Methemoglobin-induced signaling and chemokine responses in human alveolar epithelial cells.

Diffuse alveolar hemorrhage is characterized by the presence of red blood cells and free hemoglobin in the alveoli and complicates a number of serious medical and surgical lung conditions including the pulmonary vasculitides and acute respiratory distress syndrome. In this study we investigated the hypothesis that exposure of human alveolar epithelial cells to hemoglobin and its breakdown products regulates chemokine release via iron- and oxidant-mediated activation of the transcription factor NF-κB. Methemoglobin alone stimulated the release of IL-8 and MCP-1 from A549 cells via activation of the NF-κB pathway; additionally, IL-8 required ERK activation and MCP-1 required JNK activation. Neither antioxidants nor iron chelators and knockdown of ferritin heavy and light chains affected these responses, indicating that iron and reactive oxygen species are not involved in the response of alveolar epithelial cells to methemoglobin. Incubation of primary cultures of human alveolar type 2 cells with methemoglobin resulted in a similar pattern of chemokine release and signaling pathway activation. In summary, we have shown for the first time that methemoglobin induced chemokine release from human lung epithelial cells independent of iron- and redox-mediated signaling involving the activation of the NF-κB and MAPK pathways. Decompartmentalization of hemoglobin may be a significant proinflammatory stimulus in a variety of lung diseases.

Predictors of outcome in patients with cystic fibrosis requiring endotracheal intubation.

BACKGROUND AND OBJECTIVE: Acute severe clinical deterioration of patients with cystic fibrosis (CF) may mandate endotracheal intubation. The benefits of intubation were evaluated by examining which pre-admission parameters were associated with intensive care unit (ICU) outcome and assessing the potential benefits of intubation for survivors in terms of time from ICU discharge to death. METHODS: A retrospective analysis of data from a single centre was undertaken. RESULTS: Thirty patients required intubation on 34 occasions (8 per 1000 admissions). Eleven patients died in ICU and 7 after ICU but not hospital discharge. Fifty-nine per cent of 22 patients intubated for pneumothorax and/or haemoptysis survived to hospital discharge. Of the twelve intubated for infective exacerbations, 33% survived to hospital discharge. Those who died after hospital discharge survived 447 days. There were no significant differences for survivors in reasons for intubation, colonizing organism, frequency of infective exacerbations, severity of illness or pulmonary physiology. Osteoporosis and a greater fall in body mass index over the 24 months prior were more frequent in non-survivors. CONCLUSIONS: Patients with CF developing haemoptysis and/or pneumothorax should be admitted to ICU and intubated promptly, should this be required. Chronic disease markers may be more relevant prognostically than rates of hospitalization or forced expiratory volume in 1 s decline which should not be bars to invasive ventilation.

Association between preoperative plasma sRAGE levels and recovery from cardiac surgery.

BACKGROUND: The receptor for advanced glycation end products (RAGE) is an inflammation-perpetuating receptor, and soluble RAGE (sRAGE) is a marker of cellular RAGE expression. This study investigated whether raised plasma levels prior to surgery of sRAGE or S100A8/A9 (a RAGE ligand) were associated with longer duration of hospital care in patients undergoing cardiac surgery necessitating cardiopulmonary bypass. METHODS: Patients (n = 130) undergoing elective cardiac surgery were enrolled prospectively. Plasma sRAGE and S100A8/A9 concentrations were measured before and 2 h after surgery. RESULTS: Preoperative plasma sRAGE increased significantly (P < 0.0001) from 1.06 ng/mL (IQR, 0.72-1.76) to 1.93 ng/mL (IQR, 1.14-2.63) 2 h postoperatively. Plasma S100A8/9 was also significantly (P < 0.0001) higher 2 h postoperatively (2.37 µ g/mL, IQR, 1.81-3.05) compared to pre-operative levels (0.41 µ g/mL, IQR, 0.2-0.65). Preoperative sRAGE, but not S100A8/A9, was positively and significantly correlated with duration of critical illness (r = 0.3, P = 0.0007) and length of hospital stay (LOS; r = 0.31, P < 0.0005). Multivariate binary logistic regression showed preoperative sRAGE to be, statistically, an independent predictor of greater than median duration of critical illness (odds ratio 16.6, P = 0.014) and to be, statistically, the strongest independent predictor of hospital LOS. CONCLUSION: Higher preoperative plasma sRAGE levels were associated with prolonged duration of care in adults undergoing cardiac surgery requiring cardiopulmonary bypass.

