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Address for reprints: Michael P. Fischbein, MD, PhD, Department of Cardiothoracic Surgery, Stanford University, 300 Pasteur Dr, Falk CVRB, Stanford, CA 94305.
To evaluate the effect of perioperative allogeneic packed red blood cell (RBC) transfusion during aortic root replacement.
Method
We reviewed patients undergoing aortic root replacement at our institution between March 2014 and April 2020. In total, 760 patients underwent aortic root replacement, of whom 442 (58%) received a perioperative RBC transfusion. Propensity score matching was used to account for baseline and operative differences resulting in 159 matched pairs. All-cause mortality was assessed with Kaplan–Meier curves. Data were obtained from our institutional Society of Thoracic Surgeons database and chart review.
Results
After propensity score matching, the RBC-transfused and -nontransfused groups were similar for all preoperative characteristics. Cardiopulmonary bypass time, crossclamp time, and lowest operative temperature were similar between the transfused and nontransfused groups (standardized mean difference <0.05). RBC transfusion was associated with more frequent postoperative ventilation greater than 24 hours (36/159 [23%] vs 19/159 [12%]; P = .01), postoperative hemodialysis (9/159 [5.7%] vs 0/159 [0%]; P = .003), reoperation for mediastinal hemorrhage (9/159 [5.7%] vs 0/159 [0%]; P = .003), and longer intensive care unit and hospital length of stay (3 vs 2 days and 8 vs 6 days respectively; P < .001). Thirty-day operative mortality after propensity score matching was similar between the cohorts (1.9%; 3/159 vs 0%; P = .2), and 5-year survival was reduced in the RBC transfusion cohort (90.2% [95% confidence interval, 84.1%-96.7%] vs 97.1% [95% confidence interval, 92.3%-100%] P = .035).
Conclusions
Aortic root replacement frequently requires RBC transfusion during and after the operation, but even after matching for observed preoperative and operative characteristics, RBC transfusion is associated with more frequent postoperative complications and reduced midterm survival.
RBC transfusion after aortic root replacement is associated with more frequent postoperative complications and reduced midterm survival after matching for preoperative and operative characteristics.
We have propensity score–matched aortic root replacement patients who required a RBC transfusion versus those that did not based on preoperative and operative characteristics. Our results show that patients who were transfused had worse in hospital complications and reduced midterm survival, affirming recent updates to society guidelines for a restrictive transfusion threshold.
Cardiac operations consume 10% to 20% of donated blood nationally, with up to 60% of elective aortic root operations requiring a transfusion.
Blood transfusion in aortic surgery is well studied, but the impact of transfusion on long-term survival remains conflicted. Recently revised Society of Thoracic Surgeons (STS)/Society of Cardiovascular Anesthesiologists/American Society of ExtraCorporeal Technology/Society for the Advancement of Blood Management guidelines recommend a restrictive transfusion threshold of 7 to 8 g/dL based on the results of multiple randomized control trials showing noninferiority of a restrictive versus liberal (10 g/dL) transfusion threshold on mortality.
Society of Thoracic Surgeons Blood Conservation Guideline Task Force
Ferraris V.A.
Ferraris S.P.
Saha S.P.
Hessel E.A.
Haan C.K.
et al.
Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesiologists clinical practice guideline.
Recent investigations into blood transfusion in aortic surgery with deep hypothermic circulatory arrest show that blood transfusion resulted in worse operative and long-term survival, as well as greater rates of stroke, renal complications, and new dialysis;
however, very few studies have investigated the operative and midterm outcomes of blood transfusion exclusively in aortic root operations. The aim of this study is to evaluate the effect of perioperative red blood cell (RBC) transfusion on postoperative complications and midterm outcomes after aortic root replacement.
