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Anemia in Pregnancy and Anesthesia - Complete Viva Guide

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1. DEFINITION AND INCIDENCE

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2. WHO GRADES OF ANEMIA IN PREGNANCY (2024 Updated Guidelines)

The 2024 WHO guideline on haemoglobin cutoffs updated these thresholds and stratifies by trimester.

• Grade 1 (mild): Pallor of conjunctivae, inner lower eyelid
• Grade 2 (moderate): Conjunctival + palmar pallor
• Grade 3 (severe): Conjunctival + palmar + nail bed pallor
• Grade 4 (very severe): Generalized pallor - tongue, mucous membranes, skin, nail beds

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3. PHYSIOLOGIC CHANGES OF PREGNANCY RELEVANT TO ANEMIA

Normal Hemodilution (Physiologic Anemia of Pregnancy)

• Plasma volume increases ~50% by term
• Red cell mass increases only 25-30%
• Net result: relative hemodilution; Hb falls by ~1.5-2 g/dL (nadir at ~28-32 weeks)
• This is NOT pathological - it reduces blood viscosity and improves uteroplacental perfusion

Key Systemic Changes in Pregnancy

"Oxygen consumption increases steadily throughout pregnancy and is greatest at term, reaching an average of 331 mL/min at rest and 1167 mL/min with exercise." - Creasy & Resnik's, p. 1397

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4. OXYGEN FLUX (DO2) - THE FICK PRINCIPLE

• Normal DO2: ~1000 mL/min; VO2 (consumption): ~250 mL/min
• Oxygen extraction ratio = VO2/DO2 = ~25% (large reserve)
• In anemia, CO compensates - in pregnancy DO2 is maintained because CO increases 50%

"The pregnant woman depends on cardiac output for maintenance of oxygen delivery more than the nonpregnant patient." - Creasy & Resnik's, p. 1397

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5. COMPENSATORY MECHANISMS IN ANEMIA

1. Increased cardiac output (minutes) - heart rate and stroke volume rise; most rapid and effective
2. Increased 2,3-DPG (hours to days) - stabilizes deoxy-Hb, rightward shift of ODC, enhances tissue O2 unloading (lower P50 → more O2 given up at same PO2)
3. Plasma volume expansion (weeks) - maintains preload and cardiac output; can cause high-output cardiac failure if overwhelming

• Redistribution of blood flow to vital organs
• Renal EPO production increases
• Decreased blood viscosity → less resistance → improved flow

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6. TYPES AND CAUSES OF ANEMIA IN PREGNANCY

Classification by Pathophysiologic Mechanism (Box 55.1, Creasy & Resnik)

Morphologic Classification

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7. SPECIFIC ANEMIAS IN DETAIL

Iron Deficiency Anemia (IDA)

• Most common (75% of pregnancy anemias)
• Symptoms: fatigue, lethargy, pica (ice, clay, dirt), pallor, glossitis, cheilitis, koilonychia (rare)
• Labs: microcytic hypochromic, low serum iron, high TIBC, low ferritin (< 12 µg/L), low transferrin saturation
• Treatment: Ferrous sulfate 325 mg OD-TID; WHO recommends 60 mg elemental iron/day with folic acid; IV iron if severe/intolerant (iron sucrose preferred)
• Reticulocytosis expected at 7-10 days; Hb rises ~1 g/dL/week in severe anemia - Creasy & Resnik's, p. 1335

Folate Deficiency (Megaloblastic)

• Second most common in pregnancy
• Causes: inadequate dietary intake, malabsorption, multiple pregnancy, folate antagonists (methotrexate, trimethoprim, pyrimethamine)
• Labs: macrocytic, hypersegmented neutrophils, low serum and RBC folate
• Treatment: Folic acid 5 mg OD; prevention: 400 µg/day preconceptionally

B12 Deficiency

• Pernicious anemia (anti-intrinsic factor antibodies), strict vegetarians, prior gastric surgery
• Labs: macrocytic, elevated MMA and homocysteine
• Treatment: IM cyanocobalamin or hydroxycobalamin

