Mechanotransduction and the homeostatic significance of maintaining blood viscosity in hypotension, hypertension and haemorrhage

Sex difference in the association between triglyceride and intracerebral bleeding risk after intravenous thrombolysis for acute ischemic stroke, a multi-center retrospective study

Background

Whether the relationship of intracerebral bleeding risk with lipid profile may vary by sex remains unclear. This study aims to investigate potential sex differences in the association between lipid profile and the risk of symptomatic intracerebral hemorrhage (sICH) in patients with acute ischemic stroke (AIS) who received intravenous thrombolysis using recombinant tissue plasminogen activator (r-tPA).

Methods

This multicenter retrospective observational study analyzed patients with AIS treated with intravenous r-tPA. sICH was defined as a worsening of 4 or higher points in the National Institutes of Health Stroke Scale (NIHSS) score within 36 hours after intravenous thrombolysis in any hemorrhage subtype. We assessed the odds ratio (OR) with 95% confidence interval (CI) of lipid profile for sICH for each sex using logistic regression models adjusted for potential confounding factors.

Results

Of 957 participants (median age 68 (interquartile range, 59-75), men 628 (65.6%)), 56 sICH events (36 (5.7%) in men and 20 (6.1%) in women) were observed. The risk of sICH in men decreased with increasing serum levels of triglyceride after adjustment for confounding factors (vs lowest tertile, medium tertile OR 0.39, 95% CI [0.17-0.91], top tertile OR 0.33, 95% CI [0.13-0.84], overall p = 0.021; per point increase, adjusted OR 0.29, 95% CI [0.13-0.63], p = 0.002). Neither serum levels of total cholesterol nor low-density lipoprotein (LDL) was associated with sICH in men. In women, there was no association between any of the lipid levels and the risk of sICH.

Conclusions

This study indicated that the association between serum levels of triglyceride and sICH may vary by sex. In men, increased triglyceride levels decrease the risk of sICH; in women, this association was lost. Further studies on the biological mechanisms for sex differences in stroke risk associated with triglyceride are needed.

Predictive factors and prognosis of upper gastrointestinal bleeding in gastric cancer: A large population-based study (UGIB-GC trial)

BACKGROUND

Gastric cancer remains the fourth leading cause of cancer-related death worldwide. Significant number of gastric cancer patients presented with bleeding.

OBJECTIVE

This study aimed to identify risk factors and overall survival rates of bleeding gastric cancer patients.

METHODS

This retrospective cohort study was conducted between 2007-2022 at tertiary care center in Thailand. Clinical information, endoscopic findings and histological type were extensively reviewed and were compared between bleeders and non-bleeders. Patients were monitored for at least 5 years.

RESULTS

There were 20,981 patients who underwent upper gastrointestinal endoscopy during study period. Total of 201 gastric cancer patients were included in this study, 21 were excluded due to incomplete medical records. 180 gastric cancer patients were included with mean age of 60.5±14.3 years. There were 65 (36.1%) patients with gastrointestinal bleeding. Hypertension and chronic kidney disease were significantly more common in bleeders than non-bleeders (43.1% vs 23.5%, OR2.51, 95%CI 1.14.-5.52, p = 0.022; and 16.9% vs 5.2%, OR2.00, 95%CI 1.56-6.63, p = 0.025, respectively). current H. pylori infection was also significantly more common in bleeders than non-bleeders (84.6% vs. 55.7%, OR 4.39, 95%CI 1.90-10.12, p<0.001). Median overall survival of bleeders was significantly lower than non-bleeders (7±0.93 vs 10±2.10 months, p = 0.001).

CONCLUSIONS

Bleeding gastric cancer was not an uncommon condition. Majority of patients presented at advanced stage with grave prognosis. Male gender, hypertension, chronic kidney disease, and current H. pylori infection were reliable predictors for bleeding. Early diagnosis and prompt treatment are the key to improve clinical outcome.

