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T2: Theme 4: Lungs > Lecture 4: Resp failure > Flashcards

Lecture 4: Resp failure Flashcards

1
Q

What are the 4 types of hypoxia?

A

Cytotoxic - reduced ability to utilise O2

Circulatory - reduced ability to deliver O2

Anaemic - reduced ability to deliver O2

Hypoxaemic - reduced ability to deliver O2

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2
Q

What are the 5 mechanisms of hypoxaemia?

A 
Reduced PIO2
Hypoventilation
Diffusion limitations
Mismatch 
Shunt
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3
Q

Where is ventilation lowest?

A

At the apex

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4
Q

Where is ventilation highest?

A

At the base

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5
Q

Where is perfusion lowest?

A

At the apex

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6
Q

Where is perfusion highest?

A

At the base

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7
Q

What is the order of Pa, Pv and PA at the apex (zone 1)?

A

PA>Pa>Pv

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8
Q

What is the order of Pa, Pv and PA in the centre (zone 2)?

A

Pa>PA>Pv

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9
Q

What is the order of Pa, Pv and PA at the base (zone 3)?

A

Pa>Pv>PA

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10
Q

Which is greater at the apex, ventilation or perfusion?

A

Ventilation > Perfusion

V/Q > 1

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11
Q

Which is greater in the middle of the lung, ventilation or perfusion?

A

Ventilation = Perfusion

V/Q = 1

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12
Q

Which is greater at the base, ventilation or perfusion?

A

Ventilation < Perfusion

V/Q < 1

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13
Q

What is the normal range of V/Q ratios?

A

0.3 to 10

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14
Q

What is meant by V/Q = 0?

A

When no ventilation occurs in a given area

Extreme version of V/Q mismatch that is called shunt

Decreased PAO2 - hypoxaemia

Unable to compensate with increased FIO2

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15
Q

What is meant by V/Q &laquo_space;1?

A

Ventilation substantially reduced in a given area - V/Q mismatch

Decreased PAO2 - hypoxaemia

Able to compensate with increased FIO2

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16
Q

What is meant by V/Q&raquo_space; 1?

A

Wasted ventilatory effort

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17
Q

How would lung failure present?

A

Gas exchange failure manifested by hypoxaemia

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18
Q

How would pump failure present?

A

Ventilatory failure manifested by hypercapnia

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19
Q

Will giving oxygen with a higher FIO2 increase the PaO2 in hypoxaemia due to reduced PIO2?

20
Q

Will giving oxygen with a higher FIO2 increase the PaO2 in hypoxaemia due to hypoventilation?

A

Yes

As long as there is some ventilation

21
Q

Will giving oxygen with a higher FIO2 increase the PaO2 in hypoxaemia due to diffusion limitation?

22
Q

Will giving oxygen with a higher FIO2 increase the PaO2 in hypoxaemia due to V/Q mismatch?

23
Q

Will giving oxygen with a higher FIO2 increase the PaO2 in hypoxaemia due to shunt?

24
Q

What might cause hypoventilation?

A

Central nervous system disease

Drug overdose: narcotics, other depressants, alcohol with impair function of the respiratory control centre

Weakness

25
Q

What might cause diffusion limitation?

A

Interstitial oedema
Inflammation
Scarring

Increase diffusion distance and slow gas diffusion

26
Q

What is the effect of diffusion limitation of PAO2 and PaO2?

A

Normal PAO2 but reduced PaO2

27
Q

In hypoxamia from V/Q mismatch, what occurs in two alveoli where one is experiencing reduced ventilation?

A

1st alveolus: PA02 is elevated above normal due to increased ventilation causing the PCO2 to be reduced

1st alveolus: Ca02 is normal. The higher PAO2 adds hardly any more content to the blood leaving that capillary.

2nd alveolus: PA02 is decreased from increased CO2 in the alveolus

2nd alveolus: Ca02 is much reduced due to lower PaO2 - lower amount of dissolved O2 and lower amount of O2 bound to Hb

28
Q

What limits the amount of V/Q mismatch in the lungs?

A

Hypoxic pulmonary vasoconstriction directs blood flow away from poorly ventilated areas, and helps maintain overall V/Q matching

29
Q

What are the examples of abnormal shunts?

A

Intrapulmonary shunt

  • Arteriovenous malformations
  • Lung consolidation (for ex, pneumonia)

Intracardiac shunt
- Congenital or acquired heart defects

30
Q

Which causes of hypoxaemia result in increased PA-aO2?

A

Diffusion limitation

Low V/Q

Shunt

31
Q

Which causes of hypoxaemia maintain normal PA-aO2?

A

Hypoventilation

Decreased PIO2

32
Q

Which causes of hypoxaemia result in decreased PAO2?

A

Hypoventilation

Decreased PIO2

Low V/Q (locally)

33
Q

What is anatomic dead space?

A

Typically, 150 mL out of a 500 mL (~ 30%) tidal volume remains in the airways

34
Q

What is alveolar dead space?

A

Air reaches the alveoli but can’t participate in gas exchange

Normally minimal but can increase in amount in lung disease

35
Q

What is VD?

A

Dead space

36
Q

What is VT?

A

Tidal volume

37
Q

What is VD/VT?

A

Fraction of dead space

38
Q

What may cause hypercarbic respiratory failure?

A

Due to weakness, loss of drive from the respiratory centre, or failure to compensate for increased dead space

39
Q

What are the treatments for hypercarbic failure?

A

RR and tidal volume

40
Q

What are the treatments for hyperaemic failure?

A

FIO2 (21% to 100%)

Added pressure

41
Q

What is minute ventilation (VE)?

A

Amount of air, per minute, breathed into the lung

42
Q

What is VE?

A

Minute ventilation

43
Q

What is the equation of VE?

A

VE = VT x RR

44
Q

What is VA?

A

Amount of ventilation

45
Q

Why is VA not equal to VE?

A

Because of dead space

T2: Theme 4: Lungs (16 decks)

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