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,
,¶
* From the Critical Care Medicine Program, Centre for Transfusion and Critical Care Research,
Clinical Epidemiology Program, Centre for Transfusion and Critical Care Research;
Program of Urology,
Departments of Hematology, and
¶ Critical Care Medicine, University of Ottawa, Ottawa, Ontario, Canada.
Address correspondence to: Dr. Paul C. Hébert, Centre for Transfusion and Critical Care Research, Clinical Epidemiology Program, Ottawa Health Research Institute, General Campus, 501 Smyth Road, Box 201, Ottawa, Ontario K1H 8L6, Canada. Phone: 613-737-8197; Fax: 613-739-6266; E-mail: phebert{at}ohri.ca
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Abstract |
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Methods: A survey depicting three realistic clinical scenarios of elective surgical procedures with different risks of bleeding was administered to all Canadian practicing members (n = 2,100) of the Canadian Anesthesiologists’ Society. Respondents were requested to choose hemoglobin thresholds for which they would transfuse red blood cells under various conditions within each scenario.
Results: We obtained a response rate of 47% (719/1,512). Transfusion thresholds differed significantly between baseline scenarios. A threshold above 70 g·L–1 was chosen by 48% of respondents in the general surgery scenario compared to 56% in the orthopedic surgery scenario and 79% in the vascular surgery scenario (P < 0.001). A history of coronary artery disease was associated with a transfusion threshold 
100 g·L–1 in a significant proportion of respondents ranging from 20% in the orthopedic surgery scenario to 31% in the general surgery scenario and to 49% in the vascular surgery scenario (P < 0.001). Conversely, changing the patient’s age from 60 to 20 yr resulted in the adoption of a transfusion threshold 
60 g·L–1 by > 30% of respondents in two scenarios (P < 0.001). The year of respondent graduation was strongly associated with these findings.
Conclusion: There was significant variation in transfusion practices among Canadian anesthesiologists. The type of surgical procedure, patient’s age and a history of coronary artery disease influenced reported transfusion threshold. Practice variation in specific subgroups would support the need for further research to identify optimal transfusion thresholds.
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Introduction |
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100 g·L–1 in terms of effects on morbidity and mortality. Guidelines published since the reporting of the Transfusion Requirements In Critical Care (TRICC) trial have either chosen to extrapolate evidence from the critical care study3,4 or opt for recommendations that suggest the avoidance of extreme transfusion thresholds.5 A recent survey of the American Society of Anesthesiologists (ASA) noted the adoption of lower transfusion thresholds among its membership compared to a survey conducted 20 years ago.6,7 A second survey from Israel also suggested the adoption of lower transfusion thresholds.8 Given recent publications and the limited information on the views of anesthesiologists, we undertook a scenario-based survey of members of the Canadian Anesthesiologists’ Society (CAS) to better understand physician attitudes toward transfusion practices.
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Methods |
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Survey development and administration
The survey consisted of two parts: 1) three scenario-based questions designed to elucidate thresholds for RBC transfusion within realistic clinical contexts while varying physiologic parameters; 2) specific questions regarding the use of different blood conservation strategies and sources of information on transfusion practices. The scenario-based questions were developed by a panel of experts including anesthesiologists, epidemiologists and critical care physicians with previous experience in performing surveys in transfusion.9 Through extensive consultations, three scenarios were chosen to represent a reasonable spectrum of elective surgical cases frequently encountered by anesthesiologists (Table 1
). A hypothetical patient undergoing a right hemicolectomy, a second undergoing revision of a total hip replacement and a third undergoing an abdominal aortic aneurysm repair were described in order to represent a progressive increase in the risk of bleeding related to the type of surgery. Scenarios were constructed to contain potential risk factors for transfusion of RBCs previously identified by literature search and expert opinion. Thus, scenarios were based on a non-smoking 60-yr-old male patient, with a normal preoperative assessment, no comorbid illness or health concern who had an uncomplicated peri-operative course. Respondents were asked to indicate the lowest hemoglobin concentration at which they would elect to transfuse using five discrete hemoglobin concentrations: 60 g·L–1, 70 g·L–1,80 g·L–1,90 g·L–1 or 100 g·L–1. These values were based upon response patterns from previous surveys suggesting preferences for end digit "0" values.9,10 Within each scenario, this threshold for transfusion was reassessed after having systematically altered one patient characteristic or physiologic variable without modifying the remainder. Two of these variables were modified in all three scenarios: gender and coronary artery disease. Other modified variables were presence of preoperative chronic anemia, availability of autologous blood, increased perioperative bleeding, preoperative assessment instead of in the operating room and postoperative assessment for RBC requirements. These variables were modified in one or two scenarios only. Each scenario was validated for realism, content and clarity by piloting the survey to anesthesiologists (n = 5) and residents (n = 10). A French language version of the survey was also validated in the same way.