Pathological hemodynamic changes and leukocyte transmigration disrupt the blood-spinal cord barrier after spinal cord injury

BACKGROUND

Blood-spinal cord barrier (BSCB) disruption is a key event after spinal cord injury (SCI), which permits unfavorable blood-derived substances to enter the neural tissue and exacerbates secondary injury. However, limited mechanical impact is usually followed by a large-scale BSCB disruption in SCI. How the BSCB disruption is propagated along the spinal cord in the acute period of SCI remains unclear. Thus, strategies for appropriate clinical treatment are lacking.

METHODS

A SCI contusion mouse model was established in wild-type and LysM-YFP transgenic mice. In vivo two-photon imaging and complementary studies, including immunostaining, capillary western blotting, and whole-tissue clearing, were performed to monitor BSCB disruption and verify relevant injury mechanisms. Clinically applied target temperature management (TTM) to reduce the core body temperature was tested for the efficacy of attenuating BSCB disruption.

RESULTS

Barrier leakage was detected in the contusion epicenter within several minutes and then gradually spread to more distant regions. Membrane expression of the main tight junction proteins remained unaltered at four hours post-injury. Many junctional gaps emerged in paracellular tight junctions at the small vessels from multiple spinal cord segments at 15 min post-injury. A previously unnoticed pathological hemodynamic change was observed in the venous system, which likely facilitated gap formation and barrier leakage by exerting abnormal physical force on the BSCB. Leukocytes were quickly initiated to transverse through the BSCB within 30 min post-SCI, actively facilitating gap formation and barrier leakage. Inducing leukocyte transmigration generated gap formation and barrier leakage. Furthermore, pharmacological alleviation of pathological hemodynamic changes or leukocyte transmigration reduced gap formation and barrier leakage. TTM had very little protective effects on the BSCB in the early period of SCI other than partially alleviating leukocyte infiltration.

CONCLUSIONS

Our data show that BSCB disruption in the early period of SCI is a secondary change, which is indicated by widespread gap formation in tight junctions. Pathological hemodynamic changes and leukocyte transmigration contribute to gap formation, which could advance our understanding of BSCB disruption and provide new clues for potential treatment strategies. Ultimately, TTM is inadequate to protect the BSCB in early SCI.

Perioperative predictors of early surgical revision and flap-related complications after microvascular free tissue transfer in head and neck reconstructions: a retrospective observational series

Objectives

The aim of this study was to determine the influence of perioperative fluid management and administration of vasopressors on early surgical revision and flap-related complications in free tissue transfer.

Materials and methods

Intraoperative amount of fluid and of vasopressors, relevant perioperative parameters, and comorbidities were recorded in 131 patients undergoing head and neck microvascular reconstruction and compared with early surgical complications, defined as interventions requiring surgery after a flap-related complication, and/or other surgical problems in the operating room within 30 days after initial surgery. The relationship between perioperative variables for each revision category was determined using an optimized multiple logistic regression.

Results

The administration of diuretics (p=0.001) as a treatment for perioperative fluid overload and the type of flap (p=0.019) was associated with a higher risk of early surgical revisions. Perioperative fluid overload (p=0.039) is significantly related to flap-related complications. We found no effect of intraoperative administration of vasopressors on early surgical revisions (p=0.8) or on flap-related complications (norepinephrine p=0.6, dobutamine p=0.5).

Conclusion

Perioperative fluid overload is associated with higher risks of early surgical revision and flap-related complications. In contrast, the administration of vasopressors seemed to have no effect on either surgical revision rate or flap-related complications.

Clinical relevance

In patients receiving microvascular reconstructions, a balanced fluid administration perioperatively and a targeted use of vasopressors should be the necessary strategy to reduce the complication rates in head and neck surgery.

The association of estimated whole blood viscosity with hemodynamic parameters and prognosis in patients with heart failure

AIM

We aimed to investigate the association of estimated whole blood viscosity (WBV) with hemodynamic parameters and prognosis in patients with heart failure with reduced ejection fraction.

MATERIALS & METHODS

Total of 542 patients were included and followed-up for median 13 months.

RESULTS

The WBV parameters had negative relationship with right atrium pressure and positive correlation with cardiac index. The WBV parameters were found to be independent predictors of composite end point (CEP) and all-cause mortality. Every one cP increases of WBV(h) and WBV(l) were associated with 17 and 1% reductions of CEP. In Kaplan-Meier analysis, patients with low WBV quartiles were found to have significantly more CEP.