Lest we forget the endothelial glycocalyx in sepsis.

Sepsis is the third largest cause of death in industrialised countries, but treatment remains largely supportive and effective therapeutic interventions are urgently needed. Disruption and dysfunction of the microvascular endothelium leading directly or indirectly to multiple organ failure are now recognised to underpin the pathophysiology of sepsis. Biomarkers of endothelial activation may therefore assume an important role in guiding future research efforts. We suggest that integral to this approach is the investigation and evaluation of endothelial glycocalyx biomarkers, not only as indicators of the pathogenic process but also to inform the development of pharmacological and other therapies.

Changes in lung composition and regional perfusion and tissue distribution in patients with ARDS.

BACKGROUND AND OBJECTIVE: ARDS is characterized by bilateral pulmonary infiltrates and refractory hypoxemia attributed to V/Q mismatch. We used dynamic CT to characterize changes in lung composition, regional perfusion and tissue distribution in patients with ARDS in comparison with healthy subjects. METHODS: The Fick principle was applied to serial attenuation measurements constructed from sequential CT images acquired during the passage of a bolus of iodinated contrast medium in healthy subjects (n=3) and patients with ARDS (n=11). Perfusion was calculated by the Mullani-Gould method and mapped throughout both lungs. Gradients of perfusion and tissue density against vertical height were constructed. RESULTS: In comparison with normal individuals, the tissue component of lungs from patients with ARDS was significantly increased (P<0.05). Blood fraction was unchanged. There was a discernable gradient in tissue density from non dependent to dependent regions in the patients with ARDS that was significantly different from controls. The proportion of perfusion applied to consolidated areas (i.e. shunt) correlated significantly (P<0.05) with the severity of hypoxaemia. CONCLUSIONS: In patients with ARDS there are changes in both lung composition and the distribution of tissue and perfusion that may account in part for the physiological changes that define the syndrome.

Bench-to-bedside review: Inhaled nitric oxide therapy in adults.

Nitric oxide (NO) is an endogenous mediator of vascular tone and host defence. Inhaled nitric oxide (iNO) results in preferential pulmonary vasodilatation and lowers pulmonary vascular resistance. The route of administration delivers NO selectively to ventilated lung units so that its effect augments that of hypoxic pulmonary vasoconstriction and improves oxygenation. This 'Bench-to-bedside' review focuses on the mechanisms of action of iNO and its clinical applications, with emphasis on acute lung injury and the acute respiratory distress syndrome. Developments in our understanding of the cellular and molecular actions of NO may help to explain the hitherto disappointing results of randomised controlled trials of iNO.

Plasma S100A8/A9 heterodimer is an early prognostic marker of acute kidney injury associated with cardiac surgery.

AIM: We investigated whether plasma levels of the inflammation marker S100A8/A9, could predict acute kidney injury (AKI) onset in patients undergoing cardiac surgery necessitating cardiopulmonary bypass (CPB). PATIENTS & METHODS: Plasma levels of S100A8/A9 and other neutrophil cytosolic proteins were measured in 39 patients pre- and immediately post-CPB. RESULTS: All markers increased significantly post-CPB with S100A8/A9, S100A12 and myeloperoxidase levels significantly higher in patients who developed AKI within 7 days. S100A8/A9 had good prognostic utility for AKI, with an area under the receiver operating characteristic curve of 0.81 (95% CI: 0.676-0.949) and a cut-off value of 10.6 µg/ml (85.7% sensitivity and 75% specificity) irrespective of age. CONCLUSION: Plasma S100A8/A9 levels immediately after cardiac surgery, can predict onset of AKI, irrespective of age.

Variation in iron homeostasis genes between patients with ARDS and healthy control subjects.

