Metabolic acidosis not due to lactic acidosis in patients with severe acute asthma

Asthmatics seeking emergency care for severe acute asthma may show metabolic acidosis. We sought to determine the frequency of metabolic acidosis in such patients and to assess the relative contributions of renal bicarbonate loss and lactic acid accumulation to this acidosis. Twenty-two asthmatics (21-71 yr; four males, and 18 females) who came consecutively to the emergency department with severe acute asthma were studied. Most patients reported that their asthmatic symptoms had begun to worsen greater than or equal to 2 days before the emergency department visit. Within several hours, simultaneous measurements of arterial blood gases, whole blood lactate, and serum electrolytes were made. Ten of 22 patients were found to have metabolic acidosis (base deficit greater than 2 mEq/L). All ten patients had nonanion gap acidosis, while nine of ten had whole blood lactate values in the normal range (0.33 to 2.55 mmol/L). In the one patient with an elevated whole blood lactate level, the concentration of lactate in excess of normal (0.45 mmol/L) could not account for the magnitude of the base deficit (-4.9 mEq/L). We conclude that a) nonanion gap metabolic acidosis is very common in asthmatics with acute severe asthma (prevalence 45% in our series), and b) the mechanism of the base deficit in these patients is excessive renal bicarbonate excretion. We believe that the latter occurs as a renal compensatory response to a preceding period of hypocapnia due to hyperventilation related to worsening asthma.