Microdialysis-assessed interstitium alterations during sepsis: relationship to stage, infection, and pathogen

Purpose: More than a disorder of macrocirculation, sepsis is a disease affecting the microcirculation and the tissue metabolism. In vivo microdialysis (MD) is a bedside technique that can monitor tissue metabolic changes. We conducted this study aiming (1) to assess whether patients at different sepsis stages present with different MD-assessed tissue metabolic profiles and (2) to determine if different underlying types of infections and implicated pathogens are associated with dissimilar metabolic alterations. Methods: We studied 90 mechanically ventilated patients, 65 with septic shock and 25 with severe sepsis. An MD catheter was inserted in the subcutaneous adipose tissue of the upper thigh and interstitial fluid samples were collected along with arterial blood samples every 4 h for a maximum of 6 days. Lactate, pyruvate, glycerol, and glucose concentrations were measured. Results: During the study period, patients with septic shock had higher MD-assessed glycerol (P = 0.009), glycerol gradient (P = 0.016), and glucose (P = 0.004) than patients with severe sepsis, whereas tissue lactate, lactate gradient, and pyruvate dropped significantly with time (P = 0.007, <0.001, and <0.001, respectively) in both patient groups without any observed between-group difference. In addition, there was no between-group difference in their tissue lactate/pyruvate ratio on any day, nor did the ratio decrease significantly with time. Compared with pneumonia patients, and despite similar baseline clinical characteristics, those suffering from intra-abdominal infections showed a pattern of higher and progressively increasing tissue levels of glucose (P = 0.001) and glycerol (P = 0.001). Finally, patients harboring Gram-positive infections had higher tissue levels of glycerol (P = 0.027) and glycerol gradient (P = 0.029) than patients with Gram-negative infections. Conclusions: MD can detect tissue metabolic abnormalities that differ in relation to the sepsis stage and the type of underlying infection or responsible pathogen. Some of the MD-assessed abnormalities are not reflected by conventional blood measurements and possess prognostic potential. It remains to be determined if this type of metabolic monitoring can find clinical applications in the wide population of septic critically ill patients.