Study Objective: To determine whether correction of acidemia using bicarbonate improves hemodynamics in patients who have lactic acidosis. Design: Prospective, randomized, blinded, crossover study. Each patient sequentially received sodium bicarbonate and equimolar sodium chloride. The order of the infusions was randomized. Setting: Intensive care unit of a tertiary care hospital. Patients: Fourteen patients who had metabolic acidosis (bicarbonate < 17 mmol/L and base excess < -10) and increased arterial lactate (mean, 7.8 mmol/L). All had pulmonary artery catheters and 13 were receiving catecholamines. Measurements and Main Results: Sodium bicarbonate (2 mmol/kg body weight over 15 minutes) increased arterial pH (7.22 to 7.36, P < 0.001), serum bicarbonate (12 to 18 mmol/L, P < 0.001), and partial pressure of CO2 in arterial blood (Pa(CO2)) (35 to 40 mm Hg, P < 0.001) and decreased plasma ionized calcium (0.95 to 0.87 mmol/L, P < 0.001). Sodium bicarbonate and sodium chloride both transiently increased pulmonary capillary wedge pressure (15 to 17 mm Hg, and 14 to 17 mm Hg, P < 0.001) and cardiac output (18% and 16%, P < 0.01). The mean arterial pressure was unchanged. Hemodynamic responses to sodium bicarbonate and sodium chloride were the same. These data have more than 90% power of detecting a 0.5 L/min (7%) change in mean cardiac output after administration of sodium bicarbonate compared with that after sodium chloride. Even the 7 most acidemic patients (mean pH, 7.13; range, 6.90 to 7.20) had no significant hemodynamic changes after either infusion. Conclusions: Correction of acidemia using sodium bicarbonate does not improve hemodynamics in critically ill patients who have metabolic acidosis and increased blood lactate or the cardiovascular response to infused catecholamines in these patients. Sodium bicarbonate decreases plasma ionized calcium and increases Pa(CO2).