CMAJ/JAMC Special supplement
Background papers

 

Review of published recommendations and guidelines for the transfusion of allogeneic red blood cells and plasma

Lisa Calder,* BScH; Paul C. Hébert,*† MD, FRCPC, MHSc; Anne O. Carter,‡ MD, MSc, FRCPC; Ian D. Graham,† PhD

CMAJ 1997;156(11 suppl):S1-8

*Department of Medicine, University of Ottawa, Ottawa, Ont.; †Clinical Epidemiology Unit, University of Ottawa, Ottawa, Ont.; ‡Canadian Medical Association, Ottawa, Ont.

Correspondence to: Dr. Paul C. Hébert, Department of Medicine, LM-11, Ottawa General Hospital, 501 Smyth Rd., Ottawa ON K1H 8L6

Reprint requests to: Dr. Anne Carter, Director of Health Programs, Canadian Medical Association, 1867 Alta Vista Dr., Ottawa ON K1G 3Y6; fax 613 731-1779; cartea@cma.ca

© 1997 Canadian Medical Association (text and abstract)

Contents
Abstract

Objective: To evaluate published guidelines and recommendations for the transfusion of allogeneic red blood cells and plasma in terms of content and methods.

Evidence: Bibliographic search of MEDLINE database for articles making therapeutic recommendations regarding erythrocyte and plasma transfusion, between January 1966 and July 1996; manual search of bibliographies from relevant reviews, guidelines and textbooks.

Data synthesis: Evaluation focused on how the evidence was identified, selected and incorporated. Therapeutic recommendations were compared and contrasted. Time trends related to transfusion triggers were also examined.

Results: The 59 references that met our criteria consisted of 17 clinical practice guidelines (CPGs) and 42 reviews. Five CPGs addressed the use of allogeneic red blood cells, 4 focused on fresh frozen plasma and 8 did both. All CPGs were based on the recommendations of an expert panel, although no specific consensus process was described. Among the 17 CPGs, only 1 used a computerized literature search and grading of the evidence and the strength of the individual recommendations. None of the CPGs cited or discussed the few available randomized, controlled clinical trials published at least 6 months earlier. For red blood cells, only 1 set of guidelines recommended a transfusion trigger; 6 advocated a range of transfusion thresholds based on clinical judgement; 1 recommended using only clinical judgement; the 5 remaining guidelines did not comment on either. For plasma, guidelines recommended an assessment of the coagulation cascade and the risk of ongoing bleeding before administration.

Conclusions: Although several agencies have published guidelines for the use of red blood cells and plasma, rigorous, evidence-based guidelines in this area are still needed.

[ Contents ]

Introduction

Historically, the hemoglobin concentration or hematocrit value at which physicians transfuse allogeneic blood products during acute anemia, that is, the transfusion trigger or threshold, has been 100 g/L or 30%.1­6 Plasma transfusions to correct coagulation abnormalities (and in the past, to expand intravascular volume) have also been guided by standard protocols and specific triggers rather than an assessment of the individual patient's overall risks and benefits. Since 1985, concerns about the transmission of HIV and other viruses through blood products have significantly modified both real and perceived risks and benefits. Many agencies have responded by issuing clinical practice guidelines (CPGs) advocating a more restrictive approach to the use of allogeneic red blood cells and plasma.7­9

Like most clinical decisions, the administration of allogeneic red blood cells and plasma is based on the balance of benefits, risks and costs. However, physicians making such decisions are faced with massive amounts of sometimes conflicting information. Increasing oxygen delivery through allogeneic red blood cell transfusion to avoid the potential complications of anemia must be balanced against the infectious and noninfectious complications of transfusion. Similarly, the decision to administer plasma requires an assessment of the coagulation defect that is present in the patient, and the ongoing risk of bleeding must be weighed against infectious and noninfectious risks, such as pulmonary edema.

Guidelines have been issued to guide clinical decision-making in the controversial area of transfusion medicine. Traditionally, guidelines have represented a consensus of expert opinion, often defining a standard of practice. More recently, however, they have come to mean evidence-based recommendations that have been carefully developed by organizations using well-established methods.10,11 For this review, we systematically selected, evaluated and summarized guidelines for the transfusion of allogeneic red blood cells and plasma published over the past 30 years. We then examined supporting evidence for each recommendation as well as the methods by which they were derived.

[ Contents ]

Methods

Literature search

A computer search of the MEDLINE database (January 1966 to July 1996) was conducted using the medical subject headings (MeSHs) "blood transfusion," "erythrocyte transfusion," "plasma," "plasmapheresis," "plasma exchange," "plasma substitute" and "blood component transfusion." The search strategy involved looking for these terms, as key words and text words, in the titles and abstracts of all citations. The results were combined with a previous MEDLINE search (1989­93) that used the following MeSHs: "blood transfusion," "adverse effects," "post-operative complications," "aged," "immunosuppression" and "infection." No limits were placed on either search; therefore, all languages as well as animal studies were included.

