- Open Access
Transfusion trigger in critically ill patients: has the puzzle been completed?
Critical Care volume 11, Article number: 142 (2007)
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.
The transfusion of red blood cell (RBC) concentrates in critically ill patients remains controversial and has generated much research and debate in the medical literature. A recent, large, noninferiority randomized clinical trial adds an important piece to this quite complicated 'puzzle' . In stable critically ill anemic (hemoglobin <9.5 g/dl) children between 3 days and 14 years of age, this study demonstrated that a restrictive strategy, where the threshold hemoglobin concentration was 7 g/dl, significantly decreased transfusion requirements without increasing adverse outcome, defined as a composite of death and development of new or progressive organ failure, when compared to a liberal strategy with a threshold hemoglobin of 9.5 g/dl. Anemia is common in critically ill patients and results in a large number of RBC transfusions. Several studies reported that up to 50% of adult or children who were hospitalized in an intensive care unit received RBC transfusions [2–4]. Interestingly, all these observational studies reported that hemoglobin level, rather than clinical or physiological factors, drives transfusion decision. The adequacy of any hemoglobin concentration in a given clinical situation depends on whether a sufficient amount of oxygen is carried to the tissues to meet their metabolic requirements . The optimal hemoglobin threshold for RBC transfusion in different populations, and especially in critically ill patients, remains unknown.
The study of Lacroix and colleagues  confirms the results reported by two other randomized trials that evaluated the impact of a restrictive strategy on the outcome of critically ill adults  and preterm infants . Using 30-day mortality as the primary outcome in 838 euvolemic adult critically ill patients, Hébert and colleagues  demonstrated that a restrictive transfusion strategy was at least as effective as a liberal one. In addition, applying a liberal transfusion strategy resulted in a significantly higher multiple organ dysfunction score, a composite outcome taking into account 30-day mortality and the number of organ failures. This deleterious effect might be attributed to the fact that RBC units transfused in this study were not leukocyte-reduced, in contrast to the RBC units used in the study by Lacroix and colleagues. Two 'before and after' studies in adults and premature infants and one meta-analysis of randomized controlled trials have reported that leukoreduced RBC transfusion could significantly improve the outcome of high risk patients [8–10]. It has been decided, therefore, to repeat a prospective controlled randomized study to compare hemoglobin thresholds of 7 versus 9 g/dl . Using a composite primary outcome including death before home discharge or survival with any of severe retinopathy, bronchopulmonary dysplasia or brain injury on cranial ultrasound in 451 infants with birth weight <1,000 g, Kirpalani and colleagues  demonstrated that maintaining a lower hemoglobin level did not increase neonatal morbidity. Interestingly, the thresholds developed in this study were based on whether or not the infant was receiving respiratory support. Although not specified, as the study was performed after 1999 and included Canadian centers, it may be reasonably assumed that the authors used leukoreduced RBC units. The results of this study are in contrast with those of Bell and colleagues , who reported in a smaller trial (N = 100) that infants in the restrictive-transfusion group were more likely to have intraparenchymental brain hemorrhage or periventricular leukomalacia. However, this combination was not a pre-specified outcome and the study was powered for the primary outcome of number of transfusions. In all these studies, the use of a restrictive approach was associated with a decreased number of transfusions and, in most of them, with a decrease in the number of patients exposed to RBC transfusion.
Using a more liberal approach to achieve a higher hemoglobin concentration in an attempt to increase oxygen delivery and thus tissue oxygenation in stable critically ill patients does not appear to be associated with a significant clinical benefit. Several authors have suggested that the RBC storage process could affect the ability of RBCs to transport and deliver oxygen, this phenomenon being responsible for the lack of apparent improvement in tissue oxygenation after transfusion. Human studies on the effects of stored RBCs are scarce and controversial. In nine healthy volunteers undergoing acute isovolemic hemodilution, there were no differences in the ability of transfused fresh (stored <5 hours) or stored (>3 weeks) RBCs to reverse the neurocognitive deficit observed during acute anemia . In critically ill patients, the effect of RBC storage on gastric mucosal oxygenation remains controversial [14, 15]. In a randomized multicenter pilot trial, Hébert and colleagues  did not observe differences in mortality rates or life-threatening complications in patients transfused with fresh (median age 4 days) versus old (median age 19 days) RBCs. In the study of Lacroix and colleagues , the average length of storage was about 16.0 ± 10 days in both strategy groups. The effect of RBC storage time on primary outcome was not evaluated.
For stable critically ill patients with a hemoglobin concentration ranging from 6 or 7 to 10 g/dl, there is increased evidence that a restrictive transfusion approach based on a predefined hemoglobin concentration does not influence outcome. The decision to transfuse such patients would, therefore, depend primarily on clinical judgment, taking into account the ability of the patient to increase cardiac output and oxygen extraction, and the level of tissue oxygen demand . It remains to be demonstrated that, in high risk patients, a symptomatic transfusion strategy is as effective, or possibly superior, to a hemoglobin-based transfusion strategy. This is the aim of the ongoing 'FOCUS' study comparing these two strategies in patients 50 years of age or older who undergo surgical repair of a hip fracture and who have clinical evidence for cardiovascular disease or cardiovascular risk factors . Although the study of Lacroix and colleagues adds an important piece to the 'puzzle', it still remains incomplete. Will it ever be completed?
red blood cell.
