Physiologic Changes of Pregnancy

1. Physiologic Changes of Pregnancy Pouneh Taghizadeh, MD Boston University Resident Department of Anesthesiology

3. Respiratory System • Upper airways • Minute Ventilation • Lung Volumes • Oxygen consumption

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

5. Minute Ventilation MV = RR x TV • Increased circulatory progesterone • Direct ventilation stimulant • Increases central response to CO2 • Increases TV in pregnancy to dispose CO2

6. Lung Volumes

7. Lung Volumes

8. Oxygen Consumption • Increased by 20% • Anesthetic Implications -Importance of pre-oxygenation

9. Cardiovascular System • Intravascular Fluid Volume • Cardiac Output • Peripheral Circulation

10. Intravascular Fluid Volume

11. Intravascular Fluid Volume • Increase to 1500ml by term • 45% increase in plasma volume • 20% increase in erythrocyte volume • Anemia • Effects on blood pressure

12. 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

13. Cardiac Output

14. Peripheral Circulation • Systemic circulation • Pulmonary circulation • Systemic vascular resistance • Effects on central venous pressure

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

16. Gastrointestinal System • Morning Sickness • Weeks 4-6 of pregnancy • Causes: • Relaxation of smooth muscle in stomach • Increased hCG • Anxiety

17. 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

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

19. Hepatic System • Decrease in albumin:globulin ratio • Increase in free fraction of albumin bound medications • Decreased plasma cholinestrase levels • Anesthetic implications

20. Hepatic System • Lactate dehydrogenase, bilirubin, ALT/AST, alkaline phosphatase • Gallbladder emptying • Concentration of bile

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

22. Central Nervous System • Volume of epidural space • CSF volume/CSF pH • Anesthetic Implications