Transfusion trigger trial for functional outcomes in cardiovascular patients undergoing surgical hip fracture repair (FOCUS)

Transfusion thresholds and other strategies for guiding allogeneic red blood cell transfusion

BACKGROUND

Most clinical practice guidelines recommend restrictive red cell transfusion practices, with the goal of minimising exposure to allogeneic blood (from an unrelated donor). The purpose of this review is to compare clinical outcomes in patients randomised to restrictive versus liberal transfusion thresholds (triggers).

OBJECTIVES

To examine the evidence for the effect of transfusion thresholds on the use of allogeneic and/or autologous blood, and the evidence for any effect on clinical outcomes.

SEARCH STRATEGY

Trials were identified by: computer searches of the Cochrane Central Register of Controlled Trials (the Cochrane Library Issue 3, 2009), OVID MEDLINE (1966 to August 2009), Current Contents (1993 to November 2004), and the Web of Science (2004 to August 2009). References in identified trials and review articles were checked and experts contacted to identify any additional trials.

SELECTION CRITERIA

Controlled trials in which patients were randomised to an intervention group or to a control group. Trials were included where intervention groups were assigned on the basis of a clear transfusion 'trigger', described as a haemoglobin (Hb) or haematocrit (Hct) level below which an RBC transfusion was to be administered.

DATA COLLECTION AND ANALYSIS

Relative risks of requiring allogeneic blood transfusion, transfused blood volumes and other clinical outcomes were pooled across trials, using a random effects model. The risk of bias was assessed.

MAIN RESULTS

Seventeen trials involving a total of 3746 patients were identified. Restrictive transfusion strategies reduced the risk of receiving a red blood cell (RBC) transfusion by a relative 37% (RR=0.63; 95% CI 0.54 to 0.74). This equates to an average absolute risk reduction (ARR) of 33% (95% CI 21% to 45%). The volume of RBCs transfused was reduced on average by 0.75 units (95% CI 0.20 to 1.30 units). However, heterogeneity between trials was statistically significant (P<0.001; I²≥74%) for these outcomes. Restrictive transfusion strategies did not appear to impact on the rate of adverse events compared to liberal transfusion strategies (i.e. mortality, cardiac events, myocardial infarction, stroke, pneumonia and thromboembolism). Restrictive transfusion strategies were associated with a statistically significant reduction in the rates of infection (RR=0.76; 95% CI 0.60 to 0.97). The use of restrictive transfusion strategies did not reduce hospital or intensive care length of stay.

AUTHORS' CONCLUSIONS

The existing evidence supports the use of restrictive transfusion triggers in patients who are free of serious cardiac disease. The effects of conservative transfusion triggers on functional status, morbidity and mortality, particularly in patients with cardiac disease, need to be tested in further large clinical trials. In countries with inadequate screening of donor blood, the data may constitute a stronger basis for avoiding transfusion with allogeneic red cells.

The optimal hematocrit

Nearly 15 million units of packed red blood cells and whole blood are transfused annually in the United States alone. Until recently, the major risks from blood transfusion were thought to be transmission of viral infections, and overall, blood transfusion was believed by most providers to be safe. A safe hemoglobin threshold above which red cell transfusion is clearly unnecessary has not been established. This article addresses the numerous problems that surround the use and consequences of blood transfusion, such as hemoglobin and hematocrit levels, oxygenation, storage time, immunomodulation, infection, and anemia. The relevant literature is comprehensively reviewed.

Blood still kills: six strategies to further reduce allogeneic blood transfusion-related mortality

After reviewing the relative frequency of the causes of allogeneic blood transfusion-related mortality in the United States today, we present 6 possible strategies for further reducing such transfusion-related mortality. These are (1) avoidance of unnecessary transfusions through the use of evidence-based transfusion guidelines, to reduce potentially fatal (infectious as well as noninfectious) transfusion complications; (2) reduction in the risk of transfusion-related acute lung injury in recipients of platelet transfusions through the use of single-donor platelets collected from male donors, or female donors without a history of pregnancy or who have been shown not to have white blood cell (WBC) antibodies; (3) prevention of hemolytic transfusion reactions through the augmentation of patient identification procedures by the addition of information technologies, as well as through the prevention of additional red blood cell alloantibody formation in patients who are likely to need multiple transfusions in the future; (4) avoidance of pooled blood products (such as pooled whole blood-derived platelets) to reduce the risk of transmission of emerging transfusion-transmitted infections (TTIs) and the residual risk from known TTIs (especially transfusion-associated sepsis [TAS]); (5) WBC reduction of cellular blood components administered in cardiac surgery to prevent the poorly understood increased mortality seen in cardiac surgery patients in association with the receipt of non-WBC-reduced (compared with WBC-reduced) transfusion; and (6) pathogen reduction of platelet and plasma components to prevent the transfusion transmission of most emerging, potentially fatal TTIs and the residual risk of known TTIs (especially TAS).

Anemia in the preoperative patient

Anemia is commonly encountered in the preoperative patient. Determination of the cause of the anemia can affect perioperative surgical and medical management and outcome. Red blood cell transfusions are often administered during the perioperative time period in patients with preoperative anemia, although evidence to support the optimal transfusion threshold is limited. The authors review the evaluation of anemia and evidence regarding perioperative blood transfusions. Recommendations on the treatment of anemia, including perioperative blood transfusions, are outlined.

