Unmeasured anions account for most of the metabolic acidosis in patients with hyperlactatemia.

PURPOSE To characterize the different components of metabolic acidosis in patients with hyperlactatemia in order to determine the degree to which lactate is responsible for the acidosis and the relevance that this might have in the outcome of these patients. METHODS Arterial blood gas, arterial lactate, Na+, K+, Ca2+, Mg2+, Cl-, phosphate, albumin, and creatinine were measured on admission to make a diagnosis of the acid-base disturbances present. Intensive Care Unit and in-hospital mortality were also recorded. RESULTS A total of 58 patients with hyperlactatemia were included. They usually had a mild acidemia (pH 7.31 +/- 0.12) and a significantly high Standard Base Deficit (7.6 +/- 6.7 mEq/L). In addition to lactate (4.3 +/- 2.3 mEq/L), chloride (106.9 +/- 9.5 mEq/L) and unmeasured anions (8.6 +/- 5.0 mEq/L) accounted for the metabolic acidosis. Unmeasured anions were primarily responsible for the acidosis in both Intensive Care Unit survivors and nonsurvivors (44.7% +/- 26.0% and 46.0% +/- 17.5%, respectively, P = 0.871). Lactate contributed in similar percentages to the acidosis in both groups (23.0% +/- 11.8% and 24.2% +/- 9.7% in Intensive Care Unit survivors and nonsurvivors, respectively; P = 0.753). Correlation between Standard Base Deficit and lactate was found only in Intensive Care Unit nonsurvivors (r = 0.662, P < 0.01). DISCUSSION Hyperlactatemia is usually accompanied by metabolic acidemia, but lactate is responsible for a minor percentage of the acidosis; unmeasured anions account for most of the acidosis in patients with hyperlactatemia. The percentage of the acidosis due to hyperlactatemia was not relevant in terms of outcome.