CONCLUSION

Being an easily accessible and costless prognosticator, WBV seems to be a novel marker for determining prognosis and an emerging tool to individualize heart failure with reduced ejection fraction management.

Repetitive Supra-Physiological Shear Stress Impairs Red Blood Cell Deformability and Induces Hemolysis

The supra-physiological shear stress that blood is exposed to while traversing mechanical circulatory assist devices affects the physical properties of red blood cells (RBCs), impairs RBC deformability, and may induce hemolysis. Previous studies exploring RBC damage following exposure to supra-physiological shear stress have employed durations exceeding clinical instrumentation, thus we explored changes in RBC deformability following exposure to shear stress below the reported "hemolytic threshold" using shear exposure durations per minute (i.e., duty-cycles) reflective of that employed by circulatory assist devices. Blood collected from 20 male donors, aged 18-38 years, was suspended in a viscous medium and exposed to an intermittent shear stress protocol of 1 s at 100 Pa, every 60 s for 60 duty-cycles. During the remaining 59 s/min, the cells were left at stasis until the subsequent duty-cycle commenced. At discrete time points (15/30/45/60 duty-cycles), an ektacytometer measured RBC deformability immediately after shear exposure at 100 Pa. Plasma-free hemoglobin, a measurement of hemolysis, was quantified via spectrophotometry. Supra-physiological shear stress impaired RBC properties, as indicated by: (1) decreased maximal elongation of RBCs at infinite shear stress following 15 duty-cycles (P <0.05); (2) increased real-time RBC deformability during application of the supra-physiological shear stress protocol (100 Pa) following exposure to 1 duty-cycle (F (1.891, 32.15) = 12.21, P = 0.0001); and (3) increased plasma-free hemoglobin following 60 duty-cycles (P < 0.01). The present study indicates that exposure of RBCs to short-term, repeated supra-physiological shear stress, impairs RBC deformability, with the extent of impairment exacerbated with each duty-cycle, and ultimately precipitates hemolysis.

"Inside-Out" PEGylation of Bovine β-Cross-Linked Hemoglobin

The development of a blood substitute is urgent due to blood shortages and potential communicable diseases. A novel method, inside-out PEGylation, has been used here to conjugate a multiarm maleimide-PEG (Mal-PEG) to β-cross-linked (βXL-Hb) hemoglobin (Hb) tetramers through the Cys β93 residues. This method produces a polymer with a single PEG backbone that is surrounded by multiple proteins, rather than coating a single protein with multiple PEG chains. Electrophoresis under denaturing conditions showed a large molecular weight species. Gel filtration chromatography and analytical ultracentrifugation determined the most prevalent species had three βXL-Hb to one Mal-PEG. Thermal denaturation studies showed that the cross-linked and PEGylated species were more stable than native Hb. Cross-linking under oxy-conditions produced a high oxygen affinity Hb species (P₅₀  = 9.18 Torr), but the oxygen affinity was not significantly altered by PEGylation (P₅₀  = 9.67 Torr). Inside-out PEGylation can be used to produce a hemoglobin-based oxygen carrier and potentially for other multiprotein complexes.

Influence of serological factors and BMI on the blood pressure/hematocrit association in healthy young men and women

The association between mean arterial blood pressure (MAP) and hematocrit (Hct) as a surrogate for blood viscosity was investigated in a young (average 20.0±2.3 years), healthy population of 174 men and 442 women. Health status was assessed by clinical examination and serological evaluation. Individuals with severe anemia or hemoconcentration, prior traumas or major surgical intervention, smokers, and pregnant or lactating women were excluded from the study. The MAP/Hct association was positive and significant (P=0.04) for women and negative, albeit not significantly so, for men. The MAP/Hct association was also evaluated in subgroups of the same population with a progressive step-by-step exclusion of: individuals with cholesterol >200 mg/dL; triglycerides >200 mg/dL; body mass index >25 kg/m(2); and glucose >100 mg/dL. This consecutively reduced the strength of the positive MAP/Hct association in women, which became negative - although not significantly so - when all anomalously high factors were excluded. The same trend was found in men. Our study indicates that previously reported positive trends in the relationship between the MAP and Hct in the population are not present in a young, healthy population of men or women that excludes individuals with the confounding factors of above normal serological values and BMI.

