Extracorporeal Treatments for Abdominal Sepsis

Sergey Khoroshilov E mail: intensive@list.ru Несмотря на значительный прогресс в интенсивном лечении абдоминального сепсиса, летальность от данного заболевания остается крайне высокой. Системный воспалительный ответ на инфекцию характери зуется высвобождением в кровоток эндотоксина и медиаторов воспаления, которые вызывают расстройст ва кровообращения и формирование полиорганной недостаточности. Ультразвуковая высокочастотная допплерография дает возможность динамической оценки тканевой перфузии под воздействием эфферент ного лечения.

According to Russian researches sepsisis diag nosed in 3 of 1000 patients in ICU, sepsis frequency is 200-275 patients per 100 000 population per year [14,15].In 2008-2009 a two stage one day study called Prevalence of infection in the ICU and inten sive care was performed.Data demonstrated that gram negative bacteria was the leading sepsis pathogens in 72,7% and gram positive bacteria caused 23,9% cases of sepsis where as the mortality was 30,4% [16,17].
Understanding the etiopathogenesis of deep abdominal sepsis might be helpful in substantiating the application of extracorporeal detoxification in complex intensive treatment of this life threatening critical illness [21].

Abdominal sepsis pathogenesis
The pathogenesis of sepsis includes systemic inflammatory response (SIR) to periodical or contin uous bacteremia [22,23].In the mid 1900 s the term «abdominal sepsis» was defined as SIR to initial infection localized in the abdomen and/or retroperi toneal fat, with a characteristic feature such as rapid switch of microorganisms and endotoxin transloca tion mechanism from the intestinal lumen.
In norm low concentration of endotoxin is pre sented in the blood following intake from the gut and is involved in the regulation of various systemsendocrine, coagulation, central nervous systems and especially the immune system.In the blood it is detected bound to neutrophils in low concentrations (below 1,0 EU/ml), and is eliminated from the circu lation by Kupfer hepatic macrophages system.In meta analysis MEDIC performed on 857 patients in ICU, it was found that the risk of death depends on the concentration of endotoxin in the blood, and not on a bacteremia.Endotoxinemia could be found in a very heterogeneous population of patients in ICU: almost a half of them had circulating endotoxin lev els more than 2 standard deviations above the level found in healthy volunteers from the control group.However, in the study group, only 4% had gram neg ative flora inoculated from the blood (John C. Marshall, Jean Louis Vincent, etc.).This suggests that endotoxin itself, regardless of the presence and amount of gram negative bacteria in the blood, is predictive of a high lethality.
Mechanical barrier function disorder of mucous membranes of gastrointestinal tract leads to translo cation of intestinal microflora and endotoxin that can start sepsis process.
Direct damaging effect of endotoxin on endothelial cells underlies microcirculatory disfunc tions [35][36][37].The pathogenetic mechanisms lead ing to microcirculatory dysfunction include: wide spread endothelial cell damage, the activation of the coagulation cascade and the inhibition of fibrinoly sis, mitochondrial distress, hypoxia [38][39][40].All these factors are crucial for the development of mul tiple organ failure in sepsis [41][42][43].Endothelial cells according to the hemodynamic, metabolic and other regulatory signals change arteriolar muscle tone and capillary filling and control coagulation and immune function.Normally, the anticoagulant and antithrombotic activity of endothelium dominates over its procoagulant properties.Endotoxin inhibits anticoagulant potential that promotes intravascular coagulation and thrombus formation in the microvasculature.As a result, the circulatory hypox ia, ischemia and organ dysfunction is developing.[44,45].Activation of the coagulation cascade by endotoxin via Hageman factor leads to bradykinin production that is a powerful vasodilator increasing the permeability of the endothelium.Extravasation of fluid and tissue edema develops and gel matrix within the interstitial space swells and results in alterations of diffusion of oxygen and metabolites.«Capillary leak» leads to hypovolemia, oxygen trans port disruption and hypoperfusion of tissue with accumulation of metabolic products and rapid for mation of multiple organ dysfunction.
