Microdialysis-Assessed Adipose Tissue Metabolism, Circulating Cytokines and Outcome in Critical Illness.

Microdialysis (MD) can provide continuous information about tissue composition. To assess in critically ill patients adipose tissue metabolic patterns, the relationships between metabolic patterns and blood cytokine concentration associations of adipose tissue energy metabolism and clinical outcome we studied 203 mechanically ventilated general intensive care unit (ICU) patients. Upon ICU admission an MD catheter was inserted into the subcutaneous adipose tissue of the upper thigh to measure lactate (L), glucose, pyruvate (P), and glycerol. Serum concentrations of IL-10, IL-6, IL-8, and TNF-α were determined within 48 h from ICU admission. Mitochondrial dysfunction was defined as L/P ratio >30 and pyruvate ≥70 µmol/L, ischemia as L/P ratio >30 and pyruvate <70 µmol/L and no ischemia/no mitochondrial dysfunction (i.e. aerobic metabolism) was as L/P ratio ≤30. Metabolism was aerobic in 74% of patients. In 13% of patients there was biochemical evidence of ischemia and in 13% of patients of mitochondrial dysfunction. Mitochondrial dysfunction was associated with poor outcome. In conclusion, MD showed that about two thirds of critically ill patients have normal aerobic adipose tissue metabolism. Mitochondrial dysfunction was not common but was associated with poor outcome. Identifying subgroups of critically ill patients is crucial as different treatment strategies may improve survival.

Adipose Tissue Lactate Clearance but Not Blood Lactate Clearance Is Associated with Clinical Outcome in Sepsis or Septic Shock during the Post-Resuscitation Period.

No study has directly measured tissue lactate clearance in patients with sepsis during the post-resuscitation period. In this study we aimed to assess in ICU patients with sepsis (n = 32) or septic shock (n = 79)—during the post-resuscitation phase—the relative kinetics of blood/tissue lactate clearances and to examine whether these are associated with outcome. We measured serially—over a 48-h period—blood and adipose tissue interstitial fluid lactate levels (with microdialysis) and we calculated lactate clearance. Statistics included mixed model analysis, Friedman’s analysis of variance, Wilcoxon’s test, Mann-Whitney’s test, receiver operating characteristics curves and logistic regression. Forty patients died (28-day mortality rate = 28%). Tissue lactate clearance was higher compared to blood lactate clearance at 0⁻8, 0⁻12, 0⁻16, 0⁻20 and 0⁻24 h (all p < 0.05). Tissue lactate clearance was higher in survivors compared to non-survivors at 0⁻12, 0⁻20 and 0⁻24 h (all p = 0.02). APACHE II along with tissue lactate clearance <30% at 0⁻12, 0⁻20 and 0⁻24 h were independent outcome predictors. We did not find blood lactate clearance to be related to survival. Thus, in critically ill septic patients, elevated tissue (but not blood) lactate clearance, was associated with a favorable clinical outcome.

Evidence of Subcutaneous Tissue Lipolysis Enhancement by Endogenous Cortisol in Critically Ill Patients Without Shock.

BACKGROUND/AIM: Cortisol is involved in in many aspects of adipose tissue metabolism. A positive association between plasma cortisol and lipolysis has been observed. Critically ill patients exhibit 'lipemia of sepsis'. The aim of the present study was to study, in septic ICU patients, adipose tissue lipolysis in relation to tissue cortisol using microdialysis (MD). PATIENTS AND METHODS: We studied 17 mechanically-ventilated patients (9 men; mean±SD age=63±19 years) with a diagnosis of severe sepsis. Upon ICU admission, an MD catheter was inserted under sterile conditions into the subcutaneous adipose tissue of the upper thigh. On days 2, 3 and 4, MD samples were collected six times per day for glycerol (used as an index of lipolysis) and tissue cortisol determinations. The mean of these six collections was used for analysis (normal values for adipose tissue glycerol <200 µmol/l). Statistics were carried-out with analysis of covariance (ANCOVA) and linear regression. RESULTS: More than half of the samplings (19/31) indicated accentuated lipolysis with above-normal MD glycerol levels. By ANCOVA, MD glycerol (log values) was associated with MD cortisol (log values) (p=0.012) and was not associated with age or day of sampling. Furthermore, MD glycerol (log values) was positively correlated to MD cortisol (log values) (r=0.490, p=0.012). DISCUSSION: Changes in interstitial/tissue cortisol may not be reflected in (total) plasma cortisol concentration. Thus, it is interesting that we observed, albeit weak, an association between tissue lipolysis (via MD glycerol levels) and MD cortisol, verifying (although modestly so) the well-known association between lipolysis and cortisol.