Admission Anion Gap Metabolic Acidosis and Its Impact on Patients in Medical Intensive Care Unit.

Anion 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 is unclear. This study was undertaken to evaluate this relationship.  We prospectively examined the acid-base status of 500 consecutive patients at the time of MICU admission and outcome was measured in terms of mortality, length of ICU stay, need of ventilator, and laboratory parameters. The patients were divided into four stages based on the severity of AG. Outcome based on the severity of AG was measured, and comparisons that adjusted for baseline characteristics were performed.  This study showed that increased AG was associated with the higher mortality. Patients with the highest AG also had the longest length of stay in the MICU, and patients with normal acid-base status had the shortest ICU length of stays ( < 0.05).  A high AG at the time of admission to the MICU was associated with higher mortality and length of stays. 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.