Gram-negative sepsis. Background, clinical features, and intervention

The pathogenesis of sepsis. Factors that modulate the response to gram-negative bacterial infection

Gram-negative bacteria gain access to the bloodstream by evading host defenses. Once in circulation, lipopolysaccharide interacts with the host receptor CD14 and initiates the host's immune response. Lipolysaccharide stimulates the host to produce a cascade of mediators that activate and target leukocytes, opsonize the bacteria, and induce fever to defend against the invading bacteria. Unregulated release of these mediators, however, leads to the production of vasoactive substances, activation of the clotting cascade, and diminution of cardiac performance, which leads to the sepsis syndrome. This article discusses the pathogenic events that lead to sepsis syndrome and reviews critical steps in regulating these inflammatory mediators to allow the host to recover from gram-negative bacteremia.

Diffuse plasmacytosis in a child with brainstem glioma following multiagent chemotherapy and intensive growth factor support

The use of granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) in order to abrogate chemotherapy-induced neutropenia has become a routine part of many cancer treatment regimes. However, there are still very few data available about possible complications related to repeated or prolonged use of these agents in patients with malignant solid tumors. The authors report a child with brainstem glioma who received repeated cycles of multiagent chemotherapy with G- or GM-CSF support. During this period of 10 months, no clinical side effects were observed that could have been attributed to growth factor administration. However, postmortem histological examination revealed the presence of diffuse plasmacytosis, a rare hematological disorder in childhood. Undifferentiated plasma cells of nonmonoclonal origin could be demonstrated infiltrating bone marrow, lungs, and lymph nodes of the patient. Based on previously published in vitro and in vivo evidence on the interleukin-6 (IL-6)-mediated stimulatory effect of G- and GM-CSF on myeloma cell proliferation, the authors suggest a possible link between extensive growth factor support and the development of plasmacytosis in this patient.

Protection against endotoxic shock and lipopolysaccharide-induced local inflammation by tetracycline: correlation with inhibition of cytokine secretion

Septic shock results from excessive stimulation of host immune cells, particularly monocytes and macrophages, by lipopolysaccharide (LPS) released from gram-negative bacteria. Macrophage-derived cytokines, such as tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1 beta), have been identified as central mediators in the pathogenesis of septic shock and the resultant mortality. Therefore, these cytokines were targets for experimental therapy for septic shock. Because of tetracycline's ability to intervene in cellular mechanisms involved in cytokine secretion, we tested the effect of tetracycline on LPS-induced septic shock and inflammatory lesions in mice. Tetracycline was found to protect mice against LPS-induced lethality and to abolish clinical signs of LPS-induced inflammatory lesions. This protection correlates with tetracycline's ability to reduce LPS-induced TNF-alpha levels in serum. Furthermore, tetracycline was found to inhibit LPS-induced TNF-alpha and IL-1 beta secretion, but not cytokine mRNA accumulation, in human monocytes in vitro. The results presented here suggest that tetracycline is a potent drug for LPS-induced pathology and that its mechanism of action involves blockage of posttranscriptional events of cytokine production.

Bacteremia and sepsis

Recent evolution in the thinking of sepsis syndrome has provided a framework on which new clinical and basic research can be built. The separation of the inciting event and the cascade of subsequent physiologic changes has profound effects on how sepsis is thought of and ultimately how it will be treated. Early identification and treatment of infections and identifying patients at risk, to prevent SIRS, is the current role of Eps. Resuscitation of severe sepsis is more complex than other forms of shock and may require extensive resources if rapid admission or transfer to an intensive care unit is not available. As in many instances, the EP must be knowledgeable and skilled in the early identification and initial management of these patients until the definitive care can be provided. Modulation of the inflammatory response appears to be a prime prospect, but its practicality remains to be proved. Research and future roles of EPs include defining the population of ED patients at risk for SIRS and use of mediators of the inflammatory response. Emergency medicine is positioned in a critical point in the care of these patients.

Emergency percutaneous balloon mitral valvotomy in a patient with septic shock

We report an 18-year-old patient with severe mitral stenosis complicated by right lower lobe pneumonia, sepsis, and shock. Intractable low cardiac output led to an emergency percutaneous balloon mitral valvotomy in a patient, resulting in immediately improved hemodynamic parameters. We are unaware of another report of percutaneous balloon mitral valvotomy performed in a patient with sepsis and shock. This case supports previous isolated reports of the benefit from emergency percutaneous balloon mitral valvotomy in critical situations where thoracotomy is not possible due to coexisting medical problems.

