Hemodynamic oxygen transport and 2,3-diphosphoglycerate changes after transfusion of patients in acute respiratory failure

2,3-Diphosphoglyceric Acid Alleviating Hypoxic-Ischemic Brain Damage through p38 MAPK Modulation

Neonatal hypoxic-ischemic encephalopathy (HIE) is a critical condition characterized by significant brain damage due to insufficient blood flow and oxygen delivery at birth, leading to high rates of neonatal mortality and long-term neurological deficits worldwide. 2,3-Diphosphoglyceric acid (2,3-DPG), a small molecule metabolite prevalent in erythrocytes, plays an important role in regulating oxygen delivery, but its potential neuroprotective role in hypoxic-ischemic brain damage (HIBD) has yet to be fully elucidated. Our research reveals that the administration of 2,3-DPG effectively reduces neuron damage caused by hypoxia-ischemia (HI) both in vitro and in vivo. We observed a notable decrease in HI-induced neuronal cell apoptosis, attributed to the downregulation of Bax and cleaved-caspase 3, alongside an upregulation of Bcl-2 expression. Furthermore, 2,3-DPG significantly alleviates oxidative stress and mitochondrial damage induced by oxygen-glucose deprivation/reperfusion (OGD/R). The administration of 2,3-DPG in rats subjected to HIBD resulted in a marked reduction in brain edema and infarct volume, achieved through the suppression of neuronal apoptosis and neuroinflammation. Using RNA-seq analysis, we validated that 2,3-DPG offers protection against neuronal apoptosis under HI conditions by modulating the p38 MAPK pathway. These insights indicated that 2,3-DPG might act as a promising novel therapeutic candidate for HIE.

Systematic Review and Meta-Analysis of Effects of Transfusion on Hemodynamic and Oxygenation Variables

OBJECTIVES

RBC transfusions can increase oxygen availability to the tissues, but studies have provided conflicting results. The objectives of this study were, therefore, to evaluate, using systematic review and meta-analysis, the effects of transfusion on hemodynamic/oxygenation variables in patients without acute bleeding.

DATA SOURCES

PubMed, Scopus, Cochrane Database of Systematic Reviews, and Embase from inception until June 30, 2019.

STUDY SELECTION

All articles that reported values of prespecified hemodynamic or oxygenation variables before and after RBC transfusion.

DATA EXTRACTION

Publication year, number of patients, number of transfusions and the type of population studied, hemodynamic and oxygenation data (heart rate, cardiac index, mixed venous oxygen saturation or central venous oxygen saturation, oxygen delivery index, oxygen consumption index, oxygen extraction ratio, arteriovenous oxygen difference and arterial blood lactate) before and after transfusion. We performed a meta-analysis for each variable for which there were sufficient data to estimate mean differences. We also performed subgroup analyses comparing septic with nonseptic patients.

DATA SYNTHESIS

We retrieved 6,420 studies; 33 met the inclusion criteria, 14 of which were in patients with sepsis. In the meta-analysis, the estimated mean differences and 95% CIs comparing the periods before and after transfusion were -0.0 L/min/m (-0.1 to 0.1 L/min/m) (p = 0.86) for cardiac index; -1.8 beats/min (-3.7 to 0.1 beats/min) (p = 0.06) for heart rate; 96.8 mL/min/m (71.1-122.5 mL/min/m) (p < 0.01) for oxygen delivery index; 2.9% (2.2-3.5%) (p < 0.01) for mixed venous oxygen saturation or central venous oxygen saturation; -3.7% (-4.4% to -3.0%) (p < 0.01) for oxygen extraction ratio; and 4.9 mL/min/m (0.9-9.0 mL/min/m) (p = 0.02) for oxygen consumption index. The estimated mean difference for oxygen consumption index in the patients with sepsis was 8.4 mL/min/m (2.3-14.5 mL/min/m; p = 0.01).

CONCLUSIONS

Transfusion was not associated with a decrease in mean cardiac output or mean heart rate. The increase in mean oxygen delivery following transfusion was associated with an increase in mean oxygen consumption after transfusion, especially in patients with sepsis.

Cerebral Oximetry for Cardiac and Vascular Surgery

The technology of transcranial near-infrared spectroscopy (NIRS) for the measurement of cerebral oxygen balance was introduced 25 years ago. Until very recently, there has been only occasional interest in its use during surgical monitoring. Now, however, substantial technologic advances and numerous clinical studies have, at least partly, succeeded in overcoming long-standing and widespread misunderstanding and skepticism regarding its value. Our goals are to clarify common misconceptions about near-infrared spectroscopy and acquaint the reader with the substantial literature that now supports cerebral oximetric monitoring in cardiac and major vascular surgery.

Efficacy and safety of fondaparinux versus enoxaparin in patients undergoing percutaneous coronary intervention treated with the glycoprotein IIb/IIIa inhibitor tirofiban

BACKGROUND

In worldwide, the mortality rate of acute myocardial infarction (AMI) raises year by year. Although the applications of percutaneous coronary intervention (PCI) and anticoagulants effectively reduce the mortality of patients with acute coronary syndrome (ACS), but also increase the incidence of bleeding. Therefore, drugs with stable anticoagulant effects are urgently required.

