Maternal Physiology pt2 Flashcards
What cardiovascular changes occur during the first stage of labor?
- CO increases before & during contractions
- HR increases (to meet metabolic demands)
- Autotransfusion of 300-500mls from uterus to general circulation w/ each contraction.
What cardiovascular changes occur during the second stage of labor?
CO increases further by 50% due to:
- Pushing effort
- ↑ SV (dramatic increase)
- ↑HR
How does CO change immediately after delivery? What is responsible for these changes? When does CO return to normal post-delivery?
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
What happens to the airway in obstetric patients?
Airway vascular engorgement
- edema and friable tissue
- difficult airway
- prone to nose bleeds/rhinitis
What are the anesthetic implications of edematous airways?
- 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)
How does the hormone estrogen affect the obstetric patient’s pulmonary system?
Estrogen will ↑ number and sensitivity of progesterone receptors in the respiratory center of the brain.
How does the hormone Progesterone affect the obstetric patient’s pulmonary system?
- ↑ respiratory center sensitivity to CO₂
- Bronchodilates
- Causes hyperemia (excess blood) and edema of respiratory passages
How does the hormone Relaxin affect the obstetric patient’s pulmonary system?
Causes ligamentous attachments to lower ribs to relax. (ribs widen)
- subcostal angle increases
- widened AP & transverse diameter of chest wall (barrel chest)
Is Total Lung Capacity reduced or preserved during pregnancy?
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
What is FRC?
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
What is ERV?
Expiratory Reserve Volume
- Volume of air that can be expired with maximum effort at the end of normal expiration.
What is RV?
Residual Volume
- Volume of air in the lungs after ERV is expired
cannot be directly measured
RV = FRC - ERV
Uterine elevation of the diaphragm results in a _____% decrease in FRC.
20% ↓ in FRC (Both ERV and RV are decreased).
What causes the earlier closure of small airways in the obstetric patient?
Elevated Diaphragm → negative pleural pressure increases → earlier closure of small airways
(decreased FRC, ERV and RV)
What position results in a more profound decrease in FRC?
Supine position results in FRC decrease of 30%
- diaphragm further elevated
- increased alveolar atelectasis
- Closing capacity may exceed FRC
What happens if closing capacity exceeds FRC?
Small airway closure & V/Q mismatch leading to
O₂ desaturation.
small airway closure even before normal exhalation
What respiratory volumes are increased during pregnancy?
- VT ( increased metabolic CO₂ production and increased respiratory drive r/t progesterone)
- IC (Inspiratory Capacity)
IC= IRV + Vt
What respiratory volumes are unchanged by pregnancy?
- TLC (all lung volumes): d/t rib expansion/wider chest wall (relaxin)
- VC (IRV + VT + ERV)
total volume that can exhaled forcefully after a max inhalation
What are the goals for pre-oxygenation?
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
What FeO₂ (fraction of expired O₂) is ideal for preoxygenation?
0.9 or greater is ideal
What positioning is helpful for preoxygenation?
20° Reverse Trendelenburg (head up)
How much does O₂ consumption increase by at term?
20%
- increased metabolism/metabolic needs of fetus, uterus, placenta
- increased work of breathing
- increased cardiac workload.
How do minute ventilation and alveolar ventilation change in pregnancy?
Both Vm, Vt and alveolar ventilation increase.
RR increases by 1-2 breaths per minute, mediated by hormonal changes.
How do ABG’s change during pregnancy?
What does this result in?
As a result of Increased Ventilation:
- PaCO₂ decreases by ~8-10 mmHg
- PaO₂ increases by ~5 mmHg
Respiratory Alkalosis is normal in healthy pregnancies.
Compare and contrast a typical ABG vs an obstetric ABG.
What pulmonary change occurs during the first stage of labor?
Minute ventilation increases by up to 140%.
What pulmonary change(s) occurs during the second stage of labor?
- VM 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.
What hematologic changes occur during pregnancy?
- 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%
What Hgb range do we like for maternal patients?
11 - 13 g/dL
- Less than 11 is abnormal
- > 13 due to hemoconcentration.
High risk for pre-eclampsia
↑ Hgb can indicate pathology
What changes occur with platelets during normal pregnancy?
- Normal 165 - 415
- No change to moderate decrease seen with pregnancy.
Why do we care about platelets in obstetric patients?
- Risk for epidural hematoma from neuraxial techniques.
(parameters may be different from provider to provider and at different facilities)
Pregnancy produces a hypercoagulable or hypocoagulable state?
Hypercoagulable, to protect against blood loss
most coagulation factors increase (except 2, 5, 11, and 13)
What coagulation factors increase due to pregnancy?
All of them, except II, V, XI, and XIII.
What coagulation factor has the most significant increase during pregnancy?
Factor 1 (Fibrinogen)
What is hyperfibrinogenemia? What are the pros and cons of this?
Fibrinogen (Factor I) > 400mg/dL at term
- Increased clotting efficiency
- Impaired fibrinolysis
Protects against hemorrhage, but risk of blood clot increases
What factors are increased at term gestation?
Will be on test
- 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
What factors are unchanged at term gestation?
Will be on test
- II (Prothrombin)
- V (Proaccelerin)
What factors are decreased at term gestation?
Will be on test
- XI (Thromboplastin antecedent)
- XIII (Fibrin-stabilizing factor)
- PT & PTT ↓ by 20%
- Fibrinolytic activity decreases in 3rd trimester
What occurs with WBC’s during pregnancy?
- Increase steadily to 9,000 - 11,000/mm3 throughout pregnancy
- Spike up to 34,000/mm3 during labor
How does immune function change during pregnancy?
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
What are two specific methods of preoxygenation?
- 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
What are the overall ventilatory changes seen in pregnant patients?
- increased respiratory drive
- increased O2 consumption
- decreased PaCO2
- Larger pulmonary blood volume
- anemia
- nasal congestion