E5531, a pure endotoxin antagonist of high potency

Shock due to Gram-negative bacterial sepsis is a consequence of acute inflammatory response to lipopolysaccharide (LPS) or endotoxin released from bacteria. LPS is a major constituent of the outer membrane of Gram-negative bacteria, and its terminal disaccharide phospholipid (lipid A) portion contains the key structural features responsible for toxic activity. Based on the proposed structure of nontoxic Rhodobacter capsulatus lipid A, a fully stabilized endotoxin antagonist E5531 has been synthesized. In vitro, E5531 demonstrated potent antagonism of LPS-mediated cellular activation in a variety of systems. In vivo, E5531 protected mice from LPS-induced lethality and, in cooperation with an antibiotic, protected mice from a lethal infection of viable Escherichia coli.

Results of passive and active immunization directed against ferric aerobactin in experimental enterobacterial infections in mice and chickens

Production of aerobactin has been reported to be a virulence factor in members of the family Enterobacteriaceae. To investigate the protection afforded by humoral immunity directed towards aerobactin in infectious diseases caused by aerobactin-producing strains, we tested the efficacy of mAbAERO1, a murine monoclonal antibody directed to ferric aerobactin, which, in vitro, was found to impair the growth of aerobactin-dependent strains of Enterobacteriaceae under iron-limited conditions. The mortality of mice experimentally infected with the aerobactin-producing strains Escherichia coli V2019 (LD50 = 3.5 x 10(5) CFU/mice) or Klebsiella pneumoniae Caroli (LD50 = 1.3 CFU/mice) was not reduced when 1 mg of mAbAERO1 was injected intravenously 1 h before or 1 h after bacterial challenge. Nor was mortality reduced after challenge with either E. coli V2019 or K. pneumoniae Caroli, even though the active immunization of mice with purified FeAero (ferric aerobactin) conjugated with thyroglobulin as followed by a rise in systemic anti-FeAero antibodies. Lastly, chicks born of hens immunized with FeAero showed evidence of antibody transmission towards FeAero, but were not protected when challenged with E. coli MT78, an aerobactin-producing strain highly virulent for chickens. Therefore, under the experimental conditions tested, humoral immunity against aerobactin appeared to play only a minor role in protection against infections caused by aerobactin-producing members of the family Enterobacteriaceae. However, other experimental models should be tested to confirm these observations.

L-arginine: nitric oxide pathway in endotoxemia and human septic shock

OBJECTIVE

To investigate the relationship between nitric oxide production, endotoxemia, and hemodynamic alterations in human septic shock.

DESIGN

Prospective study.

SETTING

A 32-bed intensive care unit in a university referral hospital.

PATIENTS

Two groups of septic patients with shock (n = 13) or without shock (n = 16) and an additional group of nonseptic patients as control group (n = 25).

MEASUREMENTS

Plasma nitrite and nitrate concentrations were measured as an index of nitric oxide generation. Nitrite and nitrate concentrations were correlated with plasma endotoxin and hemodynamic variables.

MAIN RESULTS

Increased plasma nitrite and nitrate concentrations were found in patients with septic shock (p < .01). Nitrite and nitrate correlated directly with endotoxin concentration (r2 = .21, p < .05) and cardiac output (r2 = .49, p < .05), and inversely with systolic blood pressure (r2 = .24, p < .01).

CONCLUSIONS

This study demonstrated the activation of the L-arginine:nitric oxide pathway in human endotoxemic septic shock, suggesting that nitric oxide may be an important mediator of the hemodynamic disturbances in this pathophysiologic situation.

Microvascular perfusion is impaired in a rat model of normotensive sepsis

We hypothesized that normotensive sepsis affects the ability of the microcirculation to appropriately regulate microregional red blood cell (RBC) flux. An extensor digitorum longus muscle preparation for intravital study was used to compare the distribution of RBC flux and the functional hyperemic response in SHAM rats and rats made septic by cecal ligation and perforation (CLP). Using intravital microscopy, we found that sepsis was associated with a 36% reduction in perfused capillary density (from 35.3 +/- 1.5 to 22.5 +/- 1.0 capillaries/mm of test line) and a 265% increase in stopped-flow capillaries (from 0.9 +/- 0.2 to 3.3 +/- 0.4 capillaries/mm); the spatial distribution of perfused capillaries was also 72% more heterogeneous. Mean intercapillary distance (ICD) increased 30% (from 25.7 +/- 0.8 to 33.5 +/- 1.6 microns), and the proportion of capillary pairs with intercapillary distances > 33.8 microns (the 75th percentile of ICDSHAM) was greater with sepsis. Mean capillary RBC velocity increased 17% in CLP rats (391 vs 333 microns/s). Laser Doppler flowmetry was used to assess the functional hyperemic response of the extensor digitorum longus muscle before and after a period of maximal twitch contraction designed to increase oxygen demand. RBC flux was 36% lower in the CLP rats at rest. After contraction, RBC flux increased in both SHAM and CLP rats; however, the relative increase was less in the CLP group. We concluded that sepsis affects the ability of the skeletal muscle microcirculation to appropriately distribute RBC flux and to respond to increases in oxygen need.

