Influence of rheologic changes and platelet-neutrophil interactions on cell filtration in sepsis

Feature augmentation and semi-supervised conditional transfer learning for early detection of sepsis

Early detection of Sepsis is crucial for improving patient outcomes, as it is a significant public health concern that results in substantial morbidity and mortality. However, despite the widespread use of the Sequential Organ Failure Assessment (SOFA) in clinical settings to identify sepsis, obtaining sufficient physiological data before onset remains challenging, limiting early detection of sepsis. To address this challenge, we propose an interpretable machine learning model, ITFG (Interpretable Tree-based Feature Generation), that leverages potential correlations between features based on existing knowledge to identify sepsis within six hours of onset using valuable and continuous physiological measures. Furthermore, we introduce a Semi-supervised Attention-based Conditional Transfer Learning (SAC-TL) framework to enhance the model's generality and enable it to be used for early warning of sepsis in the target domain with less information from the source domain. Our proposed approaches effectively address the problem of systematic feature sparsity and missing data, while also being practical for different degrees of generalizability. We evaluated our proposed approaches on open datasets, MIMIC and PhysioNet, obtaining AUC of 97.98% and 86.21%, respectively, demonstrating their effectiveness in different data environments and achieving the best early detection results.

Impaired microvascular circulation in distant organs following renal ischemia

Mortality in acute kidney injury (AKI) patients remains very high, although very important advances in understanding the pathophysiology and in diagnosis and supportive care have been made. Most commonly, adverse outcomes are related to extra-renal organ dysfunction and failure. We and others have documented inflammation in remote organs as well as microvascular dysfunction in the kidney after renal ischemia. We hypothesized that abnormal microvascular flow in AKI extends to distant organs. To test this hypothesis, we employed intravital multiphoton fluorescence imaging in a well-characterized rat model of renal ischemia/reperfusion. Marked abnormalities in microvascular flow were seen in every organ evaluated, with decreases up to 46% observed 48 hours postischemia (as compared to sham surgery, p = 0.002). Decreased microvascular plasma flow was found in areas of erythrocyte aggregation and leukocyte adherence to endothelia. Intravital microscopy allowed the characterization of the erythrocyte formations as rouleaux that flowed as one-dimensional aggregates. Observed microvascular abnormalities were associated with significantly elevated fibrinogen levels. Plasma flow within capillaries as well as microthrombi, but not adherent leukocytes, were significantly improved by treatment with the platelet aggregation inhibitor dipyridamole. These microvascular defects may, in part, explain known distant organ dysfunction associated with renal ischemia. The results of these studies are relevant to human acute kidney injury.

Cargo-free particles divert neutrophil-platelet aggregates to reduce thromboinflammation

The combination of inflammation and thrombosis is a hallmark of many cardiovascular diseases. Under such conditions, platelets are recruited to an area of inflammation by forming platelet-leukocyte aggregates via interaction of PSGL-1 on leukocytes and P-selectin on activated platelets, which can bind to the endothelium. While particulate drug carriers have been utilized to passively redirect leukocytes from areas of inflammation, the downstream impact of these carriers on platelet accumulation in thromboinflammatory conditions has yet to be studied. Here, we explore the ability of polymeric particles to divert platelets away from inflamed blood vessels both in vitro and in vivo. We find that untargeted and targeted micron-sized polymeric particles can successfully reduce platelet adhesion to an inflamed endothelial monolayer in vitro in blood flow systems and in vivo in a lipopolysaccharide-induced, systemic inflammation murine model. Our data represent initial work in developing cargo-free, anti-platelet therapeutics specifically for conditions of thromboinflammation.

Mechanisms underlying the therapeutic effects of 4-octyl itaconate in treating sepsis based on network pharmacology and molecular docking

Objective: Through network pharmacology and molecular docking technology, the hub genes, biological functions, and signaling pathways of 4-Octyl itaconate (4-OI) against sepsis were revealed.

Methods: Pathological targets of sepsis were screened using GeneCards and GEO databases. Similarly, the pharmacological targets of 4-OI were obtained through Swiss TargetPrediction (STP), Similarity ensemble approach (SEA), and TargetNet databases. Then, all the potential targets of 4-OI anti-sepsis were screened by the online platform Draw Venn diagram, and the hub genes were screened by Cytoscape software. The identified hub genes were analyzed by GO and KEGG enrichment analysis, protein interaction (PPI) network, and molecular and docking technology to verify the reliability of hub gene prediction, further confirming the target and mechanism of 4-OI in the treatment of sepsis.

Results: After the target screening of 4-OI and sepsis, 264 pharmacological targets, 1953 pathological targets, and 72 genes related to 4-OI anti-sepsis were obtained, and eight hub genes were screened, namely MMP9, MMP2, SIRT1, PPARA, PTPRC, NOS3, TLR2, and HSP90AA1. The enrichment analysis results indicated that 4-OI might be involved in regulating inflammatory imbalance, immunosuppression, and oxidative stress in developing sepsis. 4-OI protects multiple organ dysfunction in sepsis by acting on hub genes, and MMP9 is a reliable gene for the prognosis and diagnosis of sepsis. The molecular docking results showed that 4-OI binds well to the hub target of sepsis.

Conclusion: 4-OI plays an antiseptic role by regulating MMP9, MMP2, SIRT1, PPARA, PTPRC, NOS3, TLR2 and HSP90AA1. These Hub genes may provide new insights into follow-up research on the target of sepsis treatment.

Platelet MHC class I mediates CD8+ T-cell suppression during sepsis

Circulating platelets interact with leukocytes to modulate host immune and thrombotic responses. In sepsis, platelet-leukocyte interactions are increased and have been associated with adverse clinical events, including increased platelet-T-cell interactions. Sepsis is associated with reduced CD8+ T-cell numbers and functional responses, but whether platelets regulate CD8+ T-cell responses during sepsis remains unknown. In our current study, we systemically evaluated platelet antigen internalization and presentation through major histocompatibility complex class I (MHC-I) and their effects on antigen-specific CD8+ T cells in sepsis in vivo and ex vivo. We discovered that both human and murine platelets internalize and proteolyze exogenous antigens, generating peptides that are loaded onto MHC-I. The expression of platelet MHC-I, but not platelet MHC-II, is significantly increased in human and murine platelets during sepsis and in human megakaryocytes stimulated with agonists generated systemically during sepsis (eg, interferon-γ and lipopolysaccharide). Upregulation of platelet MHC-I during sepsis increases antigen cross-presentation and interactions with CD8+ T cells in an antigen-specific manner. Using a platelet lineage-specific MHC-I-deficient mouse strain (B2Mf/f-Pf4Cre), we demonstrate that platelet MHC-I regulates antigen-specific CD8+ T-cell proliferation in vitro, as well as the number and functional responses of CD8+ T cells in vivo, during sepsis. Loss of platelet MHC-I reduces sepsis-associated mortality in mice in an antigen-specific setting. These data identify a new mechanism by which platelets, through MHC-I, process and cross-present antigens, engage antigen-specific CD8+ T cells, and regulate CD8+ T-cell numbers, functional responses, and outcomes during sepsis.

Effects of remote ischemic preconditioning on the deformability and aggregation of red blood cells in a rat endotoxemia model

BACKGROUND

The prevention of rheologic alterations in erythrocytes may be important for reducing sepsis-associated morbidity and mortality. Remote ischemic preconditioning (RIPC) has been shown to prevent tissue damage caused by severe ischemia and mortality resulting from sepsis. However, the effect of RIPC on erythrocytes in sepsis is yet to be determined.

OBJECTIVE

To investigate the effect of RIPC on rheologic alterations in erythrocytes in sepsis.