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The first mailing was sent in August 2002 followed four to six weeks later by a reminder card. A second mailing was sent six to eight weeks after the reminder card to 1,024 members whose form was not returned. For this second mailing, non-respondents not listed in the 2002 Canadian Medical Directory were considered ineligible and were excluded. All anesthesiologists received a survey in English language except those from the provinces of Quebec and New Brunswick who received both English and French versions of the survey.
Statistical analysis
Hemoglobin thresholds for transfusion were compared between and within the three scenarios using a Chi-square test. As a second step, we performed a logistic regression analysis to identify physicians characteristics associated with the adoption of a threshold of 70 g·L–1 in at least two of the three scenarios. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated for all demographic variables of respondents. Using the same procedure, we identified the characteristics of respondents who adopted the more extreme thresholds of a hemoglobin concentration 60 g·L–1 when the patient’s age was modified to 20 yr, and a hemoglobin concentration 100 g·L–1 when presence of coronary artery disease was suggested. In an attempt to quantify response biases, we compared anesthesiologists who responded after the first mailing to individuals who responded after the second mailing. We reported absolute P values and 95% CI. A P value < 0.05 was considered significant.
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Results |
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). From these, 549 were retained for analysis after removal of 170 questionnaires filled by respondents meeting exclusion criteria (Figure 2). Seventy-six percent of the responders were males, averaging 46 yr of age and working in a hospital with an accredited anesthesia residency program (61%). Among analyzed surveys returned within the study period, 369 surveys were after the first mailing. Missing data were < 1% for all questions except for the number of beds, where 32 respondents omitted to answer.
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). Using the original responses from the three scenarios in multivariable analysis, more recently graduated physicians were more likely to choose a threshold of 70 g·L–1 in at least two of the three scenarios (Tables II and III).
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). Indeed, a hemoglobin concentration 100 g·L–1 was chosen as a threshold by 31% of the respondents in the general surgery scenario, 20% in the orthopedic surgery scenario and 49% in the vascular surgery scenario, when a history of coronary artery disease was added as a patient characteristic. When the age of the patient in the general surgery and the orthopedic surgery scenarios was decreased from 60 to 20 yr of age, more than 85% of the respondents opted for a transfusion threshold of 70 g·L–1 or less (from base-line percentages of 52% and 44%, P < 0.001 for both scenarios). Furthermore, 39% and 31% of respondents chose a hemoglobin value 60 g·L–1 as a transfusion threshold in the general surgery and the orthopedic surgery scenarios respectively. Using logistic regression analysis, year of graduation after 1980 was the only physician characteristic that was independently associated with the choice of a hemoglobin threshold 60 in that subgroup (Tables II and III). On the other hand, physicians having graduated prior to 1981 and working in a hospital without an anesthesia residency program were more likely to adopt a threshold 100 g·L–1 to justify the decision to transfuse when a history of coronary artery disease was suggested in the scenario (Tables II and III). Finally, there were no differences noted between responses from the first and the second mailings except for the subgroup with a suggested history of coronary disease where late respondents were less likely to adopt a hemoglobin threshold 100 g·L–1 compared to early respondents (OR = 0.60, 95% CI 0.39 to 0.92, P = 0.02).
