• Hematologic Alterations
  • Increased total blood volume (25%–40%)
  • Increased plasma volume (40%–50%): Resultant relative anemia of pregnancy plateau at 32–34 weeks of gestation
  • Increased fibrinogen
  • Decreased anticoagulant activity and impaired fibrinolysis: Pregnancy is a state of chronic compensated disseminated intravascular coagulation
  • Decreased platelet count (dilution and increased consumption)
  • Decreased cholinesterase activity (20%–30%)
• Cardiovascular Changes
  • Increased cardiac output (30%–50%)
  • Aortocaval compression (supine hypotensive syndrome occurs in about 50% of parturients)
• Ventilation Changes
  • Increased minute ventilation (50%)
  • Increased alveolar ventilation (70%)
  • Decreased functional residual capacity (20%)
  • Increased oxygen consumption (20%)
  • Decreased PaCO₂ (10 mm Hg)
  • Increased PaO₂ (10 mm Hg)
  • Airway edema
• Gastrointestinal Changes
  • Delayed gastric emptying: Increased risk for aspiration
  • Decreased lower esophageal sphincter tone (heartburn)
• Altered Drug Responses
  • Decreased requirements (32%–40%) for inhaled anesthetics (MAC) by 8–12 weeks (parallels increased progesterone levels)
  • Decreased local anesthetic requirements (engorgement of veins, resulting in decreased volume of the epidural and subarachnoid space versus progesterone-induced increased sensitivity of nerves to local anesthetics)

MAC = minimum alveolar concentration.