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 ΔMFI, LC, and ΔSOFA. 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. ΔMFI, LC, and ΔSOFA were 0.1 (interquartile range [IQR] = 0 to 0.3), 18% (IQR = -10% to 46%), and -2 (IQR = -4 to 0). Both ΔMFI and LC were associated with ΔSOFA (β = -5.3, p = 0.01; and β = -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.