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 clin ical evidence of tissue hypoperfusion. Design: The preliminary study i s a report of a series of observations in 12 patients, The prospective study is also observa tional, involving the structured collection of hemodynamic and metabolic variables in a prescribed series of patients , Setting: Cardiac surgical intensive care unit of a university teachi ng hospital. Patients: Twelve patients who developed an unexplained la ctic acidosis after cardiac surgery are reported in the preliminary st udy. The prospective study involved observations in 112 consecutive pa tients undergoing cardiopulmonary bypass for cardiac surgery. Interven tions: None, Measurements and Main Results: Preliminary study: Cardiac index was increased before, during and after recovery from lactic aci dosis, Recovery from lactic acidosis was associated with a decrease in oxygen transport index and significant increases in oxygen consumptio n index and oxygen extraction ratio, Prospective study: Hemodynamic, o xygen transport, and oxy gen consumption variables, together with arte rial blood gas and lactate concentrations, were assessed every 6 hrs f or 24 hrs after surgery, Sixteen patients developed lactic acidosis (p eak lactate concentration >5.0 mmol/L). Compared with the remainder of the patients, this subgroup had longer duration of cardiopulmonary by pass (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). He modynamic variables, including cardiac index, were remarkably similar in the acidotic and nonacidotic groups, All of the acidotic p atients, in both parts of this study, recovered from their acidosis. E leven of the patients in the preliminary study and all of the 16 acido tic patients in the prospective study were ultimately discharged from the hospital, Conclusions: This report documents the occurrence of lac tic acidosis in a subgroup of patients undergoing cardiopulmonary bypa ss, The pathogenesis of this disorder is uncertain, but it appears to not relate to inadequate oxygen delivery. Systemic vasodilation and re duced oxygen extraction appear to be features of this disorder, which has an excellent prognosis.