Blood transfusion for the treatment of acute anaemia in inflammatory bowel disease and other digestive diseases

Allogeneic blood transfusion (ABT) is frequently used as the first therapeutic option for the treatment of acute anaemia in patients with inflammatory bowel disease (IBD), especially when it developed due to gastrointestinal or perioperative blood loss, but is not risk-free. Adverse effects of ABT include, but are not limited to, acute hemolytic reaction (wrong blood or wrong patient), febrile non-hemolytic transfusional reaction, bacterial contamination, transfusion-related acute lung injury, transfusion associated circulatory overload, transfusion-related immuno-modulation, and transmission of almost all infectious diseases (bacteria, virus, protozoa and prion), which might result in increased risk of morbidity and mortality. Unfortunately, the main physiological goal of ABT, i.e. to increase oxygen consumption by the hypoxic tissues, has not been well documented. In contrast, the ABT is usually misused only to increase the haemoglobin level within a fixed protocol [mostly two by two packed red blood cell (PRC) units] independently of the patient’s tolerance to normovolemic anaemia or his clinical response to the transfusion of PRC units according to a “one-by-one” administration schedule. Evidence-based clinical guidelines may promote best transfusion practices by implementing restrictive transfusion protocols, thus reducing variability and minimizing the avoidable risks of transfusion, and the use of autologous blood and pharmacologic alternatives. In this regard, preoperative autologous blood donation (PABD) consistently diminished the frequency of ABT, although its contribution to ABT avoidance is reduced when performed under a transfusion protocol. In addition, interpretation of utility of PABD in surgical IBD patients is hampered by scarcity of published data. However, the role of autologous red blood cells as drug carriers is promising. Finally, it must be stressed that a combination of methods used within well-constructed protocols will offer better prospects for blood conservation in selected IBD patients undergoing elective surgery.

Anemia in the preoperative patient

Anemia is commonly encountered in the preoperative patient. Determination of the cause of the anemia can affect perioperative surgical and medical management and outcome. Red blood cell transfusions are often administered during the perioperative time period in patients with preoperative anemia, although evidence to support the optimal transfusion threshold is limited. The authors review the evaluation of anemia and evidence regarding perioperative blood transfusions. Recommendations on the treatment of anemia, including perioperative blood transfusions, are outlined.

Perioperative anemia in the elderly

Anemia is characterized by less than the normal number of red blood cells (RBCs) (as a result of underproduction, increased loss, or destruction) or decreased quantity of hemoglobin (Hgb) in the blood, thereby reducing the blood's oxygen-carrying capacity.

Guidelines for the transfusion of red cells

The following recommendations, which aim at standardising and rationalising clinical indications for the transfusion of red cells in Belgium, were drawn up by a working group of the Superior Health Council. To this end, the Superior Health Council organised an expert meeting devoted to "Guidelines for the transfusion of red cells" in collaboration with the Belgian Hematological Society. The experts discussed the indications for red cell transfusions, the ideal red cell concentrate, the practical issues of administering red cells, and red cell transfusions in patients in a critical condition. The recommendations formulated by the experts were validated by the working group with the purpose of harmonising red cell transfusion in Belgian hospitals.

Transfusion trigger in critically ill patients: has the puzzle been completed?

In stable critically ill children, the adoption of a restrictive transfusion strategy based on a predefined hemoglobin threshold of 7 g/dl significantly decreased transfusion requirements without affecting outcome. These results strengthen previous observations made in volume resuscitated adults when a similar blood transfusion strategy was used. It also indirectly corroborates studies reporting the beneficial effects of leukoreduction of red blood cell (RBC) transfusion units on patient outcome. This study indicated that the maintenance of a higher hemoglobin concentration with RBC transfusion in an attempt to increase tissue oxygen delivery is not associated with a clinical benefit. This may be related to the storage process, which could affect the ability of RBCs to transport and deliver oxygen to the tissues. This point, however, remains controversial. It should also be remembered that increasing hemoglobin concentration will not always result in a greater oxygen delivery, as transfusion related increased blood viscosity could be associated with a reduction in blood flow. Further research should compare a symptomatic transfusion strategy to a hemoglobin-based strategy on the outcome of high risk patients.

Commentary: is it safe to limit allogeneic red blood cell transfusions to neonates?

Two randomized clinical trials, conducted independently, have reported results of neonates transfused with red blood cells (RBCs) given per either liberal (relatively high pretransfusion blood hematocrit levels) or restrictive (relatively low pretransfusion blood hematocrit levels) transfusion programs. Both found fewer RBC transfusions given per restrictive programs and comparable outcomes for several clinical endpoints. However, the Iowa trial found significantly more problems with apnea, intraparenchymal brain hemorrhage and periventricular leukomalacia in infants transfused per the restrictive program - findings not found by the Canadian trial. A critical analysis of both trials and possible reasons for the discrepant findings are discussed. Until definitive data are reported by additional studies, it seems prudent not to severely restrict/limit allogeneic RBC transfusions to neonates - except in approved investigational settings.