Pathophysiology and epidemiology of sepsis
Department of Infectious Diseases, University Medical Centre Ljubljana, Ljubljana, Slovenia
Sepsis is classicaly defined as severe clinical manifestation of bacterial or fungal infection. Although activation of the immune system during microbial invasion is generally protective, sepsis with multiorgan failure develops in a number of patients as a consequence of excessive or poorly regulated immune response to microbial products. Many mechanisms are involved in the pathogenesis of sepsis, including the release of cytokines, the activation of neutrophils, monocytes, and microvascular endothelial cells, as well as the activation of neuroendocrine system, complement, the intrinsic and extrinsic pathways of coagulation, and the fibrinolytic system. The interaction of these system produces a microvascular injury that leads to multiple organ dysfunction.
A pivotal role in inducing Gram negative sepsis has lipopolysaccharide, a component of the Gram negative cell wall. Systemic response to infection is triggered by endotoxin over activation of CD-14, Toll-like receptor-4, and protein MD-2 and many proinflammatory cytokines are released into blood. However when sepsis persists, there is a shift toward an antinflammatory cytokines. The levels of pro- and antiinflammatory cytokines are of prognostic significance and can predict organ dysfunction and death. Gram positive bacteria can cause sepsis by producing exotoxins and by components of their cell walls stimulating immune cells. Immune response is probably induced through similar mechanisms to those in Gram negative sepsis.
In the last decades the incidence of sepsis increased. Very elderly and patients with comorbidity, with malignancy, and HIV disease are belived to be at higher risk of death. In the United States, an estimated 750.000 patients with severe sepsis are diagnosed each year, accounting for 2–4% of hospital admissions. Between 1979 and 2000, there was an annualized increase in the incidence of sepsis from 83 to 240 per 100.000 population. Based on the current literature, the incidence rate for severe sepsis in European industrialized nations consistently lies between 50 and 100 cases per 100.000 individuals. The atack rate of severe sepsis in Slovenian ICUs is similar to the rate found in several other countries. We estimated the incidence of severe sepsis to be 109 cases per 100.000 in our population.
The mortality rate of sepsis is approximately 30% and is 50% or greater in patients with more severe syndrome and septic shock. Early diagnosis and treatment are still a corne stone to prevent developement of multiorgan failure. Advances in our understanding of imunopathophisiology of sepsis may create the new therapeutical strategy and improve survival rate.
Inflammatory response in sepsis
Institute of Clinical Chemistry and Biochemistry, University Medical Centre Ljubljana, Ljubljana, Slovenia
Sepsis involves a complex systemic inflammatory response caused by infection. The presence of microbial antigens triggers the response that results in disturbed balance of inflammatory and anti-inflammatory processes. Many white blood cells, including macrophages, release cytokines and other mediators, which regulate the inflammatory response and play an important role in the pathology of sepsis. Among the earliest mediators of systemic inflammation are TNF and IL-1; the cascade continues with the release of other pro-inflammatory parameters like IL-6, IL-8 and interferons. Pro-inflammatory response is further amplified by several non-cytokine factors. Arachidonic acid metabolites modulate the vascular phase of inflammation and they also influence platelet aggregation. Endotelial cells release PAF, which regulates the release of cytokines. Anti-inflammatory parameters are also synthesized in order to down regulate the excessive inflammatory response. IL-6 is predominantly a pro-inflammatory cytokine but also shows certain anti-inflammatory activity. Other anti-inflammatory mediators released in sepsis include IL-10, IL-4, IL-13, TGFb, IL-1ra and soluble TNF receptors. Distant in the inflammatory cascade, procalcitonin, CRP and other late parameters are released as a consequence of increased cytokine activity. These markers are frequently used for diagnosis and monitoring of sepsis. Cytokines and other inflammatory parameters mediate several pathological disturbances that are characteristic of sepsis. Activation of complement, coagulation and other important biochemical systems results in clinical manifestation of sepsis.
Genetic basis of immunologic response dysregulation in sepsis
Clinical Institute of Chemistry, Department of Molecular Diagnostics, Sestre milosrdnice University hospital, Zagreb, Croatia
Sepsis is an inflammation-mediated infection-initiated syndrome. It is well known that some individuals show higer susceptibility to sepsis. It is also well established that some people carry higher individual susceptibility to develop sever sepsis with serious clinical course. There is a growing body of evidence showing that the basis of such susceptibility is at least partially genetically determined. The underlying immunologic mechanism is the variability of inflammatory reaction. The question that still remains unanswered is: do we know which genes carry the risk and how to test that fact? Many candidate genes are described in the literature: Toll-like receptors (TLR), tumor necrosis factor-a (TNF-a), CD14, mannose binding lectin (MBL), ApoE, IL-1, IL-6, PAI-1, ACE and some other. There are many different ways to study that putative genetic contribution. Every study design approaches different aspect of that mechanism. Furthermore, it is of vital importance to be aware of all limitations to the study, some of which are methodological and some are due to the multifactorial nature of immunological reaction. Understanding the way the genetic determinants define the susceptibility to develop sepsis is crucial for further advancement in sepsis prevention, diagnosis and therapy. Medicine in the very near future shall be personalised, meaning that we shall be able to tailor drug selection and dosage to fit the specific needs of an individual patient, acording to his or her genetic code.
