Abnormal Pulmonary Gas Exchange Flashcards
What is normal PaO2 and PaCO2 ?
Normal PaO2- 10.5 - 13.5 kPa Normal PaCO2- 4.8-6 kPa
What is type I and type II respiratory failure ?
Type I- PaO2 <8kPa (PaCO2 normal or low)Type II PaCO2 >6.5kPa (PaO2 usually low)
What are the 4 abnormal states associated with Abnormal pulmonary gas exchange ?
Alveolar hypoventilationShuntVentilation / Perfusion ImbalanceDiffusion Impairment
What is the result of alveolar hypoventilation on PACO2 and PAO2 ?
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 )
How can you correct a fall in PaO2 due to hypoventilation ?
Raising the FIO2
Why is normal V/Q ratio 0.8 ?
Normally breathing 4 l/minCO is 5 l/min so normal V/Q is 4/5 or 0.8
What is the commonest cause of hypoxaemia clinically ?
Low V/Q
How does low V/Q sometimes arise in alveoli ?
Due to local alveolar hypoventilation due to some, focal disease
How can you treat hypoxaemia due to low V/Q ?
Increase in FIO2
Will Interstitial lung disease affect CO2 levels ?
Not usually because CO2 diffuses 20 times faster than O2
How does diffusion impairment affect diffusing speed of oxygen ?
Diffusion impairment means it takes LONGER for blood and alveolar air to equilibrate, particularly for oxygen
Why does diffusion impairment result in a fall in Pa O2 during exercise ?
Capillary transit time decreases during exercise, less time for equilibration
Why don’t we have 100% haemoglobin saturation ?
Because we have a 2-4% shunt
When do we see a pathological shunt ?
Alveolar ventilation malformations, congenital heart disease and pulmonary disease
Does large shunt respond well to increase in FIO2 ?
No, blood leaving normal sections of the lung is already 98% saturated
