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Fetal Circulation and Newborn Transition to Life Melissah Burnett & Jacqui McGregor La Trobe University, Melbourne. www.latrobe.edu.au/nursing • Some cardiac abnormalities are considered “duct-dependent”; these can be cyanotic or acyanotic • Duct-dependent defects can be related to pulmonary flow (for example pulmonary stenosis or pulmonary atresia); or related to systemic flow (for example hyperplastic left heart or transposition of the greater arteries) • If there is a definite or suspected diagnosis of a cardiac abnormality, that is duct dependent, a prostaglandin infusion is the treatment of www.latrobe.edu.au/nursing choice (a synthetic version of the hormone that Objectives • To have an understanding of the anatomy and physiology of fetal circulation • To identify the 3 fetal shunts • To have an understanding of newborn transition and conversion of fetal to neonatal circulation • Identify impediments to this transition www.latrobe.edu.au/nursing Survival Tasks The newborn, must make five major adjustments at birth. • • • • • 1) World of air 2) Circulation 3) Wastes 4) Body temperature 5) Response to infection 4 www.latrobe.edu.au/nursing Adult Heart 5 www.latrobe.edu.au/nursing Review pulmonary & systemic circulations and anatomy of the heart. 6 www.latrobe.edu.au/nursing Anatomical Structures of Fetal Circulation Includes: • Placenta • Umbilical Vein (X1) • Ductus Venosus • Foramen Ovale • Ductus Arteriosus • Umbilical Arteries (X2) www.latrobe.edu.au/nursing Placental Transport • The main functions of the placenta include: – – – – Gas exchange Nutrients Disposal of waste products Hormones • Other things can cross placenta – maternal antibodies – drugs – infectious agents 8 www.latrobe.edu.au/nursing Placenta • Facilitates gas and nutrient exchange between maternal and fetal blood. • These substances diffuse between maternal and fetal blood through the placental membrane. • The blood itself does not mix. • The placenta is a low resistance component of the fetal circulation. www.latrobe.edu.au/nursing The Placenta 10 www.latrobe.edu.au/nursing Umbilical Circulation • An umbilical vein carries oxygenated blood and nutrients from the placenta to the fetus. • A pair of umbilical arteries carry deoxygenated blood & wastes from the fetus to placenta. www.latrobe.edu.au/nursing Umbilical Vein • Transports O2 rich blood & nutrients • Enters ductus venosus • 80% saturated with O2 12 www.latrobe.edu.au/nursing Ductus Venosus • Approximately 45% of blood from the umbilical vein enters the portal circulation allowing the liver to process nutrients. • Approximately 55% of the blood passes thru the Ductus Venosus, a shunt which bypasses the liver. • The ductus venosus travels a short distance and joins the Inferior Vena Cava. 13 www.latrobe.edu.au/nursing Umbilical Vein • Blood continues to travel up the Inferior Vena Cava • Empties into the Right Atrium of the heart • A large portion of the blood is shunted into the Left Atrium through the Foramen Ovale www.latrobe.edu.au/nursing Fetal Circulation Differences 15 www.latrobe.edu.au/nursing Placenta Umbilical Vein Liver Ductus Venosus Inferior Vena Cava Right Atrium 16 www.latrobe.edu.au/nursing Foramen Ovale • Blood is shunted directly into the left atrium through an opening called the foramen ovale. Foramen Ovale • R ►L shunt • There is a valve with two flaps that prevents backflow. 17 www.latrobe.edu.au/nursing Blood Flow thru Heart • Blood continues the journey to the Left Ventricle blood is then pumped into the Aorta • Blood is circulated to the upper extremities. • Blood then returns to the Right Atrium via the Superior Vena Cava www.latrobe.edu.au/nursing Right Atrium Foramen Ovale Left Atrium Left Ventricle Aorta 19 www.latrobe.edu.au/nursing Blood flow thru Heart • The remaining of the fetal blood in the Right Atrium, including a large proportion of the deoxygenated blood returning from the Superior Vena Cava passes into the Right Ventricle and out through the Pulmonary Trunk. • The blood continues along the Pulmonary Artery the majority is shunted away from the lungs thru the Ductus Arterious into the Aorta Arch a small amount goes to the maturing lungs. www.latrobe.edu.au/nursing Fetal Circulation Routes - through the Heart Right Atrium Right Ventricle Pulmonary Artery Ductus Arteriosus Aorta www.latrobe.edu.au/nursing Aorta Common Iliacs Internal Iliacs Umbilical Arteries Placenta 22 www.latrobe.edu.au/nursing Pulmonary Resistance • ▲Pulmonary Vascular resistance due to partially collapsed alveoli • ▼blood flow to lungs • Relative hypoxia • Vasoconstriction Pulmonary Vascular Constriction 23 www.latrobe.edu.au/nursing Ductus Arteriosus • A vascular connection between the Pulmonary Artery and the Aorta. • It allows blood to bypass non-functioning lungs and return to the placenta via the Descending Aorta and Umbilical Arteries • Returns blood to placenta 24 www.latrobe.edu.au/nursing Ductus Arteriosus 25 www.latrobe.edu.au/nursing Blood Flow • Fluids always follow the path of least resistance. 