Diagnostic and prognostic markers in sepsis
Clinical Institute of Chemistry, Department of Laboratory Diagnostics, General Hospital Maribor, Maribor, Slovenia
Sepsis is the leading cause of death in crittically ill patients. Insufficient development in both medical diagnosis and treatment of sepsis has led to continued growth in reported cases of sepsis with little improvement in mortality statistics. Currently, sepsis is recognized as a heterogeneous clinical sindrome, tipically associated with underlying conditions and triggered by many kinds of microbes. It occurs when the body expiriences a systemic inflammatory response to a bacterial, viral or fungal infection. The resulting inflammatory cascade can produce complications, which can lead to septic shock and death. Rapid diagnosis and treatment of sepsis is imperative. Clinicians cannot wait for a culture results, but must presume the presence of infection (sepsis) on the basis of clinical signs and laboratory findings. A great demand exists for in vitro diagnostic markers in sepsis, and numerous markers are under consideration. The catalog of proteic molecules associated with sepsis is extensive and includes cytokines, chemokines, adhesion molecules, soluble receptors and acute-phase proteins. Some of them can be used as diagnostic, other as a prognostic marker. Current biomarker research focuses primarily on several interleukins (pro-and anti-inflammatory), procalcitonin(PCT) and lipopolysaccharide binding protein (LBP). Opinions on the diagnostic accuracy of CRP are not consistent. The current diagnostic methods should be performed on the real-time monitoring basis during the course of treatment. Because the changes during progression of inflammation to sepsis occur very fast, the necessity of measuring biomarker concentrations at regular intervals becomes evident.
Metabolic and respiratory disturbances in sepsis
Department for Laboratory Diagnostics and Transfusiology, Sveti Duh General Hospital, Zagreb
Despite improvements in the understanding of pathophisiology, sepsis still represent a major clinical problem in intensive care units. The inability to generate adequate ATP strogly relates to the mortality sepsis suffered patients. Most of the clinical laboratory tests in the critical ill patient serves as a marker for the energy pathway. During septic shock the use of glucose as an energy source and piruvate dehydrogenase activity are decreased. Elevated blood lactate is a sensitive indicator of metabolic acidosis from poor oxygenation of tissues. pH and pCO2 are used in the differential diagnosis of acid-base disorders. pH affects the strength of binding of oxygen to hemoglobin. To determine whether adequate oxygen is getting into the blood, pO2 is the most sensitive indicator for diffusion of oxygen across the alveoli. Potassium is the major intracellular cation which has several extremly important function such as regulation of neuromuscular excitability and contraction of the heart and cardiac rhythm. When muscle cell goes to action potential, iCa entering into the cell, initiating a contraction. Relaxation occurs when a Mg-ATP pump remove iCa from the cytosol. Presence of hypomagnesemia in critically ill patients is associated with an increased mortality rate. Acute renal failure occurs in aproximately 50% of patients with septic shock and significantly increases mortality. Several mechanisms have been proposed for the pathogenesis of acute renal failure in sepsis. Liver dysfunction with cholestatic jaundice may be seen in patients with sepsis. Respiratory failure is a frequent complication of septic shock. Neurologic dysfunction is common during sepsis. Encephalopathy can be due to metabolic disturbances (electrolyte imbalances, acid-base disorders, hypoglicemia). Multiple organ dysfunction syndrome is often the final result of sepsis.
Coagulopathy of sepsis
Clinical Institute of Laboratory Diagnosis, Zagreb Clinical Hospital Center and University School of Medicine, Zagreb, Croatia
Effects of the coagulation cascade, endogenous anticoagulants, and the fibrinolytic system are critically balanced to maintain blood fluidity and prevent hemorrhage. This homeostatic mechanism can be compromised in case of imbalance in one or more of the clotting factors or inhibitors due to either congenital or acquired causes. Inflammation related to sepsis is one such acquired state of dysregulated coagulation. Endothelial cells and monocytes exposed to endotoxin and proinflammantory cytokines (eg, TNF-alfa and IL-1) in sepsis express tissue factor on the cell surface. Enhanced production of tissue factor triggers coagulation via interaction with FVII followed by massive amplification of thrombin generation, as reflected by high levels of prothrombin fragments 1 and 2 and thrombin-antithrombin complex. Thrombin activation is followed by fibrin formation which is then degraded, as demonstrated by increased levels of D-dimer. Fibrinolysis, although activated, is not sufficient to counteract increased fibrin formation which contributes to organ damage and mortality in sepsis. Dysfunction of endogenous inhibitors like antithrombin, activated protein C (APC) and TFPI as a consequence of impaired liver function and coagulation activation-dependent consumption is a key point in the pathogenesis of sepsis. Understanding of the basic mechanisms of coagulation and its derangements in sepsis is crucial for the development of therapeutic strategies: three large, international, multicentric, clinical trials evaluated recombinant human antithrombin, recombinant human TFPI and recombinant human APC (drotrecogin alfa-activated). Only one, i.e.APC, proved effective: PROWESS study demonstrated that 96h continuous infusion of drotrecogin alfa-activated reduced relative all-cause 28-day mortality by 19.4% in patients with severe sepsis compared with patients treated with placebo.
