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

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)

During intense exercise, lactate buildup causes metabolic acidosis because hydrogen ions accumulate and bicarbonate is consumed to buffer them. This drives a drop in pH and a fall in bicarbonate. To compensate, the body increases ventilation to expel CO2, so arterial CO2 falls. The combination you’d see is a decreased pH with lowered bicarbonate, plus a compensatory drop in CO2 from hyperventilation. This pattern clearly points to metabolic acidosis with respiratory compensation due to lactate accumulation, helping distinguish it from respiratory alkalosis, where the primary change is low CO2 with an elevated or normal pH rather than a lowered pH.