METHODS

We enrolled 894 patients with acute coronary syndrome who underwent percutaneous coronary intervention in Shenyang Northern Hospital from February 2010 to May 2012; 430 patients were included in the fondaparinux group (2.5 mg/d), and 464 were included in the enoxaparin group (1 mg/kg twice daily). Fondaparinux and enoxaparin were applied for 3-7 days. All patients were treated with tirofiban (10 μg/kg for 3 min initially and 0.15 μg/(kg · min) for 1 to 3 days thereafter). The primary efficacy endpoint was the incidence of a major adverse cerebrovascular or cardiovascular event. The primary safety endpoint was bleeding within 30 days and 1 year after percutaneous coronary intervention.

RESULTS

One-year data were available for 422 patients in the fondaparinux group and for 453 in the enoxaparin group. The incidence of a major adverse cerebrovascular or cardiovascular event (10.9 % vs 12.6 %, P = 0.433) and cardiac mortality (0.5 % vs 1.5 %, P = 0.116) were generally lower in the fondaparinux group than in the enoxaparin group, although the differences were not significant. Compared with the enoxaparin group, the fondaparinux group had a significantly decreased rate of bleeding at 30 days (0.9 % vs 2.8 %) and 1 year (2.4 % vs 5.4 %). In addition, the rate of major bleeding events was lower in the fondaparinux group, but this difference was not significant (0.2 % vs 0.9 %, 0.2 % vs 1.1 %).

CONCLUSIONS

In tirofiban-treated patients with acute coronary syndrome undergoing percutaneous coronary intervention, fondaparinux presented similar efficacy for ischemia events as enoxaparin. However, fondaparinux significantly decreased the incidence of bleeding, thus providing safer anticoagulation therapy.

Can we optimize long-term outcomes in acute respiratory distress syndrome by targeting normoxemia?

Since its original description in 1967, acute respiratory distress syndrome (ARDS) has been recognized as a devastating condition associated with significant morbidity and mortality. Advances in critical care medicine and ARDS management have led to a substantial increase in the number of ARDS survivors. Long-term cognitive impairment after critical illness is a significant public health concern. ARDS survivors frequently experience long-term cognitive impairment, as well as physical impairment, psychiatric morbidity, and reduced health-related quality of life. At present, no intensive care unit-based intervention has been proven to reduce the risk of long-term cognitive impairment after ARDS. To address the urgent need to identify strategies to preserve long-term health, investigators have advocated the measurement of short- and long-term outcomes in clinical trials. Maintaining adequate oxygen delivery to preserve organ function is of vital importance in ARDS management. The optimal target range for arterial oxygenation in ARDS remains unknown, due in part to the challenge to maintain adequate tissue oxygenation and to minimize harm, such as oxygen toxicity. An approach targeted to subnormal oxygenation values (partial pressure of arterial oxygen, 55-80 mm Hg) has emerged as a means to accomplish these aims. In this perspective, we critically evaluate this strategy from short- and long-term perspectives, with a focus on the potential long-term cognitive effects of the strategy. We conclude with a proposal to consider resetting the target range for arterial oxygenation higher (85-110 mm Hg) as a potential strategy to improve the long-term outcomes of ARDS survivors.

Red blood cell transfusion in the neurological ICU

Red blood cell transfusion (RBCT) is a common therapy used in the intensive care unit to treat anemia. However, due to deleterious side effects and questionable efficacy, the clinical benefit of RBCT in patients who are not actively bleeding is unclear. The results of randomized controlled trials suggest there is no benefit to a liberal transfusion practice in general critical care populations. Whether the results of these trials are applicable to brain injured patients is unknown, as patients with primary neurological injury were excluded. This article reviews the efficacy and complications of RBCT, as well as the relationship between RBCT and its outcome in both the general intensive care unit and neurologically critically ill populations.

Heparin plus a glycoprotein IIb/IIIa inhibitor versus bivalirudin monotherapy and paclitaxel-eluting stents versus bare-metal stents in acute myocardial infarction (HORIZONS-AMI): final 3-year results from a multicentre, randomised controlled trial

BACKGROUND

Primary results of the HORIZONS-AMI trial have been previously reported. In this final report, we aimed to assess 3-year outcomes.

METHODS

HORIZONS-AMI was a prospective, open-label, randomised trial undertaken at 123 institutions in 11 countries. Patients aged 18 years or older were eligible for enrolment if they had ST-segment elevation myocardial infarction (STEMI), presented within 12 h after onset of symptoms, and were undergoing primary percutaneous coronary intervention. By use of a computerised interactive voice response system, we randomly allocated patients 1:1 to receive bivalirudin or heparin plus a glycoprotein IIb/IIIa inhibitor (GPI; pharmacological randomisation; stratified by previous and expected drug use and study site) and, if eligible, randomly allocated 3:1 to receive a paclitaxel-eluting stent or a bare metal stent (stent randomisation; stratified by pharmacological group assignment, diabetes mellitus status, lesion length, and study site). We produced Kaplan-Meier estimates of major adverse cardiovascular events at 3 years by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00433966.