response.Cytokines mediate their effects via cell sur face receptors.Most cytokines have pleiotropic activity and exhibit biological effects on a variety of target cells.Key mediators of the inflammatory cas cade include TNF α, interleukin 1β (IL 1β), inter leukin 6 (IL 6), Interleukin 8 (IL 8).Cytokines are primary mediators of the SIR and increased levels of cytokines in blood demonstrate stimulation of immune system cells [51,52].IL 1β/TNF α ratio is increased to 10 or higher, C3 and C4 complement component activities are decreased, low levels of IgG are evidence of immunosuppression.All these fea tures are predictors of mortality.In a local inflamma tory site, the cytokines exert their effects limited to tissue or organ, in which they are produced [53,54].Cytokines have a wide range of biological actions, which manifest itself by diverse metabolic changes, hematopoiesis, properties of the vascular wall, func tions of regulatory systems [55,56].
When overproduction of cytokines and other mediators occurs, their destructive effects begin to dominate.When there is an imbalanced SIR pro and anti inflammatory mediators cooperation, the release of a large number of pro inflammatory cytokines («cytokine storm») is initiated followed by, the increase of anti inflammatory cytokines.Compensatory anti inflammatory response develops, combined with the depletion of pro and anti inflammatory mechanisms («immune paralysis»).Increased endotoxinemia and inflammatory media tors cause disorders of systemic hemodynamics by direct myocardial depression and vasoplegia [57].
To improve the effectiveness of abdominal sep sis treatment a trigger of mediator cascade, endotox in, must be removed and SIR must be reduced via decreasing the concentration of pro inflammatory mediators to restore microcirculation and prevent miltiorgan failure [68,69].

Diagnostics of abdominal sepsis
The success of the patient' treatment occurs because of correct and in time recognition of patho logical process and its complications [70].Absence of specific sepsis biomarkers as well as instability of molecular manifestation of SIR in blood complicate diagnosis [71,72].Diagnostic search based on a com bination of clinical, laboratory, biochemical and bac teriological data, taking into account the fact that there is a dynamic sepsis process and its often sce nario usually unpredictable [73].
Criteria for diagnosis and classification of sep sis, proposed by R. Bone in 1992 [74], include clini cal and laboratory evidence of SIR accompanied by the following two and / or more signs: temperature> 38°C or <36 ° C; heart rate> 90 per minute; BH >20 min or PaCO 2 <32 mm Hg; leucocytes >12 10 9 / ml or <4 10 9 / ml, or immature form >10%.
Recent studies have revealed low sensitivity and specificity of the classification.Thus, according to the European Society of Intensive Care (ESICM) and the Society of critical care medicine (SCCM), the criteria of ACCP/SCCM do not refer to 71% of the respondents.This caused a rethinking of their role in the diagnosis and the search for new criteria.
In 2001 a group of scientists leading by M. Levy suggested the expansion of a list of sepsis crite ria: pyrexia >38,3°C or hypothermia <36°C; Heart rate >90 per minute (>2 standard deviations from the normal age level); tachypnea; impaired con sciousness; need to support the infusion (>20 ml / kg for 24 hours); hyperglycemia >7.7 mmol / l in the absence of diabetes.The following SIR criteria have been proposed: leukocytosis (>12 10 9 /l) or leukopenia (<4 10 9 /l); leukocyte shift toward immature form (>10%) with normal leukocytes; increased C reactive protein and procalcitonin con tent in plasma (>2 standard deviations from the norm), and leukocyte intoxication index >4.The
Further studies in this area have resulted in international «Surviving Sepsis Campaign» (2004) led by a group of experts in intensive care medicine.The proposed sepsis diagnosis classification differed from the R. Bone's classification by introducing an additional criterion of diagnosis -«bacteremia»the presence of viable bacteria in the blood.
