Relationship between preoperative endotoxin immune status, gut perfusion, and outcome from cardiac valve replacement surgery

Hit 'em Where It Hurts: Gram-Negative Bacterial Lipopolysaccharide as a Vaccine Target

Infections with antimicrobial-resistant (AMR) bacteria pose an increasing threat to the ability to perform surgical procedures, organ transplantation, and treat cancer among many other medical conditions. There are few new antimicrobials in the development pipeline. Vaccines against AMR Gram-negative bacteria may reduce the use of antimicrobials and prevent bacterial transmission. This review traces the origins of lipopolysaccharide (LPS)-based vaccines against Gram-negative bacteria, the role of O polysaccharides and LPS core regions as potential vaccine targets, the development of new vaccine technologies, and their application to vaccines in current development.

Hemodynamic and Intestinal Microcirculatory Changes in a Phenylephrine Corrected Porcine Model of Hemorrhage

BACKGROUND

Intraoperative hypotension is a common event, and a recent study suggests that maintenance of blood pressure may reduce complications. The splanchnic circulation provides a reservoir of blood that can be mobilized during hemorrhage; hence, intestinal microcirculation is sensitive to volume changes. The aim of this study was to assess the impact of hemorrhage on intestinal microcirculation and hemodynamics, and the effects of phenylephrine on these parameters.

METHODS

Eight anesthetized, mechanically ventilated Yorkshire/Landrace crossbreed pigs were studied. Graded hemorrhage was performed with the removal of 20% of blood volume in 5% increments. Hemodynamic and intestinal microcirculatory measurements were performed at each stage with side-stream dark field microscopy, following which mean arterial pressure (MAP) was corrected with phenylephrine to baseline values and measurements repeated. A repeated measurement 1-way analysis of variance (ANOVA) was used to compared changes from baseline measurements.

RESULTS

The mean baseline microcirculation score was 42 (standard deviation [SD] = 5). A 5% hemorrhage decreased the microcirculation score by a mean difference of 19 (95% confidence interval [CI], 12-27; P < .0001), and an additional 5% hemorrhage further reduced the microcirculation score by a mean difference of 12 (95% CI, 4-19; P = .0001). Subsequent hemorrhage or administration of phenylephrine did not significantly change the microcirculation scores except when phenylephrine was administered at the 15% hemorrhage stage, which increased the microcirculation score by a mean difference of 7 (95% CI, 1-13; P = .003). All hemodynamic variables were returned to baseline values following hemorrhage by the phenylephrine infusion.

CONCLUSIONS

Intestinal microcirculatory flow is reduced early in hemorrhage and is uncorrected by phenylephrine infusion. Hemodynamic changes associated with hemorrhage are corrected by phenylephrine and do not reflect microcirculatory flow status.

Relationship between endotoxin core, staphylococcal and varicella antibody levels and outcome following aortic valve replacement surgery: a prospective observational study

Background

Morbidity and mortality following cardiac valve surgery is high. Immunity is an important contributor to outcome. This study examines the relationship of staphylococcal and endotoxin antibody levels to outcome following cardiac surgery.

Methods

Using enzyme-linked immunosorbent assays (ELISA), we measured pre-operative levels of antibodies to endotoxin core (EndoCAb); 3 common staphylococcal epitopes and varicella on saved serum of 60 adult patients scheduled to undergo elective primary surgical aortic valve replacement (AVR). Primary outcome measure was post-operative length of stay (LOS) in hospital with secondary outcomes being development of infective complications, length of stay on the intensive care unit (ICU) and 30-day mortality. Patients were quartiled according to antibody levels and outcomes compared between the quartile groups using Mann-Whitney tests for length of stay and Fisher's test for development of infection.

Results

Sixty patients (34 M, 26 F) were recruited with mean age 73 years (IQR 66-78), mean body mass index (BMI) 27.7 (IQR 25-31) and EuroSCORE II 1.44 (0.95-1.99). Those patients in the lower quartile for pre-operative antibody level had a longer post-operative stay than the upper quartile. EndoCAb (median IgG level Q1 42.2 MU/ml vs Q4 256 MU/ml) 9 vs 6 days, p = 0.025; alpha-toxin (median IgG level Q1 63 U vs Q4 558 U) 10 vs 7 days, p = 0.034; teichoic acid (median IgG level Q1 14 U vs Q4 419 U) 10 vs 8 days, p = 0.441; staphylococcal enterotoxin A (median IgG level Q1 55 U vs Q4 427 U) 9 vs 7 days, p = 0.865; varicella zoster (median IgG level Q1 1.325 U vs Q4 2.54 U) 8 vs 7 days, p = 1.0; and combined antibody levels 10 vs 6 days, p = 0.017. There were no differences in the number developing post-operative infections for each antibody type. The combined antibody analysis suggested a reduction in proportion of individuals developing infection from the upper vs lower quartile: 0 vs 0.33, p = 0.042.

