Increased serum bicarbonate in critically ill patients: a retrospective analysis.

PURPOSE: Although metabolic alkalosis is a common occurrence, no study has evaluated its prevalence, associated factors or outcomes in critically ill patients.
METHODS: This is a retrospective study from the Multiparameter Intelligent Monitoring in Intensive Care II database. From 23,529 adult patient records, 18,982 patients met the inclusion criteria.
RESULTS: Serum bicarbonate levels demonstrated a U-shaped association with mortality with knots at 25 and 30 mEq/l. Of the total included patients, 5,565 (29.3 %) had at least one serum bicarbonate level measurement >30 mEq/l. The majority were exposed to multiple factors that are classically associated with metabolic alkalosis (mainly diuretic use, hypernatremia, hypokalemia and high gastric output). Patients with increased serum bicarbonate exhibited increased ICU LOS, more days on mechanical ventilation and higher hospital mortality. After multivariate adjustment, each 5-mEq/l increment in the serum bicarbonate level above 30 mEq/l was associated with an odds ratio of 1.21 for hospital mortality. The association between increased serum bicarbonate levels and mortality occurs independently of its possible etiologies.
CONCLUSION: An increased serum bicarbonate level is common in critically ill patients; this can be attributed to multiple factors in the majority of cases, and its presence and duration negatively influence patient outcomes.