Physiological Changes During Pregnancy

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1. Neurological

• MAC falls 40% at term - far less anesthetic needed
• Enhanced sensitivity to local anesthetics (epidural veins engorged, volume of epidural space reduced)
• Progesterone (up to 20x normal) is responsible; returns to normal by day 3 postpartum

2. Respiratory

• Minute ventilation +50% (progesterone stimulates respiratory centers)
• FRC -20% (diaphragm pushed up) + O₂ consumption +50% = rapid desaturation during apnea
• PaCO₂ drops to ~32 mmHg (compensated by HCO₃⁻ dropping to ~20 mEq/L) - pH ~7.44
• A "normal" PaCO₂ of 40 mmHg in pregnancy signals impending respiratory failure

3. Cardiovascular

• Cardiac output rises by 8-10 weeks, peaks late 2nd trimester (+40%)
• BP nadir at 24-28 weeks; rises back to near baseline at term
• Aortocaval compression after 18-20 weeks in supine position reduces venous return up to 40% - always use left uterine displacement
• During labor, CO rises another 10-45% via uterine autotransfusion

4. Hematological

• Plasma volume +55% >> RBC expansion = physiological dilutional anemia (Hgb ~10-11 g/dL is normal)
• Hypercoagulable state: clotting factors up +30-250%, protein C/S decrease = VTE risk 4-5x higher
• Virchow's triad is complete in pregnancy

5. Renal

• GFR +50% from 1st trimester; kidneys enlarge ~1 cm
• "Normal" creatinine of 1.0 mg/dL in pregnancy = impaired kidneys (normal = 0.5-0.8 mg/dL)
• Glucosuria can be physiological (tubular reabsorption doesn't scale with GFR)

6. Gastrointestinal

• Delayed gastric emptying + reduced LES tone + elevated intragastric pressure = aspiration risk
• All patients >12-16 weeks are "full stomach" for anesthesia purposes - RSI is mandatory
• Gallstones 2x more common (progesterone slows gallbladder emptying)

7. Endocrine/Hormonal

• Progesterone (up to 20x): bronchodilation, reduced GI motility, vasodilation, sedation
• hPL acts as insulin antagonist - gestational DM in ~7-10%
• Cortisol 3x normal; aldosterone 10x normal (fluid retention)

8. Musculoskeletal

• Uterine blood flow 50 ml/min → 700 ml/min at term
• Relaxin loosens pelvic ligaments
• Total body water increases 6-8 L; weight gain 11-16 kg average

Top 8 High-Yield Clinical Pearls

1. Pre-oxygenate before any GA induction - safe apnea time is very short
2. Left lateral tilt 15° - always, to prevent IVC compression
3. RSI mandatory for all GA in pregnancy >12-16 weeks
4. Hgb 10-11 is normal - do not over-transfuse
5. PaCO₂ 40 = failure in pregnancy (normal is 32 mmHg)
6. Creatinine 1.0 = investigate in pregnancy (normal is 0.5-0.8)
7. VTE prophylaxis in all high-risk obstetric patients
8. -40% MAC - reduce volatile anesthetic dose accordingly

Physiological Changes Pregnancy v2

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• Horizontal bar chart showing all key % changes (green = increase, red = decrease) for every parameter at a glance
• Full body system map with annotated callout boxes pointing to CNS, heart, lungs, kidneys, uterus, GI - with arrows connecting each organ to its changes

• Cause-and-effect flowchart: Triggers → Mechanisms → Effects → Cardiac Output
• Proportional circle diagram showing blood volume/plasma/RBC/CO/GFR expansion (bigger circle = bigger change)
• Supine hypotension step-by-step flowchart (6 boxes with arrows): supine → IVC compression → ↓venous return → ↓CO → hypotension → FIX: left tilt

• Mechanism flow (progesterone → medullary stimulation → TV ↑ → MV ↑ → PaCO₂ ↓)
• Danger chain (uterus pushes diaphragm → FRC ↓ + O₂ demand ↑ → rapid desaturation → pre-O₂ mandatory)
• Aspiration risk flowchart: Progesterone → LES tone ↓ → delayed emptying → ↑intragastric pressure → full stomach → RSI mandatory

• Virchow's triad triangle diagram with VTE at center (hypercoagulability + venous stasis + endothelial injury nodes)
• Hematological changes table with color-coded values

• Hormonal effect tree: 5 hormones (progesterone, estrogen, hPL, cortisol, aldosterone) each branching into their downstream effects
• Renal and GI tables

• Full pregnancy timeline (0-40 weeks) with labeled events above and below the line, trimester color bands
• 8 high-yield clinical pearls in a 2-column color-coded grid