Conclusions

This study again suggests the inverse relationship between endotoxin core antibody levels and outcome following aortic valve surgery as well as suggesting a similar relationship with antibodies to staphylococcus. There is no such relationship for antibody levels against an organism not providing a peri-operative threat. Understanding this relationship may enable therapeutic manipulation of immune status, re-evaluation of risk and further investigation of the low immune state.

Trial registration

The patients in this study are a sub-group of the RELIEF AS study.ClinicalTrials.gov identifier NCT02174471.

The biological activity of a liposomal complete core lipopolysaccharide vaccine

A vaccine that induces humoral immunity to lipopolysaccharide (LPS), while remaining non-pyrogenic should be beneficial, as high levels of antibodies against LPS are associated with a reduced risk of adverse outcome. However, pure LPS or bacteria expressing LPS are generally considered too toxic to be used as vaccines. Recently, a novel, immunogenic complete core lipopolysaccharide vaccine has been described, which has been designed to prevent endotoxin-related inflammatory reactions in surgical and high-risk hospitalized patients. In vivo studies have shown that while administration of the vaccine to rabbits results in no toxicity over 7 days, it does induce significantly enhanced antibody responses towards a broad range of clinically relevant Gram-negative LPSs. Here we show that encapsulation of the four complete core LPS types Escherichia coli K12, Escherichia coli R1, Bacteroides fragilis and Pseudomonas aeruginosa into liposomes greatly reduces the ability of a given amount of LPS to induce TNF-α production in vitro from human monocytes. In contrast to previous studies of liposomal LPS, we demonstrate a reduction in activity of approximately 100,000-fold; a reduction approximately 100—1,000-fold more than that previously described. The signalling by the liposomal LPS appears to be entirely dependent on serum factors, though this can be partially restored by soluble CD14 or, to a lesser extent, by lipopolysaccharide binding protein. Time-course experiments reveal that liposomal LPS signalling shows similar kinetics to pure LPS signalling. Therefore, as well as inducing specific antibody responses, liposomal LPS demonstrates characteristics suitable for use as a vaccine to be used in human beings.

Cognitive Dysfunction After Cardiac Surgery: Revisiting Etiology

Cognitive dysfunction remains a frequent complication of cardiac surgery. Despite many years of research, few preventive strategies and no definitive therapeutic options exist for the management of this troublesome clinical problem. This shortcoming may be secondary to an incomplete understanding of the pathophysiology and etiology of cognitive loss after cardiac surgery; a better understanding of the etiology is essential to finding new therapies. The etiology of cognitive dysfunction after cardiac surgery is multifactorial and includes cerebral microembolization, global cerebral hypoperfusion, systemic and cerebral inflammation, cerebral temperature perturbations, cerebral edema, and possible blood-brain barrier dysfunction, all superimposed on genetic differences in patients that may make them more susceptible to injury or unable to repair from injury once it has occurred. This review expands on these potential etiologies in detailing the evidence for their existence.

Variability of anti-staphylococcal antibodies in healthy volunteers and pre-cardiac surgery patients

Background

Pre-operative antibody levels have been shown to be inversely related to development of post-operative complications. Staphylococcal infection is a major source of morbidity following surgery.

Methods

We examined the variability of anti-staphylococcal antibody levels across a group of healthy volunteers and compared this with patients scheduled to undergo cardiac surgery.

Results

Pre-operative cardiac surgical patients exhibited significantly higher levels of staphylococcal antibodies compared with healthy volunteers.

Conclusions

The relationship between pre-surgery staphylococcal antibody levels and outcome warrants further investigation.

Probiotics can alleviate cardiopulmonary bypass-induced intestinal mucosa damage in rats

BACKGROUND

Cardiopulmonary bypass (CPB) is commonly applied to support circulation during heart surgery but frequently causes adverse effects.

AIMS

The purpose of this study was to examine the potential of probiotics to improve small intestinal mucosa barrier function after CPB.

METHODS

Twenty-four adult male SD rats were randomly divided into sham-operated (S), CPB-operated (CPB), and probiotic-fed (Y) groups. Diamine oxidase (DAO) activity and concentrations of D-lactic acid, endotoxin, TNFα, and IL-6 were measured in portal vein blood. IgA concentrations were determined in plasma and the small intestine. Vena cava blood and tissue samples were used to monitor bacterial growth. Intestinal epithelial ultrastructure was analyzed by transmission electron microscopy (TEM). Occludin and ZO-1 expression levels in the intestinal epithelium were detected by western blotting and immunohistochemistry, respectively.

RESULTS

D-lactic acid, endotoxin, TNFα and IL-6 levels, DAO activity, and bacterial translocation rate were increased (P < 0.05) in CPB and Y compared to the S group. The above indices were relatively lower (P < 0.05) in Y than in CPB. Plasma and small intestinal IgA levels were significantly lower (P < 0.05) in CPB, while in Y they were significantly increased (P < 0.05) but lower than in S (P < 0.05). These results were confirmed by TEM. Consistently, occludin and ZO-1 expression levels were significantly higher in Y than in CPB (P < 0.05) but still lower compared to S (P < 0.05).

