• Hiren J Mehta, Gautam Bhanusheli, Paul J Nietert, and Nicholas J Pastis.
• Medical University of South Carolina, Division of Pulmonary and Critical Care Medicine, Charleston, SC 29425, USA.
• J Crit Care. 2012 Jun 12.

PurposeAnion gap (AG) metabolic acidosis is common in critically ill patients. The relationship between initial AG at the time of admission to the medical intensive care unit (MICU) and mortality or length of stay (LOS) is unclear. This study was undertaken to evaluate this relationship.Materials And MethodWe prospectively examined the acid-base status of 100 consecutive patients at the time of MICU admission and recorded their mortality and LOS. The etiology of each AG was also recorded. Anion gap was corrected for albumin levels. The patients were divided into 4 stages based on severity of AG. Outcomes based on severity of AG were measured, and comparisons that adjusted for baseline characteristics were performed.ResultsThis study showed that increased AG was associated with the higher mortality and that an AG more than 30 had the highest mortality. Mortality was significantly (P = .013) increased, even after accounting for AG etiology. Patients with highest AG also had the longest LOS in the MICU, and patients with normal acid-base status had the shortest MICU LOS (P < .01).ConclusionA high AG at the time of admission to the MICU was associated with higher mortality and LOS. Initial risk stratification based on AG and metabolic acidosis may help guide appropriate patient disposition (especially in patients without other definitive criteria for MICU admission) and assist with prognosis. Mixed AG metabolic acidosis with concomitant acid-base disorder was associated with increased MICU LOS.

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