In the same year, members of the Russian Association of Specialists in surgical infections (RASSI), considered the main international rec ommendations for sepsis [ One of the gram negative sepsis markers is presepsin -circulating protein that is increased rapidly in blood when sepsis is developing.Presepsin was first described in 2005 by a group of researchers from Iwate Medical University (Japan).A key role in its formation was the activation of macrophages / monocytes.There is a macrophage membrane receptor protein, mCD14, which binds to endotoxin and induces macrophage activation signal.LPS binding protein enhances the efficacy of such binding 100 1000 times.After activation, mCD14 is detached from the membrane and enters the circulation (referred to as sCD14).Circulating sCD14 is currently considered as a marker of mono cyte response to the action of endotoxin; improving the blood sCD14 reflects the severity of inflamma tion and correlates with the development of septic shock.Activating Lysosomal proteases (cathepsin D etc specifically cleae sCD14 followed by forma tion of a subtype sCD14 ST (presepsin).In early phases of the SIR, the quantitative determining of a presepsin is considered to be the most sensitive and specific marker of sepsis, reflecting its dynamics, severity and outcome [76].
The latest revision of the recommendations of the international community «Surviving Sepsis Campaign» was released in 2012.According to the SSC 2012, sepsis is defined as infection manifested by SIR whereas septic shock is diagnosed, in addi tion, by hypotension refractory to adequate fluid resuscitation.Severe sepsis is characterized by clini cal and laboratory signs of dysfunction of at least one organ in combination with the lack of tissue perfu sion as evidenced by decrease in blood pressure, введении ранее отсутствующих маркеров (C реак тивного белка, прокальцитонина, гипергликемии и др.), позволяющих целенаправленно ориентиро ваться в клинической ситуации даже на фоне невы явленного очага инфекции [75].
Septic foci can be primary (at the entrance gate), and secondary (metastatic foci).They need to be identified and where possible to be sanitized with a mandatory microbiological examination of the obtained material.Verification of the infectious focus should be carried out by all possible methods: com puted tomography, magnetic resonance imaging, ultrasound diagnostic methods, microcirculation evaluation buy endoscopy and by various kinds of biopsy, angiography, etc. [78,79].
Alterations of tissue perfusion is an integral component of sepsis.The increase in blood lactate concentration indicates an imbalance between the oxygen supply system and a tissue need in oxygen.Therefore, the lactate concentration in the blood is an informative indicator of the adequacy of the labo ratory of tissue blood flow and oxygenation, which is necessary to control the dynamics of [80,81] .
Microcirculatory disorders in abdominal sepsis are variable both in their pathogenesis, and clinical manifestations.Due to the alterations of tissue and systemic hemodynamics in sepsis it is necessary at all stages of treatment to monitor carefully the ade quacy of tissue perfusion and tissue oxygen satura tion and effectiveness of the treatment.Therefore, the correction of microcirculatory disorders are needed using rapid assessment of blood flow at the tissue level and continuous monitoring of tissue per fusion.The study of microcirculation in patients with severe critical illness attracted the attention of researchers.Poor circulation in the limb microves sels may reflect changes in blood flow in the mesen teric vessels, and these disorders are correlated with the severity of the patients with sepsis [82].Organ blood flow evaluation can also be carried out based on data obtained by observing the peripheral tissues microcirculation using ultrasonic flowmetry.For example, study by A. A. Kosovski [83] revealed changes in the functional state of the skin capillaries patients with diffuse purulent peritonitis complicat ed by abdominal sepsis.Study demonstrated that altered skin microcirculation correlated with the average value of the changes of the microcirculation parameters of the small intestine wall.Ultrasound flowmetry was helpful in evaluating components of microvascular tone based on the oscillation micro circulation amplitude caused by the intensity of the vessel wall muscular contractions.The method allowed evaluation of basic parameters of flow: lin ear and volumetric rate, the direction of blood flow in the macro and microvessels during therapeutic effects.

Endotoxinemia diagnostics
Endotoxin concentration determination in the blood quantifies LPS translocation [86].One of the endotoxin detecting methods is a limulus amoeba lysate test (LAL test) based on the hemolymph crus tacean Limulus polyphemus ability to coagulate upon contact with LPS and form a fractal.Necessary coag ulation factors are situated in amoebocytes granuleshemolymph Limulus polyphemus immune cells.Using amoebocytes lysate the test was developed for the quantitative endotoxin determination.