BACKGROUND: Abnormal plasma and lung iron mobilization is associated with the onset and progression of ARDS and is detectable in specific at-risk populations. Patients with ARDS also have pronounced oxidative and nitrosative stress that can be catalyzed and thereby aggravated by the bioavailability of redox active iron. ARDS of pulmonary and extrapulmonary origin may differ pathophysiologically and require different ventilatory strategies. Evidence suggests that genetic predisposition is relevant to the pathogenesis of ARDS. We therefore explored the hypothesis that polymorphisms from a panel of genes encoding iron-metabolizing proteins determine susceptibility to ARDS. METHODS: Retrospective case-control study conducted at the adult ICUs of two university hospitals. Patients with ARDS (n = 122) and healthy control subjects (n = 193) were genotyped. Sequence-specific primer polymerase chain reaction was used to genotype selected biallelic single-nucleotide polymorphisms. An audit of the patient database was conducted, and 104 of the 122 ARDS patients were eligible for the final data analysis. RESULTS: Preliminary analysis indicated differences between ARDS and healthy control subjects in the incidence of polymorphism of the gene encoding ferritin light chain. Subgroup analysis indicated the prevalence of ferritin light-chain gene -3381GG homozygotes was increased in patients with ARDS of extrapulmonary origin compared to healthy control subjects. Secondly, a common haplotype in the heme oxygenase 2 gene was reduced in patients with ARDS compared to healthy control subjects and was more evident in those with ARDS of direct or pulmonary etiology. CONCLUSIONS: These results provide preliminary evidence to suggest a distinction in the genetic background of the subpopulations studied, inferring that the ferritin light-chain gene genotype confers susceptibility to ARDS, while the heme oxygenase 2 haplotype is protective against the onset of the syndrome. Such data support further previous findings that suggest abnormalities in iron handling resulting in redox imbalance are implicated in the pathogenesis of ARDS.

The promise of next generation colloids.

The aim of perioperative haemodilution is to reduce loss of red blood cells during elective surgery. The oncotic and molecular characteristics of the various plasma substitutes employed determine how effectively normovolaemia is maintained, and their non-oncotic effects include alterations in microvascular perfusion. In the previous issue of Critical Care, Martini and colleagues assessed the effects of haemodilution with either polyethylene glycol (PEG)ylated albumin or a commercially available hydroxyethyl starch-based colloid in a hamster haemorrhage model. PEGylated albumin was superior to hydroxyethyl starch, as reflected by survival, haemodynamic parameters and assessment of the microcirculation using intravital microscopy.

Bench-to-bedside review: sepsis, severe sepsis and septic shock - does the nature of the infecting organism matter?

International guidelines concerning the management of patients with sepsis, septic shock and multiple organ failure make no reference to the nature of the infecting organism. Indeed, most clinical signs of sepsis are nonspecific. In contrast, in vitro data suggest that there are mechanistic differences between bacterial, viral and fungal sepsis, and imply that pathogenetic differences may exist between subclasses such as Gram-negative and Gram-positive bacteria. These differences are reflected in different cytokine profiles and mortality rates associated with Gram-positive and Gram-negative sepsis in humans. They also suggest that putative anti-mediator therapies may act differently according to the nature of an infecting organism. Data from some clinical trials conducted in severe sepsis support this hypothesis. It is likely that potential new therapies targeting, for example, Toll-like receptor pathways will require knowledge of the infecting organism. The advent of new technologies that accelerate the identification of infectious agents and their antimicrobial sensitivities may allow better tailored anti-mediator therapies and administration of antibiotics with narrow spectra and known efficacy.

Regional pulmonary blood flow in humans and dogs by 4D computed tomography.

RATIONALE AND OBJECTIVES: Pulmonary vascular control mechanisms are complex and likely to differ between species. We wish to quantify regional perfusion and the effects of gravity using computed tomography. MATERIALS AND METHODS: Sequential density measurements following the administration of a bolus of iodinated contrast medium were acquired from four healthy human subjects and four dogs. RESULTS: In humans, perfusion (Q) was linear throughout most of the range of vertical height, with an overall gradient of -2.6% cm(-1). However, when perfusion was normalized to "tissue" density (blood plus tissue: sQt), maximum perfusion occurred around the mid-range of vertical height, being 9% (range 1-22%) greater than either the dorsal or ventral extreme. Within discrete transverse axial sections, concentric zones of perfusion centered on blood vessels were demonstrated. The relationship between sQt and vertical height in dogs was distinctly linear, with a gradient of -7.2% cm(-1). In dogs, the median gradient of Q was -13.6% cm(-1) (range -9.7 to -17.1%). CONCLUSIONS: Differences in regional pulmonary perfusion, particularly the vertical gradient observed in humans and dogs, may in part reflect anatomic differences between the symmetric dichotomous branching structure of the human pulmonary vasculature and the more asymmetrical structure found in dogs.

