Degradation of albumin in meningococcal sepsis

MECHANISMS IN ENDOCRINOLOGY: New concepts to further unravel adrenal insufficiency during critical illness

The concept of 'relative' adrenal insufficiency during critical illness remains a highly debated disease entity. Several studies have addressed how to diagnose or treat this condition but have often yielded conflicting results, which further fuelled the controversy. The main reason for the controversy is the fact that the pathophysiology is not completely understood. Recently, new insights in the pathophysiology of the hypothalamic-pituitary-adrenal axis response to critical illness were generated. It was revealed that high circulating levels of cortisol during critical illness are explained more by reduced cortisol breakdown than by elevated cortisol production. Cortisol production rate during critical illness is less than doubled during the day but lower than in healthy subjects during the night. High plasma cortisol concentrations due to reduced breakdown in turn reduce plasma ACTH concentrations via feedback inhibition, which with time may lead to an understimulation and hereby a dysfunction of the adrenal cortex. This could explain the high incidence of adrenal insufficiency in the prolonged phase of critical illness. These novel insights have created a new framework for the diagnosis and treatment of adrenal failure during critical illness that has redirected future research.

Three calculations of free cortisol versus measured values in the critically ill

OBJECTIVES

To investigate the agreement between the calculated free cortisol levels according to widely applied Coolens and adjusted Södergård equations with measured levels in the critically ill.

DESIGN AND METHODS

A prospective study in a mixed intensive care unit. We consecutively included 103 patients with treatment-insensitive hypotension in whom an adrenocorticotropic hormone (ACTH) test (250μg) was performed. Serum total and free cortisol (equilibrium dialysis), corticosteroid-binding globulin and albumin were assessed. Free cortisol was estimated by the Coolens method (C) and two adjusted Södergård (S1 and S2) equations. Bland Altman plots were made.

RESULTS

The bias for absolute (t=0, 30 and 60min after ACTH injection) cortisol levels was 38, -24, 41nmol/L when the C, S1 and S2 equations were used, with 95% limits of agreement between -65-142, -182-135, and -57-139nmol/L and percentage errors of 66, 85, and 64%, respectively. Bias for delta (peak-baseline) cortisol was 14, -31 and 16nmol/L, with 95% limits of agreement between -80-108, -157-95, and -74-105nmol/L, and percentage errors of 107, 114, and 100% for C, S1 and S2 equations, respectively.

CONCLUSIONS

Calculated free cortisol levels have too high bias and imprecision to allow for acceptable use in the critically ill.

Cortisol metabolism in critical illness: implications for clinical care

PURPOSE OF REVIEW

Critical illness is uniformly characterized by elevated plasma cortisol concentrations, traditionally attributed exclusively to increased cortisol production driven by an activated hypothalamic pituitary adrenal axis. However, as plasma adrenocorticotropic hormone (ACTH) concentrations are often not elevated or even low during critical illness, alternative mechanisms must contribute.

RECENT FINDINGS

Recent investigations revealed that plasma clearance of cortisol is markedly reduced during critical illness, explained by suppressed expression and activity of the main cortisol metabolizing enzymes in liver and kidney. Furthermore, unlike previously inferred, cortisol production rate in critically ill patients was only moderately increased to less than double that of matched healthy subjects. In the face of low-plasma ACTH concentrations, these data suggest that other factors drive hypercortisolism during critical illness, which may suppress ACTH by feedback inhibition. These new insights add to the limitations of the current diagnostic tools to identify patients at risk of failing adrenal function during critical illness. They also urge to investigate the impact of lower hydrocortisone doses than those hitherto used.

SUMMARY

Recent novel insights reshape the current understanding of the hormonal stress response to critical illness and further underline the need for more studies to unravel the pathophysiology of adrenal (dys)functioning during critical illness.

Endocrine responses to critical illness: novel insights and therapeutic implications

CONTEXT

Critical illness, an extreme form of severe physical stress, is characterized by important endocrine and metabolic changes. Due to critical care medicine, survival from previously lethal conditions has become possible, but many patients now enter a chronic phase of critical illness. The role of the endocrine and metabolic responses to acute and prolonged critical illness in mediating or hampering recovery remains highly debated.

EVIDENCE ACQUISITION

The recent literature on changes within the hypothalamic-pituitary-thyroid axis and the hypothalamic-pituitary-adrenal axis and on hyperglycemia in relation to recovery from critical illness was critically appraised and interpreted against previous insights. Possible therapeutic implications of the novel insights were analyzed. Specific remaining questions were formulated.