In the laboratory, the endotoxin content is determined photometrically.The presence of endo toxemia and its level correlate with clinical outcome.The concentration of endotoxin more than 700 pg/ml is associated with the development of shock [87].LAL test provides high sensitivity and speci ficity values for endotoxin of gram negative bacteria, although it does not identify specific pathogens, however, confirms the presence of bacteria or their endotoxins in the environment of the organism.Clinically, it is important not to define the exact infectious agent, but to determine its existence and dynamically assess the endotoxemia level.Fast and reliable identification of Gram negative infection allows to perform early treatment and determine the tactics.Advantages of this test are also in relative simplicity of analysis, low cost, reliability and obtaining speed results, high sensitivity and speci ficity to gram negative bacteria endotoxin [88].
Another way to detect endotoxin in blood is a gel clot test that is semi quantitative but requires no special equipment.A positive reaction is considered when the dense gel at the bottom of the test tube does not collapse under its turning to 180 °.It means that the concentration of endotoxin in the sample is greater or equal to the sensitivity of LAL reagent used.The reaction is considered as negative when there is no dense gel or destruction of rollover, and it means that the endotoxin concentration is below the sensitivity of LAL reagent [89].

Extracorporeal treatment of abdominal sepsis
Treatment of sepsis includes sanitation of surgi cal foci of infection and antimicrobial chemotherapy.Competent surgical approach is a key element of massive endotoxin aggression [92,93].
The use of antibiotics in the first hour after the hypotension onset is associated with survival in 79.9% cases.Every hour of antibiotic therapy delay during the first 6 h increases the mortality rate to 7.6%.Time of the antibiotic application is the most powerful predictor of outcome [106][107][108].Bactericidal antibiotics cause lysis of the microor ganisms, increases the concentration of endotoxin in the blood.The phenomenon of rising the endotoxin concentration after antibiotic action has been dis covered by experimental studies in vivo.Successful treatment of sepsis involves not only the elimination of the bacteria themselves, but also the elimination of endotoxemia.Antibiotic induced release of addi tional bacterial endotoxins can trigger the develop ment of endotoxin shock [94,95].In this case, it seems appropriate to conduct urgent endotoxin hemosorption.
Thus, understanding pathophysiology of sepsis determins the need in extracorporeal detoxification [96,97].SIR mediators, eicosanoids, complement components, and kallikrein kinin system are detoxi fication targets that is especially important when natural liver renal clearance is reduced due to multi organ dysfunction.Extracorporeal methods allows to eliminate and reduce the concentration of endo toxin and SIR mediators [98,99].Extracorporeal treatment of sepsis can be divided into selective and nonselective one.
Conventional low molecular weight substances boundary is 500 Da.These include urea, creatinine, electrolytes, glucose, amino acids molecules.Hemodialysis application bases on substances diffu sion through the semipermeable membrane.Liquid excess is removed by pressure gradient.Hemodialysis (HD) is effective for elimination of uremic toxins, and its application in abdominal sepsis treatment is expedient in the case of renal failure [100].
In 1967, Lee W. Henderson et al. [102] described a new method based on convection that was later called hemofiltration (HF).Convection is a transfer of substances dissolved in the filter accord ing to the gradient of the hydrostatic fluid pressure through a semipermeable membrane.Quantitative expression of convection is screening coefficient that represents the concentration ratio of removed sub stance in the ultrafiltrate to its level in the blood before hemofilter.Besides azotemia correction, dur ing hemofiltration anaphylatoxins (C3a and C5a), pro inflammatory cytokines (TNF α, IL1, IL6), myoglobin, parathyroid hormone, lysozyme, crea tine, and others are eliminated.In randomized study of Ronco C. and R. Bellomo [103,104] it was shown that the minimum effective substitution rate was 35 ml / h / kg, with increasing survival by removing the «middle molecules», the substances with a molecular weight greater than 500 Da.The duration of the pro cedure, blood flow and the replacement solution flow depended on the patients' health, their illness and the nature of organ dysfunction.
