ACUTE COPD

in a patient with a severe exacerbation of COPD high concentration od oxygen
administration may cause respiratory depression and worsening acidosis ..why is
it so ??  i dont understand why would high concentration of oxygen may cause
hypercapnia as there is no source of CO2 as we are administrating just oxygen
???

[David S. Wilson, MD, FCCP]

This is true and applies to only a small subset of patients with COPD.  The mechanism involves "flooding" Oxygen receptors that are used to lower oxygen levels.  Because of lower Oxygen levels on a chronic basis, these receptors are reset to expect lower levels and when flooded, trigger a decrease in respiratory drive...this leads to hypoventilation and hypercapnia