Prognostic value of blood lactate levels: does the clinical diagnosis at admission matter?

BACKGROUND Hyperlactatemia and its reduction after admission in the intensive care unit (ICU) have been related to survival. Because it is unknown whether this equally applies to different groups of critically ill patients, we compared the prognostic value of repeated lactate levels (a) in septic patients versus patients with hemorrhage or other conditions generally associated with low-oxygen transport (LT) (b) in hemodynamically stable versus unstable patients. METHODS In this prospective observational two-center study (n = 394 patients), blood lactate levels at admission to the ICU (Lac(T0)) and the reduction of lactate levels from T = 0 to T = 12 hours (DeltaLac(T0-12)) and from T = 12 to T = 24 hours (DeltaLac(T12-24)), were related to in-hospital mortality. RESULTS Reduction of lactate was associated with a lower mortality only in the sepsis group (DeltaLac(T0-12): hazard ratio [HR] 0.34, p = 0.004 and DeltaLac(T12-24): HR 0.24, p = 0.003), but not in the LT group (DeltaLac(T0-12); HR 0.78, p = 0.52 and DeltaLac(T12-24); HR 1.30, p = 0.61). The prognostic values of Lac(T0), DeltaLac(T0-12), and DeltaLac(T12-24) were similar in hemodynamically stable and unstable patients (p = 0.43). CONCLUSIONS Regardless of the hemodynamic status, lactate reduction during the first 24 hours of ICU stay is associated with improved outcome only in septic patients, but not in patients with hemorrhage or other conditions generally associated with LT. We hypothesize that in this particular group a reduction in lactate is not associated with improved outcome due to irreversible damage at ICU admission.