Maternal Physiology pt2

Question 1

What cardiovascular changes occur during the first stage of labor?

Answer 1

• CO increases before & during contractions
• HR increases (to meet metabolic demands)
• Autotransfusion of 300-500mls from uterus to general circulation w/ each contraction.

Question 2

What cardiovascular changes occur during the second stage of labor?

Answer 2

CO increases further by 50% due to:

• Pushing effort
• ↑ SV (dramatic increase)
• ↑HR

Question 3

How does CO change immediately after delivery? What is responsible for these changes? When does CO return to normal post-delivery?

Answer 3

CO: ↑60-80%

• Relief of pressure on vena cava
• uterine contractions continue/releasing blood into systemic circulation
• begins to decline 10 mins after delivery
• returns to normal 24 hours postpartum

Question 4

What happens to the airway in obstetric patients?

Answer 4

Airway vascular engorgement

• edema and friable tissue
• difficult airway
• prone to nose bleeds/rhinitis

Question 5

What are the anesthetic implications of edematous airways?

Answer 5

• Smaller ETT necessary (6.5 or 6.0)
• Avoid NGT/Nasal trumpets (bloody nose)
• Airway obstruction risk increases
• Mallampati class may progressively worsen (even during labor)

Question 6

How does the hormone estrogen affect the obstetric patient’s pulmonary system?

Answer 6

Estrogen will ↑ number and sensitivity of progesterone receptors in the respiratory center of the brain.

Question 7

How does the hormone Progesterone affect the obstetric patient’s pulmonary system?

Answer 7

• ↑ respiratory center sensitivity to CO₂
• Bronchodilates
• Causes hyperemia (excess blood) and edema of respiratory passages

Question 8

How does the hormone Relaxin affect the obstetric patient’s pulmonary system?

Answer 8

Causes ligamentous attachments to lower ribs to relax. (ribs widen)

• subcostal angle increases
• widened AP & transverse diameter of chest wall (barrel chest)

Question 9

Is Total Lung Capacity reduced or preserved during pregnancy?

Answer 9

Preserved.
Chest height is shortened but A-P dimension increases with barrel shape due to relaxin.

chest wall widening helps compensate for decreased lung expansion secondary to decreased abdominal space

Question 10

What is FRC?

Answer 10

Functional Residual Capacity

• Volume of air that prevents complete emptying of lungs and keeps small airways open.
  amount of air in lungs after expiration
  FRC= RV + ERV
  3L = 1.5 L + 1.5L

Question 11

What is ERV?

Answer 11

Expiratory Reserve Volume

• Volume of air that can be expired with maximum effort at the end of normal expiration.

Question 12

What is RV?

Answer 12

Residual Volume

• Volume of air in the lungs after ERV is expired
  cannot be directly measured
  RV = FRC - ERV

Question 13

Uterine elevation of the diaphragm results in a _____% decrease in FRC.

Answer 13

20% ↓ in FRC (Both ERV and RV are decreased).

Question 14

What causes the earlier closure of small airways in the obstetric patient?

Answer 14

Elevated Diaphragm → negative pleural pressure increases → earlier closure of small airways
(decreased FRC, ERV and RV)

Question 15

What position results in a more profound decrease in FRC?

Answer 15

Supine position results in FRC decrease of 30%

• diaphragm further elevated
• increased alveolar atelectasis
• Closing capacity may exceed FRC

Question 16

What happens if closing capacity exceeds FRC?

Answer 16

Small airway closure & V/Q mismatch leading to
O₂ desaturation.

small airway closure even before normal exhalation

Question 17

What respiratory volumes are increased during pregnancy?

Answer 17

• V_T ( increased metabolic CO₂ production and increased respiratory drive r/t progesterone)
• IC (Inspiratory Capacity)
  IC= IRV + Vt

Question 18

What respiratory volumes are unchanged by pregnancy?

Answer 18

• TLC (all lung volumes): d/t rib expansion/wider chest wall (relaxin)
• VC (IRV + V_T + ERV)
  total volume that can exhaled forcefully after a max inhalation

Question 19

What are the goals for pre-oxygenation?

Answer 19

Goals:

• bring O2 sat as close to 100% as possible
• denitrogenate the residual lung capacity
• maximize O2 storage of lungs
• denitrogenate and oxygenate bloodstream to max level

Question 20

What FeO₂ (fraction of expired O₂) is ideal for preoxygenation?

Answer 20

0.9 or greater is ideal

Question 21

What positioning is helpful for preoxygenation?