EVIDENCE SYNTHESIS

In recent years, important novel insights in the pathophysiology and the consequences of some of these endocrine responses to acute and chronic critical illness were generated. Acute endocrine adaptations are directed toward providing energy and substrates for the vital fight-or-flight response in a context of exogenous substrate deprivation. Distinct endocrine and metabolic alterations characterize the chronic phase of critical illness, which seems to be no longer solely beneficial and could hamper recovery and rehabilitation.

CONCLUSIONS

Important novel insights reshape the current view on endocrine and metabolic responses to critical illness and further clarify underlying pathways. Although many issues remain unresolved, some therapeutic implications were already identified. More work is required to find better treatments, and the optimal timing for such treatments, to further prevent protracted critical illness, to enhance recovery thereof, and to optimize rehabilitation.

Insulin-like Growth Factor I and its binding protein 3 in sepsis

OBJECTIVE

To investigate the Growth Hormone (GH)/Insulin-like Growth Factor-I (IGF-I) axis and identify the factors that determine IGF-I levels in adult septic patients of variable severity, i.e., with sepsis, severe sepsis or septic shock, in the acute phase of disease.

DESIGN

In 107 consecutive septic patients (44 with sepsis, 13 with severe sepsis, and 50 with septic shock), GH, IGF-I, Insulin-like Growth Factor Binding Protein-3 (IGFBP-3), insulin, cortisol, albumin, thyroid hormones, C-reactive protein and interleukin-6 serum levels were measured once within 48 h after onset of a septic episode. Twenty-nine healthy volunteers served as controls.

RESULTS

IGF-I and IGFBP-3 levels were decreased in patients with sepsis and severe sepsis (versus controls), decreasing further in patients with septic shock (versus sepsis). IGF-I levels were positively related to IGFBP-3, albumin, triiodothyronine and thyroxine, and inversely related to cortisol, sepsis severity, C-reactive protein, interleukin-6 and age. In multiple regression analysis, IGF-I levels were independently related to IGFBP-3 and albumin (lower in patients with decreased IGFBP-3 and albumin levels) (p<0.001 and p=0.01, respectively), and cortisol (lower in patients with increased cortisol levels) (p=0.04). IGFBP-3 accounted for most of the variance explained by the model (R(2)=0.519). GH levels were not related to IGF-I levels or mortality. IGF-I and IGFBP-3 levels were not associated with mortality.

CONCLUSIONS

The GH/IGF-I axis is severely disrupted in septic patients. IGFBP-3 is the major determinant of IGF-I levels.

Assessing adrenal insufficiency of corticosteroid secretion using free versus total cortisol levels in critical illness

PURPOSE

To study the value of free versus total cortisol levels in assessing relative adrenal insufficiency during critical illness-related corticosteroid insufficiency.

METHODS

A prospective study in a mixed intensive care unit from 2004 to 2007. We consecutively included 49 septic and 63 non-septic patients with treatment-insensitive hypotension in whom an adrenocorticotropic hormone (ACTH) test (250 μg) was performed. Serum total and free cortisol (equilibrium dialysis), corticosteroid-binding globulin (CBG) and albumin were assessed.

RESULTS

Although a low CBG resulted in a high free cortisol level relative to total cortisol, free and total cortisol and their increases were well correlated (r = 0.77-0.79, P < 0.001). In sepsis, hypoalbuminemia did not affect total and free cortisol, and increases in total cortisol upon ACTH predicted increases in free cortisol regardless of low binding proteins. In non-sepsis, total cortisol was lower with than without hypoalbuminemia; free cortisol did not differ, since hypoalbuminemia concurred with a low CBG. Increases in total cortisol depended less on binding proteins than on raw levels. The areas under the receiver operating characteristic curve for predicting increases in free from total cortisol were 0.93-0.97 in sepsis and 0.79-0.85 in non-sepsis (P = 0.044 or lower for sepsis vs. non-sepsis).

CONCLUSIONS

Although the biologically active free cortisol fraction depends on binding proteins, total cortisol correlates to free cortisol in treatment-insensitive hypotension during critical illness. In sepsis, albumin is not an important binding molecule. Subnormal increments in total cortisol upon ACTH suffice in assessing relative adrenal insufficiency, particularly in sepsis.