METHODS

Thirty male Sprague-Dawley rats were used in this study. An endotoxin-induced sepsis model was established by intraperitoneally injecting 20 mg/kg LPS (LPS group). RIPC was induced in the right hind limb using a tourniquet, with three 10-minute of ischemia and 10 min of reperfusion cycles immediately before the injection of LPS (RIPC/LPS group) or phosphate-buffered saline (RIPC group). The aggregation index (AI), time to half-maximal aggregation (T1/2), and maximal elongation index (EImax) of the erythrocytes were measured 8 h after injection.

RESULTS

The AI, T1/2, and EImax values in the LPS and RIPC/LPS groups differed significantly from those in the RIPC group, but there were no differences between the values in the LPS and RIPC/LPS groups.

CONCLUSIONS

RIPC did not prevent rheologic alterations in erythrocytes in the rat model of LPS-induced endotoxemia.

TICAM2-related pathway mediates neutrophil exhaustion

Pathogenic inflammation and immune suppression are the cardinal features that underlie the pathogenesis of severe systemic inflammatory syndrome and sepsis. Neutrophil exhaustion may play a key role during the establishment of pathogenic inflammation and immune suppression through elevated expression of inflammatory adhesion molecules such as ICAM1 and CD11b as well as immune-suppressors such as PD-L1. However, the mechanism of neutrophil exhaustion is not well understood. We demonstrated that murine primary neutrophils cultured in vitro with the prolonged lipopolysaccharides (LPS) stimulation can effectively develop an exhaustive phenotype resembling human septic neutrophils with elevated expression of ICAM1, CD11b, PD-L1 as well as enhanced swarming and aggregation. Mechanistically, we observed that TICAM2 is involved in the generation of neutrophil exhaustion, as TICAM2 deficient neutrophils have the decreased expression of ICAM1, CD11b, PD-L1, and the reduced aggregation following the prolonged LPS challenge as compared to wild type (WT) neutrophils. LPS drives neutrophil exhaustion through TICAM2 mediated activation of Src family kinases (SFK) and STAT1, as the application of SFK inhibitor Dasatinib blocks neutrophil exhaustion triggered by the prolonged LPS challenge. Functionally, TICAM2 deficient mice were protected from developing severe systemic inflammation and multi-organ injury following the chemical-induced mucosal damage. Together, our data defined a key role of TICAM2 in facilitating neutrophil exhaustion and that targeting TICAM2 may be a potential approach to treating the severe systemic inflammation.

Effects of Baseline Thrombocytopenia and Platelet Decrease Following Renal Replacement Therapy Initiation in Patients With Severe Acute Kidney Injury

OBJECTIVES

Thrombocytopenia is common in critically ill patients with severe acute kidney injury and may be worsened by the use of renal replacement therapy. In this study, we evaluate the effects of renal replacement therapy on subsequent platelet values, the prognostic significance of a decrease in platelets, and potential risk factors for platelet decreases.

DESIGN

Post hoc analysis of the Acute Renal Failure Trial Network Study.

SETTING

The Acute Renal Failure Trial Network study was a multicenter, prospective, randomized, parallel-group trial of two strategies for renal replacement therapy in critically ill patients with acute kidney injury conducted between November 2003 and July 2007 at 27 Veterans Affairs and university-affiliated medical centers.

SUBJECTS

The Acute Renal Failure Trial Network study evaluated 1,124 patients with severe acute kidney injury requiring renal replacement therapy.

INTERVENTIONS

Predictor variables were thrombocytopenia at initiation of renal replacement therapy and platelet decrease following renal replacement therapy initiation.

MEASUREMENTS AND MAIN RESULTS

Outcomes were mortality at 28 days, 60 days, and 1 year, renal recovery, renal replacement therapy free days, ICU-free days, and hospital-free days. Baseline thrombocytopenia in patients requiring renal replacement therapy was associated with increased mortality and was also associated with lower rates of renal recovery. A decrease in platelet values following renal replacement therapy initiation was associated with increased mortality. Continuous renal replacement therapy was not an independent predictor of worsening thrombocytopenia compared with those treated with intermittent hemodialysis.

CONCLUSIONS

Baseline thrombocytopenia and platelet decrease following renal replacement therapy initiation were associated with increased mortality, and baseline thrombocytopenia was associated with decreased rates of renal recovery. Continuous renal replacement therapy did not decrease platelets compared with hemodialysis.

Quantitative Measurement of Erythrocyte Aggregation as a Systemic Inflammatory Marker by Ultrasound Imaging: A Systematic Review

This systematic review is aimed at answering two questions: (i) Is erythrocyte aggregation a useful biomarker in assessing systemic inflammation? (ii) Does quantitative ultrasound imaging provide the non-invasive option to measure erythrocyte aggregation in real time? The search was executed through bibliographic electronic databases CINAHL, EMB Review, EMBASE, MEDLINE, PubMed and the grey literature. The majority of studies correlated elevated erythrocyte aggregation with inflammatory blood markers for several pathologic states. Some studies used "erythrocyte aggregation" as an established marker of systemic inflammation. There were limited but promising articles regarding the use of quantitative ultrasound spectroscopy to monitor erythrocyte aggregation. Similarly, there were limited studies that used other ultrasound techniques to measure systemic inflammation. The quantitative measurement of erythrocyte aggregation has the potential to be a routine clinical marker of inflammation as it can reflect the cumulative inflammatory dynamics in vivo, is relatively simple to measure, is cost-effective and has a rapid turnaround time. Technologies like quantitative ultrasound spectroscopy that can measure erythrocyte aggregation non-invasively and in real time may offer the advantage of continuous monitoring of the inflammation state and, thus, may help in rapid decision making in a critical care setup.

Role of matrix metalloproteinases 2 and 9, toll-like receptor 4 and platelet-leukocyte aggregate formation in sepsis-associated thrombocytopenia

Background

The development of thrombocytopenia in sepsis is a poor prognostic indicator associated with a significantly increased mortality risk. Mechanisms underlying this phenomenon remain to be clearly elucidated. Matrix metalloproteinases (MMPs) are enzymes that regulate the turnover of the extra-cellular matrix. MMP-2 is recognised as a platelet agonist with MMP-9 proposed as an inhibitor of platelet activation. The existence of MMP-9 in platelets is a subject of debate. There is limited evidence thus far to suggest that toll-like receptor 4 (TLR-4) and platelet-leukocyte aggregate (PLA) formation may be implicated in the development of sepsis-associated thrombocytopenia.

Objectives

To investigate whether MMP -2/-9, toll-like receptor 4 (TLR-4) or platelet-leukocyte aggregate (PLA) formation are implicated in a decline in platelet numbers during septic shock.

Methods

This was an observational study which recruited healthy controls, non-thrombocytopenic septic donors and thrombocytopenic septic donors. MMP-2, MMP-9 and TLR-4 platelet surface expression as well as PLA formation was examined using flow cytometry. In addition MMP-2 and MMP-9 were examined by gelatin zymography and enzyme-linked immunosorbent assay (ELISA) using a 3 compartment model (plasma, intraplatelet and platelet membrane).

Results

There was no difference found in MMP-2, MMP-9 or TLR-4 levels between non-thrombocytopenic and thrombocytopenic septic donors. PLA formation was increased in thrombocytopenic patients. MMP-9 was detected in platelets using flow cytometry, gelatin zymography and ELISA techniques.

Conclusions

Platelet consumption into PLAs may account for the development of thrombocytopenia in septic shock. MMP-9 is found in platelets and it is upregulated during septic shock.

Development of a Physiologically Based Pharmacokinetic Modelling Approach to Predict the Pharmacokinetics of Vancomycin in Critically Ill Septic Patients

BACKGROUND AND OBJECTIVES

Sepsis is characterised by an excessive release of inflammatory mediators substantially affecting body composition and physiology, which can be further affected by intensive care management. Consequently, drug pharmacokinetics can be substantially altered. This study aimed to extend a whole-body physiologically based pharmacokinetic (PBPK) model for healthy adults based on disease-related physiological changes of critically ill septic patients and to evaluate the accuracy of this PBPK model using vancomycin as a clinically relevant drug.

