6.1. Neonatology - Physiology Flashcards
What is Neonatology?
The Specialty dealing with Children less than 4 weeks old
What are the Key Stages of the In-Utero Development of the Cardiovascular System
- Begins to Develop towards the end of the 3rd Week
- Heart Starts to beat at the Beginning of the 4th Week
- Critical Period of Heart Development is from day 20-50 after Fertilization
What is the Physiology of Foetal Circulation?
- Oxygenated Blood travels into the Foetus via the Ductus Venosus
- Some Blood travels via the Foramen Ovale to Left Atrium - Left Ventricle - Aorta
- Some Blood travels to the Right Ventricle - Pulmonary Artery - Patent Ductus Arteriosus - Aorta
Note - SaO2 in Foetal Body is 60-70%
What is the Function of the Ductus Arteriosus?
- Transports Blood from the Pulmonary Artery to the Aorta
- Protects Lungs from Circulatory Overload
- Allows the Right Ventricle to Strengthen - High Pulmonary Resistance / Low Pulmonary Flow
- Carries Mostly Low O2 Saturated Blood
What is the Function of the Ductus Venosus?
- Carries Foetal Blood connecting the Umbilical Vein to the Inferior Vena Cava
- Carries Mostly Oxygenated Blood
Note - Blood Flow Regulated via Sphincter
What are the Normal Vital Signs of a Neonate:
- Blood Pressure?
- Heart Rate?
- Respiratory Rate?
- a) 1 hr - Systolic = 70 / Diastolic = 44
- b) 1 day - Systolic = 70+/-9 / Diastolic 42+/-12
- c) 3 days - Systolic = 77+/-12 / Diastolic = 49+/-10
- Normal Heart Rate = 120-160bpm
- 40-60/minute
How is Thermoregulation Maintained in a Neonate?
- Maternal Thermoregulation in the Womb
- Newborn Babies lack Shivering Thermogenesis
- Need a Metabolic Production of Heat
- Brown Fat well Innervated by the Sympathetic Neurons
- Cold Stress leads to Lipolysis and Heat Production
How can Neonates lose heat?
- Radiation - Heat Dissipated to Colder Objects
- Convection - Heat Loss by Moving Air
- Evaporation - We are born in the Water
- Conduction - Heat Loss to Surface on which the Baby Lies
How is the Physiology of Neonate Breathing Assessed, Non-Invasivly?
- Blood Gas Determination
- PaCO2 = 5-6mmHg / PaO2 = 8-12 mmHg
- Trans-cutaneous pCO2/O2 Measurement
Note - It is Dificult to Asses if Spontaneously Breathing
How is the Physiology of Neonate Breathing Assessed, Invasivly?
- Capnography
- Tidal Volume = 4-6ml/Kg
- Minute Ventilation - Tidal Volume ml/Kg x Respiratory Rate
- Flow-Volume Loop
When does Physiological Jaundice occur?
- Appears on Day of Life 2-3
- Disapears within 7-10 Days of Life (21 in Premature)
Note - 60% Term / 80% Premature Babies develop some Jaundice
What are the Features of Physiological Jaundice?
- 75% Bilirubin comes from Haemoglobin
- Metabolised (Conjugated) in the Liver
- Lipid-Soluble Thus can cross the Blood-Brain Barrier
- At High Concentrations causes irreversible changes in the Brain - Kernicterus
- Blue Light converts Bilirubin to Water Soluble Form
What is the Features of Fluid Balance in a Term Neonate?
- Full Term Infant is able to Maintain Fluid / Electrolyte Balance
- Weight Loss (up to 10% is Normal)
- Loss is Due to Shift of Interstitial Fluid to Intravascular / Diuresis
- It is normal to not Pass Urine for the first 24 hours
What is the Features of Fluid Balance in a Premature Infants?
- Less Fat in the Body Composition
- Increased Loss through Kidney:
- a) Slower GFR
- b) Reduced Na Reabsorption
- c) Decreased Ability to Concentrate or Dilute Urine
- Increased Insensible Water Loss - Via Immature Skin / Breathing
What are the Features of Physiological Anaemia of the Newborn?
- Erythrocyte Production is 10% of in Uterus - Day of Life 7
- Born with Haemoglobin of 15-20g/L
- Week 10 - Haemoglobin of 11.4g/L
- Increased Production of Erythropoetin
- Week 20 - Haemoglobin of 12.0g/L
Note - Anaemia of Prematurits - Reduced Erythropoesis / Blood Letting
