Kinetics of Adipose Tissue Microdialysis-Derived Metabolites in Critically Ill Septic Patients

Microdialysis (MD) provides the opportunity to monitor tissue metabolic changes. This study aimed to describe the kinetics of MD-derived metabolites during the course of critical sepsis, to assess whether these metabolites are useful in grading sepsis severity, and to investigate their prognostic use. To this end, 54 mechanically ventilated septic patients were prospectively studied, out of which 39 had shock. Upon sepsis onset, an MD catheter was inserted into the subcutaneous adipose tissue of the upper thigh. Dialysate samples were analyzed for glucose, pyruvate, lactate, and glycerol. Sampling was performed six times per day for a maximum of 6 days. The daily mean values of MD measurements were calculated for each patient. Arterial blood was analyzed for glucose, lactate, and glycerol concomitantly with dialysate sampling. Blood glucose and tissue glucose levels along with lactate levels were high during the entire study period. Tissue pyruvate and glycerol were also raised, whereas the lactate-pyruvate ratio was preserved. At study entry, patients with septic shock had higher tissue lactate (3.3 vs. 1.9 mmol/L, P= 0.01) and glycerol (340 vs. 169 mol/L, P= 0.04) levels compared with those without shock. Nonsurvivors had higher tissue lactate (P= 0.008), glycerol (P= 0.004), and pyruvate (P= 0.002) levels than survivors during the whole observation period. Logistic regression analysis showed that age (odds ratio OR, 1.075; 95% confidence interval CI, 1.004-1.150; P= 0.03), Sequential Organ Failure Assessment score on day 1 (OR, 1.550; 95% CI, 1.043-2.312; P= 0.03), and tissue glycerol on day 1 (OR, 1.007; 95% CI, 1.001-1.012; P= 0.01) predicted mortality independently. In conclusion, critical sepsis is characterized by high tissue lactate and pyruvate levels and a preserved lactate-pyruvate ratio, suggesting a nonischemic mechanism for raised blood lactate levels. Septic shock is associated with higher tissue lactate and glycerol levels compared with sepsis without shock. Elevated tissue lactate, pyruvate, and glycerol levels are related to poor clinical outcome, with the latter constituting an independent predictor.