Rose: Respiratory Adjustments At Birth

Front 1

Fetal gas exchange: location

Back 1

Placenta is the organ of gas exchange for fetus
Must match maternal perfusion of the placenta with fetal perfusion of the placenta to achieve gas exchange.
-Via uterine arteries and umblilical blood
-Prolonged uterine contractions changes rate of maternal blood flow to circuit. Can see compensatory changes in fetal heart rate
Exchange of O2 and CO2 between mother and fetus by diffusion

Front 2

Fetal gas exchange: anatomy

Back 2

Hemochorial placenta

Placental villi
-Trophoblastic tissue with fetal umbilical artery and vein contained inside
-Separate placenta into compartments of maternal blood lakes

Spiral arteries
-On maternal side
-Penetrate smooth muscle and enter into endometrial surface
-Fill compartments with blood

Front 3

Fetal hemoglobin and cardiac output

Back 3

Fetal hemoglobin (HbF)
-Low p50 (higher affinity for oxygen than adult hemoglobin)
-Can be more fully saturated with O2 at lower pO2

Cardiac output
-4x the relative cardiac output of an adult

Front 4

Fetal circulation

Back 4

Parallel circuit

Ductus arteriosus
-Comes off of main pulmonary artery prior to branching
-Goes directly to aorta, bypassing lungs

Foramen ovale
-Blood passes from right atrium to left atrium
-Then out left ventricle through aorta

Umbilical vein
-Highest oxygenated blood
-Goes through ductus venosus allowing blood to bypass liver into IVC
-Then blood streams through right atrium and into left atrium (via foramen ovale)

Pulmonary vasculature
-Low flow, high pressure, high resistance
-Most blood going out pulmonary artery uses ductus arteriosus and very little goes to lung

Front 5

Labor, delivery, and first breath

Back 5

Labor and delivery
-Promote initiation of respiratory activity
-Separation from placenta removes inhibitors of respiratory activity

First breath
-Catecholamines and thyroid hormones stimulated during delivery promote clearance of fluid from alveoli
-Alveoli inflate during initial respiratory effort
-Results in rapid reduction in pulmonary vascular resistance
-Allows blood to enter pulmonary vaculature
-Increased pulmonary venous return increases left atrial pressure
-Closes foramen ovale
-pO2 increases rapidly which stimulates contraction of smooth muscle in ductus arteriosus
-Placenta produces prostaglandins which keep ductus arteriosus open. When it is removed, ductus arteriosus begins to close
-Ductus arteriosus begins to close due to increased smooth muscle contraction and lack of placental prostaglandins

Front 6

How to fix problems with shunt closure

Back 6

Problems with closure of ductus arteriosus
-First try blocking with prostaglandin synthesis inhibitors
-Then surgery

Problems with closure of foramen ovale
-Transcutaneous approach
-Surgical