CONCLUSION

Pre-administration of probiotics can improve, to some extent, intestinal barrier function after CPB in rats, and this effect is likely related to inhibition of the CPB-induced inflammatory response, improvement in local intestinal immune function, and increased expression of intestinal epithelial tight junction proteins.

Gastric and intestinal barrier impairment in tropical enteropathy and HIV: limited impact of micronutrient supplementation during a randomised controlled trial

BACKGROUND

Although micronutrient supplementation can reduce morbidity and mortality due to diarrhoea, nutritional influences on intestinal host defence are poorly understood. We tested the hypothesis that micronutrient supplementation can enhance barrier function of the gut.

METHODS

We carried out two sub-studies nested within a randomised, double-blind placebo-controlled trial of daily micronutrient supplementation in an urban community in Lusaka, Zambia. In the first sub-study, gastric pH was measured in 203 participants. In the second sub-study, mucosal permeability, lipopolysaccharide (LPS) and anti-LPS antibodies, and serum soluble tumour necrosis factor receptor p55 (sTNFR55) concentrations were measured in 87 participants. Up to three stool samples were also analysed microbiologically for detection of asymptomatic intestinal infection. Gastric histology was subsequently analysed in a third subset (n = 37) to assist in interpretation of the pH data. Informed consent was obtained from all participants after a three-stage information and consent process.

RESULTS

Hypochlorhydria (fasting gastric pH > 4.0) was present in 75 (37%) of participants. In multivariate analysis, HIV infection (OR 4.1; 95%CI 2.2-7.8; P < 0.001) was associated with hypochlorhydria, but taking anti-retroviral treatment (OR 0.16; 0.04-0.67; P = 0.01) and allocation to micronutrient supplementation (OR 0.53; 0.28-0.99; P < 0.05) were protective. Hypochlorhydria was associated with increased risk of salmonellosis. Mild (grade 1) gastric atrophy was found in 5 participants, irrespective of Helicobacter pylori or HIV status. Intestinal permeability, LPS concentrations in serum, anti-LPS IgG, and sTNFR55 concentrations did not differ significantly between micronutrient and placebo groups. Anti-LPS IgM was reduced in the micronutrient recipients (P <0.05).

CONCLUSIONS

We found evidence of a specific effect of HIV on gastric pH which was readily reversed by anti-retroviral therapy and not mediated by gastric atrophy. Micronutrients had a modest impact on gastric pH and one marker of bacterial translocation.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN31173864.

Techniques to assess tissue oxygenation in the clinical setting

The microcirculation plays an essential role in health and disease. Microvascular perfusion can be assessed directly using laser Doppler flowmetry and various imaging techniques or indirectly using regional capnometry and measurement of indicators of mismatch between oxygen delivery and oxygen consumption or indices of disturbed cellular oxygen utilization. Assessment of microvascular oxygen availability implies measurement of oxygen pressure or measurement of hemoglobin oxygen saturation. Microvascular function is assessed using other methods, including venous plethysmography. In this paper, I review current knowledge concerning assessment of the microcirculation with special emphasis on methods that could be used at the bedside.

Effects of cardiopulmonary bypass on tight junction protein expressions in intestinal mucosa of rats

AIM: To investigate the tight junction protein expressions of intestinal mucosa in an experimental model of cardiopulmonary bypass (CPB) in rats.

METHODS: Thirty anesthetized rats were randomly divided into two groups: Group S (n = 10) served as sham operation and group C (n = 20) served as CPB which underwent CPB for 1 h. Expression of occludin and zonula occludens-1 (ZO-1) were determined by Western blotting and immunocytochemistry, respectively. Plasma levels of diamine oxidase (DAO) and d-lactate were determined using an enzymatic spectrophotometry.

RESULTS: Immunohistochemical localization of occludin and ZO-1 showed disruption of the tight junctions in enterocytes lining villi at the end of CPB and 2 h after CPB. The intensities of the occludin and ZO-1 at the end of CPB were lower than those of control group (76.4% ± 22.5% vs 96.5% ± 28.5% and 62.4% ± 10.1% vs 85.5% ± 25.6%, P < 0.05) and were further lower at 2 h after CPB (50.5% ± 10.5% and 45.3% ± 9.5%, P < 0.05). Plasma d-lactate and DAO levels increased significantly (8.688 ± 0.704 vs 5.745 ± 0.364 and 0.898 ± 0.062 vs 0.562 ± 0.035, P < 0.05) at the end of CPB compared with control group and were significantly higher at 2 h after CPB than those at the end of CPB (9.377 ± 0.769 and 1.038 ± 0.252, P < 0.05). There were significant negative correlations between occludin or ZO-1 expression and DAO (r² = 0.5629, r² = 0.5424, P < 0.05) or d-lactate levels (r² = 0.6512, r² = 0.7073, P < 0.05) both at the end of CPB and 2 h after CPB.