CD14 is a pattern recognition receptor

Septic shock caused by a diverse group of bacterial pathogens is a serious human disease. Recognition of bacterial envelope constituents is one mechanism used by mammalian cells to initiate responses leading to bacterial killing or, unfortunately, responses that also cause fatal septic shock. Here we show that CD14 plays a key role in initiating cell activation by a group of bacterial envelope components from Gram-negative and Gram-positive microorganisms, as well as mycobacteria. We propose that CD14 is a receptor used by mammalian cells to recognize and signal responses to a diverse array of bacterial constituents. This finding defines the molecular basis for innate microbial immunity; implicit in these findings are new possibilities for therapeutics.

Acetylcysteine as a cytoprotective antioxidant in patients with severe sepsis: potential new use for an old drug

OBJECTIVE

To stimulate debate regarding a potential new use for acetylcysteine as a cellular antioxidant in severely septic patients with systemic inflammatory response syndrome (SIRS).

DATA SOURCES

A MEDLINE review of published animal, human, and laboratory studies relating to the cytopathogenic effects of active radicals in SIRS and the protective effects of acetylcysteine and glutathione.

STUDY SELECTION

Few studies were available so all studies pertinent to the objective were reviewed.

DATA EXTRACTION

Clinical and basic science data from the available trials of the effects of acetylcysteine on active radical production or active radical cell injury were extrapolated to predict the effect of acetylcysteine on human sepsis.

DATA SYNTHESIS

Severe sepsis is a major cause of SIRS. Much of the cellular injury associated with SIRS is mediated by active radicals produced by inflammatory cells that overwhelm endogenous antioxidants. Reduced glutathione is a crucial intracellular antioxidant that becomes depleted during SIRS. Regeneration of glutathione can be achieved by acetylcysteine, which unlike glutathione itself penetrates cells. In animal models of sepsis and lung injury, acetylcysteine mitigates the cytopathologic effects of SIRS. In humans, clinical benefit has been demonstrated in the SIRS of established fulminant hepatic failure.

CONCLUSIONS

The data do not as yet lead to any firm conclusions regarding the value of acetylcysteine in the management of SIRS in severe sepsis. The animal and human studies are, however, sufficiently encouraging to warrant formal trials to test the hypothesis that acetylcysteine therapy has a cytoprotective effect in sepsis.

Recognition of endotoxin by cells leading to transmembrane signaling

Bacterial endotoxins act at picomolar to nanomolar concentrations to stimulate a wide variety of cell types including phagocytic and endothelial cells. The major elements identified to date that are crucial for recognition of endotoxin are lipopolysaccharide (LPS)-binding protein, membrane-bound CD14 and, most recently, soluble CD14. Recent results also indicate that membrane-bound CD14 is probably one part of a multi-component LPS receptor. An immediate consequence of engagement of this functional LPS receptor is protein tyrosine phosphorylation and initiation of the multiple intracellular events associated with LPS-induced cell activation.

Glycosyl-phosphatidylinositol-anchored or integral membrane forms of CD14 mediate identical cellular responses to endotoxin

Endotoxin stimulates leukocytes to release cytokines that initiate septic shock in humans and animals. CD14, a glycosyl-phosphatidylinositol-anchored membrane glycoprotein, is an endotoxin receptor on leukocytes, and endotoxin binding to CD14 induces cytokine production. Here we show that glycosyl-phosphatidylinositol-anchored or integral membrane CD14 mediates identical cellular responses to endotoxin, including NF-kappa B activation and protein tyrosine phosphorylation. We also show that an anti-CD14 monoclonal antibody that does not block endotoxin binding to CD14 nonetheless inhibits cell activation by endotoxin. These findings suggest that binding of endotoxin to cell-surface CD14 is followed by subsequent interactions of the endotoxin-CD14 complex with additional membrane component(s) that enable transmembrane signaling. This function of CD14 may be prototypic for other members of the glycosyl-phosphatidylinositol-anchored family of proteins that do not play a primary role in signal transduction but rather are the principal ligand-binding units of membrane-bound receptor complexes.

