Physiologic Changes of Pregnancy

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Physiologic Changes of Pregnancy

• Pouneh Taghizadeh, MD
• Boston University
• Resident
• Department of Anesthesiology

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Respiratory System

• Upper airways
• Minute Ventilation
• Lung Volumes
• Oxygen consumption

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Upper Airways

• Capillary engorgement of the mucosal lining of
  the respiratory tract
• - Nasopharynx
• - Larynx
• - Trachea
• - Bronchi
• Anesthetic Implications

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Minute Ventilation

• MV RR x TV
• Increased circulatory progesterone
• Direct ventilation stimulant
• Increases central response to CO2
• Increases TV in pregnancy to dispose CO2

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Lung Volumes
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Lung Volumes
TV TLC IRV ERV FRC RV VC IC

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Oxygen Consumption

• Increased by 20
• Anesthetic Implications
• -Importance of pre-oxygenation

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Cardiovascular System

• Intravascular Fluid Volume
• Cardiac Output
• Peripheral Circulation

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Intravascular Fluid Volume
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Intravascular Fluid Volume

• Increase to 1500ml by term
• 45 increase in plasma volume
• 20 increase in erythrocyte volume
• Anemia
• Effects on blood pressure

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Cardiac Output CO SV x HR

• Increased to over 40 above pre-pregnancy levels
  when standing
• 30 increase in SV
• 10 increase in HR
• Note CO is decreased in supine position after
  28 to 32 weeks gestation

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Cardiac Output
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Peripheral Circulation

• Systemic circulation
• Pulmonary circulation
• Systemic vascular resistance
• Effects on central venous pressure

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Gastrointestinal System

• Increased progesterone
• Relaxation of lower esophageal sphincter
• Decreased gastric pH
• Enlarging uterus
• Delayed gastric emptying during labor
• Anesthetic Implications

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Gastrointestinal System

• Morning Sickness
• Weeks 4-6 of pregnancy
• Causes
• Relaxation of smooth muscle in stomach
• Increased hCG
• Anxiety

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Renal System

• Increase in progesterone after 3rd Trimester
• Dilation of renal calices, pelvices, ureters
• Enlarged uterus
• Compression of ureter at pelvic brim
• Urinary stasis
• Increased incidence of UTIs

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Renal System

• GFR
• Renal plasma flow
• Creatinine clearance
• Serum creatinine
• Blood urea nitrogen
• Renin/Angiotensin levels

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Hepatic System

• Decrease in albuminglobulin ratio
• Increase in free fraction of albumin bound
  medications
• Decreased plasma cholinestrase levels
• Anesthetic implications

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Hepatic System

• Lactate dehydrogenase, bilirubin, ALT/AST,
  alkaline phosphatase
• Gallbladder emptying
• Concentration of bile

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Hematologic System

• Increased estrogen
• Increase in clotting factors
• VII, VII, X, XII, and fibrinogen
• Decrease in Antithrombin III
• Hypercoagulable state
• DVTs

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Central Nervous System

• Volume of epidural space
• CSF volume/CSF pH
• Anesthetic Implications

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