Type B lactic acidosis following cardiopulmonary bypass

Objective To describe, characterize, and identify the associations of postcardiac surgical lactic acidosis occurring in the absence of clinical evidence of tissue hypoperfusion. Design The preliminary study is a report of a series of observations in 12 patients. The prospective study is also observational, involving the structured collection of hemodynamic and metabolic variables in a prescribed series of patients. Setting Cardiac surgical intensive care unit of a university teaching hospital. Patients Twelve patients who developed an unexplained lactic acidosis after cardiac surgery are reported in the preliminary study. The prospective study involved observations in 112 consecutive patients undergoing cardiopulmonary bypass for cardiac surgery. Interventions None. Measurements and Main Results Preliminary study: Cardiac index was increased before, during and after recovery from lactic acidosis. Recovery from lactic acidosis was associated with a decrease in oxygen transport index and significant increases in oxygen consumption index and oxygen extraction ratio. Prospective study Hemodynamic, oxygen transport, and oxygen consumption variables, together with arterial blood gas and lactate concentrations, were assessed every 6 hrs for 24 hrs after surgery. Sixteen patients developed lactic acidosis (peak lactate concentration >5.0 mmol/L). Compared with the remainder of the patients, this subgroup had longer duration of cardiopulmonary bypass (116 +/- 31 vs. 76 +/- 31 mins, p < .01), greater intraoperative hypothermia (24.9 +/- 2.0 degrees vs. 26.6 +/- 2.3 degrees C, p < .01), more frequent requirement for vasopressor agents (14/16 vs. 35/96, p < .05) and a higher frequency of hyperglycemia (15/16 vs. 28/96, p < .01). Hemodynamic variables, including cardiac index, were remarkably similar in the acidotic and nonacidotic groups. All of the acidotic patients, in both parts of this study, recovered from their acidosis. Eleven of the patients in the preliminary study and all of the 16 acidotic patients in the prospective study were ultimately discharged from the hospital. Conclusions This report documents the occurrence of lactic acidosis in a subgroup of patients undergoing cardiopulmonary bypass. The pathogenesis of this disorder is uncertain, but it appears to not relate to inadequate oxygen delivery. Systemic vasodilation and reduced oxygen extraction appear to be features of this disorder, which has an excellent prognosis. (Crit Care Med 1997; 25:46-51)