Which acid-base disturbance is characterized primarily by decreased pH and normal PCO2?

Which acid-base disturbance is characterized primarily by decreased pH and normal PCO2?

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

Answer: (B)

The situation described, where there is a decreased pH accompanied by a normal PCO2, is indicative of metabolic acidosis. In metabolic acidosis, the primary disturbance is a decrease in bicarbonate (HCO3-) due to increased acid production, decreased acid excretion, or loss of bicarbonate, which results in a lower blood pH.

In this condition, the body's compensatory mechanism may attempt to correct the acidosis by increasing respiratory rate to excrete more CO2, thus reducing carbonic acid levels and helping elevate pH. However, if PCO2 remains normal, it suggests that the respiratory compensation has not yet occurred or is not sufficient to bring the pH back to baseline levels. Therefore, the hallmark of metabolic acidosis is the combination of low pH and typically normal CO2 levels, as the primary imbalance lies in metabolic factors rather than respiratory ones.

Understanding this mechanism is crucial in clinical chemistry as it helps clinicians evaluate and manage acid-base disorders effectively.