CONCLUSION: CPB markedly down-regulates the expression of occludin and ZO-1 proteins in intestinal mucosa of rats. The close correlation between expression of tight junctions (TJs) and plasma levels of DAO or d-lactate supports the hypothesis that intestinal permeability increases during and after CPB because of decreases in the expressions of TJs.

Barrier function of the gut and multiple organ dysfunction after cardiac surgery

We studied the influence of sequential involvement of the gastrointestinal (GI) tract on the development of multiple organ dysfunction (MOD) after cardiopulmonary bypass (CPB). One hundred and forty-six patients undergoing elective cardiac surgery were included in this prospective observational study. Standardized oral inert-sugar tests (sucrose, lactulose, mannitol, sucralose) were performed before and after CPB in different patients. Enzyme-linked immunosorbent assay of plasma levels of endotoxin core antibodies (EndoCAb) were performed peri-operatively. The functional mucosal surface was calculated from the amount of mannitol absorbed from the GI tract. Lower urine concentrations of absorbed mannitol were observed pre-operatively in patients developing MOD. In binary logistic regression this was an independent parameter. Decreased plasma concentrations of EndoCAb after surgery were seen in every patient, but were more significant in patients developing MOD. A reduced pre-operative functional mucosal surface may predict the early occurrence of MOD after surgery.

Effects of intra-aortic balloon counterpulsation on parameters of tissue oxygenation

BACKGROUND AND OBJECTIVE

To investigate the effects of intra-aortic balloon pump therapy on parameters of global and regional oxygenation in patients undergoing cardiac surgery.

METHODS

As part of a large surveillance study in cardiac surgery patients (n=266) we retrospectively analyzed the course of 28 patients requiring intra-aortic balloon pump therapy. Patients were grouped according to the time point of pump insertion (during weaning from cardiopulmonary bypass: group early intra-aortic balloon pumping (n=17); after admission to the intensive care unit: group late intra-aortic balloon pumping (n=9). Haemodynamic and tonometric variables, arterial lactate, and use of catecholamines were measured hourly.

MEASUREMENTS AND RESULTS

Cardiac index increased in both groups after intra-aortic balloon pump insertion (2.2+/-0.5 baseline; 3.4+/-0.8 L min-1 m-2 4 h later (group early intra-aortic balloon pumping); 2.8+/-0.5 baseline, 3.6+/-L min-1 m-2 4 h later (group later intra-aortic balloon pumping), each P<0.05), there were no differences between groups. Arterial lactate values increased in group later intra-aortic balloon pumping after pump insertion to a maximum 2 h later (8.4+/-6.1 mmol L-1 baseline; 12.7+/-7.4 mmol L-1, P<0.05), and decreased continuously afterwards. The difference of arterial and gastric CO2 showed a sharp decrease after pump insertion in group later intra-aortic balloon pumping (26.4+/-9.8 baseline; 7.0+/-11.1 mmHg, P<0.05). There were no differences between groups. Epinephrine doses were higher in group later intra-aortic balloon pumping (P<0.05).

CONCLUSIONS

Intra-aortic balloon pump therapy improved global and regional splanchnic oxygenation in cardiac surgery patients with low-cardiac-output syndrome. Gastro-intestinal tonometry could provide additional information concerning tissue oxygenation. Patients with later intra-aortic balloon pump insertion needed more catecholamine therapy to achieve similar haemodynamic values.

Abnormal gastric tonometric variables and vasoconstrictor use after left ventricular assist device insertion

BACKGROUND

Abnormal gastric tonometric variables, a surrogate for splanchnic ischemia, occur in approximately 50% of patients at the end of routine cardiac operations and are associated with postoperative morbidity. We sought to determine whether gastric tonometric variables deteriorate after left ventricular assist device insertion and to explore the association between abnormal gastric tonometric variables and vasoconstrictor use.

METHODS

Nineteen patients who had insertion of a left ventricular assist device were enrolled in a prospective, observational study. Automated air tonometry was used to determine the difference between gastric and arterial partial pressure of carbon dioxide (CO2 gap) at five time points perioperatively.

RESULTS

Compared with baseline, systemic blood flow was significantly increased at the end of operation (1.9 +/- 0.6 versus 2.9 +/- 0.7 L x min(-1) x m(-2), p < 0.0001). Tonometric variables, which were normal at baseline, became abnormal in 90% of patients (baseline CO2 gap 4 +/- 2 mm Hg versus end of operation CO2 gap 24 +/- 15 mm Hg, p < 0.0001). Elevated CO2 gaps correlated with larger doses of norepinephrine (r = 0.69, p = 0.001) and vasopressin (r = 0.88, p < 0.0001). Abnormal gastric tonometric variables at the end of operation correlated with postoperative intensive care unit length of stay (r = 0.70, p = 0.0009) and multiple organ dysfunction score (r = 0.64, p = 0.0033).

CONCLUSIONS

Despite a significant increase in systemic blood flow after left ventricular assist device implantation, abnormal gastric tonometric variables developed and were associated with larger vasoconstrictor dose. These data provide evidence that gastric ischemia can develop independently of changes in systemic blood flow and support the potential role of vasoconstrictors as a cause of splanchnic ischemia.

