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Hypoxaemia Respiratory Failure Flashcards

1
Q

What is respiratory failure ?

A

Impairment in gas exchange causing hypoxia

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2
Q

What are the two type of respiratory failure ?

A

Type 1 : low pO2 , normal or low pCO2

Type 2 : low pO2 and high pCO2

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3
Q

What can cause hypoxia ? (5)

A
  • low inspired pO2 (altitude)
  • Hypoventilation , pump failure
  • ventilation-perfusion mismatch
  • diffusion defect , pbm with capillary membrane
  • right to left shunt (cyanotic heart disease )
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4
Q

Briefly describe the ventilation and perfusion of the whole lung ?

A

Stroke volume :70 mL
HR: 70 bpm
Blood flow to lungs = ~5L

Tidal volume(500ml)-dead space (150mL) = 350 mL
RR : 15
Ventilation per minute = ~5L

Ratio V/Q = 1

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5
Q

What mechanism cause type 2 respiratory failure ?

A

Hypoventilation : entire lung is poorly ventilated

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6
Q

What is seen in terms of gases in Hypoventilation ?

A

Hypoxia and hypercapnia

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7
Q

What can cause acute Hypoventilation ?

A
  • Opiate od ,head injury,stroke
  • spinal cord trauma
  • Guillain-Barre syndrome (acute polyneuropathy)
  • myasthenia gravis
  • pneumothorax , large pleural effusion
  • resp distress of new born
  • acute asthma
  • laryngeal obstruction
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8
Q

What can cause chronic respiratory failure ?

A 
Late COPD 
Lung fibrosis 
Kyphoscoliosis 
Myopathy of muscles of respiration 
Severe obesity
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9
Q

What are the effects of hypoxaemia on the body ?

A

Impaired CNS function , confusion,irritability
Hypoxic vasoconstriction of pulmonary vessels
Cyanosis
Cardiac arrhythmias

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10
Q

When does cyanosis present ?

A

More than 50mg/L of desaturated Hb

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11
Q

How is chronic hypoxaemia compensated ?

A
  • increased EPO secretion by kidney -more Hb
  • in cases 2,3DPG

-hypoxic vasoconstriction of pulmonary vessels

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12
Q

What can be the consequence of chronic hypoxic vasoconstriction of pulmonary vessels ?

A

Pulmonary hypertension > right heart failure (Cor pulmonake: HF secondary to pulmonary hypertension )

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13
Q

What are the effect of hypercapnia in the body ?

A

Respiratory acidosis drop in pH
Impaired CNS : confusion,coma,tremors
Peripheral vasodilation
Cerebral vasodilation : headache

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14
Q

What is the effect of sustained high pCO2 on the central chemoreceptors ?

A

CO2 diffuse in CSF > pH drops > stimulate chemoreceptors > choroid plexus secrete HCO3 > pH in CSF back to normal > chemoreceptors no longer stimulated but pCO2 still high

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15
Q

Why is correction of hypoxia in patient with chronic type 2 respiratory failure potentially dangerous ?

A

Due to reset of central chemoreceptors , patient relies on hypoxic drive to breath (peripheral chemoreceptors detect hypoxia )
> treatment will remove drive> patient will Hypoventilation and hypercapnia will be worse

Also removes pulmonary hypoxic vasoconstriction > blood perfume poorly ventilated alveoli : mismatch

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16
Q

What two mechanism can cause type 1 respiratory failure ?

A

Ventilation perfusion mismatch

Diffusion defect

17
Q

What can cause V/Q mismatch ?

A

Asthma
Pneumonia
PE
Respiratory distress syndrome of the new born

18
Q

Why is the pO2 low and pCO2 normal to low in v/Q mismatch ?

A

Poorly ventilated alveoli , no gas exchange , blood has high co2 low oxygen , mix with normal blood from unaffected alveoli : overall low oxygen , high co2
> detected by chemoreceptors , hyperventilation
» unaffected segment are compensating by hyperventilation : pCO2 drops enough to compensate in mixed blood , pO2 rises but not enough to compensate as Hb is already saturated above 10kPa

19
Q

Why does V/Q mismatch occur in PE ?

A

Embolus cause redistribution of blood flow : blood is diverted to unaffected area
> affected alveoli has higher ventilation than blood supply , blood leaving is well oxygenated and low co2 , however unaffected alveoli cannot match the match increased perfusion
» overall cause hypoxaemia and hyperventilation sufficient to get rid of CO2

20
Q

Why does poor diffusion across alveolar membrane result in type 1 respiratory failure ?

A

CO2 more soluble , Diffusion of O2 more affected than CO2

21
Q

What condition can cause diffusion defects ?

A

Fibrotic lung disease

Pulmonary oedema

Resp (6 decks)

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