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Quiz 1- Fetal Circulation Flashcards

1
Q

Why are the lungs prone to collapse in the infant?

A
  • weak elastic recoil
  • weak intercostal muscles
  • intrathoracic airways collapse during expiration
  • high closing volumes encroach on FRC
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2
Q

What is a very important thing to do to prevent lung collapse in the neonate?

A

PEEP of 5 cmH2O during anesthesia—> even while spontaneous bagging

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3
Q

What is the primary event of respiratory system transition in infants?

A

The initiation of ventilation

- infant must generate high negative pressure, - 70mmHg, to inflate lungs

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4
Q

What is normal FRC for an infant?

A

25-30 ml/kg

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5
Q

What is the most common and universal sign of respiratory distress in an infant?

A

Tachypnea

Then nasal flaring, retractions, grunting, sea saw breathing, head bobbing

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6
Q

Hypercapnia causes a stress response in an infant. What are clinical symptoms of stress?

A
  • tachycardia- the degree of tachycardia shows the degree of stress
  • HTN
  • worried, anxious look on face
  • diaphoresis
  • agitation, inability to console
  • somnolence and cyanosis are late signs—> impending arrest
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7
Q

T/F chemoreceptors are not active until birth

A

True

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8
Q

The response to hypoxia is biphasic: meaning, initial __________ followed by ~2 min ______ _______.

A

Hyperpnea

Respiratory depression

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9
Q

What 2 things abolish the initial hypereneic response?

A

HYPOTHERMIA

LOW LEVELS OF ANESTHETIC GAS

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10
Q

The ___________ the child the _________ they crash.

A

Smaller

Faster

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11
Q

Hypoxia actually depresses the neonates response to hypercapnia. At what age does hypoxia start to produce sustained hyperventilation?

A

By 3 weeks of age

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12
Q

Hypoxia does what to the heart rate of infant?

A

Causes PROFOUND bradycardia

If HR ≤ 60 start CPR

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13
Q

If you are not ventilating a baby you will see bradycardia within __________.

A

1 minute

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14
Q

What percentage of muscle fibers in the diaphragm of an infant are type 1 (fatigue resistant) compared to the adult?

A

25% type 1 in infants
55% type 1 in adults

Infant will fatigue much quicker

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15
Q

What contributes to apnea of infancy?

A
  • increased O2 consumption (6mL/kg)
  • decreased FRC
  • increased closing volume
    —> once hypoxic, will see abnormal breathing patterns and apnea much sooner than older children and adults
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16
Q

Why do CV shunts exist?

A
  • to minimize blood flow to lungs

- to maximize blood flow/O2 delivery to organ systems

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17
Q

Oxygenated blood is delivered to the fetus via the umbilical vein.
What is the PaO2 in the umbilical vein?

A

35mmHg

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18
Q

What percentage of blood does the ductus venosus divert from the liver and into the IVC?

A

~ 50%

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19
Q

Pulmonary vascular resistance is ________, until umbilical cord is cut.

A

HIGH

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20
Q

Blood entering the descending aorta returns to the ________ AND feeds the _______ _________.

A

Placenta

Lower body

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21
Q

What is the PaO2 of blood in the descending aorta and eventually umbilical arteries?

A

22mmHg

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22
Q

Since a PFO allows arterial and venous circulation to mix, what must you be very vigilant about in infants?

A

Air in IV line

23
Q

What happens once the umbilical cord is cut?

A

SVR increases

Reversal of shunts

24
Q

What takes place at the onset of breathing?