[Albumin in sepsis]

Human serum albumin is a small (66kD) globular protein representing over 60 % of the total plasma protein content. It is made up of 585 amino 6 acids and contains 35 cysteine residues forming disulfide bridges that contribute to its overall tertiary structure. It has a free cysteine-derived thiol group at Cys-34, which accounts for 80 % of its redox activity. Physiologically, serum albumin exists in a reduced form with a free thiol contributing to its antioxidant properties. It is synthesized primarily in the liver and is an acute-phase protein. It is a multifunctional plasma protein ascribed ligand-binding and transport properties as well as antioxidants and enzymatic functions. It maintains colloid osmotic pressure, modulates inflammatory response and may influence oxidative damage. Hypoalbuminemia is common in the intensive care unit and may be due to decreased synthesis by the liver and/or to increased losses or increased proteolysis and clearance. Although albumin was long used to control vascular collapse in critically ill patients, the evidence suggests that it does not offer a benefit over crystalloid solutions in vascular collapse. However, human serum albumin is an important circulating antioxidant and it may be beneficial in critically ill patients to limit oxidative damage. A number of studies suggest that in specific groups of hypoalbuminemic critically ill patients, albumin administration may have beneficial effects on organ function, although the exact mechanisms remain undefined. Further trials are needed to confirm theses observations and to clearly demonstrate whether albumin should be administered in critically ill patients with hypoalbuminemia.

Urinary proteases degrade albumin: implications for measurement of albuminuria in stored samples

BACKGROUND

Previous studies have shown that albumin in stored urine samples degrades over time, and that albumin losses are greatest in samples with low pH conditions (pH < 5). Furthermore, the high-performance liquid chromatography (HPLC) assay for urinary albumin has been shown to be particularly susceptible to the effects of prolonged storage.

METHODS

Frozen urine samples, stored for 12 months at -70 and -20 degrees C, were analysed for albumin fragmentation. Urinary protease activity was investigated in vitro in urine adjusted to pH 2.3-2.5. Albumin was measured by nephelometry, HPLC and sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

RESULTS

In the unadjusted samples, albumin was degraded in 11 out of 40 samples stored at -20 degrees C. In the in vitro experiments, both endogenous albumin and exogenous albumin added to urine were rapidly degraded into large fragments within minutes after adjustment to low pH. The fragments produced were consistent with those produced during digestion with pepsin and urinary degradation was completely inhibited by pepstatin. Albumin concentration measured by HPLC was most dramatically affected, with near-complete loss of albumin-sized material within one hour of incubation at pH 2.3-2.5. Sample reactivity with antiserum in a nephelometry assay initially declined then increased, possibly due to exposure of internal epitopes during albumin digestion.

CONCLUSIONS

This study demonstrated that proteases are present and active in stored human urine samples. Urinary albumin digestion occurred in a manner consistent with activity of endogenous urinary proteases. Adjustment to neutral pH or addition of protease inhibitors may be useful techniques for sample preservation.

Two centuries of meningococcal infection: from Vieusseux to the cellular and molecular basis of disease

Scientific knowledge of meningococcal infection has increased greatly since the epidemic nature of the illness was first described by Vieusseux at the dawn of the nineteenth century. In fact, revolutionary advances have been made in public-health measures, antimicrobial therapy, diagnostic procedures, anti-inflammatory drugs and supportive care facilities. Based on the knowledge accumulated to date, it is generally accepted that the pathogenesis of meningococcal infection involves multiple links that interconnect in a complex web of phenomena from Neisseria meningitidis attachment to meningococcal sepsis or meningitis. In fact, a myriad of strongly interacting inflammatory molecules and cells have been implicated in neisserial infection, illustrating the complexity of meningococcal pathogenesis. In addition, many of these signallers are critically involved in outcomes in the human host. Deciphering the pathogenesis of meningococcal infection could expand our knowledge and provide important clues to the host-pathogen interaction, as well as leading to the development of new therapeutic tools. Herein, we review the history of the discovery and characterization of meningococcal disease, epidemiological features of the disease with an emphasis on recent developments in Brazil, the cellular and molecular basis of disease, and discuss diagnosis and therapy.

Using Automated Clinical Data for Risk Adjustment

BACKGROUND

Clinically plausible risk-adjustment methods are needed to implement pay-for-performance protocols. Because billing data lacks clinical precision, may be gamed, and chart abstraction is costly, we sought to develop predictive models for mortality that maximally used automated laboratory data and intentionally minimized the use of administrative data (Laboratory Models). We also evaluated the additional value of vital signs and altered mental status (Full Models).