Predicting the need for intensive care following lung resection.

On the basis of the evidence available, the authors would suggest a decision making algorithm to determine the need for ICU admission postoperatively similar to that shown in Fig. 1. First, patients should quit smoking at least 1 month and preferably 2 months before surgery. Those over the age of 70 years should receive elective ICU admission. Second, those at increased risk of general anesthesia, as judged by ASA and performance status scores and cardiovascular risk assessment, should be prebooked into the ICU in the postoperative period. A ppo FEV1 of less than 44% should warrant additional monitoring rather than mandate ICU admission. Pre-existing fibrotic lung disease mandates ICU admission. Third, perioperatively, protective (low tidal volume) ventilatory strategies should be applied during one lung ventilation. Patients undergoing one lung ventilation, and especially those undergoing extensive lymphatic dissection, should be monitored closely for signs of ALI in the first 5 days postoperatively. This, together with any indication of postoperative complications such as POP, BPF or empyema, should mandate immediate transfer to the ICU.

Butanol-extracted lipoteichoic acid induces in vivo leukocyte adhesion.

Lipoteichoic acid (LTA), an immunostimulatory component of the cell walls of gram positive bacteria, has pro-inflammatory effects in vitro and in vivo. However, one in vivo study concluded that LTA had no noticeable effects on leukocyte recruitment. In this study we investigated the effects of highly purified LTA, prepared by butanol extraction (Bu-LTA) at room temperature, on in vivo leukocyte adhesion. Using intravital microscopy we measured adhesion of leukocytes in mesenteric post-capillary venules of rats and mice. Topical superfusion of Bu-LTA (1 microg/ml) in rats significantly (p<0.05) increased adhesion within 30 min. By contrast, hot phenol-extracted LTA did not increase adhesion. Alkaline hydrolysis of Bu-LTA removed alanine residues and prevented adhesion. Also, pre-administration of anti-rat beta2-integrin antibody abolished Bu-LTA-induced adhesion. Finally, intraperitoneal injection of Bu-LTA (100 microg/ml) into mice also significantly (p<0.01) increased leukocyte adhesion measured at 60 min. In conclusion, Bu-LTA with intact alanine residues promotes beta2-integrin-dependent leukocyte adhesion in vivo.

Elucidation of toll-like receptor and adapter protein signaling in vascular dysfunction induced by gram-positive Staphylococcus aureus or gram-negative Escherichia coli.

Pathogens contain specific pathogen-associated molecular patterns, which activate pattern recognition receptors of the innate immune system such as Toll-like receptors (TLRs). Although there is a clear evidence of how macrophages sense pathogens, we know less about such processes in vessels. This is critical to understand because activation of vascular cells and the subsequent induction of inflammatory genes by bacteria are crucial events in the development of septic shock. In the current study we have used genetically modified mice to investigate the role of TLRs, adapter proteins, tumor necrosis factor alpha (TNFalpha), and nitric oxide synthase II (NOSII) in vascular dysfunction induced by Gram-positive (Staphylococcus aureus) or Gram-negative (Escherichia coli) bacteria. Our data show that Gram-positive S. aureus or Gram-negative E. coli causes vascular dysfunction via the induction of NOSII. For S. aureus, this process requires TLR2, TLR6, myeloid differentiation factor 88 (MyD88) adapter-like, MyD88, and TNF, but not TLR4 or TLR1. Vascular dysfunction induced by E. coli requires TLR4 but has no requirement for TLR2, TLR1, TLR6, or TNF, and a partial but incomplete requirement of MyD88 and TIR domain-containing adapter inducing interferon-beta. Staphylococcus aureus induced NOSII protein expression in vascular smooth muscle cells but not in macrophages, whereas E. coli induced NOSII in both cell types. Our data are the first to establish the definitive roles of specific TLRs in the sensing of Gram-positive and Gram-negative bacteria by vessels and demonstrate that macrophages and blood vessels may differ in their response to pathogens.

Adult congenital heart disease: intensive care management and outcome prediction.

