Which acid-base parametre from arterial blood-gas gives most informastion about lung ventilation?

Question

Is PCO2 more useful than PaO2, and why?

Answer 1

pCO2.

In young, healthy people pO2 may be around 100, where people with advanced lung disease do well will a pO2 of 60, which still leaves 90% of hemoglobin oxygenated. It's a robust system.

That being the case, only people with extremely advanced lung disease run on an oxygen drive. The vast majority of us run on a CO2 drive, adjusting our ventilation minute-to-minute as needed to maintain a normal pCO2. Again, it's only in the most extreme of people with chronic respiratory failure that you'll see a compensated respiratory acidosis.

Answer 2

Well, I am guessing CO2. Normally the pH of blood is 7.35-7.45. CO2 is acidic.  So you could actually kind of use both. If the blood pH is less than 7.35 then you probably have an excess of CO2 or not enough bicarbonate (but that is more related to the liver). If the blood pH is higher than 7.45 then you would have a CO2 deficit. Blood would have too little CO2.

Answer 3

if you could only check one parameter...

the blood pH is the one most of the physicians want if the patient is in distress.

second is the O2 sat value.

Answer 4

This question may actually deal with a question of semantics.  Two aspects of respiration are ventilation and oxygenation.  PCO2 is associated with ventilation, while PO2 is associated with oxygenation.  

This distinction comes into play with mechanical ventilators, which require different adjustments to affect each.