Methods
Patient Selection
All elements of this study were prospectively approved by the institutional review board at Stanford University, with waiver of individual patient consent (institutional review board: #50520, Approved September 14, 2021). Electronic medical record review was performed for patients undergoing aortic root surgery between March 28, 2014, and July 1, 2020, at Stanford University Medical Center. Patients undergoing aortic root replacement with a valved conduit or valve-sparing aortic root replacement (VSARR) (Current Procedural Terminology code 33863 or 33864) were included in the study. Patients younger than 18 years of age or who underwent aortic root repair operations were excluded from the cohort. Clinical and operative data were obtained from the electronic medical record and the institutional STS database. Postoperative follow-up was determined by electronic health record review and telephone follow-up.
Surgical Methods
All patients were brought to the operating room after informed consent was obtained. Antifibrinolytic therapy with either tranexamic acid or aminocaproic acid was given to all patients. The aortic root was either repaired with a VSARR or replaced with a mechanical or biological composite valve graft (CVG), homograft, or Freestyle aortic root bioprosthesis (Medtronic). For concomitant arch replacement, patients were actively cooled to 28 °C and received either selective antegrade cerebral perfusion or retrograde cerebral perfusion depending on the surgeon's preference. All patients were rewarmed before weaning from cardiopulmonary bypass. As an institution, we use a restrictive RBC transfusion threshold set to a hemoglobin of 7 to 8 g/dL, but, based on the clinical situation, the decision to transfuse is left to the discretion of the surgeon, anesthesiologist, and intensive care team. Postoperatively in the intensive care unit (ICU), all patients receive up to 2 L of crystalloid based on assessment of blood gases, hemodynamics, lactate, and urine output. More fluid is infused as needed at the discretion of the surgical and intensive care teams.
Outcome Measures
The primary goal of this study was to describe short- and midterm outcomes among patients who received an RBC transfusion during the index operation and or during the postoperative period before discharge compared with patients who did not receive an RBC transfusion during the entire index hospitalization. The short-term outcomes included in-hospital mortality, 30-day mortality, prolonged ventilation, stroke, pacemaker requirement, new dialysis requirement, and ICU and hospital length of stay. Short-term outcomes are evaluated individually. Long-term outcomes include 5-year survival.
Statistical Methods
Statistical analysis was performed in RStudio 1.4.1717 (RStudio, Inc). To improve the comparability between patients who received a blood transfusion during the operation and or postoperative period compared with those who did not, the MatchIt package in R was used to generate a propensity score–matched cohort based on age, sex, body mass index, White race, Black race, history of cerebrovascular accident, preexisting hypertension, coronary artery disease, chronic obstructive pulmonary disease, diabetes, hyperlipidemia, end-stage renal disease, bicuspid aortic valve, preoperative left ventricular ejection fraction, connective tissue disorder, redo sternotomy, emergent status (elective, urgent, emergent), root replacement type, concomitant arch operation, preoperative hemoglobin level, cardiopulmonary bypass time, crossclamp time, and lowest temperature. A common support graph shows the region of overlapping propensity scores (Figure E1) Using a 1:1 nearest neighbor propensity score matching with a caliper set at 0.2, we were able to match 318 patients into balanced groups of 159 patients (Table 1). Excellent matching was achieved with a standardized mean difference (SMD) less than 0.2 for all matched variables (Figure E2) All categorical variables are presented as a ratio (percentage) and compared using the Pearson χ2 test. Continuous variables are presented as mean (standard deviation) and compared with the Wilcoxon rank-sum test. Kaplan–Meier estimates were determined from last known survival date and date of death from the medical record or direct follow-up for patients who were missing current follow-up. Kaplan–Meier estimates were generated using the survminer R package (https://CRAN.R-project.org/package=survminer).
