Abnormal Pulmonary Gas Exchange Flashcards

1
Q

What is normal PaO2 and PaCO2 ?

A

Normal PaO2- 10.5 - 13.5 kPa Normal PaCO2- 4.8-6 kPa

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2
Q

What is type I and type II respiratory failure ?

A

Type I- PaO2 <8kPa (PaCO2 normal or low)Type II PaCO2 >6.5kPa (PaO2 usually low)

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3
Q

What are the 4 abnormal states associated with Abnormal pulmonary gas exchange ?

A

Alveolar hypoventilationShuntVentilation / Perfusion ImbalanceDiffusion Impairment

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4
Q

What is the result of alveolar hypoventilation on PACO2 and PAO2 ?

A

Hypoventilation increases PACO2 and thus increases PaCO2 Increases in PACO2 decreases PAO2, which cause PaO2 to fall Fall in PaO2 due to hypoventilation is corrected by raising FIO2(FIO2= the fraction of inspired air which is oxygen )

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5
Q

How can you correct a fall in PaO2 due to hypoventilation ?

A

Raising the FIO2

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6
Q

Why is normal V/Q ratio 0.8 ?

A

Normally breathing 4 l/minCO is 5 l/min so normal V/Q is 4/5 or 0.8

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7
Q

What is the commonest cause of hypoxaemia clinically ?

A

Low V/Q

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8
Q

How does low V/Q sometimes arise in alveoli ?

A

Due to local alveolar hypoventilation due to some, focal disease

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9
Q

How can you treat hypoxaemia due to low V/Q ?

A

Increase in FIO2

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10
Q

Will Interstitial lung disease affect CO2 levels ?

A

Not usually because CO2 diffuses 20 times faster than O2

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11
Q

How does diffusion impairment affect diffusing speed of oxygen ?

A

Diffusion impairment means it takes LONGER for blood and alveolar air to equilibrate, particularly for oxygen

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12
Q

Why does diffusion impairment result in a fall in Pa O2 during exercise ?

A

Capillary transit time decreases during exercise, less time for equilibration

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13
Q

Why don’t we have 100% haemoglobin saturation ?

A

Because we have a 2-4% shunt

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14
Q

When do we see a pathological shunt ?

A

Alveolar ventilation malformations, congenital heart disease and pulmonary disease

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15
Q

Does large shunt respond well to increase in FIO2 ?

A

No, blood leaving normal sections of the lung is already 98% saturated

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16
Q

Why is there hypoxaemia in pneumonia ?

A

Ventilation perfusion mismatch: - bronchitis/ bronchopneumonia Shunt: - severe bronchopneumonia - lobar pattern with large areas of consolidation

17
Q

Why is the hypoxaemia in COPD ?

A

V/Q mismatch- airway obstruction +/- bronchopneumonia Diffusion impairement- loss of alveolar surface area in emphysema Alveolar hypoventilation- reduced respiratory drive Shunt- only during acute exacerbation if pneumonia us extensive enough