Non-anion gap acidosis in asthma: clinical and laboratory features and outcomes for hospitalized patients

Metabolic acidosis secondary to lactic acidosis may occur in acute, severe asthma and its presence suggests that respiratory muscle fatigue and tissue hypoxia play a major part in the pathogenesis. Non-anion gap metabolic acidosis (NAG acidosis) has also been reported in acute asthma but its impact on the clinical outcome has not been evaluated. The objective of this study was to evaluate the prevalence of NAG acidosis, characterize the laboratory findings, and determine its impact on clinical outcomes. Acid-base and electrolyte status and clinical outcomes were examined over a 1-yr (2005 calendar yr) period in 109 adult patients (38 males, 71 females; age range 21 to 91 yr) hospitalized for asthma exacerbation. The cohort was divided into 3 groups: I. No metabolic acidosis (n = 66), II. Anion gap (AG) acidosis (n = 11), and III. NAG acidosis (n = 32). For each of the groups, laboratory findings were consistent, demonstrating a tendency to hyperchloremia in the NAG acidosis group. One subject in the NAG acidosis group died. NAG acidosis was associated with a statistically significant (p = 0.028) risk of requirement for mechanical ventilation necessitating admission to the Medical Intensive Care Unit (MICU); the odds ratio for intubation for NAG acidosis compared to other groups was 3.92. No difference, however, was detected in overall length of stay (LOS) in hospital for patients with NAG acidosis vs the other groups. NAG metabolic acidosis in acute asthma may be more prevalent than expected and may be associated with more frequent need for mechanical ventilation and admission to an intensive care unit.