Strategies to minimize RBC transfusions
In a separate scenario-based question on erythropoietin use, 39% of the respondents would have prescribed the drug prior to a total hip arthroplasty in a 50-yr-old male with asymptomatic anemia but otherwise healthy. Only 28% of respondents would choose to administer erythropoietin in conjunction with an autologous transfusion program. During the postoperative period, 19% of respondents agreed with the administration of erythropoietin on day five following surgery if the same patient showed mild lethargy and difficulty in ambulating. Additional evidence and lower cost would be the main incentive factors to use erythropoietin in a perioperative setting for 44% of the anesthesiologists surveyed. More than 75% of anesthesiologists stated that they never or rarely use erythropoietin in practice.
Iron therapy (53%), intraoperative blood salvage (36%), autologous RBCs (31%) and antifibrinolytics (23%) were said to be often or always used as blood conservation therapies, while antifibrinolytics and intra-operative blood salvage were said to never be used by 30% and 25% of respondents respectively. Physicians who opted to transfuse at a threshold of 70 g·L–1 or lower were more likely to adopt blood conservation techniques such as antifibrinolytics (OR = 1.95, 95% CI 1.12 to 3.39, P = 0.02) and erythropoietin (OR = 6.69, 95% CI 1.54 to 28.91, P = 0.01) in their practice.
Sources of information
Published clinical practice guidelines were the most important source cited by anesthesiologists to guide RBC transfusion followed by review articles, educational conferences, clinical trials and institutional practice guidelines. These sources of information were respectively considered important, very important or extremely important by 91%, 90%, 89%, 85% and 73% of the respondents. The TRICC trial2 (described previously) was chosen by 68% of the respondents.
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Discussion |
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In a recent survey among ASA members,7 80 g·L–1 was the median minimal hemoglobin concentration tolerated before transfusion by 39% of respondents, a similar percentage to that observed in this study (Figure 2). In the ASA survey, the authors also observed that only 9% of the physicians would have transfused patients undergoing elective surgery to reach a hemoglobin concentration 100 g·L–1. In our study, only 3% of respondents would have transfused RBCs to target a concentration of hemoglobin 100 g·L–1 in the three symptom-free scenarios. This percentage increased to 33% overall when patients were described as having varying degrees of symptoms from ischemic heart disease. Our results suggest that physicians would routinely increase their transfusion threshold in response to coronary artery disease independently of other important characteristics altering transfusion thresholds, such as age and risk of bleeding. In contrast, the ASA survey asked few questions related to different risk factors. Both surveys seem to indicate that RBC transfusion thresholds have decreased compared to the first survey in American anesthesiologists published in 1987.6 However, CAS members chose a transfusion threshold 100 g·L–1 three times less often than their American counterparts. Some of the observed differences between surveys may have been attributed to the different methodologies especially the use of realistic scenarios in the Canadian study vs generic questions in the American study. A survey performed in Israel and published in 2004 showed that obstetric anesthesiologists would choose a mean threshold for transfusion of 73 ± 5.6 g·L–1 in a clinical scenario based on a 30-yr-old woman undergoing a c-section with ongoing slow bleeding after adequate resuscitation from an initial profuse bleeding.8 The transfusion threshold among anesthesiologists in Israel appears comparable to overall responses from the three different elective surgical interventions presented in this survey. In two surveys of critical care physicians using a similar scenario-based approach, our research group observed that many clinical characteristics influenced transfusion thresholds including the age and severity of illness of the hypothetical patient.9,10 Again, patient characteristics including age and presence of coronary artery disease were noted to influence the choice of a RBC transfusion threshold. In the survey of critical care physicians performed in 2004, recent graduates reported using a threshold of 70 g·L–1 as anesthesiologists did in this survey.
