An ABG report indicates pH 7.25, PCO2 35 mm Hg, and HCO3 20 mEq/L. Which disturbance would you identify?

An ABG report indicates pH 7.25, PCO2 35 mm Hg, and HCO3 20 mEq/L. Which disturbance would you identify?

• A. Metabolic alkalosis
• B. Metabolic acidosis
• C. Respiratory acidosis
• D. Respiratory alkalosis

Answer: (B)

The key idea is to interpret arterial blood gases by looking at pH first and then identify which system is driving the change using HCO3− and PCO2. Here, the pH of 7.25 shows acidemia. The bicarbonate is low at 20 mEq/L, pointing to a metabolic process as the primary disturbance rather than a primary respiratory problem. The PCO2 is 35 mm Hg, which is not elevated and actually reflects some respiratory compensation by blowing off CO2. Put together, this pattern indicates metabolic acidosis with respiratory compensation. It wouldn’t be metabolic alkalosis (that would have a high HCO3− and a higher pH), and it wouldn’t be a primary respiratory disorder (bursting into respiratory acidosis would raise PCO2; respiratory alkalosis would lower PCO2 with a high pH).

The key idea is to interpret arterial blood gases by looking at pH first and then identify which system is driving the change using HCO3− and PCO2. Here, the pH of 7.25 shows acidemia. The bicarbonate is low at 20 mEq/L, pointing to a metabolic process as the primary disturbance rather than a primary respiratory problem. The PCO2 is 35 mm Hg, which is not elevated and actually reflects some respiratory compensation by blowing off CO2. Put together, this pattern indicates metabolic acidosis with respiratory compensation. It wouldn’t be metabolic alkalosis (that would have a high HCO3− and a higher pH), and it wouldn’t be a primary respiratory disorder (bursting into respiratory acidosis would raise PCO2; respiratory alkalosis would lower PCO2 with a high pH).