Anesth Analg 2008; 106:679-680
© 2008 International Anesthesia Research Society
doi: 10.1213/01.ane.0000308960.45453.ad
BOOK AND MULTIMEDIA REVIEWS
Blood Transfusion, Vol. 21, No. 2 in Best Practice & Research, Clinical Anesthesiology
Bruce D. Spiess, MD, FAHA
Professor of Anesthesiology and Emergency Medicine; Director of Virginia Commonwealth University Reanimation Shock Center (VCURES); Virginia Commonwealth University Medical Center Richmond, VA; BDSpiess{at}HSC.VCU.EDU
Blood Transfusion, Vol. 21, No. 2 in Best Practice & Research, Clinical Anesthesiology
Spahn DR, ed. Amsterdam: Elsevier, 2007. ISSN 1521-6896. 117 pages, $196.00 subscription for four issues or $71.02 for a single issue.
Transfusion medicine is one of the most rapidly changing specialties in all of health care. The days of HIV/AIDS and hepatitis driving transfusion behavior should be over. The key word here is "should." However, the practitioner and certainly the lay public remain focused upon the risks of virus, prion, and pathogen contamination/transmission of blood products. This issue of Clinical Anesthesiology should be read by all anesthesiologists, surgeons, and critical care and emergency physicians for it is a wonderful up-to-date review of the latest thinking regarding the science of transfusion. Unfortunately, its strength is its greatest weakness: in depth analysis. All too often, all clinicians want is simply "what do I need to know." This 9-chapter mini-text is long on science but will leave the average clinician wanting to know "so when do I transfuse." That is exactly the take home message of modern transfusion medicine. It is no longer about viruses, prions, and other pathogens.
Spahn has recruited some of the world’s most noted scientific and clinical thought leaders with regards to transfusion. The volume has a decidedly European authorship, but the Americans could well be less provincial and learn from the fact that so much cutting-edge work is being performed throughout Europe. Spahn has provided a potpourri of topics that create an overall take-home message: transfusion is so very complex. Infectious complications are no longer the major focus. Unfortunately, Dr. Spahn does not hammer that point home in his introduction. Rather, he focuses upon the need for a detailed knowledge of the complex physiology of transfusion. Herein is where the rub will begin and the beauty of this work comes out. For the true physiologist, the discussions are elegant. Four chapters: Allogeneic red blood cell transfusions: physiology of oxygen transport (Chapter 1), Physiologic transfusion triggers (Chapter 2), The impact of storage on red cell function in blood transfusion (Chapter 3), and Efficacy of allogeneic blood transfusion (Chapter 5) have some overlap. They all agree on the importance of oxygen delivery, critical oxygen supply, oxygen extraction ratio, and shock, defined as the point at which blood no longer supports aerobic glycolysis. If the practicing anesthesiologist could read these chapters to the point at which an understanding of transfusion triggers was questioned daily, collective transfusion would improve. Of particular importance are the concepts of diffusive versus conductive oxygen transport, VO2-DO2 relationships and the importance of dissolved O2 (chapter 1). Our group at Virginia Commonwealth University Reanimation Engineering Shock center (VCURES) has the majority of research based on Figure 1 of Chapter 1. In one form or another, that figure is repeated (3 times). The figure fits well in each chapter, and the concept is the basis by which all transfusion decisions should be based. Medicine is hampered in the ability to monitor critical oxygen delivery. There is a call for the need to individualize patient triggers. Arbitrary hemoglobin/hematocrit levels are inadequate surrogates of oxygen delivery.
Chapter 4 is of particular importance. It explores the biomechanical and biochemical changes that occur within red cells during storage. So many clinicians, and the lay public, harbor a belief system that transfusion will improve oxygen delivery. Such is not the case. Red cells undergo profound cell membrane changes leading to fragility, inability to perfuse the microcirculation (where O2 transfer occurs), and a shortened life span. Those effects are compounded by a number of complex biochemical changes that further restrict the red cell’s ability to unload O2, control vascular auto-regulation of flow (nitric oxide, and ATP release to endothelium), as well as a large number of other homeostatic mechanisms. This one chapter should be "must reading" for the new generation of anesthesiology residents so that they understand just how dysfunctional red cells become. The physiology is complex, new papers are being written weekly, but the excitement is that hematologists, blood bankers, and pharmaceutical houses are realizing that the product (stored red blood cells) can be dramatically improved.