An analytic study on the effect of alginate on the velocity profiles of blood in rectangular microchannels using microparticle image velocimetry

It is desired to understand the effect of alginic acid sodium salt from brown algae (alginate) as a viscosity modifier on the behavior of blood in vitro using a micro-particle image velocimetry (µPIV) system. The effect of alginate on the shape of the velocity profile, the flow rate and the maximum velocity achieved in rectangular microchannels channels are measured. The channels were constructed of polydimethylsiloxane (PDMS), a biocompatible silicone. Porcine blood cells suspended in saline was used as the working fluid at twenty percent hematocrit (H = 20). While alginate was only found to have minimal effect on the maximum velocity and the flow rate achieved, it was found to significantly affect the shear rate at the wall by between eight to a hundred percent.

[Erythrocytes and microvascular tone during acute traumatic haemorrhagic shock]

Haemorrhagic shock remains a leading cause of death in trauma patients. The concept of haematologic damage control is gradually taking place in the management of traumatic haemorrhagic shock. It is based primarily on the early implementation of a quality blood transfusion involving erythrocytes, plasmas and platelets transfusion. Red blood cell transfusion is mainly supported by the oxygen carrier properties of erythrocytes. However, it appears that erythrocytes ability to modulate the bioavailability of nitric oxide (NO) plays a major role in capillary opening and perfusion. Erythrocytes are also actively involved in the processes of hemostasis and coagulation. In this context, it seems difficult to define a threshold of hemoglobin concentration to determine the implementation of a blood transfusion in traumatic haemorrhagic shock.

Physiopathology of anemia and transfusion thresholds in isolated head injury

BACKGROUND

Blood transfusion strategies among patients with critical illness use a restrictive hemoglobin threshold. However, among patients with head injury, no outcome differences have been shown between either liberal or restrictive strategies. Several studies and literature reviews suggest that anemia is associated with markers of tissue ischemia. The paucity of prospective data confuses the association between surrogates of tissue ischemia and neurological outcome.

METHODS

A narrative review of transfusion practices among patients in the acute phase of head injury was performed using PubMed, MEDLINE, EMBASE, Cochrane, and WEB of Science databases. A total of 104 articles were reviewed.

RESULTS

There are few data to guide clinical practice. Clinicians use blood hemoglobin concentrations to trigger transfusion. Markers of potential cerebral injury are not in regular use despite experimental and observational data rising from histologic examination, microdialysis, oximetry, and flow-based multimonitoring systems recommending their use to titrate blood transfusion in neurotrauma.

CONCLUSION

The generalization of transfusion triggers is common practice. Evidence-based approaches to transfusions strategies in head injury are lacking and not based on an understanding of cerebral physiopathology.

The viscous behaviour of HES 130/0.4 (Voluven®) and HES 260/0.45 (Pentaspan®)

PURPOSE

Several fluids are available for volume therapy to address hypovolemia. We focus on two hydroxyethyl starches (HES) available for volume expansion in Canada, HES 130/0.4 (Voluven®) and HES 260/0.45 (Pentaspan®). Although information is available regarding their pharmacokinetic and risk/benefit profiles, this paper examines their viscous properties.

METHODS

Dynamic viscosities of HES 130/0.4 and HES 260/0.45 were measured through capillary viscometry at 21°C and 37°C. The viscosities of the solutions were then measured through a closed flow loop at room temperature across physiologically relevant flow rates that maintained a laminar flow regime.

RESULTS

Measured dynamic viscosity through capillary viscometry for HES 130/0.4 and HES 260/0.45 was 2.76 centipoises (cP) and 7.62 cP, respectively, at 21°C decreasing to 1.74 cP and 4.25 cP, respectively, at 37°C. Pipe flow analysis found that HES 130/0.4 (expiry 02/13) and HES 260/0.45 (expiry 10/10) displayed marginal variation in viscosity suggesting Newtonian behaviour. However, a sample of HES 130/0.4 (expiry 10/10) displayed an appreciable increase in viscosity (13%) at higher flow rates suggesting shear thickening behaviour.