Gastric hypercarbia and adverse outcome after cardiac surgery

OBJECTIVE

It has been postulated that splanchnic ischemia, as manifested by gastric hypercarbia, helps to trigger excessive systemic inflammation, which has been linked to the development of adverse postoperative outcome. This study examined whether gastric PCO(2) values are associated with adverse outcome in cardiac surgical patients.

DESIGN AND SETTING

Prospective cohort study in a tertiary-care hospital.

PATIENTS

43 patients undergoing elective cardiac surgery.

INTERVENTIONS

Simultaneous measurements of gastric PCO(2) (using automated air tonometry) and arterial PCO(2) were obtained at the beginning and end of surgery. The difference (gap) between regional PCO(2) and arterial PCO(2) (corrected for temperature) was calculated. Adverse outcome was defined as in-hospital death or prolonged (>10 days) postoperative hospitalization.

MEASUREMENTS AND RESULTS

Fourteen patients fulfilled the predefined definition for adverse outcome. Postoperative ICU stay and postoperative hospital length of stay were significantly longer in these patients. At the end of surgery gastric minus arterial PCO(2) gap was significantly larger in patients with adverse outcome. Global hemodynamic and perfusion related variables were not associated with adverse outcome (cardiac index, mean arterial pressure, mixed venous oxygen saturation, arterial lactate, arterial base excess).

CONCLUSIONS

Gastric minus arterial PCO(2) gap after surgery is larger in patients with adverse postoperative outcome, which supports the theory that gastrointestinal reduced perfusion is relevant to the pathogenesis of postoperative morbidity.

Lower endotoxin immunity predicts increased cognitive dysfunction in elderly patients after cardiac surgery

BACKGROUND AND PURPOSE

Although coronary artery bypass graft surgery (CABG) improves the quality of life and functional capacity for numerous patients, many also exhibit impairment in cognitive function immediately after surgery. Although the etiology of this cognitive decline is multifactorial, the inflammatory response to the primary insult may modulate the extent of dysfunction. Patients with low preoperative levels of anti-endotoxin core antibody (EndoCAb) are more likely to experience adverse outcomes, suggesting that decreased immunity to endotoxin causes a heightened release of inflammatory mediators. We therefore sought to determine the association of decreased EndoCAb and the incidence of postoperative cognitive decline.

METHODS

EndoCAb levels were measured before surgery in 460 patients undergoing elective CABG. Cognitive function was measured preoperatively and 6 weeks postoperatively. Multivariable analysis accounted for the effects of age, Parsonnet score, sex, body mass index, baseline cognition, years of education, history of hypertension, bypass time, cross-clamp time, and number of grafts.

RESULTS

At 6-week follow-up, 122 patients (36%) showed cognitive decline. Lower preoperative EndoCAb levels were associated with a greater incidence and severity of postoperative cognitive decline. The elderly with decreased endotoxin immunity are particularly susceptible to this decline (relative risk=1.97 for age >64).

CONCLUSIONS

Reduced preoperative endotoxin immunity is a predictor of increased postoperative cognitive dysfunction in patients undergoing CABG, particularly in those >60 years old. Interventions that increase IgM EndoCAb levels might improve cognitive function after cardiac surgery.

Novel therapies for sepsis: antiendotoxin therapies

Severe sepsis and septic shock is a common problem encountered in the critical care unit with an estimated incidence in the US of 750,000 cases/year and a mortality rate of 30-50%. Sepsis involves a complex interaction between bacterial factors and the host immune system producing a systemic inflammatory state that may progress to multiple organ failure and death. Endotoxin (a lipopolysaccharide) released from Gram-negative bacteria has been implicated as a potent, prototypical stimulus of the immune response to bacterial infection. Current antiendotoxin strategies utilise various approaches ranging from the prevention of binding to endotoxin receptors with antibodies (monoclonal or polyclonal) against endotoxin or endotoxin receptor/carrier molecules (antiCD14 or antilipopolysaccharide-binding protein antibodies), enhancing clearance or neutralisation (haemoperfusion, lipoproteins, lipopolysaccharide-neutralising proteins) or impairing cellular signalling (lipid A analogues, tyrosine kinase inhibitors). In the future, innovative therapies involving Toll-like receptors and their downstream signalling elements will be developed. This review discusses current knowledge regarding endotoxin signalling, antiendotoxin therapies currently under development, and future areas for research.

No effect of preoperative selective gut decontamination on endotoxemia and cytokine activation during cardiopulmonary bypass: a randomized, placebo-controlled study

BACKGROUND

Cardiopulmonary bypass predisposes the splanchnic region to inadequate perfusion and increases in gut permeability. Related to these changes, circulating endotoxin has been shown to rise during cardiac surgery, and may contribute to cytokine activation, high oxygen consumption, and fever ("postperfusion syndrome"). To a large extent, free endotoxin in the gut is a product of the proliferation of aerobic gram-negative bacteria and may be reduced by nonabsorbable antibiotics.

