Cardiovascular Changes of Pregnancy
Explain the physiological changes during pregnancy, and parturition
Physiological consequences of changes in posture during pregnancy
Pregnancy is a time of increased metabolic demand, which cardiovascular changes reflect. These changes include:
- Increased intravascular volume Occurs via two mechanisms:
- Increased venous return Due to increased intravascular volume and MSFP.
- Increased VR causes an increase in CO (with both an increase in HR and SV, as well a decrease in SVR)
- Decreased SVR results in SBP, DBP and MAP dropping (despite the increase in CO)
Magnitude of Changes by Trimester
|Parameter||Direction||First Trimester||Second Trimester||Third Trimester||Notes|
|Plasma volume||↑||35%||45%||50%||Peaks between 32-36th week, decreases slightly thereafter|
|Blood volume||↑||5%||15%||20%||Increases less than plasma volume, resulting in the fall in haematocrit to 33%|
|HR||↑||15%||18%||25%||Increases progressively throughout|
|SV||↑||20%||25%||30%||Increases progressively throughout|
|CO||↑||20%||40%||45%||Increases throughout and dramatically in labour|
Changes During Labour
- Uterine contraction boluses ~300ml of blood into the maternal circulation
Causes an increase in CO by up to 30% during the active phase and 45% during ejection.
- Post-partum CO is up to 80% of pre-labour values due to autotransfusion, and returns to normal within 2 weeks of delivery
- Kam P, Power I. Principles of Physiology for the Anaesthetist. 3rd Ed. Hodder Education. 2012.