What happens to arterial carbon dioxide (PaCO2) and blood pH during hyperventilation?

Hyperventilation results in excessive exhalation of carbon dioxide, which decreases the partial pressure of arterial CO2 (PaCO2 < 35 mmHg). Since CO2 combines with water to form carbonic acid (H2CO3), reduced CO2 leads to decreased hydrogen ion concentration and a rise in blood pH above 7.45 — a condition known as respiratory alkalosis. In the dental setting, anxiety-induced hyperventilation can cause symptoms including perioral tingling, lightheadedness, and carpopedal spasm. Treatment is to have the patient breathe into a paper bag (or cupped hands) to re-inhale CO2.