METHODS

The literature was searched for relevant information on physiological changes in critically ill patients with sepsis, severe sepsis and septic shock. Consolidated information was incorporated into a validated PBPK vancomycin model for healthy adults. In addition, the model was further individualised based on patient data from a study including ten septic patients treated with intravenous vancomycin. Models were evaluated comparing predicted concentrations with observed patient concentration-time data.

RESULTS

The literature-based PBPK model correctly predicted pharmacokinetic changes and observed plasma concentrations especially for the distribution phase as a result of a consideration of interstitial water accumulation. Incorporation of disease-related changes improved the model prediction from 55 to 88% within a threshold of 30% variability of predicted vs. observed concentrations. In particular, the consideration of individualised creatinine clearance data, which were highly variable in this patient population, had an influence on model performance.

CONCLUSION

PBPK modelling incorporating literature data and individual patient data is able to correctly predict vancomycin pharmacokinetics in septic patients. This study therefore provides essential key parameters for further development of PBPK models and dose optimisation strategies in critically ill patients with sepsis.

Characterizing cellular mechanical phenotypes with mechano-node-pore sensing

The mechanical properties of cells change with their differentiation, chronological age, and malignant progression. Consequently, these properties may be useful label-free biomarkers of various functional or clinically relevant cell states. Here, we demonstrate mechano-node-pore sensing (mechano-NPS), a multi-parametric single-cell-analysis method that utilizes a four-terminal measurement of the current across a microfluidic channel to quantify simultaneously cell diameter, resistance to compressive deformation, transverse deformation under constant strain, and recovery time after deformation. We define a new parameter, the whole-cell deformability index (wCDI), which provides a quantitative mechanical metric of the resistance to compressive deformation that can be used to discriminate among different cell types. The wCDI and the transverse deformation under constant strain show malignant MCF-7 and A549 cell lines are mechanically distinct from non-malignant, MCF-10A and BEAS-2B cell lines, and distinguishes between cells treated or untreated with cytoskeleton-perturbing small molecules. We categorize cell recovery time, ΔT_r, as instantaneous (ΔT_r ~ 0 ms), transient (ΔT_r ≤ 40ms), or prolonged (ΔT_r > 40ms), and show that the composition of recovery types, which is a consequence of changes in cytoskeletal organization, correlates with cellular transformation. Through the wCDI and cell-recovery time, mechano-NPS discriminates between sub-lineages of normal primary human mammary epithelial cells with accuracy comparable to flow cytometry, but without antibody labeling. Mechano-NPS identifies mechanical phenotypes that distinguishes lineage, chronological age, and stage of malignant progression in human epithelial cells.

Platelet reactivity in sepsis syndrome: results from the PRESS study

Platelet activation mediates systemic inflammatory response during infection. However, data on platelet reactivity (PR) varies among different settings. We assessed PR along different stages of sepsis and tried to predict for determinants of its variance. In parallel, we evaluated it as an early bedside diagnostic biomarker. This was an observational prospective cohort study. Incoming patients were assorted to distinct groups of uncomplicated infection, sepsis, and severe sepsis/septic shock. A control group of healthy volunteers was used as comparison. PR was assessed using the bedside point-of-care VerifyNow assay, in P2Y₁₂ reaction units (PRU) alongside with levels of major inflammatory markers and whole blood parameters. A total of 101 patients and 27 healthy volunteers were enrolled. PR significantly and reversibly increases during sepsis compared to uncomplicated infection and healthy controls (244 ± 66.7 vs 187.33 ± 60.98, p < 0.001 and 192.17 ± 47.51, p < 0.001, respectively). In severe sepsis, PR did not significantly differ compared to other groups. Sepsis stage uniquely accounts for 15.5% of PR in a linear regression prediction model accounting for 30% of the variance of PR (F = 8.836, p < 0.001). PRU >253 had specificity of 91.2% and sensitivity of 40.8% in discriminating septic from non-septic patients. The addition of PRU to SOFA and qSOFA scores significantly increased their c-statistic (AUC SOFA + PRU, 0.867 vs SOFA, 0.824, p < 0.003 and AUC qSOFA + PRU, 0.842 vs qSOFA, 0.739, p < 0.001), making them comparable (AUC SOFA + PRU vs qSOFA + PRU, p = 0.4). PR significantly and reversibly increases early in sepsis, but seems to exhaust while disease progresses. Bedside assessment of PR can provide robust discriminative accuracy in the early diagnosis of septic patients.

Comparison of endothelin and nitric oxide synthase blockers on hemorheological parameters in endotoxemic rats

BACKGROUND/AIM

Septic shock is an important health problem that vastly alters cardiovascular and hemodynamic status. Increased production of nitric oxide (NO) and endothelin is a counterpart of this endotoxemic state. This study was conducted to test the hypothesis that nonselective NO synthesis blocker (L-NAME), inducible NO synthesis blocker (L-canavanine), or endothelin receptor antagonist (bosentan) will reverse the effects of sepsis on hemorheological parameters.

MATERIALS AND METHODS

Forty-eight male Sprague-Dawley rats were used in 8 groups: saline (control), endotoxin, bosentan, L-NAME, L-canavanine, endotoxin + bosentan, endotoxin + L-NAME, and endotoxin + L-canavanine. Blood was withdrawn at the 4th hour of endotoxemic state. Erythrocyte deformability and erythrocyte aggregation were determined by laser-assisted optical rotational cell analyzer at 37 °C. Plasma viscosity (mPa.s) was measured by a cone-plate viscometer with 0.5 mL of plasma.

RESULTS

Endotoxin administration significantly increased aggregation half-time and lowered erythrocyte aggregation amplitude and aggregation index compared to the control, indicating a slower and weaker aggregation pattern. L-NAME and L-canavanine alleviated the effects of endotoxin on erythrocyte aggregation without altering the values in the control animals. However, bosentan did not perform such a restoration.

CONCLUSION

This finding suggests that these restoration effects of the blockers occur via their modulation of nitric oxide synthesis rather than through the endothelin pathway.

Microfluidic system for monitoring temporal variations of hemorheological properties and platelet adhesion in LPS-injected rats

Sepsis causes multiple organs failures and eventually death. Changes in blood constituents due to sepsis lead to alterations in hemorheological properties, and cell adhesiveness. In this study, a new microfluidic system is proposed to measure temporal variations in biophysical properties of blood after injecting lipopolysaccharide (LPS) into a rat extracorporeal model under ex vivo condition. To measure blood viscosity, the interfacial line between blood and a reference fluid is formed in a Y-shaped channel. Based on the relation between interfacial width and pressure ratio, the temporal variation in blood viscosity is estimated. Optical images of blood flows are analyzed by decreasing flow rate for examination of red blood cell (RBC) aggregation. Platelets initiated by shear acceleration around the stenosis adhere to the post-stenosed region. By applying a correlation map that visualizes the decorrelation of the streaming blood flow, the area of adhered platelets can be quantitatively attained without labeling of platelets. To assess sepsis inflammation, conventional biomarkers (PCT and IL-8) are also monitored. The increasing tendency for blood viscosity, RBC aggregation, platelet adhesion, and septic biomarkers are observed after LPS injection. This microfluidic system would be beneficial for monitoring the changes in hemorheological properties and platelet activation caused by sepsis.

The relationship between hemorheological parameters and mortality in critically ill patients with and without sepsis

PURPOSE

The prognostic scoring systems for mortality of intensive care patients estimate clinical outcome using several physiological and biochemical parameters. In altered hemodynamic conditions of critically ill patients, hemorheological variables may play a significant role in appropriate tissue perfusion. We investigated if hemorheological parameters are altered in critical status and if they could be markers of mortality.

METHODS

112 patients (67.8 ± 12 years, 58 males, 54 females) treated in intensive care unit with different non-surgical diseases were investigated. Routine laboratory parameters and prognostic scores were determined and hemorheological variables (hematocrit, plasma and whole blood viscosity, red blood cell aggregation and deformability) were measured on the 1st and the 2nd day after admission.

