Time course of blood lactate levels, inflammation, and mitochondrial function in experimental sepsis

BACKGROUND A decrease in blood lactate levels (Lac) >10% during the first hours of resuscitation in sepsis is associated with better outcomes, but the mechanisms are unclear. Our objective was to investigate the relationship between the time course of Lac, inflammatory response, and mitochondrial respiration during experimental sepsis. METHODS Original data from two previously published studies were reanalyzed. In cohort 1, pigs were randomized to be resuscitated for 48 h starting at 6, 12, and 24 h, respectively, after fecal peritonitis induction (n = 8 each). Animals were categorized according to the decrease in Lac during the first 6 h of resuscitation (early if ≥10% [Lac ≥10%] or late if <10% or increased [Lac <10%]), and systemic hemodynamics, inflammatory parameters, and mitochondrial function were compared between groups. In a second group of animals with fecal peritonitis and 24 h of resuscitation (n = 16, cohort 2), abdominal regional Lac exchange was measured, and animals were categorized according to the decrease in Lac as in cohort 1. RESULTS Overall mortality was 20% (4 of 20) in the Lac ≥10% group and 60% (12 of 20) in the Lac <10% group (p = 0.022). In cohort 1, systemic hemodynamics were similar in the Lac ≥10% (n = 13) and Lac <10% (n = 11) groups. Plasma interleukin-6 levels increased during unresuscitated sepsis and decreased during resusciation in both groups, but they were lower at study end in the Lac ≥10% group (p = 0.047). Complexes I and II maximal (state 3) and resting (state 4) isolated brain mitochondrial respiration at study end was higher in the Lac ≥10% group than in the Lac <10% group, whereas hepatic, myocardial, and skeletal muscle mitochondrial respiration was similar in both groups. In cohort 2, mesenteric, total hepatic, and renal blood flow at study end was higher in the Lac ≥10% group (n = 7) than in the Lac <10% group (n = 9), despite similar cardiac output. Hepatic lactate influx and uptake in the Lac ≥10% group were approximately 1.5 and 3 times higher, respectively, than in the Lac <10% group (p = 0.066 for both). CONCLUSIONS A decrease in Lac >10% during early resuscitation (6 h) after abdominal sepsis is associated with lower levels of plasma interleukin-6 and improved brain but not hepatic or muscle mitochondrial respiration. Blood flow redistribution to abdominal organs in animals with early decrease in Lac concentrations increases the potential to both deliver and extract Lac.