Acute Prescribing for Medical Inpatients

Question 1

What is the normal PaO2?

Answer 1

11-13kPa (Fi02-10)

Question 2

Why does PaC02 rise in COPD patients receiving oxygen therapy?

Answer 2

1. V/Q mismatch:
   - Normally reduced alveolar tension causes PaO2 to fall causing vasoconstriction
   - COPD bronchoconstriction means reduced alveolar tension. Delivery of O2 results in inappropriate vasodilation of vessels at low tension areas.
   - This requires diversion of blood flow from high tension areas resulting in increased dead space .’. cant offload CO2.
2. Haldane effect
   - deoxygenated Hb likes CO2 more than oxyHb
   - Relative hypoxia in COPD results in greater deoxyHb presence
   - Increasing O2 results in shifting from deoxy to oxyHb, releasing CO2 into the blood.

*Note: ‘Hypoxic drive’ does exist to an extent. Reduced alveolar ventilation has an acute CO2 rise but even when ventilation improves, CO2 continues to rise.

Question 3

Flow rate for Nasal cannulae

Answer 3

2-4 litres (can do 6 but risk drying out nose)

Question 4

What can a ‘simple’ face mask (Hudson/MC mask) achieve

Answer 4

40-60% between 5-10L
Dont go below 5L as risk of rebreathing CO2

Question 5

What is the use of the Venturi mask

Answer 5

Deliver set amount of 02 using filters
If patient has high resp rate (>30) you can increase the flow rate to 1.5% required to aid ventilation.

Question 6

Which patients are more likely to be retainers?

Answer 6

COPD
Neuromuscular disorders (MND)
Kyphoscoliosis

Question 7

Use of non-rebreather mask?

Answer 7

Deliver very high flow 10-15L O2.
Good in acute setting, tend to switch down as appropriate