RESULTS

ICU scores predicted 35.2-41.3% mortality rate, real mortality in intensive care unit was 37.5%, while 30-day mortality was 46.6%. Whole blood viscosity (WBV) and red blood cell (RBC) deformability were lower, red blood cell aggregation was higher in septic than in nonseptic patients (p < 0.05). In septic patients calcium was increased, osmolality was decreased, while in nonseptic patients WBV and RBC aggregation were higher in nonsurvivors compared to survivors (p < 0.05). Worsening of RBC deformability from day 1 to day 2 predicted higher mortality (p < 0.05).

CONCLUSION

Calcium and osmolality level were associated with outcome in sepsis. Whole blood viscosity, red blood cell aggregation and change in red blood cell deformability could predict mortality in nonseptic patients and they may add prognostic information over the ICU scores. Further investigations are needed to evaluate the benefit of our findings in clinical practice.

Sepsis: Current Definition, Pathophysiology, Diagnosis, and Management

Sepsis is a clinical syndrome that results from the dysregulated inflammatory response to infection that leads to organ dysfunction. The resulting losses to society in terms of financial burden, morbidity, and mortality are enormous. We provide a review of sepsis, its underlying pathophysiology, and guidance for diagnosis and management of this common disease. Current established treatments include appropriate antimicrobial agents to target the underlying infection, optimization of intravascular volume to improve stroke volume, vasopressors to counteract vasoplegic shock, and high-quality supportive care. Appropriate implementation of established treatments combined with novel therapeutic approaches promises to continue to decrease the impact of this disease.

Septic porcine blood does not further activate coagulation during in vitro membrane oxygenation

Objectives

For patients with a severe acute respiratory distress syndrome (ARDS), extracorporeal membrane oxygenation (ECMO) represents a life-saving measure. Frequently, patients with severe ARDS also show signs of severe sepsis. As blood contact with the membrane oxygenator surface leads to adverse effects due to insufficient biocompatibility partly caused by activation of platelets, coagulation factors and leucocytes, we hypothesized that these adverse effects would be amplified if septic blood in a preactivated state came into contact with the membrane oxygenator.

Methods

In a previously established in vitro 12-h ECMO test system (mock loop), we used septic or healthy domestic pig blood to analyse coagulation and inflammatory parameters. Sepsis was induced by a caecal ligation and puncture model in pigs.

Results

At the beginning of the mock loop experiments, the septic blood showed significantly increased thrombin-antithrombin complexes (76.9 vs 27.7 µg/l), D-dimers (1.2 vs 0.3 mg/l) and fibrinogen concentration (1.8 vs 1.5 g/l), as well as elevated extrinsic coagulation activity (shorter EXTEM-CT: 44.2 vs 57 s) and higher lactate (3.4 vs 1.5 mmol/l) and cytokine levels (interleukin-6: 827 vs 31 pg/ml) when compared with the blood from healthy animals. Despite the preactivated status of the septic blood, no further increase of coagulation activity, inflammatory response or increased oxygenator resistance was observed in comparison to the control experiments.

Conclusion

Septic porcine blood was not further activated due to the contact with an oxygenator, and no increased clot formation or biocompatibility problems were observed.

Effect of yeast biomass with high content of carotenoids on erythrocyte deformability, NO production and Na,K-ATPase activity in healthy and LPS treated rats

Measurements of red blood cell (RBC) deformability together with estimation of NO-synthase activity and Na,K-ATPase activity were used for characterization of RBC functionality in rats subjected to single dose of Escherichia coli lipopolysaccharides (LPS) at a dose of 1 mg/kg. We hypothesized that LPS might initiate a malfunction of RBC. We also investigated the potential effect of carotenoids (10 mg/kg/day) produced in red yeast biomass of Rhodotorula glutinis on RBC in LPS-challenged rats. LPS significantly reduced the deformability of RBC (by 14%) together with decrease of NO-synthase activity by 20%. Daily supplementation of carotenoids for 10 days attenuated the LPS-induced injury, as observed by 22% increase of RBC deformability and 23% increase of NO-synthase activity. The activity of Na,K-ATPase was also improved probably due to increased number of active enzyme molecules as indicated by 66% enhancement of Vmax value, hence maintaining the activity of erythrocyte Na,K-ATPase to the level even higher as compared with healthy control animals. It may be concluded that administration of yeast biomass with high content of carotenoids resulted in advanced function of erythrocytes as concerns their ability to squeeze through narrow capillaries of the circulation, better intrinsic production of NO and improvement of intracellular homeostasis of sodium.

Early hemorheological changes in a porcine model of intravenously given E. coli induced fulminant sepsis

The pathophysiology of hemorheological and microcirculatory disturbances in septic process -mostly during the early hours- still not clarified in all the details, yet. In anesthetized pigs living E. coli (ATCC 25922 strain) was administered intravenously with an increasing concentration and the animals were observed for 8 hours. Before the intervention and in every 2 hours arterial (cannulated femoral artery) and venous (cannulated external jugular vein) blood samples were collected for hemorheological laboratory tests: blood and plasma viscosity, ESR, leukocyte anti-sedimentation rate, erythrocyte deformability (together with osmoscan parameters) and erythrocyte aggregation (using light-transmission and laser back-scattering methods) Control animals were stable over the 8-hour anesthesia, while septic animals died by the 6th hours in a fulminant sepsis. Over the experimental period, the tendency of impairment in erythrocyte deformability (together with osmotic gradient ektacytometry parameters) and the controversial decreasing of erythrocyte aggregation values (declining all aggregation index values, elongating t1/2) were well detected in this porcine model during the early hours (4- 6) of fulminant sepsis. The in vitro effect of these bacteria on erythrocytes' micro-rheological parameter was similar: decreasing red blood cell deformability and lowering aggregation. Further studies are needed to clarify the early micro-rheological changes of bacteremia and the developing sepsis.

Neutrophil recruitment limited by high-affinity bent β2 integrin binding ligand in cis

Neutrophils are essential for innate immunity and inflammation and many neutrophil functions are β2 integrin-dependent. Integrins can extend (E(+)) and acquire a high-affinity conformation with an 'open' headpiece (H(+)). The canonical switchblade model of integrin activation proposes that the E(+) conformation precedes H(+), and the two are believed to be structurally linked. Here we show, using high-resolution quantitative dynamic footprinting (qDF) microscopy combined with a homogenous conformation-reporter binding assay in a microfluidic device, that a substantial fraction of β2 integrins on human neutrophils acquire an unexpected E(-)H(+) conformation. E(-)H(+) β2 integrins bind intercellular adhesion molecules (ICAMs) in cis, which inhibits leukocyte adhesion in vitro and in vivo. This endogenous anti-inflammatory mechanism inhibits neutrophil aggregation, accumulation and inflammation.

Basic concepts of hemorheology in microvascular hemodynamics

Blood rheology, or hemorheology, involves the flow and deformation behavior of blood and its formed elements (ie, erythrocytes, leukocytes, platelets). The adequacy of blood flow to meet metabolic demands through large circulatory vessels depends highly on vascular control mechanisms. However, the extent to which rheologic properties of blood contribute to vascular flow resistance, particularly in the microcirculation, is becoming more appreciated. Current evidence suggests that microvascular blood flow is determined by local vessel resistance and hemorheologic factors such as blood viscosity, erythrocyte deformability, and erythrocyte aggregation. Such knowledge will aid clinicians caring for patients with hemodynamic alterations.

Acute Limb Ischemia in Pediatric Population Secondary to Peripheral Vascular Cannulation

Introduction:

In this article, we discuss published literature on the management of pediatric patients with acute limb ischemia and also present our center’s experience.