FINDINGS

Compared with 1802 patients allocated to receive heparin plus a GPI, 1800 patients allocated to bivalirudin monotherapy had lower rates of all-cause mortality (5·9%vs 7·7%, difference -1·9% [-3·5 to -0·2], HR 0·75 [0·58-0·97]; p=0·03), cardiac mortality (2·9%vs 5·1%, -2·2% [-3·5 to -0·9], 0·56 [0·40-0·80]; p=0·001), reinfarction (6·2%vs 8·2%, -1·9% [-3·7 to -0·2], 0·76 [0·59-0·99]; p=0·04), and major bleeding not related to bypass graft surgery (6·9%vs 10·5%, -3·6% [-5·5 to -1·7], 0·64 [0·51-0·80]; p=0·0001) at 3 years, with no significant differences in ischaemia-driven target vessel revascularisation, stent thrombosis, or composite adverse events. Compared with 749 patients who received a bare-metal stent, 2257 patients who received a paclitaxel-eluting stent had lower rates of ischaemia-driven target lesion revascularisation (9·4%vs 15·1%, -5·7% [-8·6 to -2·7], 0·60 [0·48-0·76]; p<0·0001) after 3 years, with no significant differences in the rates of death, reinfarction, stroke or stent thrombosis. Stent thrombosis was high (≥4·5%) in both groups.

INTERPRETATION

The effectiveness and safety of bivalirudin monotherapy and paclitaxel-eluting stenting are sustained at 3 years for patients with STEMI undergoing primary percutaneous coronary intervention.

FUNDING

Boston Scientific and The Medicines Company.

Impact of anemia on clinical outcomes of patients with ST-segment elevation myocardial infarction in relation to gender and adjunctive antithrombotic therapy (from the HORIZONS-AMI trial)

The aim of this study was to assess the impact of baseline anemia on the outcomes of patients with ST elevation myocardial infarctions who underwent primary percutaneous coronary intervention in relation to contemporary adjunctive antithrombotic therapy and gender. In the Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction (HORIZONS-AMI) trial, patients were randomized to bivalirudin alone or to unfractionated heparin plus a glycoprotein IIb/IIIa inhibitor before primary percutaneous coronary intervention. Outcomes were assessed at 30 days and 1 year according to anemia and gender. Baseline anemia was present in 331 of 3,153 patients (10.5%). Patients with versus without baseline anemia had a more than twofold increase in major bleeding at 30 days (13.5% vs 6.7%, p <0.0001) and at 1 year (14.8% vs 7.2%, p <0.0001), an association that on multivariate analysis was independent of gender. Mortality was significantly higher in men with versus without baseline anemia (4.6% vs 1.8% at 30 days, p = 0.003; 8.9% vs 3.0% at 1 year, p <0.0001) but not in women (5.3% vs 3.6% at 30 days, p = 0.42; 7.5% vs 5.9% at 1 year, p = 0.54). On multivariate analysis, anemia independently predicted 1-year all-cause mortality in men but not in women. Bivalirudin compared with unfractionated heparin plus a glycoprotein IIb/IIIa inhibitor resulted in twofold lower rates of all-cause and cardiac mortality and major bleeding in patients without but not in those with baseline anemia. In conclusion, baseline anemia was associated with increased major bleeding and death in patients with ST elevation myocardial infarctions who underwent primary PCI but was a stronger predictor of early and late mortality in men than in women. Paradoxically, in this post hoc analysis, the reductions in major bleeding and mortality in ST elevation myocardial infarction afforded by bivalirudin occurred primarily in patients without baseline anemia.

Bivalirudin in patients undergoing primary angioplasty for acute myocardial infarction (HORIZONS-AMI): 1-year results of a randomised controlled trial

BACKGROUND

In the HORIZONS-AMI trial, patients with acute ST-segment elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention (PCI) who were treated with the thrombin inhibitor bivalirudin had substantially lower 30-day rates of major haemorrhagic complications and net adverse clinical events than did patients assigned to heparin plus a glycoprotein IIb/IIIa inhibitor (GPI). Here, we assess whether these initial benefits were maintained at 1 year of follow-up.

METHODS

Patients aged 18 years or older were eligible for enrolment in this multicentre, open-label, randomised controlled trial if they had STEMI, presented within 12 h after the onset of symptoms, and were undergoing primary PCI. 3602 eligible patients were randomly assigned by interactive voice response system in a 1:1 ratio to receive bivalirudin (0.75 mg/kg intravenous bolus followed by 1.75 mg/kg per h infusion; n=1800) or heparin plus a GPI (control; 60 IU/kg intravenous bolus followed by boluses with target activated clotting time 200-250 s; n=1802). The two primary trial endpoints were major bleeding and net adverse clinical events (NACE; consisting of major bleeding or composite major adverse cardiovascular events [MACE; death, reinfarction, target vessel revascularisation for ischaemia, or stroke]). This prespecified analysis reports data for the 1-year follow-up. Analysis was by intention to treat. Patients with missing data were censored at the time of withdrawal from the study or at last follow-up. This trial is registered with ClinicalTrials.gov, number NCT00433966.