Answer 21

20° Reverse Trendelenburg (head up)

Question 22

How much does O₂ consumption increase by at term?

Answer 22

20%

• increased metabolism/metabolic needs of fetus, uterus, placenta
• increased work of breathing
• increased cardiac workload.

Question 23

How do minute ventilation and alveolar ventilation change in pregnancy?

Answer 23

Both Vm, Vt and alveolar ventilation increase.

RR increases by 1-2 breaths per minute, mediated by hormonal changes.

Question 24

How do ABG’s change during pregnancy?
What does this result in?

Answer 24

As a result of Increased Ventilation:

• PaCO₂ decreases by ~8-10 mmHg
• PaO₂ increases by ~5 mmHg

Respiratory Alkalosis is normal in healthy pregnancies.

Question 25

Compare and contrast a typical ABG vs an obstetric ABG.

Answer 25

Question 26

What pulmonary change occurs during the first stage of labor?

Answer 26

Minute ventilation increases by up to 140%.

Question 27

What pulmonary change(s) occurs during the second stage of labor?

Answer 27

- V_M goes up by 200% - Maternal CO₂ decreases by 10 - 15 mmHg (↑Vm) - O₂ consumption increases - aerobic requirements increase - Maternal lactate increases *Supplemental O₂ might be necessary*.

Question 28

What hematologic changes occur during pregnancy?

Answer 28

- Plasma volume increases more than RBC mass resulting in dilutional anemia. - Hgb drops by ~2.4 g/dL (from pre-pregnancy-36 wks) - HCT decreases by ~6.5%

Question 29

What Hgb range do we like for maternal patients?

Answer 29

11 - 13 g/dL - Less than 11 is abnormal - > 13 due to hemoconcentration. **High risk for pre-eclampsia** *↑ Hgb can indicate pathology*

Question 30

What changes occur with platelets during normal pregnancy?

Answer 30

- Normal 165 - 415 - No change to moderate decrease seen with pregnancy.

Question 31

Why do we care about platelets in obstetric patients?

Answer 31

* Risk for epidural hematoma from neuraxial techniques. *(parameters may be different from provider to provider and at different facilities)*

Question 32

Pregnancy produces a hypercoagulable or hypocoagulable state?

Answer 32

Hypercoagulable, to protect against blood loss *most coagulation factors increase (except 2, 5, 11, and 13)*

Question 33

What coagulation factors increase due to pregnancy?

Answer 33

All of them, **except II, V, XI, and XIII**.

Question 34

What coagulation factor has the most significant increase during pregnancy?

Answer 34

Factor 1 (Fibrinogen)

Question 35

What is hyperfibrinogenemia? What are the pros and cons of this?

Answer 35

Fibrinogen (Factor I) > 400mg/dL at term - Increased clotting efficiency - Impaired fibrinolysis **Protects against hemorrhage, but risk of blood clot increases**

Question 36

**What factors are increased at term gestation**? *Will be on test*

Answer 36

- I (Fibrinogen) - VII (proconvertin) - VIII (Antihemophilic factor) - IX (Christmas factor) - X (Stuart-Prower factor) - XII (Hageman factor) *essentially all except 2, 5, 11, and 13*

Question 37

What factors are **unchanged** at term gestation? *Will be on test*

Answer 37

- II (Prothrombin) - V (Proaccelerin)

Question 38

What factors are **decreased** at term gestation? *Will be on test*

Answer 38

- XI (Thromboplastin antecedent) - XIII (Fibrin-stabilizing factor) - PT & PTT ↓ by 20% - Fibrinolytic activity decreases in 3rd trimester

Question 39

What occurs with WBC's during pregnancy?

Answer 39

- Increase steadily to 9,000 - 11,000/mm3 throughout pregnancy - Spike up to 34,000/mm3 during labor

Question 40

How does immune function change during pregnancy?

Answer 40

Polymorphonuclear Leukocyte function is impaired * increases risk & severity of infection * autoimmune dz symptom may improve during this time Antibody titers to certain diseases can decrease * Measles, influenza A, and Herpes simplex .

Question 41

What are two specific methods of preoxygenation?

Answer 41

* 3-5 vital capacity breaths (max inhalation) with tight mask seal delivering 100% O2 * 8 deep breaths at 10L/min O2 flow within a 60 second time period

Question 42

What are the overall ventilatory changes seen in pregnant patients?

Answer 42

* increased respiratory drive * increased O2 consumption * decreased PaCO2 * Larger pulmonary blood volume * anemia * nasal congestion