Results:

Literature review suggests that in the absence of imminent risk of limb loss, noninterventional management with anticoagulants and systemic thrombolysis is preferable and associated with better clinical outcomes than surgery such as reduced per operative morbidity and mortality. In selected more severe cases, surgery may be required. We propose an algorithm for improved clinical outcomes based on the published literature and the American College of Chest Physicians’ recommendations for antithrombotic management in the pediatric population.

Conclusion:

Literature review suggests an inverse relationship between age and surgical success, particularly in preschool pediatric population. Conservative management as a preliminary strategy seems most beneficial. It is hoped that the proposed intercalated algorithm of medical and surgical management of these patients can further improve clinical outcomes.

High-Throughput Assessment of Cellular Mechanical Properties

Traditionally, cell analysis has focused on using molecular biomarkers for basic research, cell preparation, and clinical diagnostics; however, new microtechnologies are enabling evaluation of the mechanical properties of cells at throughputs that make them amenable to widespread use. We review the current understanding of how the mechanical characteristics of cells relate to underlying molecular and architectural changes, describe how these changes evolve with cell-state and disease processes, and propose promising biomedical applications that will be facilitated by the increased throughput of mechanical testing: from diagnosing cancer and monitoring immune states to preparing cells for regenerative medicine. We provide background about techniques that laid the groundwork for the quantitative understanding of cell mechanics and discuss current efforts to develop robust techniques for rapid analysis that aim to implement mechanophenotyping as a routine tool in biomedicine. Looking forward, we describe additional milestones that will facilitate broad adoption, as well as new directions not only in mechanically assessing cells but also in perturbing them to passively engineer cell state.

Circulating platelet-neutrophil aggregates play a significant role in Kawasaki disease

BACKGROUND

Circulating platelet-neutrophil aggregates play a crucial role in amplifying acute inflammation and could promote adverse effects involving vascular injury. The aim of this study was to evaluate the role of platelet-neutrophil aggregates in Kawasaki disease (KD).

METHODS AND RESULTS

Forty patients with KD (30 intravenous immunoglobulin [IVIG] responders and 10 IVIG non-responders), 7 febrile patients with bacterial infections, and 9 normal volunteers were analyzed. Thirty-three patients with KD were treated with IVIG, and 7 were treated with IVIG plus prednisolone. We evaluated the rate of platelet-neutrophil aggregates and measured the platelet factor 4 (PF4) and β-thromboglobulin (β-TG) levels. The rate of platelet-neutrophil aggregates was significantly higher in patients with KD than those with bacterial infection and normal volunteers. The rate of platelet-neutrophil aggregates was significantly higher in patients with coronary artery abnormalities (CAA) than in those without CAA, and was correlated with PF4 and β-TG levels in patients with KD. Comparing time-course analysis, the rate of platelet-neutrophil aggregates was significantly decreased in patients treated with IVIG plus prednisolone than in those treated with IVIG alone.

CONCLUSIONS

The findings demonstrate that platelet-neutrophil aggregates are significantly present in higher rates and are closely related to pathological developments of CAA in KD. Additional prednisolone treatment for patients in the acute phase of KD could suppress platelet-neutrophil aggregates, indicating that platelet-neutrophil aggregates would inhibit amplified reciprocal vascular inflammatory activation.

Shear-sensitive regulation of neutrophil flow behavior and its potential impact on microvascular blood flow dysregulation in hypercholesterolemia

OBJECTIVE

Shear stress-induced pseudopod retraction is an anti-inflammatory measure that minimizes neutrophil activity and is regulated by membrane cholesterol. We tested the hypothesis that a hypercholesterolemic impairment of shear mechanotransduction alters the neutrophil flow behavior leading to microvascular dysfunction.

APPROACH AND RESULTS

We examined the shear effects on the flow behavior of human leukocytes. When subjected to shearing during cone-plate viscometry, leukocyte suspensions exhibited parallel time-dependent reductions in viscosity and pseudopod activity. Shear-induced reductions in suspension viscosity were attenuated by membrane cholesterol enrichment. We also showed that enhanced pseudopod activity of leukocyte suspensions in 10% hematocrit significantly (P<0.05) raised the flow resistance of microvascular mimics. These results implicate an impaired neutrophil pseudopod retraction response to shear in hypercholesterolemic microvascular dysfunction. We confirmed this using near-infrared diffuse correlation spectroscopy to assess skeletal muscle blood flow regulation in the hindlimbs of mice subjected to reactive hyperemia. Using a custom protocol for the mouse, we extrapolated an adjusted peak flow and time to adjusted peak flow to quantify the early phase of the blood flow recovery response during reactive hyperemia when shear mechanobiology likely has a maximal impact. Compared with mice on normal diet, hypercholesterolemic mice exhibited significantly (P<0.05) reduced adjusted peak flow and prolonged time to adjusted peak flow which correlated (r=0.4 and r=-0.3, respectively) with neutrophil shear responsiveness and were abrogated by neutropenia.

CONCLUSIONS

These results provide the first evidence that the neutrophils contribute to tissue blood flow autoregulation. Moreover, a deficit in the neutrophil responsiveness to shear may be a feature of hypercholesterolemia-related microvascular dysfunction.

Targeting CD162 protects against streptococcal M1 protein-evoked neutrophil recruitment and lung injury

Streptococcus pyogenes of the M1 serotype can cause streptococcal toxic shock syndrome and acute lung damage. CD162 is an adhesion molecule that has been reported to mediate neutrophil recruitment in acute inflammatory reactions. In this study, the purpose was to investigate the role of CD162 in M1 protein-provoked lung injury. Male C57BL/6 mice were treated with monoclonal antibody directed against CD162 or a control antibody before M1 protein challenge. Edema, neutrophil infiltration, and CXC chemokines were determined in the lung, 4 h after M1 protein administration. Fluorescence intravital microscopy was used to analyze leukocyte-endothelium interactions in the pulmonary microcirculation. Inhibition of CD162 reduced M1 protein-provoked accumulation of neutrophils, edema, and CXC chemokine formation in the lung by >54%. Moreover, immunoneutralization of CD162 abolished leukocyte rolling and firm adhesion in pulmonary venules of M1 protein-treated animals. In addition, inhibition of CD162 decreased M1 protein-induced capillary trapping of leukocytes in the lung microvasculature and improved microvascular perfusion in the lungs of M1 protein-treated animals. Our findings suggest that CD162 plays an important role in M1 protein-induced lung damage by regulating leukocyte rolling in pulmonary venules. Consequently, inhibition of CD162 attenuates M1 protein-evoked leukocyte adhesion and extravasation in the lung. Thus, our results suggest that targeting the CD162 might pave the way for novel opportunities to protect against pulmonary damage in streptococcal infections.

Amniotic fluid induces platelet-neutrophil aggregation and neutrophil activation

OBJECTIVE

Amniotic fluid embolism syndrome is a fatal disease in pregnant women. The exact role of platelets and neutrophils in amniotic fluid embolism syndrome is not clear. We examined whether amniotic fluid could affect platelet-neutrophil aggregation and activation and the possible mechanisms.

STUDY DESIGN

Blood samples from the pregnant women were pretreated ex vivo with their own amniotic fluid. Flow cytometry was used to measure platelet-neutrophil aggregation and activation. Neutrophil-mediated activity of p38 mitogen-activated protein kinase and extracellular signal-regulated protein kinases 1 and 2 was analyzed by Western blotting.

RESULTS

Amniotic fluid significantly induced platelet-neutrophil aggregation, neutrophil CD11b expression, and reactive oxygen species production. Amniotic fluid induced minimal platelet P-selectin expression. The increase of intracellular calcium level of neutrophils and the activity of p38 mitogen-activated protein kinase were enhanced by amniotic fluid stimulation.

CONCLUSION

Amniotic fluid was able to induce neutrophil activation and platelet-neutrophil aggregation with minimal effect on platelet activation. These findings may provide a new insight in the understanding of the pathophysiologic condition of amniotic fluid embolism syndrome.

