Respiratory failure

Question 1

what is the PaO2 cut off for T1RF?

what about PaCO2 for T2RF?

Answer 1

PaO2 < 60mm Hg

PaCO2 > 45

Question 2

which way does acidosis move the oxygen saturation curve?

Answer 2

it moves it to the right

moving to the right has a favourable effect in releasing oxygen. This favours the tissues.

If the blood was alkalotic, the curve would move left, favouring capture of oxygen from the lungs.

This is the Bohr effect

The Haldane effect is the follow on effect on the Hb-CO2 binding. Deoxyhaemoglobin has HIGHER CO2 binding at lower partial pressures. (and vice versa)

Question 3

what does a normal A-a gradient mean?

Answer 3

this indicates that hypoxaemia is due to alveolar hypoventilation alone without V/Q inequality

so, for example, the chick with a pH 7.2, paCO2 of 63 and PaO2 of 195 on 0.4 oxygen

she would have an Aa of 11.

therefore, it’s due to hypoventilation (in one such case, opioid overdose)

Question 4

what does CPAP do in APO?

(what do the studies show?

also - how does it help the body?)

Answer 4

CPAP is good for preventing intubation. There is some evidence with trends to mortality benefit, but I’m not certain about significance

in APO, CPAP is good to first of all decrease venous return.

However, it also provides thoracic cage pressure and adds extra pressure outside the heart. This helps to shrink the heart down to a size more advantageous for pumping