Sickle Cell Disease in Pregnancy

• Hb SS, SC, S-β-thal
• Complications: vaso-occlusive crisis, acute chest syndrome, stroke, splenic sequestration, increased UTI, preeclampsia, preterm labor
• Triggers for sickling: hypoxia, hypovolemia, hypothermia, acidosis, infection, dehydration
• Transfusion goals: Hb > 8 g/dL, HbA > 40% of total Hb
• Frequency of sickle cell trait: 1:122 in African-Americans

Thalassemia

• Alpha-thalassemia minor: mild hypochromic microcytic anemia; tolerated in pregnancy
• Beta-thalassemia major (Cooley's anemia): severe transfusion-dependent; iron overload; cardiomyopathy
• Beta-thalassemia trait: mild microcytic anemia; must distinguish from IDA (serum ferritin, Hb electrophoresis)

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8. EFFECTS OF ANEMIA ON MOTHER AND FETUS

• High output cardiac failure in severe anemia
• Reduced tolerance for hemorrhage at delivery
• Postpartum hemorrhage risk is 3-15x higher (mild to severe anemia)
• Placental abruption risk increased
• Increased susceptibility to infection
• Preeclampsia association

• Preterm birth, SGA, low birth weight, perinatal death - risk increases with severity
• Poor cognitive development in children born of iron-deficient mothers
• Elevated maternal Hb (>14.5 g/dL) is also associated with poor outcomes (reduced plasma expansion, placental dysfunction)
• Note: Fetal O2 consumption maintained until maternal Hct reduced by >50% (sheep model)

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9. INVESTIGATION OF ANEMIA IN PREGNANCY

• CBC, reticulocyte count, peripheral smear
• Serum ferritin (best single test for iron stores - but is an acute phase reactant)
• Serum iron, TIBC, transferrin saturation
• Folate (serum + RBC) and B12 levels

• Hb electrophoresis (sickle cell, thalassemia)
• Direct Coombs test (hemolytic)
• LDH, haptoglobin, bilirubin (hemolysis screen)
• Reticulocyte production index (RPI = reticulocyte % × Hct/45 ÷ maturation time)

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10. ANESTHESIA MANAGEMENT IN ANEMIA IN PREGNANCY

Preoperative Assessment

1. Assess severity: Hb, Hct, peripheral smear, reticulocyte count
2. Assess compensation: Resting tachycardia, orthopnea, signs of cardiac failure, functional status
3. Identify cause: See above workup
4. Assess concomitant disease: Cardiac reserve, coagulopathy (in thalassemia/aplastic anemia), platelet count (for neuraxial)
5. Blood bank: Group & crossmatch, ensure availability of packed RBCs

"The concept of an acceptable Hb level varies with the underlying medical condition, extent of physiological compensation, the threat of bleeding and ongoing blood losses." - Anaemia and Pregnancy: Anaesthetic Implications, PMC2991646

Minimum Acceptable Hemoglobin for Anesthesia

• Elective surgery: Hb ≥ 8 g/dL generally acceptable (individualized)
• Obstetric surgery (LSCS): Pre-transfusion target Hb ≥ 8-10 g/dL; historically 10 g/dL ("10/30 rule") but evidence for this is not conclusive
• Emergency surgery: Proceed with resuscitation, transfuse intraoperatively

Preoperative Optimization (Elective)

• Mild-moderate IDA: Oral iron for 2-4 weeks to raise Hb by 1-2 g/dL before elective surgery
• Severe IDA or intolerance to oral: IV iron sucrose 200-300 mg over 30-60 min (faster response)
• Folate/B12 deficiency: Treat cause, start supplementation
• Very severe anemia (Hb < 6): Pre-operative transfusion - packed red cells
• Treat underlying cause, optimize nutrition, ensure euvolemia

Key Anesthetic Goals (Both GA and RA)

1. Minimize O2 consumption - avoid pain, shivering, anxiety (increase O2 demand)
2. Maximize O2 delivery - maximize FiO2, ensure adequate CO, avoid hypotension
3. Avoid conditions shifting ODC LEFT (would impair O2 unloading):
   • Hypothermia
   • Respiratory alkalosis (hyperventilation) - keep normocarbia
   • Alkalemia
   • Hypophosphatemia
4. Maintain cardiac output - aggressive fluid management, vasopressors for spinal hypotension
5. Warm all IV fluids and blood products
6. Prevent blood loss - meticulous hemostasis, tranexamic acid, cell salvage where appropriate