OBJECTIVE

To evaluate the effect of preoperative selective gut decontamination (SGD) on the incidence of endotoxemia and cytokine activation in patients undergoing open heart surgery.

DESIGN

Prospective, randomized, placebo-controlled double-blind trial.

SETTING

Tertiary-care university teaching hospital.

INTERVENTION

Preoperative administration for 5 to 7 days of oral nonabsorbable antibiotics (polymyxin B and neomycin) vs. placebo. The efficacy of SGD was assessed by culture of rectal swabs.

PATIENTS

Forty-four patients (median age 65 yrs, 29 males) were included in a pilot study to establish the sampling points of perioperative measurements. Seventy-eight consecutive patients (median age 65 yrs, 55 males) were enrolled for the prospective study; of these, 51 were randomly allocated to take SGD (n = 24) or placebo (n = 27); 27 were included in a control group (no medication).

MEASUREMENTS AND RESULTS

SGD but not placebo effectively reduced the number of rectal swabs that grew aerobic gram-negative bacteria (27% vs. 93%, respectively; p < .001). SGD did not affect the occurrence of perioperative endotoxemia, nor did it reduce the tumor necrosis factor-alpha, interleukin-10, or interleukin-6 concentrations (p > .20), as determined before surgery, upon aorta declamping, 30 mins into reperfusion, or 2 hrs after surgery. Also, SGD did not alter the incidence of postoperative fever or clinical outcome measures such as duration of artificial ventilation and intensive care unit and hospital stay.

CONCLUSION

SGD effectively reduces the aerobic gram-negative bowel flora in cardiac surgery patients but fails to affect the incidence of perioperative endotoxemia and cytokine activation during cardiopulmonary bypass and the occurrence of a postperfusion syndrome.

Endotoxin-neutralizing capacity of serum from cardiac surgical patients

OBJECTIVE

To determine if endotoxin core antibody (EndoCAb) from the serum of cardiac surgical patients neutralizes endotoxin in an ex vivo biologic assay.

DESIGN

Prospective blinded cohort study.

SETTING

Academic medical center.

PARTICIPANTS

Patients (n = 203) undergoing cardiac surgery.

INTERVENTIONS

Sera were obtained from patients preoperatively.

MEASUREMENTS AND MAIN RESULTS

EndoCAb levels were determined by enzyme-linked immunosorbent assay. Sera were incubated for 15 minutes at 37 degrees C with varying concentrations of endotoxin from a clinically relevant bacterium (Escherichia coli serotype O18), then tested for the presence of endotoxin activity using the validated Limulus amebocyte lysate assay. Median (interquartile range) IgM and IgG EndoCAb levels were 118 median units (range, 31 to 259 median units) and 208 median units (range, 108 to 401 medium units). Increasing levels of IgM EndoCAb were associated with increased neutralization of endotoxin (p < 0.0001). Increasing levels of IgG EndoCAb were associated with increased neutralization of endotoxin (p < 0.0001). An additive effect of IgM and IgG EndoCAb levels on endotoxin neutralization was observed without evidence of synergistic or plateau effects. EndoCAb levels did not completely predict serum neutralization capacity.

CONCLUSION

Anti-EndoCAbs of both classes (IgM and IgG) were able to neutralize lipopolysaccharide from a clinically relevant bacterium in an ex vivo model. Neither Igm nor IgG appeared to be more capable of neutralization in this model. These antibodies did not completely predict neutralization capacity; other endogenous factors in human serum must be capable of lipopolysaccharide neutralization.

The impact of anti-endotoxin core antibodies on endotoxin and cytokine release and ventilation time after cardiac surgery

OBJECTIVES

We hypothesized that a temporary cardiopulmonary bypass (CPB)-induced reduction of endotoxin antibody levels contributes to elevated endotoxin levels and the associated inflammatory consequences, with a significant influence on the postoperative ventilation time period.

BACKGROUND

Cardiac surgery using CPB induces a systemic inflammatory response syndrome with an associated risk of increased postoperative morbidity and mortality.

METHODS

A total of 100 consecutive patients undergoing elective coronary artery bypass graft surgery using CPB were prospectively investigated. Endotoxin core antibodies (immunoglobulin [Ig] M/IgG against lipid A and lipopolysaccharide), endotoxin, interleukin (IL)-1-beta, IL-6, IL-8 and tumor necrosis factor-alpha were measured serially from 24 h preoperatively until 72 h postoperatively.

RESULTS

Eighty-five patients had no complications (group 1), whereas 15 patients required prolonged ventilation (group 2). In both groups, there was a decrease of all antibodies 5 min after CPB onset, compared with baseline values (p < 0.001), an increase of endotoxin and IL-8 peaking at 30 min postoperatively (p < 0.001) and an increase of IL-6 peaking 3 h postoperatively (p < 0.001). In group 2, preoperative antibody levels were lower (p < 0.01)--specifically, the decrease in IgM was significantly stronger and of longer duration (p < 0.002)--and levels of endotoxin (p < 0.001) and IL-8 (p < 0.001) were higher at 30 min postoperatively.