CONCLUSION

This study represents an innovative characterization of not only the viscosity of two commonly utilized HES solutions but also their viscous behaviour across physiologically relevant flow rates. The shear thickening behaviour of a sample of HES 130/0.40 (expiry 10/10) at high flow rates was not expected, and the effect this result may have on endothelial cell function is unknown.

Small-volume resuscitation from hemorrhagic shock using high-molecular-weight tense-state polymerized hemoglobins

BACKGROUND

The objective of this study was to determine the role of plasma oxygen carrying capacity during resuscitation from hemorrhagic shock (HS).

METHODS

Hemodynamic responses to small-volume resuscitation from HS with hypertonic saline followed by infusion of ultrahigh-molecular-weight tense-state polymerized hemoglobins (PolyHbs) were studied in the hamster window chamber model. HS was induced by withdrawing 50% of the blood volume (BV), and hypovolemic state was maintained for 1 hour. Resuscitation was implemented by infusion of hypertonic saline (3.5% of BV) followed by 10% of BV infusion of polymerized human Hb (PolyHbhum, P50=49 mm Hg), polymerized bovine Hb (PolyHbbov, P50=40 mm Hg), or human serum albumin (HSA), all at 10 g/dL. Resuscitation was monitored over 90 minutes.

RESULTS

PolyHbhum elicited higher arterial pressure, produced vasoconstriction, and decreased perfusion. In contrast, PolyHbbov and HSA exhibited lower blood pressure and partially restored perfusion and functional capillary density compared with PolyHbhum. Blood gas parameters showed a pronounced recovery after resuscitation with PolyHbbov compared with both PolyHbhum and HSA. Tissue PO2 was significantly improved in the PolyHbbov group, showing that the moderate increase in P50 of PolyHbbov compared with hamster blood (P50=32 mm Hg) was beneficial during resuscitation. However, an excessive increase in oxygen release between the central and peripheral circulation, as induced by PolyHbhum produced vasoconstriction and hypoperfusion, limiting the benefits of additional oxygen carrying capacity.

CONCLUSIONS

Appropriately engineered PolyHb will enhance/reinstate oxygenation, without hypertension or vasoconstriction, to be used in situations where blood transfusion is not logistically feasible.

Vital organ tissue oxygenation after serial normovolemic exchange transfusion with HBOC-201 in anesthetized swine

This study determined the effects of serial, normovolemic, stepwise exchange transfusions with either 6% human serum albumin (HSA) or the hemoglobin-based oxygen carrier, HBOC-201, on tissue oxygenation of the heart, brain, and kidney in intact anaesthetized pigs. Exchange transfusions to 10%, 30%, and 50% of the pigs' total blood volume were completed at a withdrawal rate of 1.0 mL·kg(-1)·min(-1) followed by an infusion rate of 0.5 mL·kg(-1)·min(-1) of HBOC-201 or iso-oncotically matched 6% HSA. Measurements included invasive systemic hemodynamic (blood pressures, left ventricular end-diastolic pressure), hematolic (hemoglobin, hematocrit, methemoglobin), acid-base (pH, PCO2), and biochemistry (serum lactate) measurements. Brain and kidney tissue oxygenation (tPO2) was determined by electron paramagnetic resonance and heart tPO2 by O2 sensitive fiberoptic probe. The main results demonstrated that tPO2 after HBOC-201 remained stable despite significant decreases in hematocrit and changing hemodynamics. In vivo tPO2 measurements (heart tPO2 average ≥22 mmHg, brain tPO2 average ≥8 mmHg, and kidney tPO2 average ≥10 mmHg) were maintained in all groups at all times. Blood pressures were 20 to 30 mmHg higher after HBOC-201 compared with HSA controls. Heart rate and left ventricular end-diastolic pressure were not different among treatment groups. In conclusion, the administration of HBOC-201 maintained tPO2 in three vital organs after profound hemodilution.

