Flashcards in Maternal Physiology (Pregnancy) Deck (54)
What is the purpose of maternal cardiovascular changes occurring with pregnancy?
Improve foetal oxygenation and nutrition
What are the CV anatomic changes of pregnancy?
-heart displaced upward and to left
-heart assumes more horizontal position (apex moved laterally)
-ventricular muscles mass increase (due to inc in circulating blood volume)
Occur due to diaphragmatic elevation by enlarging uterus
What is the primary functional change of CV system with pregnancy?
Increase in CO
How much does CO increase with pregnancy?
50% of increase in first 8 weeks
what is the mechanism of increased CO during pregnancy?
-First half: due to inc SV
-Second half: inc HR (SV returns normal)
What causes the alterations in stroke volume?
Alterations in circulating blood volume and systemic vascular resistance
When is the peak increase in blood volume during pregnancy?
Peak of 45% increase at 32 weeks
Why does systemic vascular resistance decrease?
-1. Progesterone relaxing SM
-2. Inc production of vasodilators (PGs, NO, ANP)
-3. Arteriovenous shunting to uteroplacental circulation
What may cause a decrease in CO during pregnancy?
Venous return to heart being impeded by venal caval obstruction by enlarging gravid uterus
What is the path of venous return from lower extremities in the setting of complete vena caval obstruction in term pregnancy?
Dilated paravertebral collateral circulation
How does maternal HR change in pregnancy?
Increases as pregnancy progress.
Increases 10-18bpm over non pregnant value by term
What happens to dBP with pregnancy?
Decreases begin in 7th week; maximal decrease of 10mmHg by 24-32 weeks
What is inferior vena cava syndrome?
10% women have symptoms of:
when lying supine. May be due to insufficient shunting by paravertebral circulation when gravid uterus occludes IVC
What are the normal CV PEx findings during pregnancy?
-Increased S2 split with inspiration
-Distended neck veins
-Low grade systolic ejection murmur (? due to increased flow across aortic and pul valves)
-Many have S3 gallop
What is the primary mediator of the respiratory changes occurring with pregnancy?
How does oxygen consumption change with pregnancy?
20% increase (50mL/min)
How is the increased oxygen consumption utilised within the pregnant body?
Ff the increase:
-50% used by uterus and contents
-30% heart and kidneys
-18% respiratory muscles
-remainder to mammary tissues
What is the primary respiratory parameter changed with pregnancy?
30-40% increase in minute ventilation
What are the results of the increased minute ventilation?
Changes in acid-base
-progesterone sensitises central chemoreceptors to CO2 -> increased respiration and decreased arterial PCO2
-respiratory alkalosis compensated by renal excretion of bicarbonate
What causes the dyspnoea of pregnancy?
Physiologic response to low arterial PCO2
URT changes pregnancy
-allergy like symptoms or chronic colds
-mucosal hyperemia producing nasal stuffiness and increased nasal secretions
What do ABGs in pregnancy usually show?
Compensated respiratory alkalosis
What are the haematologic changes of pregnancy?
-increase in plasma volume
-increase in red cell volume
-increase in coagulation factors
When does maternal plasma volume peak?
30-34 weeks then stabilises
What is the mean plasma volume increase?
-Greater if multiple
What is the maternal blood volume increase with pregnancy?
35% by term
What is the total additional iron requirement during pregnancy?
-500mg to increase red cell mass
-300mg to foetus
-200mg to compensate for iron loss
What is the recommended daily iron need in a pregnant woman who is not anemic?
How do WBCs change during pregnancy?
-Mild increase throughout
-More pronounced increase in labour: primarily increased granulocytes linked with stress induced demargination (cf disease associated inflammatory response)