The adoption of a threshold for transfusion 100 g·L–1 in hypothetical patients with ischemic heart disease is consistent with results from a large retrospective study. Wu et al. documented a decrease in hospital mortality among older patients who were transfused RBCs following myocardial infarction as compared to patients who were not, when hematocrit values were below 33%.11 Our survey was conducted soon after the publication of this retrospective study. Results observed could then represent its influence. However, a more recent study by Rao et al., published after the administration of this survey did not detect similar associations.12 Interestingly, we also noted that a significant proportion of anesthesiologists reported using a transfusion threshold as low as 60 g·L–1 before transfusing RBCs to healthy young patients undergoing elective surgery with low bleeding risk. The low risk of subsequent bleeding, the absence of comorbid illness and ongoing concerns about transfusion-transmitted infections may explain this lower threshold reported by anesthesiologists. The patient’s gender did not modify transfusion thresholds in this study, a result that was comparable to previous critical care surveys performed by our group.9,10,13 This would suggest that more women than men reach a transfusion threshold in clinical practice since gender is frequently identified as a risk factor for transfusion in retrospective studies.14,15
In this study, differences found in relation with the year of graduation likely reflect guidelines or consensus in effect during these respective periods of training. Indeed, thresholds for RBC transfusions were observed to be in accordance with results from previous surveys performed during these different decades.6,10,16 On the other hand, differences found in the proportion of respondents who chose a threshold for transfusion 100 g·L–1 in the hypothetical patient with ischemic heart disease must be considered with discernment since this difference was not seen in any other subgroups (Table III).
In this survey, we also noted that most CAS members considered published clinical practice guidelines as their primary source of information in influencing their RBC transfusion practices, closely followed by review articles. Conversely, blood conservation strategies seemed to be advocated by a significant proportion of respondents despite the actual low-level evidence of a clinical benefit for most of it. Reasons explaining these choices were not integrated into the questionnaire.
The major limitation of this study is the hypothetical nature of this exercise. Results of our previous scenario-based surveys of transfusion practice in the critical care population were reasonably consistent with actual practice patterns.9,17 However, given this study was conducted by the same investigative team that published much of the literature on restrictive transfusion strategies, there may have been a response bias favouring a lower threshold for RBC transfusion. Moreover, despite an inability to detect consistent modifications in responses from mailing to mailing except in one subgroup, non-responder biases may be present. In this survey, we have chosen to sample a population of certified anesthesiologist members of the CAS, a population that most certainly differs from all health professionals who have an anesthesia practice in Canada. On the other hand, a significant proportion of respondents practiced in academic centres and regional variations in transfusion practices were noted. This survey may therefore better represent the perspective of opinion leaders rather than all practitioners. In addition, this survey was designed to identify individual physician and patient characteristics that affected the hypothetical transfusion thresholds. Because physicians work together within institutional and group practices, we cannot exclude that some individual variables could be affected by a potential clustering effect. The influence of patient and physician variables on response patterns was considered as hypothesis generating and relatively weak. Further information on anesthetic practices might have assisted in better understanding differences in practice patterns at an institutional and regional level.
In this survey, we cannot exclude that the low response rate could have introduced a bias. However, considering the large practice variability already observed, this bias would be more likely in the direction of the actual findings. Thus, we could argue that an increased response rate would have enhanced the actual variability in response patterns rather than minimized it.
In summary, Canadian anesthesiologists appear to have adopted a transfusion threshold comparable to their critical care colleagues.9 The type of surgical procedure and several patient characteristics such as the patient’s age and the presence of coronary artery disease were also noted to modify hypothetical transfusion thresholds. We identified a group of practitioners who adopted a threshold 60 g·L–1 in healthy patients with low bleeding risk. Ongoing practice variation among anesthesiologists would support the need for further research that would identify an optimal transfusion threshold, especially in patients with coronary artery disease. Updated transfusion guidelines may also be warranted.
