You will agree that the patient's pH is within normal range.
Her arterial PCO2 is low. PCO2 is an index of alveolar ventilation. A low PCO2 is indicative of alveolar hyperventilation. The normal response for hyperventilation is alkalosis. However, our patient has a normal pH. This is due to compensatory excretion of bicarbonate by the kidneys. Since this process takes approximately one day, we can assume that her problem is at least that long.
Her arterial PO2 is within normal range.