Abnormal pulmonary gas exchange Flashcards
What is normal PaO2 and PaCO2?
What is type 1 and type 2 respiration failure?
What are the 4 abnormal states associated with Abnormal pulmonary gas exchange?
Alveolar hypoventilation
Shunt
Ventilation / Perfusion Imbalance
Diffusion Impairment
What is the resut of alveolar hypoventilation on PACO2 and PAO2 ?
Hypoventilation increases the PACO2 and therefore decreases PaCO2
Increased PACO2 takes up space in the alveoli and therefore causes PAO2 and PaO2 to fall
How can you correct a fall in PaO2 due to hypoventilation?
Raising the FIO2
What is the commones cause of hypoxaemia clinically?
V/Q mismatch
Why is normal V/Q ration 0.8?
•Normally breath 4 l/min. CO is 5 l/min so normal V/Q is 4/5 or 0.8
How can you treat hypoxaemia due to low V/Q?
Increase in FIO2
Will Interstitial lung disease affect CO2 levels?
Not usally becuase 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
What is equilibration time for patients with diffusino impairment?
May take as long as 0.75 seconds - the same time as capillary transit time. Normally the equillibration takes 0.25 seconds.
Why does diffusion impairment result in a fall in Pa O2 during exercise?
Capillary transit time decreases during exercise, less time for equillibration.
Why don’t we have 100% haemoglobin saturation?
Because we have a 2-4% shunt
When do we see a pathological shunt?
Alveolar ventilatino 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
