Hypercapnia

[SBURNSTEVEN]

How does a patient with COPD and therefore chronically Hypercapnia not have a respiratory acidosis (acute decompensation due to respiratory infection can cause respiratory acidosis)....but why not normally? I'm assuming because of their kidneys compensation with bicarbonate?

[bmxRRT]

Careful, not all COPD'ers are chronically hypercapneic! Many of them have normal range PCo2, it has a lot to do with the severity of their disease and the amount of time they've been at that level of severity. If a patient has a chronically high PCo2 the kidneys will compensate by excreting more HCO3- to make the pH more alkalotic to bring it back into 7.35-7.45 range, so yes you are correct on that. It doesn't happen overnight, it takes a good amount of time for the kidneys to react in this manner. The kidney's reabsorb more bicarbonate if it senses a low pH (acidic), instead of excreting it into the urine. It's all apart of homeostasis.