Table 1Matching characteristics
Prematch
Postmatch
No transfusion N = 318
Transfusion N = 442
SMD
No transfusion N = 159
Transfusion N = 159
SMD
Year
2018 (2017, 2019)
2017 (2016, 2019)
0.26
2017 (2016, 2019)
2018 (2016, 2019)
0.02
Age
56 (43, 64)
60 (48, 70)
0.53
57 (45, 65)
58 (41, 69)
0.05
Male
285 (90%)
305 (69%)
0.33
135 (85%)
124 (78%)
0.15
White
249 (78%)
281 (64%)
0.02
112 (70%)
107 (67%)
0.07
Black
13 (4.1%)
20 (4.5%)
0.24
6 (3.8%)
9 (5.7%)
0.09
BMI
27.8 (25.2, 30.9)
26.5 (23.5, 30.3)
0.26
27.4 (24.8, 30.2)
26.8 (24.1, 30.0)
0.06
Previous stroke
19 (6.0%)
80 (18%)
0.38
12 (7.5%)
17 (11%)
0.08
Hypertension
222 (70%)
337 (76%)
0.15
110 (69%)
112 (70%)
0.03
Coronary artery disease
180 (57%)
205 (46%)
0.21
87 (55%)
83 (52%)
0.05
Chronic lung disease
22 (6.9%)
52 (12%)
0.17
9 (5.7%)
11 (6.9%)
0.04
LV ejection fraction
60 (55, 62)
60 (54, 61)
0.09
60 (55, 62)
60 (54, 60)
0.02
Diabetes
35 (11%)
50 (11%)
0.01
15 (9.4%)
17 (11%)
0.04
Hyperlipidemia
163 (51%)
199 (45%)
0.13
67 (42%)
74 (47%)
0.09
End-stage renal disease
2 (0.6%)
4 (0.9%)
0.03
1 (0.6%)
2 (1.3%)
0.07
Bicuspid aortic valve
0.23
0.04
No
143 (45%)
248 (56%)
80 (50%)
73 (46%)
Yes
125 (39%)
141 (32%)
60 (38%)
65 (41%)
Unknown
50 (16%)
53 (12%)
19 (12%)
21 (13%)
Connective tissue disorder
0.07
0.00
No
300 (94%)
418 (95%)
152 (96%)
149 (94%)
Marfan syndrome
8 (2.5%)
13 (2.9%)
5 (3.1%)
7 (4.4%)
Loeys-Dietz syndrome
5 (1.6%)
7 (1.6%)
2 (1.3%)
3 (1.9%)
Other connective tissue disorder
5 (1.6%)
4 (0.9%)
0 (0%)
0 (0%)
Redo sternotomy
36 (11%)
139 (31%)
0.51
27 (17%)
31 (19%)
0.05
Urgency
0.71
0.05
Elective
285 (90%)
268 (61%)
133 (84%)
130 (82%)
Urgent
17 (5.3%)
81 (18%)
13 (8.2%)
12 (7.5%)
Emergent
16 (5.0%)
93 (21%)
13 (8.2%)
17 (11%)
Root replacement type
0.70
0.02
Biological CVG
84 (26%)
231 (52%)
46 (29%)
75 (47%)
Mechanical CVG
57 (18%)
98 (22%)
38 (24%)
23 (14%)
VSARR
169 (53%)
100 (23%)
73 (46%)
56 (35%)
Homograft
0 (0%)
3 (0.7%)
0 (0%)
0 (0%)
Freestyle
8 (2.5%)
10 (2.3%)
2 (1.3%)
5 (3.1%)
Concomitant aortic arch replacement
63 (20%)
196 (44%)
0.54
50 (31%)
49 (31%)
0.01
Preoperative Hgb, g/dL
14.70 (13.90, 15.50)
13.60 (11.83, 14.60)
0.82
14.50 (13.60, 15.25)
14.20 (13.20, 15.25)
0.12
Cardiopulmonary bypass time, min
212 (162, 273)
268 (216, 324)
0.67
236 (181, 286)
235 (176, 294)
0.04
Crossclamp time, min
162 (122, 207)
190 (151, 236)
0.45
172 (134, 222)
174 (130, 218)
0.02
Lowest operative temperature, °C
29.5 (27.8, 34.0)
28.0 (25.6, 30.2)
0.57
28.0 (27.4, 32.4)
28.0 (27.1, 32.4)
0.01
SMD, Standardized mean difference; BMI, body mass index; LV, left ventricular; CVG, composite valve graft; VSARR, valve-sparing aortic root replacement; Hgb, hemoglobin; IQR, interquartile range.
