Histopathological changes of organ dysfunction in sepsis.

BACKGROUND: Sepsis is a highly lethal disorder. Organ dysfunction in sepsis is not defined as a clinicopathological entity but rather by changes in clinical, physiological, or biochemical parameters. Pathogenesis and specific treatment of organ dysfunction in sepsis are unknown. The study of the histopathological correlate of organ dysfunction in sepsis will help understand its pathogenesis. METHODS: We searched in PubMed, EMBASE, and Scielo for original articles on kidney, brain, and liver dysfunction in human sepsis. A defined search strategy was designed, and pertinent articles that addressed the histopathological changes in sepsis were retrieved for review. Only studies considered relevant in the field were discussed. RESULTS: Studies on acute kidney injury (AKI) in sepsis reveal that acute tubular necrosis is less prevalent than other changes, indicating that kidney hypoperfusion is not the predominant pathogenetic mechanism of sepsis-induced AKI. Other more predominant histopathological changes are apoptosis, interstitial inflammation, and, to a lesser extent, thrombosis. Brain pathological findings include white matter hemorrhage and hypercoagulability, microabscess formation, central pontine myelinolysis, multifocal necrotizing leukoencephalopathy, metabolic changes, ischemic changes, and apoptosis. Liver pathology in sepsis includes steatosis, cholangiolitis and intrahepatic cholestasis, periportal inflammation, and apoptosis. There is no information on physiological or biochemical biomarkers of the histopathological findings. CONCLUSIONS: Histopathological studies may provide important information for a better understanding of the pathogenesis of organ dysfunction in sepsis and for the design of potentially effective therapies. There is a lack of clinically available biomarkers for the identification of organ dysfunction as defined by the histological analysis.

Acute Respiratory Distress Syndrome and Diffuse Alveolar Damage. New Insights on a Complex Relationship.

Acute respiratory distress syndrome (ARDS) is a major clinical problem with high morbidity and mortality. Diffuse alveolar damage (DAD) is considered the histological hallmark for the acute phase of ARDS. DAD is characterized by an acute phase with edema, hyaline membranes, and inflammation, followed by an organizing phase with alveolar septal fibrosis and type II pneumocyte hyperplasia. Given the difficulties in obtaining a biopsy in patients with ARDS, the presence of DAD is not required to make the diagnosis. However, biopsy and autopsy studies suggest that only one-half of patients who meet the clinical definition of ARDS also have DAD. The other half are found to have a group of heterogeneous disorders, including pneumonia. Importantly, the subgroup of patients with ARDS who also have DAD appears to have increased mortality. It is possible that the response of these patients to specific therapies targeting the molecular mechanisms of ARDS may differ from patients without DAD. Therefore, it may be important to develop noninvasive methods to identify DAD. A predictive model for DAD based on noninvasive measurements has been developed in an autopsy cohort but must be validated. It would be ideal to identify biomarkers or imaging techniques that help determine which patients with ARDS have DAD. We conclude that additional studies are needed to determine the effect of DAD on outcomes in ARDS, and whether noninvasive techniques to identify DAD should be developed with the goal of determining whether this population responds differently to specific therapies targeting the molecular mechanisms of ARDS.

Acute respiratory distress syndrome in patients with and without diffuse alveolar damage: an autopsy study.

OBJECTIVE: To demonstrate that among patients with acute respiratory distress syndrome (ARDS), the presence of diffuse alveolar damage (DAD) at histological examination, as compared to its absence, defines a specific subphenotype. METHODS: We studied 149 patients who died in our ICU with the clinical diagnosis of ARDS according to the Berlin Definition (BD) and who had autopsy examination. We compared the change over time of different clinical variables in patients with (n = 49) and without (n = 100) DAD. A predictive model for the presence of DAD was developed and validated in an independent cohort of 57 patients with ARDS and postmortem examination (21 of them with DAD). RESULTS: Patients with DAD, as compared to patients without DAD, had a lower PaO2/FiO2 ratio and dynamic respiratory system compliance, and a higher SOFA score and INR, and were more likely to die of hypoxemia and less likely to die of shock. In multivariate analysis, variables associated with DAD [odds ratio, 95% confidence interval (CI)] were PaO2/FiO2 ratio [0.988 (0.981-0.995)], dynamic respiratory system compliance [0.937 (0.892-0.984)] and age [0.972 (0.946-0.999)]. Areas under the ROC curve (95 % CI) for the classification of DAD using the regression model or the BD were, respectively, 0.74 (0.65-0.82) and 0.64 (0.55-0.72) (p = 0.03). In the validation cohort, the areas under the ROC curve for the diagnosis of DAD were 0.73 (0.56-0.90) and 0.67 (0.54-0.81) for the regression model and the BD, respectively. CONCLUSIONS: The presence of DAD appears to define a specific subphenotype in patients with ARDS. Targeting patients with DAD within the population of patients with the clinical diagnosis of ARDS might be appropriate to find effective therapies for this condition.

Acute respiratory distress syndrome: does histology matter?

Kao et al. have reported in Critical Care the histological findings of 101 patients with acute respiratory distress syndrome (ARDS) undergoing open lung biopsy. Diffuse alveolar damage (DAD), the histological hallmark of ARDS, was present in only 56.4% of cases. The presence of DAD was associated with higher mortality. Evidence from this and other studies indicates that the clinical criteria for the diagnosis of ARDS identify DAD in only about half of the cases. On the contrary, there is evidence that the clinical course and outcome of ARDS differs in patients with DAD and in patients without DAD. The discovery of biomarkers for the physiological (increased alveolocapillary permeability) or histological (DAD) hallmarks of ARDS is thus of paramount importance.