Alveolar-Arterial (A-a) PO2 Difference (PK5) Flashcards
1
Q
What is the value of PAO2?
A
13kPa
2
Q
What is PaO2 where gas is exchanging?
A
13kPa
3
Q
What is PaO2 when blood actually leaves the heart?
A
12kPa
4
Q
2 reasons for drop in PaO2 by the time blood has left the heart
A
- Shunts
- Ventilation-perfusion mismatch
5
Q
What causes the V/Q mismatch?
A
- Lung receives 4 litres/min alveolar ventilation
- Lung receives 5 litres/min blood flow
- Therefore total lung V/Q ratio = 0.8
6
Q
What increases the A-a difference?
A
- Increasing shunt fraction
- Increasing V/Q mismatch
- Age (due to V/Q ratio change)