Platelet-neutrophil aggregate formation in blood samples from dogs with systemic inflammatory disorders

OBJECTIVE

To evaluate platelet-neutrophil aggregate (PNA) formation and neutrophil shape as indicators of neutrophil activation in dogs with systemic inflammatory diseases and after blood sample incubation with various platelet and neutrophil agonists.

ANIMALS

20 dogs with systemic inflammatory response syndrome (SIRS) and 10 healthy Beagles.

PROCEDURES

Neutrophils were isolated from blood samples directly after blood sample collection and after incubation of blood samples with phorbol myristate acetate, collagen, adenosine diphosphate, epinephrine, or various concentrations of lipopolysaccharide or arachidonic acid. CD61+ neutrophils as an indicator of PNA formation were evaluated, and neutrophil size and granularity were assessed via flow cytometry.

RESULTS

Dogs with SIRS had more PNA formation, larger neutrophil size, and less granularity relative to control dogs, but no differences were evident when these dogs were grouped by whether they had sepsis (n = 6) or disseminated intravascular coagulation (12). A significant increase in PNA formation occurred after neutrophil incubation with all agonists, and incubation with phorbol myristate acetate elicited the strongest response. Neutrophils increased in size and decreased in granularity after incubation with all agonists except epinephrine. Incubation with lipopolysaccharide or arachidonic acid resulted in a dose-dependent effect on PNA formation and neutrophil shape.

CONCLUSIONS AND CLINICAL RELEVANCE

SIRS appeared to increase the degree of PNA formation and neutrophil shape change. Similar changes after neutrophil incubation with platelet agonists suggested that platelet activation has a role in PNA formation. Additional studies are necessary to determine the clinical importance and diagnostic value of PNA formation in dogs with SIRS and sepsis.

Red blood cell clearance in inflammation

SUMMARY

Anemia is a frequently encountered problem in the critically ill patient. The inability to compensate for anemia includes several mechanisms, collectively referred to as anemia of inflammation: reduced production of erythropoietin, impaired bone marrow response to erythropoietin, reduced iron availability, and increased red blood cell (RBC) clearance. This review focuses on mechanisms of RBC clearance during inflammation. We state that phosphatidylserine (PS) expression in inflammation is mainly enhanced due to an increase in ceramide, caused by an increase in sphingomyelinase activity due to either platelet activating factor, tumor necrosis factor-α, or direct production by bacteria. Phagocytosis of RBCs during inflammation is mediated via RBC membrane protein band 3. Reduced deformability of RBCs seems an important feature in inflammation, also mediated by band 3 as well as by nitric oxide, reactive oxygen species, and sialic acid residues. Also, adherence of RBCs to the endothelium is increased during inflammation, most likely due to increased expression of endothelial adhesion molecules as well as PS on the RBC membrane, in combination with decreased capillary blood flow. Thereby, clearance of RBCs during inflammation shows similarities to clearance of senescent RBCs, but also has distinct entities, including increased adhesion to the endothelium.

Platelet and neutrophil responses to Gram positive pathogens in patients with bacteremic infection

BACKGROUND

Many Gram-positive pathogens aggregate and activate platelets in vitro and this has been proposed to contribute to virulence. Platelets can also form complexes with neutrophils but little is however known about platelet and platelet-neutrophil responses in bacterial infection.

METHODOLOGY/PRINCIPAL FINDINGS

We added isolates of Gram-positive bacteria from 38 patients with a bacteremic infection to blood drawn from the same patient. Aggregometry and flow cytometry were used to assess platelet aggregation and to quantify activation of platelets, neutrophils, and platelet-neutrophils complexes (PNCs) induced by the bacteria. Fifteen healthy persons served as controls. Most isolates of Staphylococcus aureus, beta hemolytic streptococci, and Enterococcus faecalis induced aggregation of platelets from their respective hosts, whereas pneumococci failed to do so. S. aureus isolates induced platelet aggregation more rapidly in patients than in controls, whereas platelet activation by S. aureus was lower in patients than in controls. PNCs were more abundant in baseline samples from patients than in healthy controls and most bacterial isolates induced additional PNC formation and neutrophil activation.

CONCLUSION/SIGNIFICANCE

We have demonstrated for the first time that bacteria isolated from patients with Gram-positive bacteremia can induce platelet activation and aggregation, PNC formation, and neutrophil activation in the same infected host. This underlines the significance of these interactions during infection, which could be a target for future therapies in sepsis.

Beyond thrombosis: the versatile platelet in critical illness

Sepsis, acute lung injury, and ARDS contribute substantially to the expanding burden of critical illness within our ICUs. Each of these processes is characterized by a myriad of injurious events, including apoptosis, microvascular dysfunction, abnormal coagulation, and dysregulated host immunity. Only recently have platelets--long considered merely effectors of thrombosis--been implicated in inflammatory conditions and the pathobiology of these disease processes. A growing body of evidence suggests a prominent role for maladaptive platelet activation and aggregation during sepsis and ARDS and has begun to underscore the pluripotential influence of platelets on outcomes in critical illness. Not only do platelets enhance vascular injury through thrombotic mechanisms but also appear to help orchestrate pathologic immune responses and are pivotal players in facilitating leukocyte recruitment to vulnerable tissue. These events contribute to the organ damage and poor patient outcomes that still plague the care of these high-risk individuals. An understanding of the role of platelets in critical illness also highlights the potential for both the development of risk stratification schema and the use of novel, targeted therapies that might alter the natural history of sepsis, acute lung injury, and ARDS. Future studies of adenosine, platelet polyphosphates, and the platelet transcriptome/proteome also should add considerably to our ability to unravel the mysteries of the versatile platelet.

Non-invasive Assessment of the Microcirculation in Critically Ill Patients

Sepsis is associated with abnormalities of muscle tissue oxygenation and of microvascular function. We investigated whether the technique of near-infrared spectroscopy can evaluate such abnormalities in critically ill patients and compared near-infrared spectroscopy-derived indices of critically ill patients with those of healthy volunteers.

We studied 41 patients (mean age 58±22 years) and 15 healthy volunteers (mean age 49±13 years). Patients were classified into one of three groups: systemic inflammatory response syndrome (SIRS) (n=21), severe sepsis (n=8) and septic shock (n=12). Near-infrared spectroscopy was used to continuously measure thenar muscle oxygen saturation before, during and after a three-minute occlusion of the brachial artery via pneumatic cuff.

Oxygen saturation was significantly lower in patients with SIRS, severe sepsis or septic shock than in healthy volunteers. Oxygen consumption rate during stagnant ischaemia was significantly lower in patients with SIRS (23.9±7.7%/minute, P <0.001), severe sepsis (16.9±3.4%/minute, P <0.001) or septic shock (14.8±6%/minute, P <0.001) than in healthy volunteers (35.5±10.6%/minute). Furthermore, oxygen consumption rate was significantly lower in patients with septic shock than patients with SIRS. Reperfusion rate was significantly lower in patients with SIRS (336±141%/minute, P <0.001), severe sepsis (257±150%/minute, P <0.001) or septic shock (146±101%/minute, P <0.001) than in healthy volunteers (713±223%/minute) and significantly lower in the septic shock than in the SIRS group.

Near-infrared spectroscopy can detect tissue oxygenation deficits and impaired microvascular reactivity in critically ill patients, as well as discriminate among groups with different disease severity.

Is thenar tissue hemoglobin oxygen saturation in septic shock related to macrohemodynamic variables and outcome?

INTRODUCTION

The study objectives were to evaluate septic shock-induced alterations in skeletal muscle hemoglobin oxygenation saturation (StO2) using near-infrared spectroscopy (NIRS) and forearm skin blood flow velocity using laser Doppler (LD) to determine the relationship of macroperfusion and microperfusion parameters, and to test the relationship of the worst NIRS parameters during the first 24 hours of shock with 28-day prognosis.

