A common cause of respiratory alkalosis is:

• A. Vomiting
• B. Starvation
• C. Asthma
• D. Hyperventilation

Answer: (D)

Respiratory alkalosis happens when ventilation rises enough to blow off CO2 faster than it’s produced, so PaCO2 falls and pH rises. CO2 forms carbonic acid, then H+ and bicarbonate; lowering CO2 shifts the balance toward fewer H+ and a higher pH. The kidneys later compensate by excreting bicarbonate, but the primary change is driven by ventilation. Hyperventilation is the typical cause because it directly reduces CO2 levels, producing an alkalemic state. Vomiting causes loss of stomach acid (HCl), which leads to metabolic alkalosis with elevated bicarbonate rather than a primary respiratory change. Starvation often leads to metabolic acidosis from ketone production, not a respiratory alkalosis. Asthma can cause respiratory issues with CO2 retention and a tendency toward respiratory acidosis, though severe distress might show rapid breathing, the classic and most common link to respiratory alkalosis is hyperventilation.