Aerial blood gases obtained while the patient is receiving oxygen reveal the following values: pH 7.30; PCO2 39; bicarbonate 18 mEq/L; oxygen saturation 85%. The patient is:

The serum bicarbonate is somewhat low (normal is 22 to 24 mEq/L); therefore, the patient has a moderate metabolic acidosis. The aerial PCO2 of 39 is within normal limits; therefore, the patient has neither a respiratory acidosis nor a compensating respiratory alkalosis. However, the absence of a respiratory alkalosis is worrisome. Early in an attack of asthma, hyperventilation in response to hypoxia leads to a fall in aerial PCO2. The "normal" PCO2 suggests that this patient is no longer able to hyperventilate effectively and compensate for the abnormalities of ventilation-perfusion ratios in his lungs. Metabolic acidosis is common in patients with status asthmaticus and probably reflects tissue hypoxia. Ref: Cho K.C. (2013). Chapter 21. Electrolyte & Acid-Base Disorders. In M.A. Papadakis, S.J. McPhee, M.W. Rabow (Eds), CURRENT Medical Diagnosis & Treatment 2013.