Lactate Clearance in Septic Shock Is Not a Surrogate for Improved Microcirculatory Flow

Background: Failure to normalize lactate is associated with poor outcomes in septic shock. It has been suggested that persistently elevated lactate may result from regional ischemia due to disturbed and/or heterogenous microcirculatory blood flow. Objectives: The goal of this study was to determine if lactate clearance (LC) may serve as a surrogate marker for changes in microcirculatory blood flow in patients with septic shock. Methods: This was a prospective observational study performed within a previously published clinical trial of L-carnitine for the treatment of vasopressor-dependent septic shock. Intravital video microscopy was performed at enrollment and 12 hours later, and microcirculatory flow index (MFI) was assessed. Associations between enrollment MFI, lactate, and Sequential Organ Failure Assessment (SOFA) score were determined, in addition to associations between Delta MFI, LC, and Delta SOFA. A preplanned subgroup analysis of only patients with an elevated initial lactate was performed. Results: We enrolled a total of 31 patients, 23 with survival and sufficient quality videos both at enrollment and at 12 hours. Delta MFI, LC, and Delta SOFA were 0.1 (interquartile range [IQR] = 0 to 0.3), 18% (IQR = -10% to 46%), and -2 (IQR = -4 to 0). Both Delta MFI and LC were associated with Delta SOFA (beta = -5.3, p = 0.01; and beta = -3.5, 0.047), but not with each other, even in the subgroup of patients with an initially elevated lactate. Conclusions: We observed no association between degree of LC and change in microcirculatory blood flow in patients with septic shock. These data suggest against the hypothesis that LC may be used as a surrogate marker of microcirculatory blood flow. (C) 2016 by the Society for Academic Emergency Medicine