Hyperventilation syndrome classically causes which symptom due to low carbon dioxide levels?

• A. Productive Cough with Purulent Sputum
• B. Paresthesias Around the Mouth and in the Extremities
• C. Chest Pain that Worsens with Inspiration
• D. Hyperglycemia and Dehydration

Answer: (B)

When CO2 falls from rapid breathing, you get respiratory alkalosis. The rise in pH increases the binding of calcium to albumin, which lowers the amount of free (ionized) calcium in the blood. This functional hypocalcemia heightens nerve and muscle excitability, producing tingling and numbness around the mouth and in the extremities—the classic paresthesias of hyperventilation. Lightheadedness or dizziness from cerebral vasoconstriction can also accompany this state.

The other options don’t fit the low-CO2 mechanism: productive cough with purulent sputum points to infection with mucus production; chest pain that worsens with inspiration suggests pleuritis or another pleural process; hyperglycemia with dehydration reflects metabolic disturbances unrelated to CO2 levels.