METHODS

Six models predicting in-hospital mortality for ischemic and hemorrhagic stroke, pneumonia, myocardial infarction, heart failure, and septicemia were derived from 194,903 admissions in 2000-2003 across 71 hospitals that imported laboratory data. Demographics, admission-based labs, International Classification of Diseases (ICD)-9 variables, vital signs, and altered mental status were sequentially entered as covariates. Models were validated using abstractions (629,490 admissions) from 195 hospitals. Finally, we constructed hierarchical models to compare hospital performance using the Laboratory Models and the Full Models.

RESULTS

Model c-statistics ranged from 0.81 to 0.89. As constructed, laboratory findings contributed more to the prediction of death compared with any other risk factor characteristic groups across most models except for stroke, where altered mental status was more important. Laboratory variables were between 2 and 67 times more important in predicting mortality than ICD-9 variables. The hospital-level risk-standardized mortality rates derived from the Laboratory Models were highly correlated with the results derived from the Full Models (average rho = 0.92).

CONCLUSIONS

Mortality can be well predicted using models that maximize reliance on objective pathophysiologic variables whereas minimizing input from billing data. Such models should be less susceptible to the vagaries of billing information and inexpensive to implement.

Calciphylaxis, proteases, and purpura: an alternative hypothesis for the severe shock, rash, and hypocalcemia associated with meningococcal septicemia

The hallmarks of severe meningococcal sepsis include the rapid onset of shock, purpuric rash, and metabolic derangement, in particular, hypocalcemia. The severe ecchymoses and purpura associated with meningococcal sepsis are usually attributed to acute thrombotic episodes, attributable to the associated procoagulation disorder. An alternative explanation for the rash is a sudden extravasation of calcium from the intravascular space into the tissues. We will argue that in meningococcal sepsis, cleavage of albumin into fragments by protease(s) occurs and these fragments, along with calcium, cross the endothelium into the interstitium. The fragmentation of albumin and its loss through the endothelium would also provide a more rational explanation for the rapidity of the shock and the hypocalcemia that is so characteristic of the disease.

Clinical presentation and outcome of bacteraemia caused by beta-haemolytic streptococci serogroup G

There has been a considerable increase in annual cases of bacteraemia caused by beta-haemolytic streptococci serogroup G (GGS) and we therefore undertook a retrospective case review in the Danish County of Northern Jutland. During a 19-year period (1981-1999) 94 cases were identified in a regional bacteraemia register, and the annual incidence rose from 3.0 per 106 inhabitants in 1981-1987 to 7.4 in 1988-1993 and 17.2 in 1994-1999. Clinical charts were available for 92 cases. The male/female ratio was 52/40 and the median age 71 years, range 15-97 years. Twenty-seven patients had reduced functional capacity. Fifty-two cases were community-acquired. The most common site of infection was the skin followed by the lungs and the urogenital tract. Eleven patients had no apparent site of infection. Underlying disease was present in 81 patients, who shared 149 co-morbid conditions, and the overall one-month case fatality rate was 23% (95% confidence limits 15-33%). We conclude that GGS are of increasing importance as a cause of bacteraemic infections and first and foremost affect patients who are aged, debilitated, or suffer from severe or multiple underlying diseases.

Pro/con clinical debate: do colloids have advantages over crystalloids in paediatric sepsis?

Despite decades of resuscitating patients with intravenous fluids in intensive care units, it is somewhat surprising that very little consensus exists regarding the type of fluid physicians should choose. Factors that influence decisions are often local culture or politics, hospital administrators, history (i.e. 'I've always done it this way') and budgets, as opposed to strong evidence. In the present issue of Critical Care we are presented with compelling arguments for and against the administration of colloids (as opposed to crystalloids) in paediatric sepsis. One point that appears to be clear is that the ideal choice of intravenous fluid goes beyond the simple haemodynamic effect. As such, in the future, clinicians will need to consider other factors when making their decision. In addition, large-scale quality randomised studies are desperately needed to guide clinicians.

Current concepts in the role of the host response in Neisseria meningitidis septic shock

Lipopolysaccharides in the outer membrane of Neisseria meningitidis are key molecules that induce inflammation and cause meningitis and shock. Mutant strains, with altered lipid A, the toxic moiety of lipopolysaccharide, or completely lacking lipopolysaccharide, induce significantly less inflammation than wild-type strains. Polymorphism of the Fc gamma receptors and interleukin-10 gene but not of the Toll-like receptor 4 may influence the development of meningococcal infection. Mannan-binding lectin is involved in complement activation, the regulation of adhesion molecules and cytokine production induced by meningococci. The activation of protein C by the thrombomodulin protein C receptor complex on the endothelial cell surface appears to be reduced in meningococcal sepsis but is still sufficient to convert protein C to activated protein C in patients treated with concentrated protein C.