FINDINGS

1-year data were available for 1696 patients in the bivalirudin group and 1702 patients in the control group. Reasons for participant dropout were loss to follow-up and withdrawal of consent. The rate of NACE was lower in the bivalirudin group than in the control group (15.6%vs 18.3%, hazard ratio [HR] 0.83, 95% CI 0.71-0.97, p=0.022), as a result of a lower rate of major bleeding in the bivalirudin group (5.8%vs 9.2%, HR 0.61, 0.48-0.78, p<0.0001). The rate of MACE was similar between groups (11.9%vs 11.9%, HR 1.00, 0.82-1.21, p=0.98). The 1-year rates of cardiac mortality (2.1%vs 3.8%, HR 0.57, 0.38-0.84, p=0.005) and all-cause mortality (3.5%vs 4.8%, HR 0.71, 0.51-0.98, p=0.037) were lower in the bivalirudin group than in the control group.

INTERPRETATION

In patients with STEMI undergoing primary PCI, anticoagulation with bivalirudin reduced the rates of net adverse clinical events and major bleeding at 1 year compared with treatment with heparin plus a GPI. This finding has important clinical implications for the selection of optimum treatment strategies for patients with STEMI.

FUNDING

Cardiovascular Research Foundation, with unrestricted grant support from Boston Scientific Corporation and The Medicines Company.

Prognostic impact of blood transfusion after primary angioplasty for acute myocardial infarction: analysis from the CADILLAC (Controlled Abciximab and Device Investigation to Lower Late Angioplasty Complications) Trial

OBJECTIVES

We sought to determine the relationship between red blood cell (RBC) transfusion and clinical outcomes in patients undergoing primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI).

BACKGROUND

The implications of RBC transfusion in patients undergoing primary PCI for AMI have not been evaluated.

METHODS

Clinical outcomes of patients from the prospective, randomized CADILLAC (Controlled Abciximab and Device Investigation to Lower Late Angioplasty Complications) trial were analyzed by administration of in-hospital RBC transfusion not related to coronary artery bypass surgery.

RESULTS

Of 2,060 randomized patients, 82 (3.98%) received RBC transfusion during the index hospitalization, including 33 (1.60%) with moderate/severe bleeding and 49 (2.38%) without overt major bleeding. Transfusion was independently associated with baseline anemia (odds ratio [95% confidence interval]: 4.44 [2.60 to 7.58], p < 0.0001), older age (1.03 [1.01 to 1.06], p = 0.002), triple-vessel disease (2.54 [1.47 to 4.38], p = 0.0008), and female sex (1.04 [1.02 to 1.06], p = 0.0008). Patients transfused versus not transfused had significantly higher rates of 1-year mortality (23.9% vs. 3.4%), disabling stroke (2.5% vs. 0.5%), reinfarction (7.0% vs. 2.2%), and composite major adverse cardiac events (41.0% vs. 16.6%) (all p values < 0.01). After multivariable adjustment for potential confounders including transfusion propensity, RBC transfusion was independently associated with mortality at 30 days (hazards ratio: 4.71, p = 0.0005) and 1 year (hazards ratio: 3.16, p = 0.0005).

CONCLUSIONS

An RBC transfusion after primary PCI in AMI may be harmful, which is consistent with the findings from other studies after PCI in the noninfarct setting. Alternatively, RBC transfusion may be a marker of markedly increased risk. Randomized studies are warranted to determine the optimal threshold for RBC transfusion in patients with AMI undergoing mechanical reperfusion therapy.

Blood tranfusion in critically ill patients: state of the art

Anemia is one of the most common abnormal findings in critically ill patients, and many of these patients will receive a blood transfusion during their intensive care unit stay. However, the determinants of exactly which patients do receive transfusions remains to be defined and have been the subject of considerable debate in recent years. Concerns and doubts have emerged regarding the benefits and safety of blood transfusion, in part due to the lack of evidence of better outcomes resulting from randomized studies and in part related to the observations that transfusion may increase the risk of infection. As a result of these concerns and of several studies suggesting better or similar outcomes with a lower transfusion trigger, there has been a general tendency to decrease the transfusion threshold from the classic 10 g/dL to lower values. In this review, we focus on some of the key studies providing insight into current transfusion practices and fueling the current debate on the ideal transfusion trigger.

Congestive heart failure-related anemia and a role for erythropoietin

Congestive heart failure (CHF) is a common clinical problem, especially affecting the elderly. Current strategies of neurohormonal blockade with medications like angiotensin converting enzyme inhibitors have improved morbidity and mortality, but further improvement in outcomes requires new strategies. Both anemia and chronic renal disease commonly accompany congestive heart failure; their close relationship, in which one disease exacerbates the other, has been termed the cardio-renal-anemia syndrome. Correction of anemia in CHF patients using recombinant erythropoietin is feasible; small studies suggest that anemic congestive heart failure patients may have improved morbidity with this therapy. Recent animal and human studies of erythropoietin have shown that its benefit may be derived from both hematological and newly discovered non-hematological properties. Anemia might soon be considered a modifiable risk factor for optimal CHF management.

The Impact of Anemia in Patients With Respiratory Failure

Healthy individuals are able to tolerate profound, short-term decreases in hemoglobin levels and oxygen saturation without serious consequences, but critically ill patients in respiratory failure lack the necessary reserve capacity to preserve tissue oxygenation. The development of progressive anemia in ICU patients has led to much interest and debate about transfusion practices, yet optimal hemoglobin levels and how they should be achieved remain unclear. Animal and human studies regarding critical oxygen delivery provide the rationale for optimizing hemoglobin levels and supporting cardiovascular function during respiratory failure. Theoretically, the oxygen-carrying benefit of RBCs should hasten recovery from respiratory failure, and transfusions would therefore be expected to shorten the duration of mechanical ventilation. However, evidence to the contrary has been reported. Controversies related to transfusions and their inability to improve outcomes suggest that further research regarding transfusion alternatives is needed, especially in anemic patients with respiratory failure.