Chapter 5 is a thorough discussion of the impact of transfusions on outcome. Unfortunately, the chapter starts out with a positive statement that the impact of transfusions in many cases are life-saving, yet there is really very little data to support this allegation. The quote of transfusions being life-saving in children from Kenya who present with hemoglobin less than 4 gm/dL fits so wonderfully well with the entire book’s discussion of critical O2 delivery that this reviewer wishes the authors had made that connection obvious. Some data from brain trauma show that increased red cell mass/hematocrit (i.e., transfusion) does improve brain oxygenation and perhaps outcome. But the remainder of the data is woefully one-sided. Yet the impression, indeed the first few lines of the chapter, and the practice by most anesthesiologists, is that blood transfusion is life-saving. It must be for massive blood loss, yet those cases are not the ones studied in most of the references quoted. The reader would do well to ponder on some of the distinctions. Go back to the point Spahn is trying to make: when 1-3 units of blood are utilized, it may be a very tricky physiologic question as to whether O2 delivery (outcome) is improved or worsened. The discussion of transfusion in cardiac disease is well outlined in a short paragraph as well as chapter 6 with the limits of hemodilution. Each of these explanations (coronary artery disease, transfusion, anemia, hemodilution) is physiologically evidence-based. The rush to transfuse is simply not supported by the evidence when it comes to acute or corrected (CABG surgery and or percutaneous coronary intervention-PCI).
Three other chapters round out the potpourri. Chapter three is about transfusion associated acute lung injury (TRALI). TRALI is now the number one risk of transfusion (not HIV/AIDS or hepatitis). Since this wonderful book was sent to print, more new sobering evidence has been published.1,2 TRALI is by definition a diagnosis of exclusion. Perhaps its real occurrence is not 1/5000 units, but may be the more common 1/2000. The take-home points regarding TRALI should be embraced. The fact that physicians continue to make TRALI a diagnosis of exclusion subtly means that there still is a belief that transfusion is good.
Chapter 7 discusses another vexing problem, the use of anti-platelet drugs. These agents have made the use of PCI more successful. They constantly have the underlying problem of a baseline bleeding event. When patients are treated by cardiologists and do not present to the operating room, our specialty does not have to deal with these drugs. But, once again, one needs to look closely at attitudes and realize that the data regarding bleeding, transfusion, and outcome are often dismissed in major cardiology trials as "minor risks" or that the drugs were well tolerated. Yet over time, the bleeding risks mount. Indeed, if patients are on these drugs for life, then the bleeding risk is an arithmetic summary of the risk per year that the patient will endure. As more and more patients get stents worldwide and more get "drug eluting" stents that carry recommendations for combination anti-platelet therapies for life, the overall risks of severe and life-threatening bleeds will increase. Rao et al.3 did point out that those patients transfused during PCI carried a fourfold increase in mortality with all confounders controlled. More patients will be in operating rooms with these drugs, the consequences of acute cerebral bleeds, trauma with anti-platelet agents in the patient, etc. Anti-platelet drugs are no longer a problem just for the cardiac anesthesiologist.
The final chapter regarding costs and transfusion was outdated by the time it was published. But it is sobering and the best there is to date. There is no real-time up-to-date information. Cost of transfusion will increase. Of that there is no doubt. Most hospital administrators realize that their budget for blood products is one of the fastest and most uncontrollable parts of their economy. The reader with no budgetary influence within the hospital should ponder what all this data means. It sends a message that each unit is precious, not only because of scarcity, but because of cost. In Europe, Japan, and Australia costs may not be evident as they are in patient billing within the United States. But, data from Austria, Germany, and other countries are quite telling. There is a societal cost to transfusion not just for the cost of acquiring and processing, but also for the complications associated with transfusion. The costs are truly astronomical, although computer generated analyses have not been done on many of the most recently appreciated complications (TRALI).
In conclusion, this short 9-chapter book entitled Blood Transfusion is a wonderful contemporary discussion of physiology and a few other key elements of the transfusion decision. At the end of the day, however, the reader is left wondering "So what do I do?" The answer lies in each chapter, wherein research and take-home points are nicely highlighted in boxes. Please read those and do the work. Transfusion has never been safety- and efficacy-tested. Spahn provides a great view into physiology with over 500 key references and indirectly challenges us to do the research necessary to help our patients.
REFERENCES
- Rana R, Fernandez-Perez ER, Khan SA, et al. Transfusion-related acute lung injury and pulmonary edema in critically ill patients: a retrospective study. Transfusion 2006;46:1478–83[Web of Science][Medline]
- Khan H, Belsher J, Yilmaz M, et al. Fresh-frozen plasma and platelet transfusions are associated with development of acute lung injury in critically ill medical patients. Chest 2007;131:1308–14[Web of Science][Medline]
- Rao SV, Jollis JG, Harrington RA, et al. Relationship of blood transfusion and clinical outcomes in patients with acute coronary syndromes. JAMA 2004;292: 1555–62[Abstract/Free Full Text]
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