Choice of Anesthetic Technique

• Spinal or epidural/CSE for LSCS is preferred in anemia
• Advantages: avoids airway manipulation, reduces blood loss vs GA, provides good post-op analgesia
• Spinal precautions: Use low-dose spinal + adjuvants (fentanyl/morphine) to minimize sympathectomy and hypotension
• Treat spinal hypotension aggressively: left uterine displacement, IV fluids, vasopressors (phenylephrine/ephedrine)
• Check platelet count before neuraxial block (> 80,000 generally acceptable; > 100,000 preferred)

• Required for: severe thrombocytopenia, coagulopathy, patient refusal of RA, failed RA, emergency with unstable patient
• Key considerations in anemia:
  • Pre-oxygenate thoroughly (FRC already reduced in pregnancy)
  • Rapid sequence induction (full stomach precaution)
  • Use etomidate or ketamine for induction if hemodynamically compromised (avoid propofol in severe anemia - myocardial depression, risk of hypotension)
  • Maintenance: volatile agents are myocardial depressants - use with care; nitrous oxide can be used but avoid in folate/B12 deficiency (inhibits methionine synthase)
  • Avoid barbiturates for induction in severe anemia (reduced dose requirements, more prone to hypotension)
  • Maintain normothermia, normocarbia
  • Avoid N2O in megaloblastic anemia

Monitoring in Severe Anemia

• Standard: ECG, NIBP, SpO2, EtCO2, temperature
• Consider invasive monitoring in severe anemia with anticipated major blood loss:
  • Arterial line (continuous BP, serial ABG, Hb monitoring)
  • CVP
  • Urinary catheter (hourly output)
  • ABG (pH, lactate, Hb, base excess)
  • Mixed venous O2 saturation (SvO2) in critical cases

Intraoperative Management

• Maintain FiO2 0.4-1.0 (based on severity)
• Warm all IV fluids and blood products
• Aggressive uterotonic management postpartum (syntocinon, ergometrine, carboprost)
• Activate massive obstetric hemorrhage protocol early if bleeding
• Transfusion trigger: Hb < 7-8 g/dL in stable patient; transfuse at higher threshold if symptomatic, ongoing bleeding, or cardiac compromise
• Target: Hb ≥ 8 g/dL, normothermia, pH > 7.35, calcium > 1.1 mmol/L

Special Anesthetic Considerations by Type

• Avoid: hypoxia, hypovolemia, hypothermia, acidosis, stasis, infection
• Regional anesthesia preferred (avoids catecholamine surge, maintains warmth)
• Both neuraxial and GA acceptable if above triggers avoided
• Pre-operative transfusion goal: Hb > 8 g/dL, HbA > 40%
• Avoid tourniquets; maintain hydration

• Iron overload → cardiomyopathy → reduced cardiac reserve
• Difficult airway possible (hepatosplenomegaly may push diaphragm; maxillary changes from bone marrow expansion)
• Both GA and neuraxial acceptable after platelet count review
• Avoid further iron loading (no unnecessary transfusions)
• Echocardiography preoperatively to assess cardiac function

• Pancytopenia: anemia + thrombocytopenia + neutropenia
• Thrombocytopenia may preclude neuraxial anesthesia → GA often required
• Platelet transfusion preoperatively to target > 50,000 (neuraxial) or > 100,000 (platelet-rich field)
• Extreme care with infection prevention (neutropenia)
• GA with meticulous aseptic technique

• Monitor for hemolytic crisis perioperatively
• Regional anesthesia preferred (reduces perioperative stress)
• Avoid blood stasis, hypothermia, oxidant drugs in G6PD deficiency
• In G6PD: avoid methylene blue, primaquine, nitrofurantoin, dapsone

Postoperative Care

• Continue oxygen supplementation (SpO2 monitoring)
• Adequate analgesia (reduces O2 consumption from pain response)
• Vigilance for postpartum hemorrhage (reduced uterine contractility in severe anemia)
• Continue oral/IV iron supplementation
• Monitor Hb at 24 hours post-delivery
• Delayed cord clamping at delivery to maximize neonatal iron transfer

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11. QUICK VIVA SUMMARY TABLE

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