A simple multiple system organ failure scoring system predicts mortality of patients who have sepsis syndrome

A simple multiple system organ failure (MSOF) score may predict mortality of patients who have sepsis syndrome. Using an MSOF scoring system, we prospectively determined the presence or absence of respiratory, cardiovascular, renal, hepatic, gastrointestinal, hematologic, and neurologic organ failure on day 1 of sepsis syndrome in 154 consecutive patients who had sepsis syndrome in the ICU of a tertiary care, teaching hospital. We used 30-day hospital mortality as the primary outcome variable. Overall 30-day mortality was 34 percent. There was a strong linear association between number of organ system failures and 30-day mortality (p < 0.0001). Mortality was 20 percent in patients who had less than 3 organ system failures (n = 111) and 70 percent in patients who had 3 or more organ system failures (n = 43). Survival was assessed using the Cox proportional hazards model and was found to be significantly different (p < 0.01) between the two groups defined by the aforementioned dichotomy after adjustment for age and sex using time to death as the primary outcome. The increase in relative risk of death associated with 3 or more organ system failures was 2.77 (95 percent confidence interval, 2.74 to 2.83). Using logistic regression, the adjusted odds ratios (OR) for covariates most predictive of mortality were hematologic (OR = 6.2), neurologic (OR = 4.4), hepatic (OR = 3.4), cardiovascular (OR = 2.6), and age (1.05 per year). The logistic model using the seven organ system failures and age as covariates accurately predicted outcome 75 percent of the time with a sensitivity of 51 percent and specificity of 87 percent. In conclusion, a simple scoring system tabulating the number of organ system failures present on day 1 of sepsis syndrome predicts the mortality of patients who have sepsis syndrome with reasonable accuracy.

Multiple organ failure after mitral valve repair with intravascular hemolysis and its recovery due to mitral valve replacement

We present a patient with evidence of severe intravascular hemolysis after mitral valve repair, an established method for the surgical treatment of mitral valve disease to avoid prosthesis related complications. The coincidence of this uncommon complication with hemodynamic instability due to pre-existing myocardial dysfunction and Gram-negative pneumonia promoted the development of simultaneous dysfunction of liver, kidney and the cardio-respiratory system. Elimination of the source of hemolysis by re-operation with mitral valve replacement on the ninth postoperative day allowed prompt recovery from severe organ dysfunction. Free hemoglobin may have perpetuated progressive organ failure in our patient.

Septic shock in critically ill patients: aetiology, management and outcome

Over a period of 28 months, 45 episodes of septic shock from 83 episodes of bacteraemia were studied prospectively to evaluate their clinical profile, management and outcome. Thirty-six patients were studied, the overall incidence of septic shock being 54.2%. Gram-negative organisms accounted for 23 (51.1%) of such episodes, Gram-positive 17 (37.8%), and three episodes were polymicrobial (6.7%). The organisms isolated most frequently were Staphylococcus epidermidis (17.8%), Pseudomonas aeruginosa (13.3%), Escherichia coli and Klebsiella sp. (each 11.1%). Coagulation abnormalities were detected in 32 episodes (78%) and disseminated intravascular coagulation (DIC) occurred in 11 of these with high mortality. The most common underlying conditions were respiratory, hepatic and renal failures. The majority of these patients received crystalloids, colloids, vasopressor drugs and blood. Swan-Ganz catheters (SGC) were inserted on eight occasions, the majority of times indicating a hyperdynamic circulatory response. The overall mortality was 40%, despite aggressive management and intensive care. The most important factor in reducing mortality is early detection of bacteraemia and prompt management of these patients.

Studies of the effect of a platelet-activating factor antagonist, CL 184,005, in animal models of gram-negative bacterial sepsis

The effect of CL 184,005, a potent and specific platelet-activating factor antagonist, has been examined in a variety of animal models relevant to gram-negative bacterial sepsis. Pretreatment of mice with CL 184,005 protected them from the lethal effects of platelet-activating factor. When rats or primates rendered hypotensive with endotoxin were treated with CL 184,005, blood pressure was normalized. Pretreatment of rats with CL 184,005 protected them from the gastrointestinal lesions induced by endotoxin. Pretreatment of rats and mice with CL 184,005 protected them from the lethal effects of endotoxin. Plasma tumor necrosis factor levels in endotoxin-treated mice were lower when the mice were pretreated with CL 184,005. These observations suggest that CL 184,005 may be potentially useful in the treatment of gram-negative bacterial sepsis, and the agent is undergoing clinical evaluation.