A 21-year-old woman in the emergency room is displaying rapid and deep, labored breathing. Her room ABG reveals a pH of 7.25, PaCO2 of 28, HCO3– of 14 mEq/L, and a base excess of –14 mEq/L

How would the respiratory therapist assess her acid-base condition?
1. Severe hyperventilation
2. Partially compensated metabolic acidosis
3. Compensatory response to the metabolic acidosis
4. Severe hypoventilation
a. 1, 2, and 3 only
b. 1 and 3 only
c. 3 only
d. 2, 3, and 4 only

ANS: A
First, the patient's pH must be categorized. The patient's pH is below the range of 7.35 to 7.45, which indicates acidemia. Second, respiratory involvement must be determined. The PaCO2 is well below the normal range of 35 to 45 mm Hg, indicating severe hyperventilation. By itself, this would cause alkalosis, but the presence of a low pH indicating acidemia, this rules out the cause as primary respiratory alkalosis. The low PaCO2 is probably a compensatory response to primary metabolic acidosis, although the response is insufficient to restore pH to its normal range. Third, a determination of metabolic involvement must be analyzed. The HCO3– is severely re-duced below the normal range of 22 to 26 mEq/L. This result is consistent with the low pH. In the presence of low pH and low PaCO2 and a low HCO3– low indicates primary metabolic acido-sis. This is also confirmed by the large BE value. Finally, a confirmation of compensation must be made. The severe hyperventilation represents a compensatory response to the primary metabolic acidosis, although compensation is far from complete. Nevertheless, the pH level would be even lower if the PaCO2 were normal.