9/9/20 maternal physiology - malik

9/9/20 maternal physiology - malik

Transcript

1. Introduction to OB Maternal Physiology M. Faysal Malik, MD
3. OB Exam Category: Clinical Subspecialties (23% ) Topic: Obstetric Anesthesia min. of 7 questions, max 9 total Exam Overall: 4.5% of Qs
4. Learning Objectives Upon completion of this activity, participants should be able to: 1. Describe the basic alterations in cardiovascular physiology. 2. List most common changes in pulmonary physiology including a “normal” ABG in a parturient. 3. Describe changes to the gastrointestinal tract both during pregnancy and specific to labor.
5. Learning Objectives 4. List physiologic changes in hematologic and renal systems during pregnancy. 5. Describe anesthetic implications of physiologic changes in pregnancy.
6. Cardiovascular Changes in Pregnancy
7. Cardiovascular Changes Structural Heart Changes • Left Ventricular Hypertrophy • PMI shift to the left • LAD on EKG
8. Cardiovascular changes • Cardiac output (CO) increases as a result of both stroke volume and heart rate • By the end of the 2nd trimester CO is elevated 40-50% above prepregnancy levels, of that approximately 25% is due to stroke volume and 15% is due to heart rate • During labor CO increases further due to uterine contractions, increased venous return and increased sympathetic activity • Immediately after delivery, CO increases even more due to autotransfusion once the placenta is delivered – This is the time that patients with pre-existing cardiac conditions are at the most risk – CO returns to nearly normal by about 2 weeks postpartum
9. Cardiovascular changes Maintenance of BP • In order to maintain normal blood pressure in the face of increased cardiac output, the systemic vascular resistance decreases during pregnancy • Overall decrease in systolic and diastolic blood pressure are around 10-20% and is secondary to maternal vasodilation from elevated progesterone levels as well as the presence of the low-resistance uteroplacental bed • Blood pressure nadirs at the end of the second trimester and will be close to pre-pregnancy values closer to term.
10. Cardiovascular changes
11. Cardiovascular changes • Blood volume increases • At term blood volume is approximately 40-50% higher • Dilutional anemia of pregnancy • A normal Hb at term parturient is ~11 g/ dL. • Blood volume returns to pre- pregnancy state after a little over 6 weeks
12. Aortocaval Compression Supine Hypotension Syndrome of Pregnancy
13. Aortocaval Compression • Mechanism: – Compression of IVC by gravid uterus after 16-20 wks EGA • Causes decreased venous return, decreased preload and decreased cardiac output – Compression of the aorta • Increases afterload, can impair uterine blood flow • Symptoms: Maternal hypotension, lightheadedness, dizziness and decreased FHT may be seen • Recommend 15-30 degrees of left uterine displacement
14. Changes in Organ Perfusion • Generalized increase in all organ perfusion with increase in CO Specifically: – Kidneys: 60% increase in RBF – Uterus/Placenta: Blood flow increases nearly 10x Non-pregnant 50–100 mL/min vs Term = 700 – 900 mL/min [nearly 10% CO]
15. Anesthetic Considerations • Late manifestation of signs/symtpoms of large volume blood loss • Increased risk of bloody tap • Need for higher dose of vasopressors • Aggravation of supine hypotension
16. Pulmonary changes in Pregnancy
17. Anatomical Changes  Increased chest AP diameter and chest wall circumference  Increased diaphragmatic excursion  Dilation of large airways  Capillary engorgement
18. Lung Volumes & Capacities Increased: • Inspiratory Capacity • Tidal Volume Decreased: • Total Lung Capacity • FRC • Expiratory Reserve Vol • Residual Volume No Change: • Vital Capacity • Inspiratory Reserve Volume
19. Lung Volumes & Capacities
20. Ventilatory Changes • Increased Minute Ventilation – MV increases up to 45% at term – Due to increased RR and Vt – 1st stage and 2nd labor MV can be as high as 300% • Increased O2 consumption (20-40%) • During labor O2 consumption increases further • 45% increase in the 1st stage • 75% increase in the 2nd stage
21. Normal Pregnancy ABG • Changes in baseline ABG primarily due to increased MV – pH = 7.44 – PaCO2 = 30 – 32 mmHg – PaO2 = 100 – 104 mmHg – HCO3 - = 18 – 20
22. Anesthetic Considerations • Difficult Airway • Rapid desaturation
23. Gastrointestinal Changes in Pregnancy
24. Gastrointestinal Changes in Pregnancy • Anatomic changes: – Elevation in stomach position cephalad – Loss of lower esophageal sphincter tone secondary to position change and progesterone levels – Increased intragastric pressure
25. Gastrointestinal Changes in Pregnancy • Changes in gastric emptying – Pregnancy: no change per se – Labor: once labor starts gastric motility can be significantly delayed • Aspiration Risk – Consider all pregnant patients from 16-20 weeks GA as full stomachs – Therefore they are at increased risk for aspiration – They need aspiration prophylaxis with non-particulate antacids and require RSI
26. Renal Changes in Pregnancy
27. Renal Changes in Pregnancy • Renal blood flow during pregnancy increases • This leads to increased GFR with consequently increased creatinine clearance and decreased serum creatinine • Normal creatinine at term is 0.5 – 0.6 mg/ dL • “Abnormal” creatinine = > 1.0 mg/ dL • Kidneys may enlarge during pregnancy up to 30% • There is increased sodium retention due to increased renin and aldosterone.
28. Hematology Changes in Pregnancy • Pregnancy is a hypercoaguable state during which the majority of clotting factors increase • Elevated fibrinogen (Normal = 350 – 650 mg/ dL) • During pregnancy there is increased platelet turnover but overall the concentration remains for the most part unchanged. • Laboratory analysis in pregnant patients may reveal a mild decrease in PT/ INR and PTT, but this is not clinically significant.
29. Hematology Changes in Pregnancy