METHODS

A prospective, observational study was performed in a 21-bed university hospital surgical intensive care unit. Forty-three septic shock patients with at least another organ failure underwent a 3-minute, upper arm (brachial artery) vascular occlusion test (VOT). Microperfusion parameters (thenar eminence StO2 and forearm LD skin blood flow) were collected on days 1, 2 and 3, before (baseline StO2 and LD values) and during the 3-minute VOT with calculation of occlusion and reperfusion slopes for StO2 and LD. Daily Sequential Organ Failure Assessment (SOFA) score, macrohemodynamic parameters (systolic arterial blood pressure, cardiac output (pulmonary artery catheter or transesophageal Doppler), mixed venous oxygen saturation (pulmonary artery or superior vena cava catheter)) and metabolic parameters (pH, base excess, lactate) were determined.

RESULTS

Baseline StO2 (82% (75 to 88) vs. 89% (85 to 92), P = 0.04) and reperfusion slope (2.79%/second (1.75 to 4.32) vs. 9.35%/second (8.32 to 11.57), P < 0.0001) were lower in septic shock patients than in healthy volunteers. StO2 reperfusion slope correlated with occlusion slope (P < 0.0001), cardiac output (P = 0.01) and LD reperfusion slope (P = 0.08), and negatively with lactate level (P = 0.04). The worst StO2 reperfusion slope during the first day of shock was lower in nonsurvivors than in survivors (P = 0.003) and improved significantly the predictive value of Simplified Acute Physiology Score II and SOFA scores.

CONCLUSIONS

The alteration of StO2 reperfusion slope in septic shock patients compared with healthy volunteers was related with macrohemodynamic, microhemodynamic and metabolic parameters. The addition of the worst value of the day 1 StO2 reperfusion slope improved the outcome prediction of Simplified Acute Physiology Score II and SOFA scores.

How microcirculation data have changed my clinical practice

PURPOSE OF REVIEW

The present review discusses how microcirculation assessment, which was recently made feasible, has altered clinical practice.

RECENT FINDINGS

Experimental data have provided important information on microcirculation alterations in disease states. Recent advances in imaging techniques have allowed microcirculation studies in critically ill patients. Derangements in microcirculation are variable and unpredictable, associated with organ dysfunction and outcome, and can be improved by therapeutic interventions. Recent studies not only confirm the beneficial effects of some drugs on the microcirculation, but also suggest new mechanisms of actions of these drugs. In particular, the interaction between the endothelial surface and circulating cells, and especially white blood cells, seems to be crucial. Although these imaging techniques provide important information, these remain difficult to implement at the bedside. Assessment of vasoreactivity using transient occlusion tests and indirect measurements of microvascular blood flow with laser Doppler or near infrared spectroscopy may be good alternatives.

SUMMARY

Microcirculation alterations are present in shock states, mainly septic shock, and can have a prognostic role and be the target of therapeutic interventions. To date, microcirculation analysis remains in the field of clinical investigation, but recently interesting clinical data have encouraged assessment of the microcirculation at the bedside.

Impaired blood rheology in critically ill patients in an intensive care unit

Critically ill patients are at increased risk of thromboembolic complications. Japanese patients admitted to the intensive care unit of Gunma University Hospital were divided into critically ill (high score) and moderately ill (low score) groups according to mean Acute Physiology and Chronic Health Evaluation (APACHE) II score. White blood cell count, potassium, creatinine, immunoglobulin G and blood passage time, measured using the microchannel method, were significantly higher and the platelet aggregation score and platelet count were significantly lower in the high-score group than in the low-score group, but other haemorheological parameters did not differ significantly between the two groups. White blood cell count, potassium, creatinine, APACHE II score and levels of immunoglobulins G, A and M were positively correlated with blood passage time in all patients. Critically ill patients had impaired blood rheology, which could result from increased white blood cell count, potassium, creatinine and immunoglobulins and may be associated with the pathophysiology of the thromboembolic process.

Effect of recombinant activated protein C and low-dose heparin on neutrophil-endothelial cell interactions in septic shock

OBJECTIVE

To examine the effects of recombinant activated protein C (rhAPC) and low-dose heparin on neutrophil-platelet-endothelial cell interactions in septic shock.

DESIGN

Controlled experiments using phase contrast microscopy to study neutrophil, platelet, and endothelial cell interactions in flowing cell suspensions under simulated physiologic conditions.

SETTING

University research laboratory.

PATIENTS

Adult patients with septic shock and normal volunteers.

INTERVENTIONS

Neutrophils and platelets removed from control subjects were stimulated with plasma and serum from 21 patients in septic shock and perfused over endothelial cells. Activated protein C, low-dose heparin, and low-dose heparin with rhAPC were added to cells suspended in septic plasma. Neutrophil rolling velocity and the number of neutrophils adherent to endothelial cells and in aggregates were determined. Flow cytometric analysis of CD11b/CD63 cells was used to identify platelet-neutrophil aggregates.

MEASUREMENTS AND MAIN RESULTS

Activated protein C significantly decreased neutrophil adhesion and aggregation and increased rolling velocity in cells stimulated with both septic serum and septic plasma. Significant decreases in platelet-neutrophil aggregates induced by septic plasma were also observed. Low-dose heparin alone had no effects on these variables. The addition of low-dose heparin to cells suspended in septic plasma and rhAPC attenuated the benefits observed with rhAPC alone in each of these variables.

CONCLUSIONS

These data suggest that the in vitro addition of rhAPC decreases sepsis-induced interactions between isolated platelets, neutrophils, and endothelial cells. Low-dose heparin attenuates the benefits observed with rhAPC. The changes in neutrophil-endothelial cell interactions demonstrated with rhAPC may play a role in preserving microvascular patency in patients with septic shock.

Isoflurane Prevents Platelets from Enhancing Neutrophil-Induced Coronary Endothelial Dysfunction

We evaluated whether platelets can enhance polymorphonuclear neutrophil-induced coronary endothelial dysfunction, and, after observing this, whether isoflurane can prevent the effect. Neutrophils, coronary artery segments, and platelets were obtained from 25 healthy dogs. Coronary artery rings were exposed to neutrophils activated with platelet-activating factor (1.0 microM), and after washing and preconstriction with U46619, were evaluated for concentration-related responses to acetylcholine, an endothelium-dependent vasorelaxing drug. Superoxide production by activated neutrophils was measured spectrophotometrically. Adherence of the activated neutrophils to the endothelium of coronary segments was assessed by direct counting of neutrophils labeled with fluorescent dye. Measurements were performed in absence and presence of isoflurane (1 minimum alveolar concentration) both with and without platelets. The presence of platelets enhanced the neutrophil-induced rightward shift in the concentration-vasorelaxation response curve to acetylcholine (the concentration of acetylcholine required to elicit 50% of maximal relaxation (-log M) was increased from 6.78 +/- 0.7 to 5.26 +/- 0.6), and it increased superoxide oxide production from 45.0 +/- 4.2 to 54.3 +/- 4.2 nM O2-/5 x 10(6) neutrophils and adherence of activated neutrophils from 204 +/- 10 to 268 +/- 5 neutrophils/mm2. Isoflurane abolished these effects of platelets. In conclusion, platelets enhanced the ability of neutrophils to cause coronary endothelial dysfunction. This effect was prevented by isoflurane. This may be attributable to an inhibitory action on superoxide production by the neutrophils leading to reduced expression of endothelial adhesion molecules and, in turn, reduced neutrophil adherence.

Association between hematological parameters and high-density lipoprotein cholesterol

PURPOSE OF REVIEW

The ability of high-density lipoprotein cholesterol to reverse atherosclerosis and reduce cardiovascular disease has been shown in several randomized controlled trials. One mechanism by which high-density lipoprotein cholesterol protects the vascular system includes hemorheology, the study of blood flow.