The collection of transfusion medicine publications of one of the reviewers (PH) supplemented the results of these searches. A manual search was conducted of the bibliographies of 3 major surgery texts,12­14 4 anesthesia texts,15­18 2 texts of transfusion medicine,19,20 a hematology text,21 an internal medicine text22 and 4 critical care texts.23­26 The references of all review articles and guidelines were also searched manually. Unpublished material was not included.

Literature selection

In total, 8426 articles were identified through computer and manual searches. Of these, 1424 were determined to be relevant to CPGs on transfusion of red blood cells and plasma. These were categorized as reviews, guidelines, editorials or book chapters. Abstracts from these selected citations were evaluated independently by 2 reviewers (LC,PH) to determine their eligibility for this study. Of the 1424, 118 were broadly categorized as reviews or guidelines; 59 were rejected because they did not make treatment recommendations regarding allogeneic red blood cell or plasma transfusions, leaving 42 reviews and 17 guidelines for the systematic review. Primary studies describing original research and other articles based on a neonatal population were excluded. Disagreements over selection were resolved by consensus. The 59 selected articles were further categorized according to the definitions outlined below.

Definitions

We defined "reviews" as articles that generally represented an assessment of the literature related to allogeneic blood transfusion. They were further divided into "narrative reviews," which combined expert opinion with evidence27 without an explicit question or method, or "systematic reviews," which addressed a specific question and used an explicit, structured method to identify, select and provide an unbiased synthesis of the relevant evidence (meta-analyses were included in this category). Within the narrative review category, articles were further classified as "textbook reviews" (reviews published as textbook chapters), "historical reviews" (describing the role of the intervention in medicine over time) or "background reviews" (providing a general discussion of a topic).

CPGs have been defined by the Institute of Medicine as "systematically developed statements to assist practitioners and patient decisions about appropriate health care for specific clinical circumstances."28 For our purposes, CPGs had to have cited primary studies, included recommendations on the clinical indications for the use of red blood cells and plasma and been sponsored or endorsed by a medical society or organization. We also distinguished between guidelines and recommendations. For the purposes of this overview, "recommendations" were statements within guidelines, which gave practical, unambiguous advice about a specific aspect of transfusion therapy29 whereas "guidelines" consisted of 1 or more therapeutic recommendations within a document.

Among the guidelines, 5 addressed the use of allogeneic red blood cells, 4 focused on fresh-frozen plasma and 8 did both. All guidelines were based on the recommendations of an expert panel, although no specific consensus process was described.

Data synthesis

The therapeutic recommendations in each article were categorized according to topic and examined to determine the strength of evidence supporting them. Guidelines were evaluated using a checklist that focused primarily on how the evidence was identified, selected and incorporated. The use of a transfusion trigger and the role of clinical judgement over time were also compared.

The checklist was adapted from several articles describing how to develop and use guidelines.10,11,28­32 Objective criteria from each article were compiled and modified to examine several different aspects of guideline development methods. The checklist was used to evaluate relevance, objectives, methods, results, the strength of the evidence and the final recommendations. Each guideline was evaluated independently by 2 authors (AC,PH).

[ Contents ]

Results

Reviews

Among the 42 reviews, 2 were classed as systematic,33,34 31 narrative,35­65 5 historic,2,66­69 3 text chapters70­72 and 1 pamphlet.73 Most reviews (15) focused on the perioperative setting, 6 addressed allogeneic transfusions in trauma situations, 5 focused on chronic anemia and 13 covered both nonoperative and operative settings as well as chronic and acute anemia. Until about 1987, reviews generally advocated the use of a transfusion trigger. Subsequently, most authors denounced this idea; however, a few continued to support the transfusion trigger concept, often citing the National Institutes of Health (NIH) consensus conference guidelines published in 1988 as a source advocating the 70 g/L threshold.

Red blood cell guidelines

Of the 13 guidelines addressing red blood cell transfusions, only 8 fulfilled all aspects of the CPG definition.7,9,74­79 The 3 guidelines developed by the Canadian Red Cross Society80­82 were published as pamphlets without any reference to published research. The guidelines endorsed by the American Association of Blood Banks (AABB)83 were developed to provide standard criteria for utilization reviews and were not to be used to guide clinical practice. Finally, the surgical red blood cell transfusion practice policies84 were not endorsed by a medical society or organization. Despite these limitations and concerns, these 5 guidelines were included in this review.