A

PVR decreases and shunts are reversed

  • increases arterial and alveolar PO2- which dilates pulmonary vasculature
  • PVR decreases dramatically
  • pulmonary blood flow increases 450%
  • LA pressure increases, RA pressure decreases
    • foramen ovale closes
25
What percentage of adults have a PFO?
25-30%
26
The ductus arteriosis constricts within several minutes of the onset of breathing due to what 2 factors?
- increased PO2 - decreased circulating prostaglandins This causes the ductus venosus to become fibrous over time and close
27
What is given to CV kids to keep shunts open?
Prostaglandins
28
What is Persistent Pulmonary hypertension of the newborn (PPHN)?
- persistent fetal shunting beyond normal transition period in the absence of structural heart defect - since shunts are not anatomically closed immediately after birth
29
What are some consequences of PPHN?
- increased PVR - pulmonary HTN - decreased pulmonary blood flow - RAP > LAP - increased ductal flow —> can open foramen ovale
30
What are S/S of PPHN?
- marked cyanosis - tachypnea - acidosis —> RT-lt shunt across FO and DA = cyanotic shunt
31
Before anatomical closure of shunts, transient rt-lt shunting may occur in normal neonates during:
- coughing - bucking - straining during anesthesia induction or emergence
32
What is the treatment for PPHN?
- hyperventilation - maintain alkalosis - pulmonary vasodilators- prostaglandins - minimal handling - avoidance of stress * *** adequate ventilation and oxygenation is key! ****
33
What is the tidal volume for the neonate and child up to 12 years?
10mL/kg (use IBW if obese)
34
What is the major function of the fetal renal system?
Passive production of urine, which contributes to formation of amniotic fluid
35
What is important about amniotic fluid?
- important for normal development of fetal lung | - acts as shock absorber for fetus
36
What are characteristics of the fetal kidney?
- low renal blood flow | - low GFR
37
Why is there such low blood flow and GFR in fetal kidneys?
- structurally immature- size and # of glomeruli - low systemic arterial pressure - high renal vascular resistance - low permeability o f glomerular capillaries
38
How do transitional changes in the newborn affect the renal system?
- systemic arterial pressure increases - renal vascular resistance decreases - increase in size and function occur through maturity
39
At which gestational age are all nephrons developed?
34 weeks A premature infant has incomplete renal development —>> post conceptual age matters here
40
What contributes to neonates being “obligate Na+ losers” ?
- normal RAAS- facilitates Na+ reabsorption in distal tubules BUT - immature neonatal tubules—> do not completely reabsorb Na+ under the stimulus of aldosterone —> result is neonate will continue to excrete Na+ even in the presence of severe Na+ deficit
41
What are the urine Na+ levels for adults and neonates?
Adult: 5-10mEq/L Neonates: 20-25mEq/L
42
What is the consequence of Na+ loss in neonates?
3rd spacing RAAS is the primary compensatory mechanism for reabsorption of Na and water losses of plasma, blood, GI tract fluid and 3rd spacing
43
What IVF should be used as maintenance and replacement fluid in neonates?
- maintenance fluid: usually D5 .2% NS | - replacement fluid: LR or NS
44
** What is the lowest acceptable Hg/Hct for neonates and infants due to high O2 demand and limited ability to increase CO?
Hct 35% | Hgb > 10
45
** What other reasons warrant a higher Hgb/Hct in neonates and infants?
- increased blood volume per unit weight | - increased CO per unit weight
46
How much blood volume is in a term baby? Pre-term baby?
- term baby: 90mL/kg | - preterm baby: 100mL/kg
47
What limits neonates thermal range?
- size - increased surface area to volume ratio - increased thermal conductance —> their ability to thermo regulate is limited and easily overwhelmed
48
T/F Despite poikilothermic behaviors infants are homeotherms.
True
49
What are the 2 stages of heat loss?
1.) internal heat gradient: transfer of heat from body core to skin surface 2.) external heat gradient: dissipation of heat from skin surface to environment —> both stages are governed by the laws of convection, conduction, radiation, evaporation
50
How can heat loss be prevented?
- CONDUCTION: (cutaneous blood flow/am cutaneous tissue Make sure surface they lay on is warm - short cases: warm blankets - longer cases: heating mattress or bear hugger - CONVECTION: (air temp, air velocity and volume of air flow) Decrease air movement across body - most NICU ORs are kept at 80˚F - RADIATION: (temperature gradient b/t skin and surrounding surfaces, total radiating surface of infant) ** major source of heat loss ** Warm OR room, radiant lamps “French fry lights” - EVAPORATION: (relative humidity, minute ventilation) Cover exposed body cavities Heat and humidify inspired gases
51
How is heat production achieved in the infant?
- voluntary muscle activity - involuntary muscle activity - NON-SHIVERING THERMOGENISIS—> major component in neonate
52
What is non-shivering thermogenesis?
Metabolism of brown fate that occurs with cold stress Mediated by SNS stimulation Heat is a product of fatty acid metabolism
53
What are some facts about brown fat?
- develops b/t 26-30 weeks gestation - 2-6% of neonatal total body weight - abundant vascular supply and rich innervation of SNS
54
Where can brown fate be found?
- mediastinum - b/t scapula - around adrenals and axilla

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