How can you differentiate metabolic acidosis due to lactate accumulation from respiratory alkalosis during exercise testing?

• A. Metabolic acidosis from lactate shows decreased pH with increased bicarbonate.
• B. Metabolic acidosis from lactate shows decreased pH with low CO2.
• C. Respiratory alkalosis shows decreased pH with high CO2.
• D. Metabolic acidosis from lactate shows decreased pH with lowered bicarbonate and compensatory hyperventilation.

Answer: (D)

Lactate buildup during intense exercise causes metabolic acidosis because lactate production accompanies hydrogen ions, and bicarbonate buffers these acids, so bicarbonate levels fall. The body tries to compensate by increasing ventilation, blowing off CO2, which lowers arterial CO2. This combination yields a decreased pH with lowered bicarbonate and a compensatory drop in CO2 from hyperventilation. That is why this choice is the best: it describes the metabolic acidosis from lactate plus the respiratory compensation that accompanies it. Respiratory alkalosis, by contrast, lowers CO2 and raises pH, not produces a low pH, and a metabolic acid scenario typically includes a reduced bicarbonate rather than increased.