Target populations for the guidelines were quite diverse: 7 addressed general patient populations;7,76,78,80­83 3 focused on specific patient populations (i.e., patients undergoing coronary artery bypass grafting,79 those with leukemia75 and obstetric patients77); and 3 addressed the administration of red blood cells solely in the perioperative period.9,74,84 Many of the recommendations from the AABB primarily addressed the issue of chronic anemia.76

The issue of a transfusion trigger was addressed in the text or the recommendations of all published guidelines. If we define a transfusion trigger or threshold as a hemoglobin concentration or hematocrit below which most patients should receive at least 1 unit of red blood cells, then only 1 guideline75 recommended a transfusion trigger. Six guidelines7,9,74,76,77,83 advocated a range of transfusion thresholds based on clinical judgement or specific risk factors; 1 guideline84 recommended using clinical judgement without any specific trigger and the other 578­82 did not make any recommendation about clinical judgement or a transfusion trigger. The number of recommendations within each guideline ranged from 19 to 3184 (Table 1). The 31 detailed recommendations within the surgical red blood cell transfusion practice policies84 were devoted to perioperative patients. A significant number of recommendations in this report addressing the use of alternatives to red blood cell transfusions (e.g., autologous programs, erythropoietin and other medications), the perioperative use of anticoagulants and antiplatelet medications as well as anesthetic and surgical technique.

In contrast, the guidelines of the American College of Physicians (ACP)7 contained 26 recommendations focused primarily on red blood cell transfusion, with a few advocating alternatives. Of the 26, 7 were general recommendations about transfusion and 19 were directed at specific patient populations. In this guideline, the avoidance of allogeneic red blood cells was one of the overriding principles.

The guidelines developed by the American Society of Anesthesiology74 included not only recommendations regarding red blood cells but also for plasma, platelet and cryoprecipitate. For red blood cells, they state that transfusions are particularly beneficial when hemoglobin concentration is between 60 and 100 g/L. In addition, the transfusion decision should incorporate an assessment of risks for complications resulting from inadequate oxygenation. Alternatives were also mentioned as potentially beneficial.

One of the first guidelines regarding red blood cell transfusion from the NIH addressed 4 issues: the criteria for transfusions, the morbidity associated with anemia, the risks of transfusion and acceptable alternatives in the perioperative setting.

Plasma guidelines

Twelve CPGs addressing the use of plasma were published between 1985 and 1996.8,74,76,77,79­83,85­87 Of these, 3 were dedicated to plasma transfusions in specific clinical settings: massive transfusion,87 coronary artery bypass grafting79 and perioperative use.74 The remaining guidelines provided general indications for use, particularly the appropriate clinical settings.8,85,86 All guidelines were developed and endorsed by major United States or British medical societies.

None of the guidelines advocated the routine use of plasma to treat coagulation abnormalities. Rather they recommended that the administration of plasma be guided by an assessment of the coagulation cascade. With the exception of those of the College of American Pathologists,85 the guidelines recommended an assessment of the risk of ongoing bleeding as well as the elucidation of specific coagulation abnormalities.

Appraisal of the CPGs

The methods used to develop 17 of the guidelines were evaluated using a checklist of 26 criteria (Table 2). The 2 reviewers disagreed on only 8 (1.9%) of 416 potential interpretations of these criteria. Seven guidelines reported a method, but with insufficient details. Only 2 guidelines reported a computer search of the literature,7,74 and only 174 graded the evidence and the strength of individual recommendations in a systematic fashion. Regarding the completeness of the evidence reviewed, none of the guidelines cited or discussed the small number of available randomized, controlled clinical trials that had been published at least 6 months before the publication of the guideline. None of the guidelines described a specific consensus process in the formulation of recommendations by expert panels. Only 1 guideline clearly indicated the expertise (or representation) of its committee members74 and none described the membership selection process. Thus, we were unable to determine the committee composition for most guidelines.

[ Contents ]

Discussion

In this review of published CPGs on the transfusion of red blood cells and plasma, we noted that most of the 16 guidelines were weak in terms of the methods they used, compared with current norms.28,29,88,89 Only 2 described a literature search and the selection and appraisal strategy in any detail, and none described important aspects of the guideline formulation process. These findings illustrate the need for rigorously developed, evidence-based guidelines in the area of allogeneic red blood cell and plasma transfusion.

Identifying all relevant evidence and subjecting it to critical appraisal are the most important elements of an evidence-based guideline process. Unbiased selection and evaluation of the published material assures the practitioner that practice guideline developers are reflecting the current state of knowledge rather than their opinions. Although 2 guidelines reported using electronic searches, the small number of published randomized, controlled clinical trials comparing transfusion practices were not cited, and insufficient information was reported to allow the searches to be reproduced.