Values are presented as median (interquartile range) or n (%).
There were 768 patients who underwent aortic root replacement at Stanford Healthcare between March 2014 and September 2020. Patients younger than 18 years old (n = 8, 1%) were excluded. Of the 760 patients undergoing aortic root replacement, 41% (n = 315) received a biological CVG, 20% (n = 155) a mechanical CVG, 35% (n = 269) a VSARR, 2.4% (n = 18) a Freestyle aortic root bioprosthesis, and less than 1% received a homograft (n = 3) (Figure 1, A). Reoperative surgery was performed in 23% (n = 175) and de novo operation in the remaining 77% (n = 585) (Figure 1, B). In total, 58% (n = 442) of patients received a RBC transfusion during the hospitalization, whereas 42% (n = 318) did not; 17% (n = 76) received intraoperative RBC transfusion; 34% (n = 149) received a postoperative RBC transfusion; and 49% (n = 217) received both intraoperative and postoperative RBC transfusions. Before propensity matching, the RBC transfusion group had an increased frequency of female sex, non-White race, previous cerebrovascular accident, redo sternotomy, urgent/emergent surgery, and older age. In addition, the RBC transfusion group had greater rates of biological CVG, mechanical CVG, and arch operations, whereas the nontransfused cohort more commonly received a VSARR (Table 1). Preoperative hemoglobin was lower, cardiopulmonary bypass time and crossclamp time were longer, and operative cooling temperature was lower in the transfused cohort. Propensity score matching resulted in 159 pairs with no significant difference in baseline characteristics between transfused and nontransfused cohorts. The SMD was less than 0.2 for all variables, signifying no imbalance between groups.
Figure 1Distribution of (A) aortic root-replacement types and (B) reoperative cardiac surgery for the entire cohort of 760 patients. CVG, Composite valve graft; VSARR, valve-sparing aortic root replacement.
In the matched cohort, the RBC transfusion arm included 19% (n = 30) of patients with intraoperative RBC transfusion, 83% (n = 85) of patients receiving postoperative RBC transfusion, and 28% (n = 44) of patients getting both intraoperative and postoperative RBC transfusion. Median intraoperative RBC products per patient were 0 (interquartile range [IQR], 0-2) and 2 (IQR, 1-4) postoperative.
Reoperative sternotomy (19% vs 17%; P = .6), urgent surgery (7.5% vs 8.2%; P = .7), emergent surgery (11% vs 8.2% P = .7), and arch operation (31% vs 31%; P > .9) were similar between the transfused and nontransfused groups; however, aortic root type was slightly different between the groups (biological CVG: 47% vs 29%; mechanical CVG: 14% vs 24%; VSARR: 35% vs 46%; and Freestyle: 3.1% vs 1.3%; P = .002, SMD = 0.02). Cardiopulmonary bypass time (235 vs 236 minutes; P > .9), aortic cross times (174 vs 172 minutes; P = .7), circulatory arrest frequency (36% vs 36%; P > .9), circulatory arrest duration (20 vs 21 minutes; P = .9) and lowest temperature (28 vs 28 °C; P > .9) were similar between nontransfused and transfused groups (Table 2).
In-hospital and 30-day mortality were similar between patients who were transfused versus those who were not transfused (in-hospital: 2.5%; n = 4 vs 0%; P = .12; 30 days: 1.9%; n = 3 vs 0%; P = .2.). In addition, no difference in permanent stroke, defined as clinical stroke symptoms lasting greater than 24 hours (3.1% vs 1.9%; P = .7), or permanent pacemaker requirement (5.7% vs 3.8%; P = .4) was observed between groups. Patients who were transfused had greater frequencies of prolonged ventilation greater than 24 hours (23% vs 12%; P = .01); new hemodialysis (5.7% vs 0%; P = .003); reoperation for mediastinal hemorrhage (5.7% vs 0%; P = .003); ICU length of stay (3 vs 2 days; P < .001); and hospital length of stay (8 vs 6 days; P < .001). Hemoglobin level trended lower in the transfusion cohort at discharge; however, this was not significant (8.9 g/dL vs 9.2 g/dL; P = .5) (Table 3).
