Question

A hyperventilating patient has ABG value of pH = 7.53, pCO₂ = 20 mmHg, HCO₃ = 26 meq. What is the diagnosis?

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

Hint:

Assess the pCO₂ to determine whether the primary disturbance is respiratory or metabolic.

Answer 1

The Correct Option is B

Step 1: Interpret the pH.
pH = 7.53 is alkalotic (normal 7.35-7.45). Since pH > 7.45, this is an alkalosis.

Step 2: Identify the primary disturbance.
pCO₂ = 20 mmHg (normal 35-45 mmHg) -- markedly low. A low pCO₂ causes alkalosis because CO₂ is an acid gas. The primary problem is respiratory: reduced pCO₂ due to hyperventilation.

Step 3: Check the bicarbonate.
HCO₃ = 26 meq (normal 22-26 meq) -- at the upper limit of normal, not significantly decreased. In acute respiratory alkalosis there is no renal compensation yet; in chronic forms the kidneys excrete HCO₃ to compensate.

Step 4: Conclusion.
High pH + low pCO₂ + near-normal HCO₃ in a hyperventilating patient = Respiratory alkalosis. This is a primary decrease in pCO₂ caused by increased ventilation (hyperventilation), leading to a rise in pH. Common causes include anxiety, pain, fever, hypoxia, and pulmonary embolism.