Sodium alginate as viscosity modifier may induce aggregation of red blood cells

Viscosity of blood substitutes is among the important determinants to restore microcirculation. Sodium alginate (SA) is always mentioned as "viscosity modifier" in creating blood substitutes. In the present study, the whole blood was diluted using SA solutions to final hematocrits of 10%, 20%, and 35%, respectively. The whole blood viscosity (WBV) at different shear rates, plasma viscosity (PV), and rheological behavior of red blood cells (RBCs) was studied in vitro. The results show that SA may induce RBCs aggregation in a dose-dependent manner. Furthermore, the effect of SA on RBCs aggregation maybe involve the regulation of microcirculation.

Ascites in Adult Patients With Cyanotic Congenital Heart Disease

Hematologic, neurologic, renal, and rheumatic complications in patients with cyanotic congenital heart disease are well known. However, the effects of this condition on the liver are poorly described. Between April 2005 and April 2010, 25 adults with cyanotic congenital heart disease were studied to determine clinical history, liver ultrasonographic data, and liver histological presentation. Twenty-five patients, with a median age of 28.7 ± 8.3 years and a basal tissue hemoglobin oxygen saturation of 83.3% ± 6.8%, were studied. Liver ultrasonographic examination showed abnormalities in 10 of 20 patients (50%): 6 patients (30%) had hepatomegaly, 2 patients (10%) heterogeneous parenchyma echo pattern, and 2 patients (10%) increased portal echogenicity. Ascites was found in 7 patients (28%): 4 patients had refractory ascites and 3 patients anasarca. Patients with anasarca responded well to oral and intravenous furosemide, but those with isolated ascites did not. No data to indicate severe ventricular dysfunction or severe valve regurgitation were seen. In patients with refractory ascites who had therapeutic paracentesis, serum–ascites albumin gradient in ascites was greater than 1.1 g/dL. No significant association was found between patients with or without ascites when laboratory data and New York Heart Association functional class were compared. Liver biopsy was performed in 6 patients (24%). The most remarkable liver histological finding, in those with refractory ascites, was the existence of periportal fibrosis associated with sinusoidal dilatation. Periportal liver fibrosis associated with congestive heart failure, sepsis, or a long-term Fontan procedure can trigger refractory ascites formation.

Both passive leg raising and intravascular volume expansion improve sublingual microcirculatory perfusion in severe sepsis and septic shock patients

PURPOSE

To assess sublingual microcirculatory changes following passive leg raising (PLR) and volume expansion (VE) in septic patients.

METHODS

This prospective study was conducted in two university hospital intensive care units and included 25 mechanically ventilated patients with severe sepsis or septic shock who were eligible for VE in the first 24 h of their admission. Pulse pressure variation (ΔPP), cardiac output (CO) and sublingual microcirculation indices were assessed at five consecutive steps: (1) semi-recumbent position (Baseline 1), (2) during PLR manoeuvre (PLR), (3) after returning to semi-recumbent position (Baseline 2), (4) at the time when VE induced the same degree of preload responsiveness as PLR (VE(∆PP = PLR)) and (5) at the end of VE (VE(END)). At each step, five sublingual microcirculation sequences were acquired using sidestream darkfield imaging to assess functional capillary density (FCD), microcirculatory flow index (MFI), proportion of perfused vessels (PPV) and flow heterogeneity index (FHI).

RESULTS

The PLR, VE(∆PP = PLR) and VE(END) induced a significant increase in CO and a significant decrease in ΔPP compared to Baseline 1 and Baseline 2 values. Both PLR and VE induced significant increases in FCD, MFI and PPV and a significant decrease in FHI compared to Baseline 1 and Baseline 2 values.

CONCLUSIONS

In preload responsive severe septic patients examined within the first 24 h of their admission, both PLR and VE improved sublingual microcirculatory perfusion. At the level of volume infusion used in this study, these changes in sublingual microcirculation were not explained by changes in rheologic factors or changes in arterial pressure.