Hemodiafiltration (HDF) combines the princi ples of low and medium weight substances diffusion and convection through a semi permeable membrane from the blood into the effluent [105].While HDF diffusion and convection occur simultaneously: diffu sion decreases the concentration of low molecular weight compounds that lead to their smaller convec tive removal, and convection decreases the rate of blood flow in the dialyzer, and hence the driving force for diffusion.Diffusion transportation requires the dialysis fluid presence flowing through the dialyzer in the direction opposite to blood flow [106].To ensure the convective transport, a large volume of ultrafil tration is required that significantly exceeds the allowable dehydration.The fluid balance is provided by replacement of infusion solution before the filterpre dilution and post dilution.In sepsis treatment HDF is used to reduce the level of cytokines in the systemic circulation.C. Ronco in a randomized trial (n=425) showed a mortality reduction with increas ing replacement doses during the prolonged HDF.In 72% patients with septic shock and normo or hyper kinetic hemodynamic profile under the influence of HDF produced significant improvements in systemic hemodynamics and oxygen transport.In 58% patients with acute lung injury improvement in gas exchange increased with increasing oxygenation index and decreasing of pulmonary shunt and alveo lar arterial oxygen difference [107].ных эндотоксинов может спровоцировать разви тие эндотоксинового шока [94,95].В этом случае представляется целесообразным неотложное про ведение гемосорбции эндотоксина.
В 1967 году Lee W. Henderson с соавторами [102] описали новый метод, основанный на кон векции, впоследствии названный гемофильтраци ей (ГФ).Под конвекцией подразумевается пере нос субстанций, растворенных в фильтрующейся по градиенту гидростатического давления жидко сти через полупроницаемую мембрану.Количест венным выражением конвекционной способности является коэффициент просеивания, представля ющий из себя отношение концентрации удаляе мого вещества в ультрафильтрате к его уровню в крови до гемофильтра.Помимо коррекции азоте Increased convective removal of inflammatory mediators may be performed by enlarging of pore size of the membrane hemofilter.Membrane permeability for saluted substances and sieving characteristics are determined by pore size and a number of limitations that affect the molecules «dragging» through the membrane by liquid current.Sieving coefficient is a ratio of concentrations of the substance in the filtrate and the blood in the absence of its absorption on the membrane (values from 0 to 1).Sieving coefficient value is equal 0.1 representing the cut off point.In recent years, the membrane with the SUPER FINE sieving coefficient (high cut off) become «popular» in practice.Such membranes are permeable to light immunoglobulin chains, and therefore can be used in acute kidney injury treatment (acute renal failure) in sepsis.Clinical studies deploying high cut off mem branes with increased pore diameter showed their effectiveness in the removal of medium weight sub stances.Study S. Morgera (2006) demonstrated reduction in vasopressor requirement in the group, where hemofilters with High Cut Off membranes were used (mean dose 31 ml/kg/hour, observation period 48 hours) [108].
Plasmapheresis (PF) enables to remove sub stances with a molecular weight of 50-60 kDacirculating immune complexes, immunoglobulins, clotting factors, and others.The positive PF influ ence on hemostasis and rheological blood properties is the level of fibrinogen reduction, spontaneous platelet aggregation reduction in combination with the appearance in the blood fibrin degradation prod ucts, which probably serves as a marker of the microvasculature release [109].B.G. Stegmayr in a literature review described the efficacy of PF in sep sis and septic shock resulted in improved survival in patients with sepsis to 70-75%.It should be noted that during PF not only weight toxic products are eliminated from the blood, but large molecules that can penetrate through the membrane, disappeared, too, demonstrating non selectivity of the method.In clinical practice, there are common situations when large volume of plasma exchange is not possi ble since the cardiovascular failure and bacterial invasion is usually accompanied by vasodilation, vascular permeability disorders and hemostasis caused by endotoxemia.
Selective hemosorbtion of endotoxin represents a pathogenetic treatment.Positive results can be achieved if the mediator cascade is interrupted from the beginning, at the stage of endotoxemia, where the process has not yet taken out of control.It is known that the weak side of almost all non selective sorbents used in the clinical practice is their ability to absorb, in concert with the desired toxins, other plasma components.Negative consequences of this eliminations includes hypoproteinemia, secondary immunodeficiency, coagulation disorders that is   [107].
