Fetal and Neonatal Physiology

2. Fetal and Neonatal Physiology 新光醫院 小兒科 穆淑琪醫師

3. Definitions

4. Classification Significance • Preterm Infants • Not yet matured • Incomplete but normal IUG • Prone to IRDS, IVH, PDA, apnea, ROP, hypothermia • Small for Gestational Age • Matured but prone to certain conditions • IUGR for varied reasons • Prone to hypoglycemia, infection, pneumonia, seizures (not apnea)

7. NEONATAL PHYSIOLOGY

8. The Respiratory System • Airway Differences • Obligate nasal breather • Easy airway obstruction • Anatomic differences complicate ETT intubation • Straight blade, uncuffed ETT preferred

9. 缺氧窒息(Asphyxia)的生理變化: 胎兒之肺臟(Lung)及血液循環 Fetus

10. Fetus 胎兒之肺臟及血液循環 Diminished Blood Flow Through Fetal Lungs

11. 出生時的轉變 • 肺泡之肺液吸收 • 臍靜脈及臍動脈收縮 • 肺血管擴張

12. 肺液的吸收 • 生產前開始減少 • 有效的初始呼吸可以促進吸收 • 減緩吸收 • 出生時不呼吸 • 淺而無效的呼吸

14. Birth

17. Decreased Pulmonary Perfusion

18. 缺氧窒息(Asphyxia) • 新生兒因活動力不佳，而不能建立有效之呼吸，缺氧狀態可能接續進行而導致缺氧窒息。 • 缺氧窒息的定義: 不斷加重的缺氧、二氧化碳堆積及酸血症(acidosis)。 • 缺氧窒息進行到某個程度會造成永久性腦部傷害或死亡。

19. 缺氧窒息 • 初始反應 • 肺部、腸、胃、腎臟、肌肉及皮膚的血流量均減少，所保存的血主要用來供應心臟及腦部。 • 後期反應 • 當窒息持續時，心肌也受傷害，心輸出量減少，到重要器官之血流量也減少。

20. 干擾轉變的因素 • 呼吸不足，呼吸道阻塞。 • 失血過多、心臟收縮力不佳、或缺氧造成心搏緩慢 • 肺血管持續收縮。

21. Chronological Development of Organs, Systems, and Body form-I • ORGAN CHRONOLOGY OF DEVELOPMENT • Bronchial apparatus and pharyngeal pouches 4th week--ridges and grooves appear over the future neck region • Thyroid gland 4th week--endoderm appears over the floor of the pharynx • Tongue 4th week--primordia appear in the of the pharynx • Face End of 4th week--primordia appear • Palate Begins in the 5th week • Upper respiratory system 4th week--laryngotracheal groove appears

22. Chronological Development of Organs, Systems, and Body form-II • ORGAN CHRONOLOGY OF DEVELOPMENT • Kidneys,urinary bladder,urethra 5th week, permanent adult kidney begins to develop • Adrenal glands 5th week,primordia of adrenal glands develop • Conads,genital ducts,external genitalia 5th week, gonadal ridges form • Heart3rd week,development of the heart begins • Atria 5th week, the atria are formed • Ventricles 5th week,the ventricles form

23. ORGAN CHRONOLOGY OF VELOPMENT • Fetal circulation3rd week,embryonic blood vessels develop • Brain and spinal cord End of 4th week,primary vesicles form and walls of the neural tube thicken to form the spinal core • Pituitary 6th week,connection of Rathke’s with oral cavity disappears • Limbs End of 4th week,limb buds appear • Skull 7th week,paired cartilages begin to fuse to form the cranium

24. Apnea • Absence of respirations for 20 sec, causing cyanosis and bradycardia • At-risk neonates • Preterm and ex-preterm infants to 50 wks PCA • Risk is ~60% at 42 wks PCA, <1% 54 wks PCA

25. Apnea: Primary Apnea 缺氧窒息(Asphyxia)的生理變化 : 呼吸暫停(Apnea)

26. Apnea : Secondary Apnea 缺氧窒息(Asphyxia)的生理變化 : 呼吸暫停(Apnea)

27. The Respiratory System • Thorax and Lungs • Increased O2 consumption (6 ml/kg/min) • Due to high BMR (+100%) • Prone to cyanosis • Lung volumes vs. age – no change • RR is increased • Diaphragmatic breathing • Susceptible to abdominal distension • Fatigable – preterm infants

