what does it mean when COPD retain PaC02?

Answer 1

Peachtool is almost right.

In a patient with COPD (chronic obstructive pulmonary disease) they have difficulty getting air in and out of their lungs. This is because of one form of airway obstruction or other: airway swelling and oedema, mucous plugging, airway constriction (smooth muscle contraction) etc.

This traps stale air inside the lungs to some degree

It also prevents fresh air from getting into the lungs.

In mild cases, this does not affect the exchange of CO2 significantly, and may not affect the uptake of O2 significantly.

In severe cases, this means the body cannot take in new O2 and cannot get rid of it's CO2.

When we cannot get rid of our CO2 this actually changes the acid/base balance of our body and gives us a condition called Respiratory Acidosis

CO2 + H2O -> H2CO3 -> HCO3- (ie bicarbonate) + H+

This makes us very unwell and usually drives us to hyperventilate like crazy.

In people who have bad lung disease, sometimes they have to put up with high CO2 levels and they sort of get used to it and lose the ability to drive their breathing in this manner. This is what is known as a "CO2 retainer" - they are patients who will not compensate for high CO2 levels in the blood because their lungs are so bad they are used to high levels all the time.

When the CO2 levels go REALLY high, this actually makes us drowsy and eventually comatose. This is usually considered a bad thing.

If your pCO2 level > 55mmHg, you are considered to have type 2 respiratory failure. In CO2 retainers, I have seen the pCO2 level exceed 100mmHg!!! They are very sick!

Answer 2

I believe that it refers to the increased amount of CO2 gas (carbon dioxide) left in the lungs after a person with COPD exhales. This is due to the fact that they can not exhale with great enough force to expel a higher amount of gas.