Question

There are five primary causes of hypoxaemia (low blood oxygen content):

1. Diffusion limitation which limits the transfer of oxygen between the alveoli and blood (such as pulmonary oedema).
2. Hypoventilation
3. Reduced atmospheric oxygen (such as high altitude)
4. Ventilation/perfusion (VQ) mismatch (for some reason poorly ventilated alveoli are still receiving blood flow)
5. Shunt- some alveoli are completely blocked either by obstruction or are completely filled with fluid such as in pneumonia, but still receive blood flow.

The first four of these can be helped by giving the patient oxygen which in turn increases their arterial PO₂. However, giving oxygen has little impact on a patient with a pulmonary shunt.

For each of the above causes, briefly (1-2 sentences) describe how it would lead to low arterial PO₂. Then describe why giving a patient 100% oxygen would increase their arterial PO₂ (for the first four), and why it would not significantly improve in a patient with a pulmonary shunt. Explain your reasoning. 4 and 5 are the most challenging and will require more description than the first 3. (2-6 total sentences each)

Diffusion Limitation :

Hypoventilation :

Reduced atmospheric oxygen :

V/Q Mismatch:

Shunt

Answer 1

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