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Medical Emergencies · single question

A patient begins hyperventilating during a dental procedure. Which of the following BEST describes the resulting acid-base change?

  1. Increased paCO2 leading to respiratory acidosis
  2. Decreased paCO2 leading to respiratory alkalosis
  3. Decreased paO2 leading to hypoxia
  4. Increased paCO2 leading to metabolic alkalosis
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Correct answer: B. Decreased paCO2 leading to respiratory alkalosis

  • A. Increased paCO2 (hypercapnia) occurs in hypoventilation (COPD exacerbation, opioid overdose), producing respiratory acidosis — the opposite of hyperventilation.
  • B. CORRECT. Hyperventilation = excessive CO2 removal via the lungs. This causes paCO2 to DROP below 35 mmHg (hypocapnia). Lower CO2 shifts the bicarbonate buffer equation leftward, decreasing H+ concentration → respiratory alkalosis. Symptoms include dizziness, perioral tingling, and carpal spasm.
  • C. paO2 may actually be normal or slightly increased with hyperventilation. Decreased paO2 = hypoxia, which occurs in airway obstruction or lung disease.
  • D. Metabolic alkalosis is caused by non-respiratory mechanisms (vomiting, diuretics), not by changes in ventilation.

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