Увеличить конвекционное удаление медиа торов воспаления можно посредством увеличе ния размеров пор в мембране гемофильтра.Про ницаемость мембраны для растворенных веществ, характеристики просеивания, определяются раз мером пор и рядом ограничений, влияющих на «протаскивание» молекул через мембрану током жидкости.Коэффициент просеивания представ ляет собой соотношение концентраций этого ве щества в фильтрате и крови, при отсутствии его абсорбции на мембране (и принимает значения от highly undesirable for critical illness patients.The sorbents are designed for the selective endotoxin removal (Toraymyxin and LPS Adsorber) possess all the necessary features for an effective and safe treat ment of sepsis (high absorption capacity and rate of sorption, structural stability, compatibility with blood due to absence of mechanical and chemical damage of the blood) [110].Therapeutic effect of selective hemosorption was demonstrated when eliminating the endotoxin from circulation and interstitial sector.The first publications on clinical use of the sorbent based on polymyxin B appeared in 1994, when H. Aoki and M. Kodama showed the effectiveness of the sorbent in sepsis treatment with MODS.Sorbent covalently bonded to chemically modified polystyrene and immobilized on a polypropylene fiber neutralized the biological activi ty of endotoxin by binding to lipid A. The side effects of systemic polymyxin B usage was due to its nephrotoxicity and neurotoxic effects.In hemoper fusion with a sorbent covalently bound polymyxin B this effect was not observed.LPS Adsorber column consists of 20 plastic plates on which the special NAE 27 peptide capable to endotoxin adsorbtion is immobilized.Significant decrease in blood concen trations of endotoxine, inflammation mediators and hemodynamic improvement during hemosorption with column Alteco LPS Adsorber have been repeat edly demonstrated [111].
The study EUPHAS [112], devoted to the early use of selective hemosorption, showed an increase in mean arterial pressure, decrease in vasopressor usage and reducion the severity of the multiorgan failure as demonstrated by SOFA scale.Twenty eight day mor tality was 32% with selective hemosorption and 53% in the comparison group.A multicenter, placebo con trolled study EUPHRATES, in which the absence of the SIR was not an exclusion criterion, and the level of endotoxin in the blood was determined by a EAA test, confirmed high efficiency of selective hemosorp tion [113].In a latter study, Cruz D.N. et al. retro spectively evaluated 1425 patients from 28 clinical trials with sepsis of various etiologies.It was noted that as a result of the selective endotoxin removal the hemodynamics was normalized, a need in vasopressor support was reduced and index PaO 2 /FiO 2 increased.In blood values IL 6, IL 10, IL 18, TNF α, plasmino gen activator inhibitor 1, neutrophil elastase, platelet factor 4, soluble P selectin and endogenous cannabi noids were decreased.
Despite the fact that deploying the selective endotoxin adsorption is pathogenetically justified, the isolated elimination of endotoxin from the blood circulation alone could not lead to complete regres sion of the SIR due to continuous circulation of cytokines [114].
Extracorporeal methods of detoxication are actively deployed in life threatening critical illness [117][118][119].Despite the proven efficacy of extracor poreal detoxification in septic shock, there is no gen erally accepted guidelines for choosing the treatment regimen and the approach remains predominantly empirical.
The combination of selective and non selective methods of extracorporeal detoxification looks promising to break the «vicious circle» through removing the effects of «mediator storm» and elimi nating microcirculatory disorders.Timely and methodically correct deployment of extracorporeal detoxification and keeping focus on infectious sani tation associated with a rational antibiotic therapy should definitely prevent the development of multi organ dysfunction.

Conclusion
Abdominal sepsis is one of the most difficult problems of contemporary medicine characterized by rapid translocation of microorganisms and toxins in systemic blood flow saturation as a result of increased permeability of entero hematic barrier.These features distinguish abdominal sepsis from other patterns of sepsis development in which the bowel dysfunction is secondary.Development and progression of infectious toxic shock, multiple organ failure and a high mortality rate are very common in abdominal sepsis.
Effect of endotoxemia is mediated by direct damage of cell and tissues and indirectly via activa tion of cellular and mediator systems.Direct toxicity alters vascular endothelium and liver sinusoids that form a base of microcirculatory disorders.Improving microcirculation is an important strategy to improve clinical results in septic patients.One efferent treat ment strategy includes the increasing tissue perfu sion that becomes significant target for both thera pies and monitoring of treatment efficiency.Therefore, when assessing the therapeutic effects including extracorporeal microcirculation, the prop er methods of assessment should be employed.