Physiologic aspects of anemia

The most important adaptive responses from a physiological stance involved the cardiovascular system, consisting in particular of elevation of the cardiac output and its redistribution to favor the coronary and cerebral circulations, at the expense of the splanchnic vascular beds. The evidence regarding these physiological responses, especially in experimental studies that permit the control of many variables, is particularly powerful and convincing. On the other hand, there is a remarkable lack, in quality and quantity, of clinical studies addressing how normal physiological adaptive responses may be affected by a variety of diseases and conditions that often accompany and may complicate anemia, and interactions with other such compounding variables as age and different patient populations. For these reasons, it is not possible to offer guidelines on how to increase, maintain, or even to determine optimal DO2 in high-risk patients and how best transfusion strategies might be used under these conditions. From the brief review of physiological principles and the strong consensus in the literature, it is evident that cardiac function must be a central consideration in decisions regarding transfusion in anemia, because of the critical role it plays in assuring adequate oxygen supply of all vital tissues. Particular attention should be paid to the possible presence of CAD or incipient or cardiac failure, as these conditions may require careful transfusions to improve DO2 at levels that may not necessitate such interventions when cardiac disease is absent. Although the cerebral circulation also serves an obligate aerobic organ unable to tolerate significant hypoxia, there is little convincing evidence to support the notion that cerebral ischemia is aggravated by anemia and that this can be prevented by improved DO2 through rapid correction of anemia. Consequently, the arguments favoring transfusions in the presence of ischemic heart disease do not appear to apply to occlusive cerebrovascular disease. Because firm evidence is lacking on the interactions of concurrent diseases and anemia in various patient populations, understanding of the physiological consequences of anemia, and of the diseases concerned, is useful but not fully sufficient to provide firm and rational guidance to transfusion practice in specific complex clinical instances. A good deal of clinical and experimental investigation is required to support fully rational and comprehensive guidelines. In the meantime, prudent and conservative management, based on awareness of risks and sound understanding of the normal and pathological physiology, must remain the guiding principle.

Efficacy of red blood cell transfusion in the critically ill

This article has evaluated the published data regarding the efficacy of RBC transfusions in the critically ill. Taken together, these studies generally support conservative RBC transfusion strategies in critical care to reduce the risk of transfusion-related adverse effects. The TRICC trial has established the safety ofa restrictive transfusion strategy, suggesting that physicians could minimize exposure to allogeneic RBCs by lowering their transfusion threshold. Further research will add to the generalizability of this study and explore the possible mechanism to explain why RBC transfusions do not improve outcomes in the critically ill. Additional studies will be necessary to determine the effects of RBC storage time and the presence of allogeneic leukocytes in allogeneic RBC. The following conclusions are evident: 1. RBC transfusion does not improve tissue oxygen consumption consistently in critically ill patients, either globally or at the level of the micro-circulation. 2. RBC transfusion is not associated with improvements in clinical outcome in the critically ill and may result in worse outcomes in some patients. 3. Specific factors that identify patients who will improve from RBC transfusion are difficult to identify. 4. Lack of efficacy of RBC transfusion likely is related to storage time, increased endothelial adherence of stored RBCs, nitric oxide binding by free hemoglobin in stored blood, donor leukocytes, host inflammatory response, and reduced red cell deformability.

Assessment of cerebral tissue oxygenation in patients with sickle cell disease: effect of transfusion therapy

This study used spatially resolved transcranial near-infrared spectroscopy (NIRS) to compare brain tissue oxygenation in sickle cell disease (SCD) patients with that of healthy children. In addition, NIRS was used to measure the dynamic response of cerebral oxygen balance to erythrocytapheresis. Transcranial NIRS measurements were obtained from 25 children with SCD who were not receiving transfusion or hydroxyurea therapy (NT-SCD). These patients were divided into two subgroups, those with mild (n = 10) or severe (n = 15) SCD symptoms. In addition, NIRS measurements were performed in 16 SCD patients with severe disease maintained on long-term erythrocytapheresis (T-SCD) and in 35 control children. The lowest mean brain tissue oxygen saturation occurred in the NT-SCD subgroup with severe symptoms (48 +/- 9%; P < 0.001 vs. control). NT-SCD patients with mild symptoms had higher saturation (62 +/- 8%; P < 0.001 vs. control), while the highest appeared in the control group (72 +/- 7%). In T-SCD patients, however, brain tissue oxygen saturations were higher than severely symptomatic NT-SCD children and similar to mildly symptomatic NT-SCD children (65 +/- 7%). Non-invasive measurements of brain tissue oxygenation with NIRS revealed that abnormal oxygen saturation levels in SCD patients correlated with the severity of their clinical manifestations. Additionally, cerebral oxygen balance seems to be favorably affected by erythro-cytapheresis.