26 www.latrobe.edu.au/nursing Umbilical Arteries • Returns deoxygenated blood from Descending Aorta to placenta • Re-oxygenated in the placenta 27 www.latrobe.edu.au/nursing Fetal vs. Neonatal Circulation Fetal • Low pressure system • Lungs non-functional • Right to left shunting in the heart • High pulmonary resistance • Low systemic resistance Neonate • High pressure system • Lungs functional • Left to right blood flow in the heart • Low pulmonary resistance • High systemic resistance www.latrobe.edu.au/nursing Intra-Uterine Circulation • High pressure in right atrium and low pressure in left atrium • RL via foramen ovale • Fetal pulmonary vascular resistance high • RL via ductus arteriosus • Fetal systemic vascular resistance low www.latrobe.edu.au/nursing 30 www.latrobe.edu.au/nursing Conversion: Fetal to Neonatal Circulation • At birth the first breaths are the catalyst for the transition to neonatal circulation – Lungs inflate with oxygen with an increased atmospheric pressure – Lungs now become a low-pressure system as pulmonary vessels dilate with rise in oxygen level – Alveolar fluid is displaced 31 www.latrobe.edu.au/nursing 32 www.latrobe.edu.au/nursing Transition 33 www.latrobe.edu.au/nursing Decreased Pulmonary Resistance • Pulmonary vessels vasodilate • Fall in PVR • Increased PBF 34 www.latrobe.edu.au/nursing Closure of the Ductus Arteriousus • Highly oxygenated arterial blood in the Ductus Arteriosus causes it constrict. • Cessation of circulating PGE2 from maternal circulation. And increased metabolism of circulating prostaglandins by the lungs • Bradykinin – released on lung inflation • Within 10-15 hours the DA constricts and will eventually become the Ligamentum Arteriosus 35 www.latrobe.edu.au/nursing Increased Systemic Pressures • Clamping the cord shuts down the low pressure placental system and increases systemic vascular resistance • Blood is now pumped to the heart and lungs for oxygenation rather than the placenta www.latrobe.edu.au/nursing Closure of the Foramen Ovale • Increased blood flow of oxygenated blood returning from the lungs • Increases the pressure to the left side of the heart forces blood against the Septum Primum causing the Foramen Ovale to close and become Fossa Ovalis 37 www.latrobe.edu.au/nursing Closure of the Ductus Venosus • Clamping of the umbilical cord increases systemic vascular resistance • Ductus Venosus constricts and becomes the Ligamentum Venosum www.latrobe.edu.au/nursing Function/Structural Closure • Functional closure of the foramen ovale and ductus arteriosus occurs soon after birth • Overall anatomic changes are not complete for weeks 39 www.latrobe.edu.au/nursing Extra-uterine Circulation • Lungs inflate decrease in pulmonary vascular resistance and increase in pulmonary vascular flow • Blood O2 levels rise further decrease in pulmonary vascular resistance and ductus arterious constricts • Increased pressure in LEFT atrium and decreased pressure in RIGHT atrium formamen ovale closes • Umbilical cord is clamped ductus venosus closes increased systemic vascular resistance 40 www.latrobe.edu.au/nursing Conversion: Fetal to Infant Circulation • What happens to these special structures after birth? – Umbilical arteries atrophy – Umbilical vein becomes part of the fibrous support ligament for the liver – The foramen ovale, ductus arteriosus, ductus venosus atrophy and become fibrous ligaments 41 www.latrobe.edu.au/nursing Conversion: Fetal to Neonatal Circulation Foramen ovale Closes shortly after birth, fuses completely in first year. Ductus arteriousus Closes soon after birth, becomes ligamentum arteriousum in about 3 months. Ductus venosus Ligamentum venosum Umbilical arteries Medial umbilical ligaments Umbilical vein Ligamentum teres www.latrobe.edu.au/nursing 43 www.latrobe.edu.au/nursing www.latrobe.edu.au/nursing http://www.youtube.com/watch?v=T79sMq vN3BE www.latrobe.edu.au/nursing Common Defects • Patent Ductus Arteriousus – Prems, hypoxia, immaturity • Patent Foramen Ovale 46 www.latrobe.edu.au/nursing Stimuli To Initiate The First Breath • • • • • • • • Temperature change Light stimulation Noise Cold Touch Physical stimulation /proprioception Respiratory and metabolic acidosis Negative pressure in the chest cavity resulting from the recoil of the chest after exiting the