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Acknowledgments |
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Footnotes |
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Accepted for publication July 4, 2005. Revision accepted October 11, 2005.
This article is accompanied by an editorial. Please see Can J Anesth 2006; 53: 331–5.
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2 Hebert PC, Wells G, Blajchman MA, et al. A multicenter, randomized, controlled clinical trial of transfusion requirements in critical care. Transfusion Requirements in Critical Care Investigators. Canadian Critical Care Trials Group. N Engl J Med 1999; 340: 409–17. Erratum: N Engl J Med 1999; 340: 1056.
3 Murphy MF, Wallington TB, Kelsey P, et al. Guidelines for the clinical use of red cell transfusions. Br J Haematol 2001; 113: 24–31.[Medline]
4 British Columbia Transfusion Medicine Advisory Group. Guidelines for red blood cell transfusion. November 2003. Available from URL; http://www.bloodlink.bc.ca/RBCGuidelines.pdf.
5 Anonymous. Practice guidelines for blood component therapy: a report by the American Society of Anesthesiologists Task Force on Blood Component Therapy. Anesthesiology 1996; 84: 732–47.[Medline]
6 Stehling LC, Ellison N, Faust RJ, Grotta AW, Moyers JR. A survey of transfusion practices among anesthesiologists. Vox Sang 1987; 52: 60–2.[Medline]
7 Nuttall GA, Stehling LC, Beighley CM, Faust RJ; American Society of Anesthesiologists Committee on Transfusion Medicine. Current transfusion practices of members of the American Society of Anesthesiologists. A survey. Anesthesiology 2003; 99: 1433–43.[Medline]
8 Matot I, Einav S, Goodman S, Zeldin A, Weissman C, Elchalal U. A survey of physicians’ attitudes toward blood transfusion in patients undergoing cesarean section. Am J Obstet Gynecol 2004; 190: 462–7.[Medline]
9 Hebert PC, Fergusson DA, Stather D, et al.; Canadian Critical Care Trials Group. Revisiting transfusion practices in critically Ill patients. Crit Care Med 2005; 33: 7–12.[Medline]
10 Hebert PC, Wells G, Martin C, et al. A Canadian survey of transfusion practices in critically Ill patients. Transfusion Requirements in Critical Care Investigators and the Canadian Critical Care Trials Group. Crit Care Med 1998; 26: 482–7.[Medline]
11 Wu WC, Rathore SS, Wang Y, Radford MJ, Krumholz HM. Blood transfusion in elderly patients with acute myocardial infarction. N Engl J Med 2001; 345: 1230–6.
12 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.
13 Laverdiere C, Gauvin F, Hebert PC, et al.; Canadian Critical Care Trials Group. Survey on transfusion practices of pediatric intensivists. Pediatr Crit Care Med 2002; 3: 335–40.[Medline]
14 Nilsson KR, Berenholtz SM, Dorman T, et al. Preoperative predictors of blood transfusion in colorectal cancer surgery. J Gastrointest Surg 2002; 6: 753–62.[Medline]
15 Berenholtz SM, Pronovost PJ, Mullany D, et al. Predictors of transfusion for spinal surgery in Maryland,1997 to 2000. Transfusion 2002; 42: 183–9.[Medline]
16 Irving G. Survey of the use of blood and blood components among South African anaesthetists working in teaching hospitals. S Afr Med J 1992; 82: 324–8.[Medline]
17 Corwin HL, Gettinger A, Pearl RG, et al. 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.[Medline]
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  N. Shehata and C. D. Mazer Optimizing transfusion practice/Une pratique transfusionnelle optimale. Can J Anesth, April 1, 2006; 53(4): 331 - 335. [Full Text] [PDF]
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