High-Risk Obstetric Anesthesia

Maternal Physiology in High-Risk Pregnancy - Body Under Duress

• Normal pregnancy adaptations are stressed, often decompensating.
• Cardiovascular:
  • ↑Cardiac Output (CO) (30-50%) faces limits (e.g., cardiac disease).
  • Preeclampsia: ↑Systemic Vascular Resistance (SVR), vasospasm, endothelial dysfunction.
  • Peripartum cardiomyopathy: Left ventricular dysfunction.
• Respiratory:
  • ↓Functional Residual Capacity (FRC) (~20%) worsens (obesity, multiple gestations); rapid desaturation risk.
  • ↑O2 consumption.
• Hematological:
  • Exaggerated hypercoagulability (e.g., Antiphospholipid Syndrome - APLAS).
  • Thrombocytopenia (e.g., HELLP, ITP); anemia often severe.
• Renal & Hepatic:
  • Preeclampsia: Proteinuria, ↓Glomerular Filtration Rate (GFR). HELLP: ↑Liver Function Tests (LFTs), liver dysfunction.
• Gastrointestinal (GI): ↑Aspiration risk (obesity, diabetes, GERD).

⭐ In severe preeclampsia, intravascular volume is often decreased despite generalized edema, due to capillary leak and endothelial dysfunction, complicating fluid management.

Hypertensive Disorders - Pressure Point Perils

• Spectrum:

  • Chronic HTN: BP ≥ 140/90 mmHg <20 wks gestation.
  • Gestational HTN: BP ≥ 140/90 mmHg >20 wks, no proteinuria.
  • Preeclampsia: HTN >20 wks + Proteinuria (≥300mg/24h) OR end-organ damage (e.g., BP ≥ 160/110 mmHg, Plt <100,000/µL, ↑LFTs, Cr >1.1 mg/dL, pulmonary edema, cerebral/visual symptoms).
  • Eclampsia: Preeclampsia + Seizures.
  • HELLP Syndrome: Hemolysis, Elevated Liver enzymes, Low Platelets.

• Anesthetic Goals:

  • Seizure control ($MgSO_4$).
  • BP control (Labetalol, Hydralazine); Target SBP 140-155 mmHg, DBP 90-105 mmHg.
  • Judicious fluid management.
  • Safe delivery (neuraxial preferred if no contraindications).

• Key Anesthetic Points:

  • ↑Airway edema risk; careful airway assessment.
  • $MgSO_4$: Potentiates neuromuscular blockers (NMBs). Monitor for toxicity (↓DTRs, respiratory depression). Antidote: Calcium gluconate.
  • Neuraxial (epidural/spinal): Preferred if Platelets >70,000-80,000/µL & no coagulopathy.
  • General Anesthesia (GA): Rapid Sequence Intubation (RSI). Attenuate pressor response to laryngoscopy.
  • HELLP: High risk of bleeding/hematoma. Neuraxial often contraindicated.

⭐ Magnesium sulfate is the drug of choice for eclampsia seizure prophylaxis and treatment; therapeutic range 4.8-8.4 mg/dL (2-3.5 mmol/L).

Obstetric Hemorrhage - Code Red Crisis

• Life-threatening bleeding: Antepartum (APH) or Postpartum (PPH).
  • PPH: Blood loss >500mL (vaginal), >1000mL (CS) in 24h.
• 📌 PPH Causes (4 T's):
  • Tone: Atony (70-80%). Uterotonics.
  • Trauma: Lacerations, rupture. Repair.
  • Tissue: Retained products. Evacuate.
  • Thrombin: Coagulopathy. Correct.
• CODE RED Protocol:
  • Team alert (OB, Anesthesia, Blood Bank).
  • 2 large IVs, O₂, warming. Monitor Shock Index ($SI = HR/SBP$).
  • MTP: PRBC:FFP:Platelets 1:1:1. Consider Calcium.
  • Anesthesia: Regional (stable) vs. GA (unstable/urgent).

⭐ Tranexamic acid (TXA) 1g IV within 3h of PPH onset reduces bleeding deaths. Repeat dose if bleeding continues after 30 min or restarts within 24h.

Coexisting Medical Conditions - Complex Challenges

• Cardiac Disease:
  • NYHA class guides risk; aim for ↓cardiac stress, maintain perfusion.
  • Epidural ideal (slow onset, stable hemodynamics).
  • Avoid: Ketamine (↑HR/BP), Ergometrine (↑BP).
  • Mitral Stenosis: Maintain HR & preload; avoid tachycardia, fluid overload.
  • Aortic Stenosis: Maintain SVR crucial; avoid spinal hypotension.
  • Eisenmenger's: Very high maternal mortality; strictly avoid ↓SVR, hypoxia.
• Diabetes Mellitus:
  • Risks: Macrosomia, neonatal hypoglycemia.
  • Goal: Euglycemia; epidural preferred.
  • GA: Monitor glucose; DKA risk.
• Obesity (BMI >30 kg/m²):
  • Challenges: Airway, IV access, regional anesthesia.
  • ↑Risks: GDM, OSA, VTE; drug dose adjustments.
• Asthma:
  • Optimize pre-op; regional preferred.
  • GA: Ketamine, sevoflurane. ⚠️ PGF2α (Carboprost) contraindicated (bronchospasm).

⭐ Parturients with severe mitral stenosis are highly sensitive to changes in heart rate; maintaining sinus rhythm and avoiding tachycardia is crucial.

High-Yield Points - ⚡ Biggest Takeaways

• Preeclampsia/Eclampsia: Magnesium sulfate for seizures; neuraxial if platelets >70k & no coagulopathy.
• HELLP Syndrome: Severe preeclampsia variant; high risk of epidural hematoma with neuraxial.
• Placenta Previa/Accreta: Anticipate massive hemorrhage; GA often for accreta, ensure blood.
• Amniotic Fluid Embolism: Sudden CV collapse, hypoxia, DIC; aggressive supportive care.
• Cardiac Disease (e.g., Eisenmenger): Maintain hemodynamic stability; GA often for severe cases.
• Morbid Obesity: Increased difficult airway risk; neuraxial preferred, careful positioning.
• Antepartum Hemorrhage: Rapid resuscitation and urgent delivery are critical.