CONCLUSIONS

We conclude that an CPB-associated temporary reduction of anti-endotoxin core antibody levels contributes to elevated endotoxin and IL-8 release. Furthermore, lower levels of IgM anti-endotoxin core antibodies were associated with a greater rise in endotoxin and IL-8, as well as prolonged respirator dependence.

Prognostic factors in intensive care

Predicting the outcome of critical illness remains an evolving art despite many recent advances. This review article describes the tools currently employed, appraising each in turn. The subject is viewed from the perspective that physiological reserve and inflammatory response are the essential elements in assessing prognosis in patients with multi-organ dysfunction/failure, the most commonly encountered syndrome in intensive care practice.

Endotoxin, cytokines and lipid peroxides in children with intussusception

BACKGROUND

Intussusception is a relatively common paediatric surgical emergency. The aim of this study was to investigate selected inflammatory mediators in children with acute intussusception and to identify potentially useful plasma markers of clinical outcome.

METHODS

Clinical, radiographic, operative and pathological details were recorded prospectively of all children presenting to a single institution with a confirmed diagnosis of acute intussusception during 1 year. Paired acute and convalescent venous blood samples were collected in a standard manner for blinded analysis of the following: malondialdehyde, C-reactive protein (CRP), interleukin (IL) 6, neopterin, tumour necrosis factor alpha, endotoxin, and immunoglobulin (Ig) G and IgM antiendotoxin core antibody (EndoCAb).

RESULTS

Thirty-two consecutive children (23 boys, nine girls) with a median age of 4 months were studied. Acute ileocolic intussusception was managed by air enema reduction (n = 19), operative reduction (n = 8) or surgical resection (n = 5). Peripheral blood cultures were sterile. Acute levels of plasma IL-6, neopterin and CRP were significantly raised in comparison to both normal laboratory ranges and convalescent samples (P < 0.001). Using stepwise discriminant analysis, CRP was identified as the best variable at distinguishing between the three treatment groups (P < 0.001). IgM EndoCAb concentrations were significantly greater in the convalescent sera of all the patients (P < 0.001).

CONCLUSION

Acute ileocolic intussusception in childhood is associated with endotoxinaemia and significantly raised levels of circulating inflammatory cytokines. Plasma CRP at diagnosis showed a statistically significant positive correlation with disease severity.

Preparation and preclinical evaluation of a novel liposomal complete-core lipopolysaccharide vaccine

Our objective is to develop a prophylactic vaccine strategy that can be evaluated for surgical and other high-risk hospitalized patients. In this paper, we describe the preparation and preclinical evaluation of a liposomal complete-core lipopolysaccharide (LPS) vaccine that is nontoxic and broadly antigenic. Complete-core (Ra-chemotype) LPSs were isolated from four gram-negative bacterial strains (Escherichia coli K-12, E. coli R1, Pseudomonas aeruginosa PAC608, and Bacteroides fragilis), mixed together to form a cocktail of complete-core LPSs, and then incorporated into multilamellar liposomes consisting of dimyristoyl phosphatidyl choline, dimyristoyl phosphatidylglycerol, and cholesterol in a 4:1:4 molar ratio. The endotoxic activities of these LPS-containing liposomes were less than 0.1% of the endotoxicities of the original free LPSs as measured by the Limulus amoebocyte lysate assay. In vivo administration of liposomal complete-core LPS mixed with Al(OH)(3) to rabbits resulted in no pyrogenicity or overt toxicity over a 7-day period. In immunoblots, sera from rabbits following active immunization elicited cross-reactive antibodies to a large panel of rough and smooth LPSs from numerous clinically relevant gram-negative bacteria, including E. coli (serotypes O1, O4, O6, O8, O12, O15, O18, O75, O86, O157, and O111), P. aeruginosa (Fisher-Devlin serotypes 1, 2, and 3, which correspond to International Antigenic Typing Scheme types 6, 11, and 2, respectively), Klebsiella pneumoniae (serotypes O1, O2ab, and O3), B. fragilis, and Bacteroides vulgatus. Active immunization of mice with liposomal complete-core LPS provided protection against a lethal challenge with E. coli O18 LPS. The vaccine tested was nontoxic, nonpyrogenic, and immunogenic against a wide variety of pathogens found in clinical settings.

