Fetal And Neonatal Circulaation Flashcards
What are the cardiovascular changes in pregnancy?
- Cardiac output is increased
- Systemic vascular resistance (decreased)
- Blood volume & RBC mass is increased
- Blood pressure is decreased
Satisfy the increased metabolic demands of mother and fetus
Ensure adequate uteroplacental circulation for fetal growth and development
Insufficient—> maternal & fetal morbidiity
How are cardiac output, stroke volume and heart rate affected in labor and delivery?
CO is about 70%
-increased stroke volume
- heart rate due to pain and anxiety
- increased stroke volume (SV) due to increased preload-due to venous return. (Autotransfusion of 300-500 ml of blood from uterus into systemic circulation immediately after each contraction)
Postpartum (after delivery )-
Temporary increase venous return (VR) —> increase SV and CO
Mean blood pressure & SV normal 24 hrs after delivery
What are the 4 shunts of fetal circulation?
- Umbilical/placenta
- Ductus venosus
- Foramen ovale
- Ductus arteriosus
Describe neonatal hypoxia
Hypoxia results in:
- Pulmonary vascular resistance & pressure remains high
- Ductus Arteriosus remains patent (open)
-Thus patent Ductus Arteriosus maintains a right to left shunt (or fetal circulation retained)
Describe the fetal cardiovascular response to acute hypoxia in early gestation
Early gestation-immature response to acute hypoxia. Tachycardia, no increase peripheral vascular resistance to maintain arterial blood pressure
Describe the fetal cardiovascular response to acute hypoxia in late gestation
Acute hypoxia-CV response to sustain perfusion and cardiac output (CO). Response is not all or none, but TITRATED to degree of hypoxia
Explain the symptoms of Acute hypoxemia
Vasoconstriction, hypertension, bradycardia
- decreased blood oxygen levels (hypoxemia)
- chemoreceptors reflex- constriction of blood vessels in non vital peripheral areas (kidney, GI, lower extremities)
- this diverts moire blood flow to vital organs (adrenal glands, heart, and brain)
The peripheral vasoconstriction results in:
- Increase blood pressure (hypertension). Maintain perfusion of vital organs.
- Hypertension results in baroreceptor mediated vagal response which slows the heart rate (bradycardia)
- Bradycardia- maintains cardiac output(increases EDV)
- Fetal late heart rate decelerations (measured by ECG or HR)
Explain 3 important changes from fetal to neonate
At birth,
1 . Clamping of the umbilical cord: sudden massive increase in systemic vascular resistance with removal of placental circulation. Left ventricle has to pump against this new resistance. This resultant increase in left atrial (LA) pressure leading to the closure of the Foramen ovale
- Entry of air into the lungs: fall in the pulmonary vascular resistance and the lungs become the principal oxygenator. Initial ventilatory movements, lungs expand —pulmonary vasc. Resistance & pulmonary artery pressure decrease Right ventricle per fuses lungs
- Increased oxygen concentration: vasoconstriction and closure of the ductus arteriosus (DA). This causes systemic and pulmonary circulation to run in parallel. Increased oxygen to peripheral tissues causes vasoconstriction n most body organs (tissues are less hypoxic)
Overall the circulation changes to adult type
Describe the active agent of Ductus Arteriosus closure fetal vs neonate
Active agent: PGE1 regulates ductus arteriosus (DA) muscle sphincter (note: PGE1-is a prostaglandin)
Fetus: high levels of PGE1–> relax smooth muscle ductus arteriosus. (PGE1 is generated in response to a relative hypoxia)
Neonate: PGE1 levels decline as PO2 rises and the ductus arteriosus muscular wall constricts
In premature and abnormal mature infants, the DA fails to constrict—> Patent Ductus Arteriosus (PDA)
Describe the path o physiology of patent ductus arteriosus
Persistent shunt between descending aorta and left pulmonary artery
Blood flow is from aorta to the pulmonary artery(pressure gradient)—> Pulmonary circulation, LA and LV become volume overloaded
—> LV dilatation and left sided heart failure
Children with large left to right-shunts: congestive cardiac failure, tachycardia
What are the features of PDA?
Murmur heard during systole and diastole- continuous murmur (machinery) murmur
What is the treatment of patent ductus arteriosus?
Surgical closure
Explain the symptoms of patent ductus arteriosus
Symptoms 2-3 days after birth
Continuous blood flow into the pulmonary circulation —> continuous murmur(machinery sounding)and early onset PAH
Left—> right blood shunting of blood results in
-excessive blood flow through pulmonary circulation (aorta to pulmonary artery)
-hypoperfusion “ductal seal” of the systemic circulation
Moderate to large shunts
-pulmonary edema, hemorrhage , bronchopulmonary dysplasia
What is the clinical significance of the Foramen ovale?
Birth: Pressure reversal causes flap over Foramen ovale to close
Persistent left—> right shunting, frequent in first few weeks of life, and premature infants
About 70-75% septa with holes 3-8 mm fuse @ 2 years
Patent Foramen ovale: failure to close
-defects 1-10 mm maximum diameter
Describe the clinical manifestation of patent Foramen ovale
- Most patients remain asymptomatic
- Clinical presentation is ischemic stroke due to a paradoxical embolism
- An increased prevalence of PFO in patients who have had a cardiogenic stroke, particularly in patients less than 55 years old
Cryptogenic stroke- a stroke in absence of identified cardioembolic or large vessel source and not consistent with small vessel disease.( Cryptogenic stroke accounts for approximately 20 to 40 percent of ischemia strokes)