Lacroix J, Hébert PC, Hutchison JS, Hurne HA, Tucci M, Ducruet T, Gauvin F, Collet J-P, Toledano BJ, Robillard P, et al.: Transfusion strategies for patients in pediatric intensive care units. N Engl J Med 2007, 356: 1609-1619. 10.1056/NEJMoa066240
Corwin HL, Gettinger A, Pearl RG, Fink MP, Levy MM, Abraham E, MacIntyre NR, Shabot MM, Duh M-S, Shapiro MJ: The CRIT Study: Anemia and blood transfusion in the critically ill – Current clinical practice in the United States. Crit Care Med 2004, 32: 39-52. 10.1097/01.CCM.0000104112.34142.79
Vincent J-L, Baron JF, Rheinhart K, Gattinoni L, Thijs LG, Webb A: Anemia and blood transfusion in critically ill patients. JAMA 2002, 288: 1499-1507. 10.1001/jama.288.12.1499
Armano R, Gauvin F, Ducruet T, Lacroix J: Determinants of red blood cell transfusions in a pediatric critical care unit: a prospective descriptive epedemiological study. Crit Care Med 2005, 33: 2637-2644. 10.1097/01.CCM.0000185645.84802.73
Van der Linden P: Transfusion strategy. Eur J Anaesthesiol 2001, 18: 495-498. 10.1046/j.1365-2346.2001.00883.x
Hébert PC, Wells G, Blajchman MA, Marshall J, Martin C, Pagliarello G, Tweeddale MG, Schweitzer I, Yetisir E: A multicenter randomized controlled clinical trial of transfusion requirements in critical Care. N Engl J Med 1999, 340: 409-417. 10.1056/NEJM199902113400601
Kirpalani H, Whyte RK, Andersen C, Asztalos EV, Heddle N, Bla-jchman MA, Peliowski A, Rios A, LaCorte M, Connelly R, et al.: The premature infants in need of transfusion (PINT) study: a randomized controlled trial of a restrictive (low) versus liberal (high) transfusion threshold for extremely low birth weight infants. J Pediatr 2006, 149: 301-307. 10.1016/j.jpeds.2006.05.011
Hébert PC, Fergusson D, Blajchman MA, Wells GA, Kmetic A, Coyle D, Heddle N, Germain M, Goldman M, Toye B, et al.: Clinical outcomes following institution of the Canadian universal leukoreduction program for red blood cell transfusions. JAMA 2003, 289: 1941-1949. 10.1001/jama.289.15.1941
Fergusson D, Hébert PC, Blajchman MA, Lee SK, Walker CR, Barrington KJ, Joseph L, Blajchman MA, Shapiro S: Clinical outcomes following institution of universal leukoreduction of blood transfusions for premature infants. JAMA 2003, 289: 1950-1956. 10.1001/jama.289.15.1950
Fergusson D, Khanna MP, Timmouth A, Hébert PC: Transfusion of leukoreduced red blood cells may decrease postoperative nfections: two meta-analyses of randomized controlled trials. Can J Anesth 2004, 51: 417-425.
The SOAP Study[http://www.intensive.org/soap/index.asp]
Bell EF, Strauss RG, Widness JA, Mahoney LT, Mock DM, Seward VJ, Cress GA, Johnson KJ, Kromer IJ, Zimmerman MB: Randomized trial of liberal versus restrictive guidelines for red blood cell transfusion in preterm infants. Pediatrics 2005, 115: 1685-1691. 10.1542/peds.2004-1884
Weiskopf RB, Feiner J, Hopf H, Lieberman J, Finlay HE, Quah C, Kramer JH, Bostrom A, Toy P: Fresh blood and aged stored blood are equally efficacious in immediately reversing anemia-induced brain oxygenation deficits in humans. Anesthesiology 2006, 104: 911-920. 10.1097/00000542-200605000-00005
Marik PE, Sibbald WJ: Effects of stored blood transfusion on oxygen delivery in patients with sepsis. JAMA 1993, 269: 3024-3029. 10.1001/jama.269.23.3024
Walsh TS, McArdle F, McLellan SA, Maciver C, Maginnis M, Prescott RJ, McClelland DBL: Does the storage time of transfused red blood cells influence regional or global indexes of tissue oxygenation in anemic critically ill patients? Crit Care Med 2004, 32: 364-371. 10.1097/01.CCM.0000108878.23703.E0
Hébert PC, Chin-Yee IH, Fergusson D, Blajchman MA, Martineau R, Clinch J, Olberg B: A pilot trial evaluating the clinical effects of prolonged storage of red cells. Anesth Analg 2005, 100: 1433-1438. 10.1213/01.ANE.0000148690.48803.27
Carson JL, Terrin ML, Magaziner J, Chaitman BR, Apple FS, Heck DA, Sanders D: Transfusion trigger trial for functional outcomes in cardiovascular patients undergoing surgical hip fracture repair. Transfusion 2006, 46: 2192-2206. 10.1111/j.1537-2995.2006.01056.x
The authors declare that they have no competing interests.
About this article
Cite this article
Reiles, E., Van der Linden, P. Transfusion trigger in critically ill patients: has the puzzle been completed?. Crit Care 11, 142 (2007). https://doi.org/10.1186/cc5936
- Periventricular Leukomalacia
- Transfusion Strategy
- Multiple Organ Dysfunction Score
- Restrictive Strategy
- Isovolemic Hemodilution