CPG experts have indicated that several steps in the formulation of the recommendations or guidelines may be important in elucidating important values and biases interjected into the process.28,32,90 To this end, aspects of the guideline formulation process were examined. All guidelines were developed using expert panels; however, none of the guidelines described the selection and expertise of the panelists, the mechanism used in resolving disagreements or how expert opinion rather than evidence was used in the formulation of individual recommendations. Despite these major shortcomings, the recommendations may not have been significantly affected by the various consensus processes because the clinical evidence is rather weak.

There is also some question as to which method is best; however, an explicit description of the method would make the process more transparent and perhaps more credible. The more rigorous reporting of guidelines, evident in recent publications, has only been advocated by experts in the field over the past few years.28,29,88,89 Thus, older guidelines should not be expected to fulfill newer and more demanding standards.

The need for CPGs for the use of allogeneic red blood cells and plasma stems from a major change in the risks, both real and perceived, of contact with blood products following the realization that blood transmits viruses such as HIV and hepatitis. Because of these perceptions, many guidelines have promoted a philosophy of blood and plasma avoidance with less consideration for the consequences of withholding transfusions. The ACP recommendations,7 for both chronic and acute anemia, espoused such an approach. Unfortunately, there have been very few clinical trials that adequately describe all clinically important benefits, risks and costs of various transfusion strategies in different patient populations. The paucity of randomized, controlled trials has ensured that the recommendations in published guidelines rely heavily on expert opinion, which has sometimes (particularly more recently) valued the risks of viral transmission through blood products above all other consequences of the transfusion decision.

Although guidelines have received increased attention in recent years, recommendations for allogeneic blood transfusion therapy were in existence as early as 1941.1 In 1960, Graham-Stewart91 published criteria for a justifiable transfusion. Like many of the more recent guidelines, the author advocated the use of clinical judgement when making a decision to transfuse, going as far as declaring that all traditional dogma surrounding transfusion medicine should be abandoned in favour of evaluating each case on its own merit.

The most recently published guideline is also the most rigorously developed and methodologically sound.74 Like several other guidelines, those of the American Society of Anesthesiology Task Force advise against a "transfusion trigger," although they suggest a range of hemoglobin levels that may guide the clinician. This task force recommended that the decision to transfuse should be based upon a patient's risk for complications from inadequate oxygenation, as well as all other important physiologic and surgical factors. Interestingly, the recommendations were fewer in number and less specific in guiding clinical decision-making compared with the surgical practice policies84 and the practice strategies for elective red blood cell transfusion from the ACP.7

One decision of the task force was to limit the available evidence to clinical outcomes-based studies, which clearly introduces a distinct bias in a field with such limited evidence. Although the guidelines were evidence-based, the recommendations on autologous transfusion, intraoperative salvage and hemodilution did not cite nor report on a considerable number of existing clinical trials.

Interestingly, 10 of the 17 guidelines were sponsored by organizations in the United States. Of the remaining 7, 3 were published Canadian transfusion guidelines that did not fully satisfy our definition because there was no synthesis of the available literature and they did not include any references. In addition, they were developed by transfusion specialists rather than a cross-section of potential users. They were also not subjected to any form of peer review, and they did not describe the methods used.

In conclusion, the concept of an arbitrary transfusion trigger for allogeneic red blood cell transfusions or standard protocols for plasma use was refuted by most guidelines; instead most advocated an assessment of clinical need or use of clinical judgement. There was a wide range in the number of recommendations and the breadth of content included in the various guidelines. The published allogeneic red blood cell and plasma transfusion guidelines thus have significant methodologic limitations, and it is unclear whether the values of Canadian patients and practitioners are reflected in their recommendations. We recommend that future guidelines in transfusion medicine be evidence-based and report in detail the methods used in their formulation.

This work was supported by the Canadian Medical Association. Financial support was provided by the Health Canada, the Canadian Blood Agency and the Canadian Red Cross Society, Blood Services. Dr. Hébert is an Ontario Ministry of Health career scientist. Dr. Graham is a postdoctoral fellow of the Medical Research Council of Canada.

We are grateful to Patricia Chung, Eric Partington, Ling Qu and the Canadian Medical Association Expert Working Group for Guidelines on Transfusion of Red blood Cells and Plasma in Adults and Children for their support and assistance in preparing this manuscript. We also thank Dr. Morris Blajchman for reviewing the manuscript and providing detailed comments. Finally, we thank Christine Niles for her assistance in the preparation of the manuscript.

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| CMAJ June 1, 1997 (vol 156, no 11) / JAMC le 1er juin 1997 (vol 156, no 11) |
| Background papers / Documents de fond |
| Guidelines for red blood cell and plasma transfusion |
| Lignes directrices sur la transfusion de globules rouges et de plasma |