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Physiologic Adaptations at BirthMa. Luisa de Villa-Manlapaz, MD, MHPEdFebruary 8, 2011ASMPH

Learning ObjectivesTo review the fetal circulationTo learn the changes in the pulmonary and cardiovascular system that occur during birthTo learn the hepatic adaptations in glucose metabolism, bilirubin metabolism, and vitamin K productionTo learn how a newborn achieves thermoregulation

Fetal CirculationPlacenta is responsible for exchange of gases, nutrients and metabolic waste productsFetus receives blood from the placenta and returns it to the placentaFetal CirculationBlood flows from the placenta into the umbilical veinThe blood which contains a PO2 of approx 35 mmHg passes through the liver and ductus venosus

Fetal CirculationBlood from ductus venosus drains into the inferior vena cava foramen ovale left atrium

Blood entering the left atrium because of the streaming across the foramen ovale, has a higher PO2 that would be possible without the streaming effect.5Fetal CirculationSuperior vena cava drains de-oxygenated blood from the brain into the right atrium. right ventricle.90% of blood from RA shunted through the ductus arteriosus10% ejected to pulmonary artery lungs

The amount of blood entering the lungs is limited because of the high pulmonary vascular resistance present during the fetal life; also, the lungs are not needed for gas exchange until after birth.PO2 in RV is between 19 and 21 mmHg because of the mixing in the right atrium (blood from SVC and from IVC).6Fetal Lungs and Circulation

Alveoli filled with lung fluidPulmonary arterioles constrictedPulmonary blood flow diminished

1-7Click on the image to play video7Blood flow through the fetal lung is markedly diminished compared with that required after birth, as the pulmonary arterioles are constricted and blood flow is diverted across the ductus arteriosus.Neonatal Circulation

After birth, umbilical cord is cutSystemic vascular resistance increases (BP in aorta increases)Pulmonary vascular resistance decreases ((BP in lungs decreases)Lungs and CirculationAfter DeliveryLungs expand with airFetal lung fluid leaves alveoli

1-9Click on the image to play video9At birth, as the newborn takes the first few breaths, several changes occur, whereby the lungs take over the lifelong function of respiration.

Following birth, the lungs expand as they are filled with air. The fetal lung fluid gradually leaves the alveoli.

Lungs and CirculationPulmonary arterioles dilatePulmonary blood flow increases

1-1010At the same time as the lungs are expanding and the fetal lung fluid is clearing, the arterioles in the lungs begin to open, allowing a considerable increase in the amount of blood flowing through the lungs.

Lungs and CirculationBlood oxygen levels riseDuctus arteriosus constrictsBlood flows through lungs to pick up oxygen

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11As blood levels of oxygen rise, the ductus arteriosus begins to constrict.

Blood previously diverted through the ductus arteriosus flows through the lungs, where it picks up oxygen for transport to tissues throughout the body. The ductus remains constricted, and the normal extrauterine circulatory pattern is established.

Normal TransitionFluid in alveoli absorbed and replaced by airUmbilical arteries and vein constrict thus increasing blood pressureBlood vessels in lungs relax, increasing pulmonary blood flow

1-12The following major changes take place within seconds after birth:12Normally, there are 3 major changes that take place within seconds after birth.

Alveolar fluid is absorbed into lung tissue and replaced by air. Umbilical arteries and veins are clamped, removing the low resistance placental circuit and increasing systemic blood pressure. Blood vessels in lung tissue relax, increasing pulmonary blood flow.Baby cries and take first breath which help open alveoliSurfactant keeps the alveoli from collapsing after they expandMetabolic AdaptationIn utero, fetus relies primarily on placental transfer of glucose and nutrients from mother to meet energy demandsFetus has limited ability to convert glycogen into glucose and therefore relies primarily on placental transfer of glucose and amino acids to meet in utero demands

14Metabolic AdaptationFetus stores glucose in the form of glycogen in last trimester especially in last month of trimester

15After BirthEnzymes activate breakdown of glycogen back into glucose moleculesGlucose released into bloodstream to maintain blood sugar

Normal glucose utilization rate in fasting healthy term infant is 4-6 mg/kg/minWhen the cord is cut, the infant no longer gets glucose from the mother. The glucose from the glycogen stores then meets the energy needs after birth16Factors which influence glucose levelsGlycogen stores

Insulin levels

Glucose utilizationPremature baby

Infant of diabetic mother

Sick infantThermoregulationIn utero, the fetus is in a warm and dark environmentTemperature is controlled

At birth, newborn has to produce as much heat as much as is lostTHERMOREGULATION

Normal Response to Cold StressVasoconstriction in arms and legsIncreased movement and flexion of extremitiesBrown fat metabolism

Vasoconstriction in arms and legs blood stays in the core of body; prevents blood from reaching skin surface where heat loss occursInc movement and flexion of extremities- generates warmth in muscles; decreases surface area for heat loss20Brown Fat Metabolism

Heat lossOccurs on a gradient from warmer to cooler

Babys warm body to cooler air or surface

Heat loss accentuated by:Wet skinCool air temperatureDrafts

Cool air temperature delivery room, home delivery, emergency department

Drafts increase movement or velocity of air past infant22

Kangaroo mother careMother provides warmth to the baby by skin to skin contact.

Provides easy access to the breasts, promoting breastfeeding

Hepatic adaptationMinor role of fetal liver portal circulation shunted through the ductus venosus

Majority of bilirubin pigment transferred unaltered across the placenta to the maternal circulation

Fetus has a high percentage of circulating red blood cells to utilize all available oxygen in a low oxygen environment

PHYSIOLOGIC JAUDICE

Increased bilirubin load on liver cellIncreased erythrocyte volumeDecreased erythrocyte survivalIncreased enterohepatic circulation of bilirubin

Immature liver functionHepatic AdaptationLiver manufactures clotting factors needed for blood coagulation

Several factors need Vitamin K for their productionBacteria that produce Vitamin K are normally found in the gastrointestinal tractHowever, the gastrointestinal tract of the newborn is sterileTherefore newborn cannot manufacture vitamin K which is needed to produce some clotting factorsNewborns are given Vitamin K either intramuscularly or orally at birth to prevent bleeding disordersLearning ObjectivesTo review the fetal circulationTo learn the changes in the pulmonary and cardiovascular system that occur during birthTo learn the hepatic adaptations in glucose metabolism, bilirubin metabolism, and vitamin K productionTo learn how a newborn achieves thermoregulation

Brazeltons States of Reactivity1. Deep sleep: quiet, non-restless sleep state

2. Light sleep: eyes closed but more activity is noted; newborn moves actively; may show sucking behaviour

3. Drowsy: eyes open and close and eyelids look heavy; body activity is present with episodes of fussiness

4. Quiet alert: quiet state with little body movement, but the newborns eyes are open and she is attentive to people and things that are near her

5. Active alert: eyes are open and active body movements are present; newborn responds to stimuli actively6. Crying: eyes may be tightly closed, thrashing movements are made together with active crying Adapted from Howard-Glenn, 2000. p.36441