Sepsis remains a major cause of morbidity and mortality worldwide, with increased burden in low- and middle-resource settings. The role of the inflammatory response in the pathogenesis of the syndrome has supported the modern concept of sepsis. Nevertheless, a definition of sepsis and the criteria for its recognition is a continuous process, which reflects the growing knowledge of its mechanisms and the success and failure of diagnostic and therapeutic interventions. Here we review the evolving concepts of sepsis, from the “systemic inflammatory response syndrome triggered by infection” (Sepsis-1) to “a severe, potentially fatal, organic dysfunction caused by an inadequate or dysregulated host response to infection” (Sepsis-3). We focused in the pathophysiology behind the concept and the criteria for recognition and diagnosis of sepsis. A major challenge in evaluating the host response in sepsis is to characterize what is protective and what is harmful, and we discuss that, at least in part, the apparent dysregulated host response may be an effort to adapt to a hostile environment. The new criteria for recognition and diagnosis of sepsis were derived from robust databases, restricted, however, to developed countries. Since then, the criteria have been supported in different clinical settings and in different economic and epidemiological contexts, but still raise discussion regarding their use for the identification versus the prognostication of the septic patient. Clinicians should not be restricted to definition criteria when evaluating patients with infection and should wisely use the broad array of information obtained by rigorous clinical observation.

In this study, our aims were to evaluate the reactive oxygen species (ROS) and nitric oxide (NO) generation by monocytes and neutrophils from septic patients and to correlate their levels with clinical outcomes. Forty-nine septic patients and 19 healthy volunteers were enrolled in the study. The ROS and NO production was quantified in monocytes and neutrophils in whole blood by flow cytometry, constitutively, and after stimulation with Staphylococcus aureus and Pseudomonas aeruginosa. Nitric oxide production by monocytes was higher in septic patients compared with healthy volunteers for all conditions and by neutrophils at baseline, and ROS generation in monocytes and neutrophils was higher in septic patients than in healthy volunteers for all conditions. Nitric oxide production by monocytes and neutrophils was decreased at day 7 compared with that at admission (day 0) in survivors at baseline and after stimulation with S. aureus. Reactive oxygen species production by the monocytes and neutrophils was decreased in survivors at day 7 compared with day 0 under all conditions, except by neutrophils at baseline. No difference was found in NO and ROS generation by monocytes and neutrophils between day 7 and day 0 in nonsurvivors. Generation of NO and ROS by neutrophils and monocytes is increased in septic patients, and their persistence is associated with poor outcome.

BackgroundThe nature of the inflammatory response underscoring the pathophysiology of sepsis has been extensively studied. We hypothesized that different cell functions would be differentially regulated in a patient with sepsis. We evaluated the modulation of monocyte functions during sepsis by simultaneously assessing their phagocytic activity, the generation of reactive oxygen species (ROS) and nitric oxide (NO), and the production of inflammatory cytokines (IL-6 and TNF-α).MethodsWhole blood was obtained from patients with severe sepsis and septic shock both at admission (D0, n = 34) and after seven days of therapy (D7, n = 15); 19 healthy volunteers were included as a control group. The cells were stimulated with LPS, Pseudomonas aeruginosa, and Staphylococcus aureus. The ROS and NO levels were quantified in monocytes in whole blood by measuring the oxidation of 2,7-dichlorofluorescein diacetate and 4-amino-5-methylamino-2,7-difluorofluorescein diacetate, respectively. Intracellular IL-6 and TNF-α were detected using fluorochrome-conjugated specific antibodies. Monocyte functions were also evaluated in CD163+ and CD163− monocyte subsets.ResultsThe monocytes from septic patients presented with preserved phagocytosis, enhanced ROS and NO generation, and decreased production of inflammatory cytokines compared with the monocytes from healthy volunteers. TNF-α and IL-6 increased and ROS generation decreased in D7 compared with D0 samples. In general, CD163+ monocytes produced higher amounts of IL-6 and TNF-α and lower amounts of ROS and NO than did CD163− monocytes.ConclusionsWe demonstrated that monocytes from septic patients, which are impaired to produce inflammatory cytokines, display potent phagocytic activity and increased ROS and NO generation.