vaginal canal www.latrobe.edu.au/nursing Normal Transition • These major changes take place within seconds of birth: • Fluid in the alveoli is absorbed and replaced by air • Umbilical arteries and veins constrict with clamping • Blood vessels in lung tissue relax increasing pulmonary blood flow www.latrobe.edu.au/nursing First breath • PVR SVR 49 www.latrobe.edu.au/nursing http://www.embryology.ch/anglais/pcardio/u mstellung02.html www.latrobe.edu.au/nursing When things go wrong in the Transition Group Work www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Failure to take first breath and/or sustain adequate breathing www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Excessive blood loss or poor cardiac contractility www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Sustained constriction of pulmonary arterioles www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Stress www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Prematurity www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Inter-uterine distress www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Congenital cardiac abnormalities www.latrobe.edu.au/nursing What may contribute to abnormal transition and what will be the outcome in relation closure of fetal shunts ......... Pulmonary abnormalities www.latrobe.edu.au/nursing www.latrobe.edu.au/nursing Birth Asphyxia • Failure to initiate and sustain breathing at birth • Cascading events • Hypoxaemia hypoxia damage 61 www.latrobe.edu.au/nursing Abnormal Transition • In response to interruption in normal transition • lungs fail to relax • arterioles in bowel, kidneys, muscles and skin CONSTRICT www.latrobe.edu.au/nursing Abnormal Transition • Blood flow is redirected to the heart, brain and adrenals PRESERVED • If oxygen deprivation continues: • Myocardial function and cardiac output fall DETERIORATE www.latrobe.edu.au/nursing Abnormal Transition Blood flow to all organs is reduced lack of adequate organ perfusion & tissue oxygenation brain damage & multisystem organ damage DEATH www.latrobe.edu.au/nursing Impediments To The Transition. • The Five H’s –Hypothermia –Hypoxia –Hypoglycaemia –Hypotension –Hypercarbia 65 www.latrobe.edu.au/nursing Impediments To The Transition. • Inter-uterine distress • Congenital cardiac abnormalities • Pulmonary abnormalities www.latrobe.edu.au/nursing What Can Go Wrong During Transition? • Insufficient ventilation and/or airway blockage • Excessive blood loss or poor cardiac contractility • Sustained constriction of pulmonary arterioles www.latrobe.edu.au/nursing Clinical Manifestations Associated with Asphyxia • • • • • • Factors Influencing Organ Injury Duration of the insult Adaptive mechanisms of the fetus Cause of the asphyxial process e.g.abruption versus infection Associated event/s- e.g.meconium www.latrobe.edu.au/nursing Clinical Manifestations Associated with Asphyxia • CNS- may range from hyper alert to moderate and/or severe encephalopathy seizures • Renal - oliguria (UO < 1 cc/kg/hr) or anuria • Fluid retention- maybe secondary to urine output, SIADH, rhabdomyolysis • Cardiac dysfunction- right or left sided ventricular dysfunction alone/combined hypo/hypertension www.latrobe.edu.au/nursing Clinical Manifestations Associated with Asphyxia • Pulmonary - PPHN, haemorrhage • Gastro-intestinal- ileus, bloody stools, NEC • Hepatic- transaminase elevation, cholestatic jaundice • Metabolic/endocrine-hypoglycaemia, hypocalcaemia hypomagnesaemia, • Hematological-bleeding www.latrobe.edu.au/nursing References • • • • • American Academy of Pediatrics – Textbook of Neonatal Resuscitation 4th Ed (2000) – NRP Slide Presentation Kit Askin,D.F. (2001) Complications in the Transition from Fetal to Neonatal Life JOGNN Vol33(3) 318-327 Blackburn,S. (2006) Placental Fetal and Transitional Circulation Revisited. Perinatal Neonatal Nursing Vol20 (4) 290-294 Witt C. (1997) Cardiac Embryology. Neonatal Network Vol16(1) 43-49 Merenstein, G.B & Gardner, S.L, (2002), Handbook of Neonatal Intensive Care , 5th Ed, Mosby, St. Louis. • • • • www.echocharity.org.uk http://www.nhlbi.nih.gov/health/dci/Diseases/pda/pda_heartworks.html http://user.gru.net/clawrence/vccl/chpt1/fetcirc.HTM http://www.cayugacc.edu/people/facultypages/greer/biol204/heart4/heart4.html • http://www.indiana.edu/~anat550/cvanim/fetcirc/fetcirc.html • http://www.embryology.ch/anglais/pcardio/umstellung01.html • http://mcb.berkeley.edu/courses/mcb135e/fetal.html www.latrobe.edu.au/nursing Good Websites • http://www.indiana.edu/~anat550/cvanim/f etcirc/fetcirc.html • http://www.embryology.ch/anglais/pcardio/ umstellung01.html • http://www.youtube.com/watch?v=T79s MqvN3BE 72 www.latrobe.edu.au/nursing