Endotoxin in pooled pericardial blood contributes to the systemic inflammatory response during cardiac surgery

Although endotoxin has been implicated as an important contributor to the systemic inflammatory response (SIR) during cardiopulmonary bypass (CPB), its source remains unclear. While gut translocation has traditionally been perceived as the primary source of endotoxemia, accumulation of endotoxin in pooled pericardial blood may represent an additional source of endotoxin that is continually reinfused into the CPB circuit. Eighteen patients undergoing primary coronary revascularization procedures were prospectively evaluated. Shed blood pooled in the pericardial space was returned to the CPB circuit through cardiotomy suction catheters at 45 min after placement of the aortic cross-clamp. Simultaneous samples of pooled pericardial and peripheral arterial blood were obtained and analyzed by a limulus amebocyte lysate assay for the determination of endotoxin concentration, and an enzyme-linked immunosorbent assay for tumor necrosis factor (TNF-alpha) levels. Significant elevations in endotoxin were demonstrated in pooled pericardial blood samples compared with arterial blood (3.5 +/- 0.5 vs 0.8 +/- 0.2 pg/ml; p < 0.05). TNF-alpha levels were below the limits of detection in both samples. These data implicate pooled pericardial blood as an important primary source of endotoxin that, when continually reinfused throughout CPB, may contribute to the overall SIR. Because endotoxemia has been identified as an important predictor of adverse outcomes following cardiac surgery, removal of endotoxin antigen in shed pericardial blood, prior to its reinfusion into the CPB circuit, may provide a directed means to improve perioperative outcome without compromising established blood conservation techniques.

Exposure to bacteroides fragilis endotoxin during cardiac surgery

Although endotoxemia has been observed during cardiac surgery, the identity of endotoxins to which patients are exposed is unknown. We tested the hypothesis that antibodies to Bacteroides fragilis (an anaerobic gut commensal and a common pathogen) decrease during cardiac surgery, thereby reflecting systemic exposure to this type of endotoxin. Serum antiendotoxin antibody levels were measured in 55 patients during routine cardiac surgery at the following times: Preoperatively, Pre-CPB (immediately before initiation of cardiopulmonary bypass [CPB]), Pre-CPB+5 (5 min after initiation of CPB), and End (end of surgery). Antiendotoxin antibody levels were determined by using enzyme-linked immunosorbent assay. Total immunoglobulin M (IgM) levels were measured by using laser nephelometry and decreases in total IgM levels were used to control changes in antiendotoxin antibody levels attributable to hemodilution. Median (interquartile range) hemodilution corrected IgM anti-B fragilis antibody levels decreased by 12% (5%-20%) from Preoperatively to End of surgery (P < 0.001). In contrast, median hemodilution corrected anti-B fragilis antibody levels did not change significantly from Pre-CPB to Pre-CPB+5, validating the correction for hemodilution. Immunoglobulin G anti-B fragilis antibody levels and IgM and immunoglobulin G anticore antibody levels decreased similarly during surgery. Intraoperatively, levels of anti-B fragilis endotoxin antibodies decreased significantly out of proportion to hemodilution. These results suggest that cardiac surgical patients are exposed to B fragilis endotoxin.

IMPLICATIONS

We prospectively measured hemodilution-corrected antiendotoxin antibody levels in 55 cardiac surgical patients. We observed significant decreases in hemodilution-corrected levels of antibody to both Bacteroides fragilis and the core of endotoxin.

Update on antiendotoxin therapies

Endotoxin has been implicated in the processes that can lead to organ failure and death after surgery and critical illness. While there are no currently available commercial therapies directed against endotoxin, many have been tried or are in an experimental stage. In this article we outline past, present and future approaches to anti-endotoxin therapy.

Does steroid pretreatment increase endotoxin release during clinical cardiopulmonary bypass?

OBJECTIVE

The mechanism involved in the endotoxemia frequently recognized during cardiopulmonary bypass remains unclear. It has also been suggested that endotoxin levels were higher in steroid-pretreated patients undergoing cardiopulmonary bypass.

METHODS

Twenty patients undergoing cardiopulmonary bypass were randomly pretreated with steroids (methylprednisolone, 30 mg/kg) or placebo. Blood samples for endotoxin measurement were drawn simultaneously from the superior and inferior venae cavae before heparin administration, 5 and 50 minutes after the onset of bypass, 5 minutes after aortic declamping, at the end of bypass, and 1, 2, and 20 hours after the end of cardiopulmonary bypass.

RESULTS

The perioperative variables in the two groups were similar. Blood endotoxin levels were higher in the inferior vena cava than in the superior vena cava immediately after the onset of bypass. Endotoxin levels in inferior vena cava blood were significantly lower in steroid-pretreated patients than those in patients not receiving steroids.

CONCLUSIONS

Endotoxin is released during cardiopulmonary bypass from the region drained by the inferior vena cava. Steroid pretreatment may actually reduce endotoxin release during bypass.

All accessible epitopes in the Salmonella lipopolysaccharide core are associated with branch residues

Antisera generated against each of the nine known chemotypes of Salmonella lipopolysaccharide (LPS) core were characterized in order to delineate cross-reactive epitopes and define the bases for their accessibility. Strongly cross-reactive epitopes were associated with three chemotypes: Ra and Rb4, which recognized alpha-GlcNAc-1-->2-alpha-Glc, and Rd1, which recognized L-alpha-D-heptose-1-->7-L-alpha-D-heptose. Both these disaccharides and the more weakly cross-reactive alpha-Gal-1-->6-alpha-Glc terminal in Rb3 LPS represent branch points along the core oligosaccharide. Therefore, branch points in endotoxin core oligosaccharides may generally be cross-reactive.