The effect of the transfusion of stored RBCs on intestinal microvascular oxygenation in the rat

BACKGROUND

Although it is known that the transfusion of stored RBCs does not always improve tissue O(2) consumption under conditions of limited tissue oxygenation, the efficiency of O(2) delivery to the microcirculation by stored RBCs has never been determined.

STUDY DESIGN AND METHODS

In a rat hemorrhagic shock model, the effects of resuscitation with fresh or 28-day-old RBCs stored in CPD plasma, saline-adenine-glucose-mannitol, and CPDA-1 plasma were investigated. Systemic hemodynamic and intestinal oxygenation measures were monitored. Intestinal microvascular PO(2) was determined with the O(2)-dependent quenching of palladium-porphyrin phosphorescence, and the RBC deformability was measured with a Laser-assisted optic rotational cell analyzer.

RESULTS

Hemodynamic and oxygenation measures were significantly decreased during hemorrhagic shock. Intestinal oxygen consumption and mesenteric venous pO(2) were restored with the transfusion of both fresh and stored RBCs, except for CPD-stored RBCs. The intestinal microvascular pO(2) improved only with the transfusion of fresh RBCs. Deformability of the stored RBCs was significantly decreased.

CONCLUSION

In contrast to that of fresh RBCs, the transfusion of stored RBCs did not restore the microcirculatory oxygenation, possibly because of impaired O(2) unloading, but, except for CPD-stored RBCs, the storage-induced changes were not enough to impair intestinal VO(2) and mesenteric venous pO(2).

A practical approach to achieving bloodless surgery

The term bloodless surgery refers to the practice of performing surgical procedures without the use of allogenic blood and avoiding the use of stored blood, including autologous blood, entirely. This article reviews the scientific and clinical literature regarding bloodless surgery and describes the application of a full-service, bloodless program within a community hospital.

Effect of hematocrit on regional oxygen delivery and extraction in an adult respiratory distress syndrome animal model

BACKGROUND

The purpose of this prospective, randomized, controlled study was to investigate the effects of hematocrit (Hct) on regional oxygen delivery and extraction following induction of adult respiratory distress syndrome (ARDS) in an animal model.

METHODS

Animals were instrumented to monitor central venous pressure (CVP), systemic mean arterial pressure (MAP), pulmonary artery occlusion pressure (PAOP), and cardiac output (CO) and to measure blood flow in the renal, hepatic, and superior mesenteric arteries and portal vein. ARDS was induced, positive end expiratory pressure (PEEP) applied and CO was maximized with volume loading and epinephrine infusion. Data were acquired at baseline (BL) and at Hct levels ranging from 25% to 50%.

RESULTS

Systemic DO(2) increased steadily and significantly with increased Hct. Systemic O(2) extraction ratio (O(2)ER) decreased significantly with increasing Hct until a threshold value of 40%, after which further increases in Hct did not cause a statistically significant decrease in O(2)ER. Similarly, renal and hepatic DO(2) increased and O(2)ER decreased in a statistical significant manner with transfusions up to a Hct of 35%. In the splanchnic circulation blood transfusions did not cause any statistically significant increase in DO(2), and O(2)ER showed no decrease after an Hct of 35%. Systemic, renal, hepatic, and splanchnic VO(2) were not affected by changes in Hct. Blood viscosity decreased from a baseline value of 2.9+/-0.2 centipoise at a Hct of 38% to 2.3+/-0.1 centipoise at a Hct of 25% (P<0.05). Viscosity increased progressively with increasing hematocrits and reached the value of 4.2+/-0.2 centipoise at an Hct of 50% (P<0.05 versus Hct 30%, 35%, 40%, 45%).

CONCLUSIONS

Based on the results of this non-supply-dependent animal model we conclude that a progressive increase in Hct up to 40% causes a corresponding increase in systemic DO(2) associated with a decrease in O(2)ER. However, there is no improvement in renal, hepatic, and splanchnic DO(2) and O(2)ER after a threshold Hct of 35%. All other factors being the same, an Hct greater than 35% may in fact cause a decrease in blood flow rate and change in blood flow characteristics as a consequence of increased blood kinematic viscosity, which may alter and compromise cellular oxygen transfer.

Mechanisms of improvement in pulmonary gas exchange during isovolemic hemodilution

Severe anemia is associated with remarkable stability of pulmonary gas exchange (S. Deem, M. K. Alberts, M. J. Bishop, A. Bidani, and E. R. Swenson. J. Appl. Physiol. 83: 240-246, 1997), although the factors that contribute to this stability have not been studied in detail. In the present study, 10 Flemish Giant rabbits were anesthetized, paralyzed, and mechanically ventilated at a fixed minute ventilation. Serial hemodilution was performed in five rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; five rabbits were followed over a comparable time. Ventilation-perfusion (VA/Q) relationships were studied by using the multiple inert-gas-elimination technique, and pulmonary blood flow distribution was assessed by using fluorescent microspheres. Expired nitric oxide (NO) was measured by chemiluminescence. Hemodilution resulted in a linear fall in hematocrit over time, from 30 +/- 1.6 to 11 +/- 1%. Anemia was associated with an increase in arterial PO(2) in comparison with controls (P < 0.01 between groups). The improvement in O(2) exchange was associated with reduced VA/Q heterogeneity, a reduction in the fractal dimension of pulmonary blood flow (P = 0.04), and a relative increase in the spatial correlation of pulmonary blood flow (P = 0. 04). Expired NO increased with anemia, whereas it remained stable in control animals (P < 0.0001 between groups). Anemia results in improved gas exchange in the normal lung as a result of an improvement in overall VA/Q matching. In turn, this may be a result of favorable changes in pulmonary blood flow distribution, as assessed by the fractal dimension and spatial correlation of blood flow and as a result of increased NO availability.