Division of Laboratory Hematology and Coagulation, Clinical Institute of Chemistry, Sestre milosrdnice University Hospital, Zagreb, Croatia
Neonatal sepsis is a syndrome characterized by common signs of infection and bacteriemia during the first days of the newborn’s life. Based on the data by the Croatian Institute of Public Health, it was the cause of death in 3–4/1000 livebirths in 2004. The efforts to further reduce the incidence of neonatal sepsis could be, among others, earlier identification of infected newborns, which is why numerous studies attempt to find a diagnostic test and marker that would be the earliest indicator of infection prior to its confirmation by the blood culture. Current diagnostic approach includes determination of “classical” markers of sepsis screen: total leuckocyte count, absolute neutrophil count, immature/total neutrophil count ratio (I/T) and C-reactive protein (CRP) on two occasions, i.e. 12 and 24 hours after birth, providing high negative predictive value (97–99.5%). Diagnostic significance has been confirmed for the determination of the cytokines TNF-a, IL-1b, IL-6,IL-8 and procalcitonin (PCT) levels. The results showed that plasma IL-8 level in combination with CRP has demonstrated better sensitivity and specificity than sole PCT determination. The clinical applicability of the cytokine measurement as a standard diagnostic procedure in the early diagnosis of neonatal sepsis has been made difficult by relatively scarce data on normal ranges of concentrations during the immediate postanal period. This may explain the conflicting cutoff points for abnormal values that have been reported for these markers.Some confounding factors, per se, shoud be taken into account to define “physiologic” concentrations of cytokines and PCT (kinetics is dependent on gestational and postnatal period). At the same time, investigations of the triggering receptor expressed on myeloid cells (TREM1) have demonstrated its characteristics of a good marker of unspecific immunity, which is important in newborns. In the future, introduction of molecular diagnostic methods might solve analytical and postanalytical limitations in the early diagnostics of sepsis in neonates. This expectation is supported by confirmational results of molecular analysis by polymerase chain reaction (PCR) for bacterial DNA component encoding 16s RNA.
Critical illnes polyneuropathy and myopathy in sepsis
Vanja Bašić Kes
Department of neurology, Sestre milosrdnice University hospital, Zagreb, Croatia
Sepsis may cause not only failure of parenchymal organs but can also damage to peripheral nerves and skeletal muscles. It is now recognized that sepsis-mediated disorders of the peripheral nerves and the muscle, called critical illness myopathy, are responsible for weakness and muscle atrophy occurring de novo in intensively treated patients. CIP represents an acute axonal neuropathy that develops during treatment of severely ill patients and remits spontaneously, once the critical condition is under control.
Among the critical illness myopathies, three main types have been identified:a non necrotizing «cachectic» myopathy (critical illness myopathy in the strict sense), a myopathy with selective loss of myosin filaments (“thick filament myopathy”) and an acute necrotizing myopathy of intensive care.
Clinical manifestation of both critical illness myopathies and CIP include delayed weaning from the respirator, muscle weakness, and prolonging of the mobilization phase. The pathogenesis of these neuromuscular complications of sepsis is not understood in detail but most authors assume that the inflammatory factors that mediate systemic inflammatory response are closely involved.
Specific therapies have not been discovered. Stabilization of the underlying critical condition and elimination of sepsis appear to be of major importance.
Congenital immunodeficiencies and sepsis
Department of Anaesthesiology and Intensive Care, Sestre milosrdnice University Hospital, Zagreb, Croatia
Congenital or primary immunodeficiencies demonstrate that specific cellular, soluble and genetic components within the immune system are required for the defence against environmental pathogens.The most common clinical presentation of congenital immunodeficiency is a recurrent common infection, or in some cases, a predisposition to severe or atypical infection. Clinical course of infection can have a milder form due to incomplete inflammatory response or a more severe one due to the loss of regulatory mechanisms within the immune system. Congenital defects in the innate immunity system are devided into four categories.The first category includes complement and MBL (Manonose-Binding Lecitin). The second comprises effects in the of NF-(kappa)B activtion. The third consists of specific defects of phagocyte quantity and quality. The fourth is made up of defects in the type 1 cytokine response axis. Congenital defects of the adaptive immune system include SCID (Severe Combined Immunodeficiency), agammalobulinaemia, hyper IgM globulinaemia, common variable immunodeficiency (CVID), transient hypogammaglobulinemia, IgG subclass defficiency, ataxia teleangiectasia, IPEX (immunodysregulation, polyendocrinopathy, enteropathy-X-linked) and Wiskott-Aldrich sindrom (WAS). Specific genetic testing for congenital immunodeficiencies is not recommended as a routine procedure in septic patients. However, low leucocyte or lymphocyte count or a lack of recovery of lympocyte populations over time might indicate that some form of primary immunodeficiency might be present. Alterations in the immunoelectrophoresis can indicate a possible congenital immunodeficiency, as well.