RECENT FINDINGS

Blood viscosity, or the resistance of flow, can be altered by red blood cell aggregation, red blood cell deformability, and plasma viscosity. Elevated high-density lipoprotein cholesterol levels may improve all of these rheological mediators. An infusion of recombinant high-density lipoprotein cholesterol can immediately release nitric oxide, a potent vasodilator and responder to changes in rheology, into the arteries by activation of endothelial nitric oxide synthase. The stimulation of nitric oxide release by high-density lipoprotein cholesterol may also alter blood rheology.

SUMMARY

In this article, we will review hemorheology, particularly blood viscosity along with other hemorheological factors, and examine their association with high-density lipoprotein cholesterol.

Pentoxifylline attenuates the increase in whole blood viscosity after transfusion

BACKGROUND

Pentoxifylline improves tissue oxygenation and intestinal blood flow in models of haemorrhagic shock, and it has been used for the treatment of intermittent claudication due to its beneficial effects on haemorheology. We investigated the effects of pentoxifylline on whole blood viscosity during packed red-blood cell transfusion in critically ill adult patients.

METHODS

Twenty critically ill patients were randomly assigned to one of two groups (pentoxifylline group: n = 11, placebo group: n = 9) and prospectively studied. Forty-five minutes before and during the packed red-blood cell transfusion (10 ml min(-1)) over a period of 80 min, 1.5 mg kg(-1) . h(-1) pentoxifylline or placebo were administered intravenously. Haematocrit, plasma fibrinogen concentration, total protein concentration, whole blood viscosity (at a shear rate of 10 s(-1), 50 s(-1), and 100 s(-1)) and plasma viscosity were measured.

RESULTS

After the packed red-blood cell transfusion, haematocrit levels increased significantly in both groups (pentoxifylline group: from 26.1 +/- 2.8% to 33.0 +/- 3.2; placebo group: from 24.4 +/- 3.3% to 32.6 +/- 2.6%; means +/- standard deviation). Compared to baseline, whole blood viscosity increased in both groups at all shear rates after the transfusion, but the increase was significantly less in the pentoxifylline group (26 +/- 15% vs. 49 +/- 14%, 23 +/- 11% vs. 39 +/- 12%, and 22 +/- 11% vs. 35 +/- 12% for the pentoxifylline vs. placebo groups at shear rates of 10 s(-1), 50 s(-1), and 100 s(-1), respectively). Plasma viscosity, total protein concentration, and fibrinogen concentration remained unchanged and no significant differences among groups were observed.

CONCLUSIONS

These results suggest that pentoxifylline is effective in attenuating the increase in whole blood viscosity after a transfusion of packed red-blood cells. Plasma viscosity is not influenced by pentoxifylline.

Mechanisms of early pulmonary neutrophil sequestration in ventilator-induced lung injury in mice

Polymorphonuclear leukocytes (PMN) play an important role in ventilator-induced lung injury (VILI), but the mechanisms of pulmonary PMN recruitment, particularly early intravascular PMN sequestration during VILI, have not been elucidated. We investigated the physiological and molecular mechanisms of pulmonary PMN sequestration in an in vivo mouse model of VILI. Anesthetized C57/BL6 mice were ventilated for 1 h with high tidal volume (injurious ventilation), low tidal volume and high positive end-expiratory pressure (protective ventilation), or normal tidal volume (control ventilation). Pulmonary PMN sequestration analyzed by flow cytometry of lung cell suspensions was substantially enhanced in injurious ventilation compared with protective and control ventilation, preceding development of physiological signs of lung injury. Anesthetized, spontaneously breathing mice with continuous positive airway pressure demonstrated that raised alveolar pressure alone does not induce PMN entrapment. In vitro leukocyte deformability assay indicated stiffening of circulating leukocytes in injurious ventilation compared with control ventilation. PMN sequestration in injurious ventilation was markedly inhibited by administration of anti-L-selectin antibody, but not by anti-CD18 antibody. These results suggest that mechanical ventilatory stress initiates pulmonary PMN sequestration early in the course of VILI, and this phenomenon is associated with stretch-induced inflammatory events leading to PMN stiffening and mediated by L-selectin-dependent but CD18-independent mechanisms.

Importance of platelets and fibrinogen in neutrophil-endothelial cell interactions in septic shock

OBJECTIVE

To examine the role of platelets, fibrin, and adhesion molecules in mediating neutrophil-endothelial cell interactions in septic shock.

DESIGN

Controlled experiments using phase contrast microscopy to examine neutrophil, platelet, and endothelial cell interactions in flowing cell suspensions under simulated physiologic conditions.

SETTING

University research laboratory.

PATIENTS

Adult patients with septic shock and normal volunteers.

INTERVENTIONS

Microslides were coated with human umbilical vein endothelial cells. Neutrophils were removed from control subjects and patients in septic shock and were perfused over endothelial cells at rates representing a range of physiologic shear stresses. In an attempt to examine the effects of fibrin deposition on neutrophil-endothelial cell interactions, neutrophils, with and without platelets, were suspended in plasma and serum was removed from patients in septic shock. In addition, blocking monoclonal antibodies against the platelet receptor P-selectin and neutrophil receptor CD11b/CD18, and a platelet glycoprotein IIb/IIIa inhibitor, were incubated with cells suspended in plasma. Phase contrast video microscopy was used to count the number of neutrophils/mm adherent to endothelial cells during cessation of flow. Neutrophil rolling velocity was calculated as the time required for neutrophils to move across a 1-mm field (mm/sec). Leukoaggregation was defined as the number of neutrophils in aggregates (three or more nuclei) across a 1-mm field.

MEASUREMENTS AND MAIN RESULTS

Normal neutrophils exposed to plasma from patients with septic shock demonstrated significant increases in aggregation and endothelial cell adherence with associated decreases in neutrophil rolling velocity. These changes were significantly enhanced in the presence of platelets and significantly attenuated in the presence of serum, which is fibrinogen depleted. Preincubation with antibodies to the surface receptors P-selectin, CD11b/CD18, and glycoprotein IIb/IIIa abrogated the changes in neutrophil aggregation, adhesion, and rolling velocity.

CONCLUSIONS

These data suggest that platelets and fibrinogen play an important role in mediating neutrophil-endothelial cell adherence in septic shock.

Persistent microcirculatory alterations are associated with organ failure and death in patients with septic shock

OBJECTIVE

To characterize the time course of microcirculatory alterations and their relation to outcome in patients with septic shock.

DESIGN

Prospective, observational study.

SETTING

Thirty-one-bed, medico-surgical intensive care unit in a university hospital.

PATIENTS

Forty-nine patients with septic shock.

INTERVENTIONS

The sublingual microcirculation was investigated with an orthogonal polarization spectral imaging device on the day of onset of septic shock (baseline) and each day until resolution of shock.

MEASUREMENTS AND MAIN RESULTS

Five sequences of 20 secs each were recorded and analyzed off-line by a semiquantitative method. Data were analyzed with nonparametric tests and presented as median (25th-75th percentiles). Three patients died after the resolution of shock from unrelated causes and were excluded. Of the other 46 patients, 26 survived and 20 died: 13 due to unresolving shock and seven due to persistent multiple organ failure after resolution of shock. At the onset of shock, survivors and nonsurvivors had similar vascular density (5.6 [4.7-7.0] vs. 6.2 [5.4-7.0]/mL; p = nonsignificant) and percentage of perfused small vessels (65.0 [53.1-68.9] vs. 58.4 [47.5-69.1]%; p = nonsignificant). Small vessel perfusion improved over time in survivors (analysis of variance, p <.05 between survivors and nonsurvivors) but not in nonsurvivors. Despite similar hemodynamic and oxygenation profiles and use of vasopressors at the end of shock, patients dying after the resolution of shock in multiple organ failure had a lower percentage of perfused small vessels than survivors (57.4 [46.6-64.9] vs. 79.3 [67.2-83.2]%; p =.02).

CONCLUSIONS

Microcirculatory alterations improve rapidly in septic shock survivors but not in patients dying with multiple organ failure, regardless of whether shock has resolved.