28. The Cardiovascular System

29. The Cardiovascular System • Myocardium • Unable to  SV by contractility • CO is primarily rate-controlled • Non-compliant ventricles • CHF • Bradycardia implies hypotension • High vagal tone at birth • PNS mature (not SNS)

30. The Cardiovascular System • Pulmonary Vasculature • Reactive, thick muscularis layer • Acidosis, hypercarbia, hypoxemia, stress • Stressors may cause acute CHF • Acidosis results and worsens

31. Fetal Cardiovascular System • UV →RA (FO) → AO • SVC→PA→(DA)→AO • Ductus Arteriosus (DA) • Foramen Ovale (FO) • Umbilical Arteries and Veins

33. Perinatal Cardiorespiratory physiology • Fetal lungs • 24 days -arises from the foregut • 26-28 weeks -terminal airways developed • 30-32 weeks -final surface active material (SAM) developed • Plasma ultrafiltrate is a normal part of the lungs • Every day IU (intrauterine) 50-150 ml/kg/day of plasma is produced • Plasma is swallowed in the gut and excreted by kidneys

34. Perinatal Cardiorespiratory physiology • Plasma ultrafiltrate (2) • 2/3 is expelled during vaginal delivery • 1/3 is removed capillaries, lymphatics, breathing • If fluid is retained into lungs causes TTBN • (transient tachypnea of newborn) • Causes: • Small infants • Preterm infants • Rapidly born • Cesarean section born babies

35. Perinatal Cardiorespiratory physiology

36. Perinatal Cardiorespiratory physiology • Normal breathing - 30/min at 90 sec of age (reminder) • Normal breathing - 40-60/min at few minutes of age: • Removal of increased CO2 produced • High metabolic rate • Helps maintain FRC

37. Perinatal Cardiorespiratory physiology • Circulation of the fetus: • RV ~ 2/3 CO • LV ~ 1/3 CO • Foramen ovale • Ductus arteriosus • Blood is coming from placenta - high O2 content • 95% of the blood coming from placenta goes to LA through foramen ovale

38. Perinatal Cardiorespiratory physiology • Circulation of the newborn: • PVR is  due to pulmonary expansion, breathing,  pH, and  O2 tension • If neonate is born by CS -  PAP’s and PVR • PVR is : • Hypoxia Acidosis • Hypovolemia Hypoventilation • Atelectasis Cold

39. Perinatal Cardiorespiratory physiology • Changes in circulation of the newborn: •  PVR -  pulmonary blood flow • Right/left shunting will be decreased • LA pressures are , and seal foramen ovale • Ductus arteriosus closes (10-14 days) in response to • O2 • Ach • Parasympathetic nerve stimulation • PG

40. Asphyxia  PaO2  PCO2  pH  Uteroplacental blood flow Maternal or Fetal disease (cause)

41. Asphyxia • Intrauterine asphyxia: • PaO2 decreases from 25-40 to 5 mmHg • Anaerobic metabolism occurs • pH drops < 7.0 : respiratory and metabolic acidosis • Lactate is accumulating in the body • Redistribution of blood flow in the body • CO starting normal is now decreasing • Because of high doses of opioids in the blood fetus may survive severe hypoxia (may reduce total O2 consumption)

42. Development and maturation of the cardiopulmonary systemThe Fetal Circulation • Four unique shunts Placenta Ductus Venosus Foramen Ovale Ductus Arteriosus

44. Cardiopulmonary Adjustments at Birth-I • Loss of the placental circulation • Newborn breathe on its own • Mild hypoxia Mild hypercapnia Tactile stimuli trigger the first breath Cold skin

45. Respiratory Distress Syndrome Etiology-Surfactant deficiency during disease

46. High risk: Prematurity Asphyxia IDM ( Infant of Diabetic Mother ) Maternal hemorrhage C/S Multiple births Male >female Low risk: IUGR Maternal hypertension Steroids Placental insufficiency Heroin addictive Factors precipitating to HMD

48. Synthesis of surfactant • Maturation of alveolar type II cells and the subsequent synthesis of surfactant --started since 24 wks’ gestation --complete by 32 wks’ gestation

49. Pathophysiology • Reduce lung compliance • Reduce FRC • Poor lung distensibility • Poor alveolar stability • Right-to-left shunt • Reduce effective pulmonary blood flow

50. Clinical signs • Onset near the time of birth • Retraction and tachypnea • Expiratory grunting • Cyanosis • Systemic hypotension • Characteristic chest radiography • Course lasts 3-5 days