Which statement best characterizes respiratory alkalosis?

• A. Decreased pH with increased PCO2
• B. Increased pH with decreased PCO2
• C. Normal pH with normal PCO2
• D. Increased bicarbonate with increased PCO2

Answer: (B)

Respiratory alkalosis happens when ventilation drives CO2 out of the body faster than it’s produced, so the blood becomes more basic. The defining pattern is a higher-than-normal pH with a lower-than-normal PCO2. The statement that describes increased pH with decreased PCO2 matches this relationship exactly. CO2 contributes to the acid balance through the carbonic acid–bicarbonate system, so reducing CO2 lowers hydrogen ion concentration and raises pH. Over time the kidneys compensate by reducing bicarbonate to bring pH back toward normal, but the immediate feature is low PCO2 with high pH. The other descriptions describe different states or conditions that don’t characterize respiratory alkalosis.