Hyperventilation is defined as which of the following?

• A. An excessive rate (>20 breaths/min) and depth of respiration leading to the abnormal loss of CO2 from the blood (alkalosis)
• B. A mild increase in respiration
• C. A severe obstruction of airways
• D. Breathing with shallow breaths

Answer: (A)

Hyperventilation means breathing beyond the body's needs, blowing off more CO2 than is produced. This is shown by an excessive rate (more than about 20 breaths per minute) and greater depth of breathing, which together cause a rapid drop in arterial CO2 and result in respiratory alkalosis (blood becomes more alkaline). That combination—high rate and deep breaths with CO2 loss—is why this option is best. The other choices describe a mild increase in breathing, a severe airway obstruction, or shallow breathing, none of which capture the excessive ventilation and CO2 depletion that define hyperventilation.