Blood transfusion and lung function in chronically anemic patients with severe chronic obstructive pulmonary disease

OBJECTIVE

To study in anemic patients with chronic obstructive pulmonary disease (COPD) whether blood transfusion reduces minute ventilation and work of breathing (WOB).

DESIGN

We prospectively evaluated the minute ventilation and WOB in 20 anemic adults (hemoglobin of <11 g/dL). Ten patients had severe COPD and ten patients were without lung disease. Measurements were made before and after receiving red blood cell transfusion; post-transfusion measurements were made 24 to 36 hrs after the last transfusion.

SETTING

The study was performed in the intensive care unit of a tertiary referral center for home mechanical ventilation and for patients considered difficult to wean from mechanical ventilation.

PATIENTS

Twenty clinically stable patients (12 female, eight male) with chronic anemia were studied. Ten patients with COPD (mean forced expiratory volume in 1 sec: 0.55+/-0.1 [SD] L) were compared with ten patients without lung disease. All participants had adequate renal and left ventricular function.

INTERVENTIONS

Patients received 1 unit of packed red blood cells for each g/dL that their hemoglobin value was less than an arbitrarily defined target value of 11.0 to 12.0 g/dL. Each unit was transfused over 2 hrs and < or =3 units in total was given.

MEASUREMENTS AND MAIN RESULTS

Esophageal pressure was measured from a catheter which was positioned in the middle of the esophagus. Flow was measured using a pneumotachygraph connected to a mouthpiece while a nose clip closed the nostrils during the measurements. From these data, respiratory rate, minute ventilation, and inspiratory resistive WOB were computed. Arterial blood gas values, oxygen saturation, hemoglobin, and hematocrit were also measured, and oxygen content was calculated before and 24 to 36 hrs after transfusion. In patients with COPD, hemoglobin increased from 9.8+/-0.8 to 12.3+/-1.1 g/dL due to a mean transfusion of 2.2+/-0.4 (SD) units of red blood cells. There was a reduction in the mean minute ventilation from 9.9+/-1.0 to 8.2+/-1.2 L/min (p < .0001); correspondingly, WOB decreased from 1.03+/-0.24 to 0.85+/-0.21 WOB/L (p< .0001). The capillary P(CO2) increased from 38.1+/-6.0 to 40.7+/-6.8 torr (5.1+/-0.8 to 5.8+/-0.9 kPa) (p < .05). Similarly, capillary P(O2) changed from 56.9+/-8.9 to 52.8+/-7.0 torr (7.6+/-1.2 to 7.0+/-0.9 kPa) (p < .05). In anemic patients without lung disease, minute ventilation, WOB, and the capillary blood gas values did not change after increase of the hemoglobin by a similar degree.

CONCLUSIONS

We conclude that red blood cell transfusion in anemic patients with COPD leads to a significant reduction of both the minute ventilation and the WOB. In these patients, transfusion may be associated with unloading of the respiratory muscles, but it may also result in mild hypoventilation.

Red cell transfusion therapy in the critical care setting

According to our own experience and published reports the frequency of red cell transfusion in intensive care units is in the range of 0.2 to 0.4 units per patient per day and is dependent upon the local strategy, the patients involved and the kind of surgery performed. The rationale for red cell transfusion is to maintain or restore the oxygen carrying capacity of the blood to avoid tissue hypoxia which occurs when oxygen delivery drops below a certain critical value. Besides bleeding, phlebotomy is also a significant source of blood loss in critically ill patients. According to several recent reviews and consensus articles there is no basis for a fixed indicator for transfusion, such as a haemoglobin concentration of < 100 gL-1. The decision to transfuse has to be made according to the patients individual status. The major adaptive mechanism in response to acute anaemia is an increase in cardiac output and hence blood flow to tissues. As a consequence even moderate degrees of acute anaemia may not be tolerated by patients with cardiac disease, whilst marked anaemia carries a considerable risk of ischaemia in patients with brain lesions or cerebral arterial stenoses. In critically ill patients it has been postulated that supply dependency of oxygen consumption occurs over a wide range of oxygen delivery, far above the critical values of oxygen delivery seen under normal conditions. Maximising oxygen delivery was therefore formulated as a goal in these patients. However, whether pathological supply dependency of oxygen delivery really exists in critically ill patients is still under discussion and recent studies found no benefit in maximising oxygen delivery to this patient group. However, individualised triggers for red blood cell transfusion are adequate for critically ill patients considering their co-morbidities and severity of disease. Finally, the decision to transfuse must also take into account the potential risks (infectious and non-infectious), as well as benefits for the individual patient. In the future, the level of transfusions may be reduced by using blood sparing techniques such as blood withdrawal in closed systems, bedside microchemistry, intravascular monitors, or autotransfusion of drainage blood in intensive care units.