Both passive leg raising and intravascular volume expansion improve sublingual microcirculatory perfusion in severe sepsis and septic shock patients

PURPOSE

To assess sublingual microcirculatory changes following passive leg raising (PLR) and volume expansion (VE) in septic patients.

METHODS

This prospective study was conducted in two university hospital intensive care units and included 25 mechanically ventilated patients with severe sepsis or septic shock who were eligible for VE in the first 24 h of their admission. Pulse pressure variation (ΔPP), cardiac output (CO) and sublingual microcirculation indices were assessed at five consecutive steps: (1) semi-recumbent position (Baseline 1), (2) during PLR manoeuvre (PLR), (3) after returning to semi-recumbent position (Baseline 2), (4) at the time when VE induced the same degree of preload responsiveness as PLR (VE(∆PP = PLR)) and (5) at the end of VE (VE(END)). At each step, five sublingual microcirculation sequences were acquired using sidestream darkfield imaging to assess functional capillary density (FCD), microcirculatory flow index (MFI), proportion of perfused vessels (PPV) and flow heterogeneity index (FHI).

RESULTS

The PLR, VE(∆PP = PLR) and VE(END) induced a significant increase in CO and a significant decrease in ΔPP compared to Baseline 1 and Baseline 2 values. Both PLR and VE induced significant increases in FCD, MFI and PPV and a significant decrease in FHI compared to Baseline 1 and Baseline 2 values.

CONCLUSIONS

In preload responsive severe septic patients examined within the first 24 h of their admission, both PLR and VE improved sublingual microcirculatory perfusion. At the level of volume infusion used in this study, these changes in sublingual microcirculation were not explained by changes in rheologic factors or changes in arterial pressure.

Seasonal hematocrit variation and health risks in the adult population of Kinshasa, Democratic Republic of Congo

Hematocrit (Hct) as an indicator of blood viscosity and mean arterial blood pressure (MAP) were assessed according to the season in adult participants of health screenings conducted throughout Kinshasa, Democratic Republic of Congo. Data was collected at the end of summer (April) and the end of winter (August) and identified by gender. Male Hcts in August were significantly higher (P < 0.0001) than in April (48.3% ± 4.2% and 45.7% ± 2.3%, respectively) while male MAP (85.0 ± 8.4 mm Hg) was identical to that recorded in April (85.4 ± 7.7 mm Hg). August female Hcts (41.4% ± 3.1%) were statistically higher than those recorded in April (39.6% ± 1.9%, P = 0.001), MAP being 82.3 ± 7.3 vs 87.9 ± 6.6 mm Hg, respectively (P = 0.0001). Systolic and diastolic blood pressures, heart rate, body mass indices, ages, and personal and familial medical histories of the August and April groups were not significantly different. This study offers further support for the assertion that the relationship between blood viscosity and pressure of a healthy population shows that increased Hct, and therefore increased blood viscosity is associated with lowered MAP, and presumably peripheral vascular resistance.

Effects of different resuscitation fluids on the rheologic behavior of red blood cells, blood viscosity and plasma viscosity in experimental hemorrhagic shock

BACKGROUND

Hemorrhagic shock is associated with severe rheological abnormalities. We hypothesized that in the setting of hemorrhagic shock, resuscitation can alter hemorheological characteristics dramatically, and different fluids cause different effects. The aim of this study was to investigate whether the type of fluid administered has an impact on hemorheological characteristics at the early stage of resuscitation in a rodent model of hemorrhagic shock.

METHODS

Animals were randomized into five groups: (1) sham hemorrhage (SHAM); (2) shock and sham resuscitation (SHOCK); (3) shock and resuscitation with normal saline 32 ml/kg (NS); (4) shock and resuscitation with 7.5% hypertonic saline 4 ml/kg (HS); (5) shock and resuscitation with 7.5% hypertonic saline/6% Dextran 70 4 ml/kg (HSD). Hemorheological characteristics were measured at 60 min after resuscitation.