OBJECTIVE: Improved patient survival and increasingly complex surgery have expanded the requirement for specialist care for patients with adult congenital heart disease (ACHD). Despite the recent publications of management guidelines for ACHD, data concerning optimal patterns of care in the peri-operative/critical care period of this challenging population are sparse. The aims of the current study were to therefore to determine the pattern of intensive care unit (ICU) management, resource utilisation and predictors of mortality in critically ill ACHD patients. DESIGN, SETTING AND PATIENTS: Data were collected prospectively for patients with ACHD stratified for complexity of disease admitted to the ICU of a tertiary cardiothoracic centre (1997-2002). Multivariate analysis of pre-operative indices as predictors of mortality was performed. Of 342 ACHD admissions (total mortality 4.4%, simple 0%, moderate/complex 10.6%), the requirement for specialist investigations and interventions was high, reflected in ICU admission costs per patient (simple $5391+/-130, moderate $13218+/-261, complex $30074+/-689). Standard severity of illness scoring systems did not accurately predict mortality; however, abnormal pre-operative thyroid function (p=0.0048), creatinine (p=0.0032) and bilirubin (p=0.0021) were highly predictive of mortality. CONCLUSIONS: Peri-operative mortality in patients with ACHD is low overall but varies with disease complexity. Such patients have a high requirement for specialist ICU investigation/intervention. Although standard severity of illness scoring is unhelpful, simple pre-operative parameters may predict peri-operative mortality. These findings reflect the requirement for specialist care, and have implications for planning service provision, training and operative consent in ACHD patients.

Persistently low plasma thioredoxin is associated with meningococcal septic shock in children.

OBJECTIVE: To compare plasma levels of thioredoxin (Trx), TNF-alpha and IL-1 beta in children during the acute phase of meningococcal septic shock (MSS) and in convalescence. DESIGN AND SETTING: Retrospective, observational study in the paediatric intensive care unit of a postgraduate teaching hospital. PATIENTS: Thirty-five children requiring intensive care for meningococcal sepsis; paired convalescent samples from 30 survivors (median interval between samples 62 days); 25 healthy control children. MEASUREMENTS AND RESULTS: Plasma Trx levels were significantly lower in the children with MSS, both during the acute illness (5.5 ng/ml, IQR 1.4-11.4) and in convalescence (2.5 ng/ml, IQR 0.4-6.9) than controls (18.8 ng/ml, IQR 7.9-25.0). Levels of IL-1 beta and TNF-alpha were higher in patients with acute MSS (30.3 pg/ml, IQR 3.6-63.6, and 145.9 pg/ml, IQR 31.8-278.1 respectively) than controls (3.7 pg/ml, IQR 0-36.9, and 23.8 pg/ml, IQR 0-124.3, respectively). Levels fell in convalescence (3.7 pg/ml, IQR 0-25.5, 3.7 pg/ml, IQR 0-304.8, respectively). Plasma Trx was higher in non-survivors, albeit a small group (n=5), than in survivors (n=30). Trx, IL-1 beta, and TNF-alpha levels were not correlated with predicted mortality as assessed by the paediatric risk of mortality (PRISM) score. CONCLUSIONS: Children with MSS exhibit persistently low plasma levels of Trx during acute illness and in convalescence.

Acute lung injury outside the ICU: a significant problem.

The incidence of acute lung injury (ALI) is influenced by nature of the underlying clinical condition. The frequency with which ALI is likely to be encountered by those practicing outside the intensive care unit (ICU) setting is largely unknown. Data from the paper under discussion indicates that ALI is seen relatively frequently in general wards and can be managed there until death or recovery. In patients with predisposing illnesses directly involving the lung, progression to ALI can be rapid.

Organ dysfunction during sepsis.

BACKGROUND: Multiple organ dysfunction syndrome is the commonest reason for sepsis-associated mortality. DISCUSSION: In the 40 years since it was first described understanding of its pathophysiology has improved, and novel methodologies for monitoring and severity of illness scoring have emerged. These, together with the development of systematic strategies for managing organ dysfunction in sepsis, and potentially effective new therapeutic interventions, should assist in reducing sepsis-associated mortality. CONCLUSION: These historical developments are discussed, and the reader is directed to these references for further guidance.