Analysis of P50 and oxygen transport in patients after cardiac surgery

OBJECTIVE

To determine whether standard P50 after cardiac surgery decreases and whether decreased P50 is related to the transfusion of red blood cells (RBCs), acid-base changes, body temperature, oxygen parameters and/or duration of cardiopulmonary bypass (CPB).

DESIGN

Pilot study in cardiac surgery patients.

SETTING

University hospital.

PATIENTS

12 Consecutive elective cardiac surgery patients.

INTERVENTIONS

Blood was taken before surgery, after CPB and in the intensive care unit until 18 h post-operatively. Cardiac output and oxygen consumption were measured. Buffy coat-poor RBCs were transfused, anticoagulated with citrate-phosphate-dextrose buffer and stored in saline-adenine-glucose-mannitol at 4 degrees C, when haemoglobin was < 5.6 mmol.l-1.

MEASUREMENTS AND RESULTS

Standard P50 was calculated from measured partial pressure of oxygen and of carbon dioxide, pH and oxygen saturation in mixed venous blood (SvO2) using the Severinghaus formula. Median length of RBC storage was 25 days. Standard P50 after surgery was significantly lower than baseline value (p = 0.0001). The number of RBC units transfused and duration of CPB were conjointly associated with P50 (R2 = 0.72). Patients who received more RBCs consumed more oxygen.

CONCLUSION

Cardiac surgery patients receiving more RBC units have lower standard P50 and consume more oxygen. P50 decreased more when the CPB took longer. Because a decrease in P50 implies a low ratio of mixed venous oxygen tension (PvO2) to SvO2, a shift in P50 should be taken into account when using SvO2 as a measure of global oxygen availability. When a direct measurement of SvO2 is not available, PvO2 should be used instead of calculated SvO2.

Influence of the cryoprotective agents glycerol and hydroxyethyl starch on red blood cell ATP and 2,3-diphosphoglyceric acid levels

Because hydroxyethyl starch (HAES) is used for volume replacement therapy and as a cryoprotectant for frozen red blood cells (RBCs), this compound, in contrast to glycerol, does not require labor-intensive removal from thawed cells prior to transfusion. We here report the effect of both glycerol and HAES on the RBC organic phosphates ATP and 2,3-diphosphoglyceric acid (2,3-DPG). The CPD-A1-stabilized RBCs of 20 healthy donors (3 females, 17 males) were separately frozen in either 40% glycerol or 6% HAES, of molecular weight 200,000. ATP and 2,3-DPG concentrations were determined in CPD-A1 RBCs before addition of cryoprotectant and in cryopreserved thawed RBCs after 24 h storage at -80 degrees C (glycerol) and -196 degrees C (HAES). It appears that HAES, but not glycerol, significantly reduces ATP concentrations whereas both lead to a reduction of 2,3-DPG concentrations; this reduction was more pronounced with glycerol than with HAES. Experiments with the blood of 6 donors demonstrated that HAES affects autohemolysis by 16%, in contrast to glycerol, after which cryoprotectant autohemolysis was affected by 3.1% only. RBC recoveries were comparable using glycerol or HAES as cryoprotectants. A distinct pattern of reduction of 2,3-DPG levels by glycerol and less by HAES, and of ATP levels by HAES but not by glycerol, emerges. Our findings may be of importance if HAES is to be introduced as a convenient cryoprotectant.

Hemodynamic aspects of multiple organ failure

Multiple organ failure (MOF) secondary to sepsis is associated with a high mortality. A large body of evidence suggests that the disturbed relationship between oxygen supply and oxygen uptake plays an important role in the pathogenesis of MOF. The relationship between oxygen-supply dependency and MOF and the practical implications of the relationship are reviewed. It is concluded that, apart from the all-important eradication of the source of the sepsis, optimizing oxygen transport is the best method of preventing the development of MOF. Since the effects of hemodynamic and ventilatory treatments on oxygen uptake are often unpredictable, the impact of the treatments on oxygen uptake should be evaluated directly.

Right ventricular tissue PO2 in dogs. Effects of hemodilution and acute right coronary artery occlusion

Right ventricular (RV) epicardial tissue oxygen pressure (PtO2) was measured polarographically by means of a platinum multiwire surface electrode on the in situ beating heart of ten anesthetized dogs prior to and after moderate (Hct 28%) normovolemic hemodilution (HD) with dextran 60. In five dogs the effect of acute occlusion of the right coronary artery (RCA) on PtO2 was analyzed. The PtO2 histograms at baseline revealed a bell-shaped configuration and a mean PtO2 of 46.2 +/- 7.1 mm Hg which coincides with the PtO2 on the left ventricle (LV) reported by others. After HD mean PtO2 increased to 51.4 +/- 8.5 mm Hg (P = 0.02) without alterations of the histogram's configuration. Hemodynamics and blood gas analyses were unchanged after HD. RCA ligature was followed by non-uniform changes in the PtO2 pattern. Thus, despite marked differences in external work and O2 consumption, the PtO2 in both RV and LV myocardium are similar at rest. The increase of PtO2 in the RV at reduced Hct values, which is not seen in the LV myocardium, can be related to differences in functional capillary density between both ventricles.