RESULTS

Results showed that NS resuscitation deteriorated red blood cell (RBC) deformability compared with the SHOCK group. The HS group showed improved RBC deformability compared with the NS group, although the differences were not statistically significant. There were significant improvements of RBC deformability at all shear rates in the HSD group compared with the NS group. Whole blood and plasma viscosities decreased significantly in the SHOCK group compared with the SHAM group. At shear rates of 60 and 150 s(-1), the NS group decreased whole blood viscosity compared with the SHOCK group. The HSD group showed elevated plasma viscosity compared with the SHOCK, NS and HS groups.

CONCLUSION

These results suggested that at the early stage of hemorrhagic shock resuscitation, hypertonic-hyperoncotic resuscitation could improve RBC deformability compared with isotonic crystalloid resuscitation. Dextran 70 could elevate plasma viscosity to nearly baseline level. These effects of hypertonic-hyperoncotic resuscitation could be beneficial to maintain microcirculation.

Optimal hemoglobin concentration in patients with subarachnoid hemorrhage, acute ischemic stroke and traumatic brain injury

PURPOSE OF REVIEW

The review outlines recent clinical and experimental studies regarding the effects of red blood-cell transfusion on clinical outcome in neurocritical patients, including patients with subarachnoid hemorrhage, acute ischemic stroke and traumatic brain injury. Optimal hemoglobin transfusion trigger and the role of other transfusion indicators for neurocritical patients are discussed.

RECENT FINDINGS

Acute anemia (hemoglobin levels near 7 g/dl) is well tolerated by healthy subjects, but extreme anemia might negatively affect clinical outcome of neurocritical patients. Conversely, high hemoglobin levels, attained by means other than red blood-cell transfusion, improve clinical outcome, whereas red blood-cell transfusion is associated with poorer clinical outcome (mortality, length of stay and disability) in patients presenting subarachnoid hemorrhage, acute ischemic stroke and traumatic brain injury. Studies defining the optimal hemoglobin concentration in neurocritical patients are lacking, but a restrictive transfusion policy seems to be safe and is often recommended. In the near future, signals coming from the brain, such as brain tissue oxygen tension and regional cerebral oxygen saturation, might potentially be developed into transfusion triggers.

SUMMARY

Both severe anemia and red blood-cell transfusion may negatively influence clinical outcome in neurocritical patients. Acceptance of low hemoglobin concentrations may be justified by avoiding negative transfusion effects. No evidence-based transfusion trigger in neurocritical patients can be recommended.

Intermittent hypoxia modulates nitric oxide-dependent vasodilation and capillary perfusion during ischemia-reperfusion-induced damage

The microvascular function of nitric oxide (NO) during ischemia-reperfusion (I/R) in intermittent hypoxia (IH)-pretreated hamsters was analyzed using 20 mg/kg of the nonselective NO inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME) and 5 mg/kg of the preferential inducible NO inhibitor S-methylisothiourea sulphate (SMT) injected before I/R. Studies were made in the hamster cheek pouch microcirculation (intravital fluorescence microscopy). IH consisted of 6 min of 8% O(2) breathing followed by 6 min of 21% O(2) for every 8 h for 21 days. Normoxia controls (NCs) were exposed to room air for the same period. The effects were characterized in terms of systemic hemodynamics, diameter, flow, wall shear stress in arterioles, capillary perfusion, and the concentrations of thiobarbituric acid-reactive substances (TBARS) and plasma NO, assessed as nitrite/nitrate (NOx) levels. IH did not change arterial blood pressure and increased hematocrit and shear stress. IH increased NOx and TBARS levels and reduced arterial diameter, blood flow, and capillary perfusion versus the NC. Conversely, TBARS and NOx were lower during I/R in IH-pretreated hamsters, resulting in vasodilation and the increase of capillary perfusion and shear stress. After IH, capillary perfusion was reduced by 24% (2.3%) and enhanced by 115% (1.7%) after I/R (P < 0.05). Both modalities of NO blockade decreased NOx generation and increased TBARS versus IH. l-NAME and SMT induced a significant decrease in arteriolar diameter, blood flow, and capillary perfusion (P < 0.05). l-NAME enhanced TBARS more than SMT and aggravated I/R damage. In conclusion, we demonstrated that preconditioning with IH greatly reduces oxidative stress and stimulates NO-induced vasodilation during I/R injury, thus maintaining capillary perfusion.