp: ↓FRC, ↑O₂ demand (rapid desaturation risk).
  • GI: ↓Gastric emptying, ↓LES tone (↑aspiration risk).
  • Nervous: ↑LA sensitivity (↓dose ~30%); engorged epidural veins (↓epidural volume).
• RA Advantages (Obstetrics):
  • Maternal: Superior analgesia, awake patient, ↓aspiration, ↓opioids.
  • Fetal: Minimal drug transfer, better uteroplacental perfusion (normotension).
• Indications: Labor analgesia (epidural, CSE); C-section (spinal, epidural, CSE).
• Contraindications (Absolute): 📌 I CHOP: Infection (site), Coagulopathy (Plt < 80,000/µL)/Severe Hypovolemia, ↑ICP, Patient refusal.
• Techniques & Levels:
  • Epidural: Slower, titratable. Labor: T10-L1. C-section: T4.
  • Spinal: Rapid, dense. C-section: T4.
  • CSE: Spinal speed + epidural flexibility.

⭐ Aortocaval compression by the gravid uterus causes supine hypotension syndrome; left uterine displacement (LUD) is crucial.

Pharmacology of RA - Mommy's Magic Mix

Local Anesthetics (LAs):

• Bupivacaine: Potent, long-acting; racemic ↑cardiotoxicity.
• Levobupivacaine: S-enantiomer of bupivacaine, ↓cardiotoxicity.
• Ropivacaine: ↓cardiotoxicity & ↓motor block vs Bupivacaine.
• Lidocaine: Fast onset, short duration; for surgical epidurals.
• Properties: pKa (onset), Lipid Sol. (potency/duration), Protein Bind. (duration).
• Differential Block: Sensory > Motor.
• Cardiac Toxicity: Bupivacaine > Ropivacaine/Levobupivacaine.
• Placental Transfer & Ion Trapping: LAs cross placenta; fetal acidosis → LA accumulation in fetus.

⭐ Levobupivacaine and Ropivacaine have a better safety profile (less cardiotoxic) than racemic Bupivacaine.

Neuraxial Opioids:

• Lipophilic (fast onset, short duration): Fentanyl (Epidural 50-100 mcg, IT 10-25 mcg), Sufentanil (Epidural 5-20 mcg, IT 1-5 mcg).
• Hydrophilic (slow onset, long duration): Morphine (IT 50-150 mcg).
• Benefits: Synergy with LAs (↓LA dose).
• Side Effects: 📌 Pruritus (common), N/V, Resp. Depression (early-lipo, delayed-hydro).

Adjuvants:

• Epinephrine: Test dose marker (15 mcg), prolongs block (e.g., 1:200,000 / 5 mcg/mL).
• Clonidine ($\alpha_2$-agonist): Prolongs analgesia (Epidural 75-150 mcg).

Patient-Controlled Epidural Analgesia (PCEA):

• Concept: Patient-controlled epidural boluses for labor.
• Advantages: ↑Maternal satisfaction, ↓motor block, ↓total drug.
• Typical Mix: Bupivacaine 0.0625%-0.125% + Fentanyl 1-2 mcg/mL.

Complications & Special Cases - Wobbly Walk & Woes

• Maternal Hypotension: Common. Prevent: LUD, IV fluid co-load. Manage: Phenylephrine 50-100 mcg IV.

• PDPH (Post-Dural Puncture Headache): Postural headache. Prevent: Atraumatic needles. Manage: Conservative; EBP (15-20 mL blood).

• High/Total Spinal: Rapid ↑ block, respiratory distress, ↓BP. Manage: ABCs, intubate if needed.

• LAST (Local Anesthetic Systemic Toxicity): 📌 SAMS (Slurred speech, Agitation, Metallic taste, Seizures). Manage: Stop LA, ACLS, Intralipid 20% (1.5 mL/kg bolus, 0.25 mL/kg/min infusion).

  ⭐ For LAST management, lipid emulsion therapy (Intralipid 20%) should be initiated early along with standard ACLS protocols, avoiding vasopressin, CCBs, beta-blockers or lidocaine for arrhythmias.

  

• Neuro Complications: Rare. Nerve injury, epidural hematoma/abscess (urgent MRI).

• Failed Block: Troubleshoot: reposition, supplemental LA, convert to GA.

• Special Cases:

  • Preeclampsia: Platelets >80,000/µL for neuraxial.
  • Cardiac disease: Careful titration.
  • Coagulopathy: Contraindication if significant for neuraxial anesthesia.

High‑Yield Points - ⚡ Biggest Takeaways

• Epidural analgesia is the gold standard for labor pain relief.
• Spinal anesthesia is preferred for elective Cesarean sections due to rapid onset and dense block.
• Combined Spinal-Epidural (CSE) offers rapid onset of spinal with prolonged analgesia via epidural catheter.
• Hypotension is the most common side effect of neuraxial anesthesia; manage with IV fluids and vasopressors.
• Bupivacaine is commonly used; ropivacaine and levobupivacaine offer ↑ cardiac safety.
• PDPH is a key complication; manage conservatively, then epidural blood patch.