Question

The acid-base status of a patient is as follows: pH 7.45, pCO2 30 mm Hg, pO2 105 mm Hg. The patient has partially compensated:

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

Hint:

High-normal pH with a low pCO2 driving the change.

Answer 1

The Correct Option is D

Interpret the blood gas in the standard sequence. First the pH of 7.45 tips toward the alkaline side, so whatever the primary disturbance is, it is an alkalosis. Next look at carbon dioxide: a pCO2 of 30 is below the normal range, and since carbon dioxide is an acid gas, removing it pushes the pH upward. That means the respiratory system, not the metabolic side, is the engine of the alkalosis here, so the primary problem is a respiratory alkalosis produced by hyperventilation. Finally, gauge compensation. If the alkalosis were uncompensated the pH would be clearly high, but it has been dragged back to merely the upper normal limit by the kidneys excreting bicarbonate; because the pH has not fully normalised this is partial compensation. Putting the pieces together gives a respiratory alkalosis that is partially compensated.
$ \uparrow\text{pH} + \downarrow\text{pCO}_2 \Rightarrow \text{respiratory alkalosis (partially compensated)} $
\[\boxed{\text{Respiratory alkalosis}}\]