In chronic respiratory acidosis due to COPD, metabolic compensation results in which change on ABG?

In chronic respiratory acidosis due to COPD, metabolic compensation results in which change on ABG?

• A. Increased HCO3-
• B. Decreased HCO3-
• C. No change in HCO3-
• D. Decreased PaCO2

Answer: (A)

Chronic CO2 retention from COPD triggers the kidneys to compensate by boosting bicarbonate reabsorption and generating new bicarbonate. This metabolic adjustment raises HCO3- on ABG, helping to neutralize the excess acid from the elevated CO2. In a long-standing process, the pH tends to normalize toward the low end of normal, even though PaCO2 remains high. So the best answer is an increased HCO3-. Decreases in bicarbonate would worsen acidosis, and no change would indicate no compensation, which isn’t the case in chronic COPD. Decreased PaCO2 isn’t expected because CO2 retention is the problem in COPD.

Chronic CO2 retention from COPD triggers the kidneys to compensate by boosting bicarbonate reabsorption and generating new bicarbonate. This metabolic adjustment raises HCO3- on ABG, helping to neutralize the excess acid from the elevated CO2. In a long-standing process, the pH tends to normalize toward the low end of normal, even though PaCO2 remains high. So the best answer is an increased HCO3-. Decreases in bicarbonate would worsen acidosis, and no change would indicate no compensation, which isn’t the case in chronic COPD. Decreased PaCO2 isn’t expected because CO2 retention is the problem in COPD.