Neonatal Physiology

Question 1

When does CVS begin to develop? When does heart start to beat? What is critical period?

Answer 1

• —Begins to develop toward the end of the third week.
• —Heart starts to beat at the beginning of the fourth week.
• The critical period of heart development is from day 20 to day 50 after fertilization

Question 2

How are the placenta and foetal heart entwined?

Answer 2

• Oxygenated blood via umbilical vein – Ductus Venosus.
• Some blood via Foramen Ovale to Left Atrium – Left Ventricle – Aorta (Ao).
• Some of blood to Right Ventricle – Pulmonary Artery (PA) - Patent Ductus Arteriosus (PDA) from PA to Ao.
• Saturation SaO2 in foetal body is 60-70%.

Question 3

What is the role of the ductus arteriosus?

Answer 3

• —Protects lungs against circulatory overload
• —Allows the right ventricle to strengthen
• Carries low oxygen saturated blood

Question 4

What is the role of the ductus venosus?

Answer 4

• —Foetal blood vessel connecting the umbilical vein to the IVC
• —Blood flow regulated via sphincter
• —Carries mostly oxygenated blood

Question 5

What happens as the bambino takes it’s first breath?

Answer 5

1. Ductus arteriosus becomes a ligament
2. Foramen ovale closes and leaves a depression
3. Ductus venosus becomes a ligament
4. Umbilical vein becomes a ligament
5. Umbilical arteries become ligaments

Question 6

What is the normal vital signs of a full term new born: BP, HR, RR?

Answer 6

BP:

• 1hr: 70/44
• 1 day: 70/42
• 3 days:77/49

HR:

• 120-160

RR:

• 30-60/min

Question 7

How is thermoregulation of neonate carried out?

Answer 7

• —Maternal thermoregulation in the womb.
• —Newborn babies lack shivering thermo genesis thus need a metabolic production of the heat.
• —Brown fat well innervated by sympathetic neurons.
• —Cold stress leads to lipolysis and heat production.

Question 8

How can we non-invasively assess a new-born’s breathing?

Answer 8

• —Non invasive:
  
  • —Blood gas determination
  • —PaCO2 5-6 kPa, PaO2 8-12 kPa
  • —Trans-cutaneous pCO2/O2 measurement

Question 9

How do we invasively assess new-born’s breathing?

Answer 9

• —Capnography
• —Tidal volume 4-6 ml/kg
• —Minute ventilation:
  
  • —Tidal Volume ml/kg x respiratory rate
• —Flow-volume loop.

Question 10

What is weight loss due to in newborn? Is if normal?

Is it normal for newborn to pass urine in first 24hrs?

Answer 10

• —Weight loss up to 10% is normal.
• —Loss is due to:
  
  • —Shift of interstitial fluid to intravascular
  • —Diuresis
• —It is normal not to pass urine for the first 24 hrs!

Question 11

How can fluid be lost in premature infants?

Answer 11

• —Less fat in body composition
• —Increased loss through kidney:
  
  • —Slower GFR
  • —Reduced Na reabsorption
  • —Decreased ability to concentrate or dilute urine
• — Increased Insensible Water Loss (IWL)
  
  • —Via immature skin and breathing
  • —Physiological IWL is 20-40 ml/kg/day but could be up to 82 ml/kg/day in 750-1000 g

Question 12

What are causes of physiological anaemia of the newborn?

Answer 12

• —Born with - Hb 15-20 g/l
• —Week 10 - Hb 11.4 g/l
• —Increase production of Erythropoetin
• —Week 20 - Hb 12.0 g/l
• —Anaemia of prematurity:
  
  • —Reduced erythropoesis.
  • —Infection
  • —Blood letting – most important cause!