RBC transfusion significantly impaired 5-year survival, as depicted by Kaplan–Meier analysis for all-cause mortality (90.2%; 95% confidence interval, 84.1%-96.7% vs 97.1%; 95% confidence interval, 92.3%-100%; P = .035) (Figure 2, A). Median follow-up time for the transfused cohort was 2.08 years (IQR, 0.86-4.4) and for the nontransfused group 2.31 years (IQR, 0.85-3.73). The timing of RBC transfusion influenced survival—when transfusion was limited to either intraoperatively or postoperatively, 5-year survival was not significantly different (intraoperative: 96.7%; postoperative: 95.2%); however, RBC transfusion both intraoperatively and postoperatively significantly reduced predicted 5-year survival to 77.5% (P = .004) (Figure 2, B). Kaplan–Meier curves were also generated for the number of RBC units transfused after grouping into 1 to 3 units, 3 to 6 units, or greater than 6 units transfused during the entire hospitalization. Survival was not significantly changed compared with no transfusion when up to 6 units of RBCs were transfused (no transfusion: 97.0%; 1-3 units: 98.5%; 3-6 units: 94.1%). A significant decrease in 5-year survival was observed when greater than 6 units of RBCs were transfused (>6 units; 74.7% P < .001) (Figure 2, C).
Figure 2Midterm survival for aortic root replacement after propensity score matching for perioperative RBC transfusion. A, Survival data split by presence or absence of RBC transfusion. B, Survival data of only patients who were transfused split by timing of transfusion. C, Survival data split by number of RBC units transfused. P value indicates log-rank test result. pRBC, Packed red blood cells; CI, confidence interval.
Packed RBC transfusion remains a lifesaving and essential treatment during cardiac surgery but comes with unintentional, well-documented, adverse risks, such as hemolytic reactions, allergic transfusion reaction, transfusion-associated circulatory overload, transfusion-related acute lung injury, and infectious transmission.
Revealing the postoperative complications and reduced midterm survival associated with RBC transfusion during aortic root replacement accentuates the ramifications of RBC transfusion during the operation and postoperative recovery.
Cardiac surgery collectively uses RBC transfusions more frequently compared with other surgical specialties.
Blood use tends to be particularly high in aortic surgery due to multiple suture lines, lower systemic blood temperatures on cardiopulmonary bypass, longer crossclamp times, and the use of circulatory arrest. The long-term implications of blood transfusion in aortic surgery and especially aortic root replacement surgery have infrequently been studied. Cardiopulmonary bypass length, cooling temperature, and length of circulatory arrest have previously been associated with blood transfusion requirement.
Furthermore, older age, lower baseline hemoglobin, emergent status, and redo sternotomy have also been shown to increase the probability for RBC transfusion during cardiac surgery.
This study is the largest, fully inclusive, single-center study of RBC transfusion in patients undergoing aortic root replacement surgery, showing 58.2% of patients received a RBC transfusion during the index hospitalization. To isolate the contribution of RBC transfusion on mortality and minimize confounding factors, we employed propensity score matching based on preoperative characteristics, aortic root replacement type, and procedural characteristics such as cardiopulmonary bypass time, lowest temperature, and concomitant aortic arch replacement. With all else equal, we show that RBC transfusion was associated with prolonged ventilation, reoperation for mediastinal hemorrhage, new hemodialysis, and both ICU and hospital length of stay. In-hospital and 30-day mortality were increased in the transfused cohort, but this did not reach significance because of the small number of mortalities; however, midterm survival decreased with RBC transfusion especially when more than 6 units of RBCs were transfused (Figure 3). The majority of mortalities occurred within the first postoperative year in the RBC transfusion cohort. The cohort of patients receiving greater than 6 units of RBCs during their hospitalization is likely responsible for the mortality difference observed in the entire cohort. RBC transfusion is often binarily categorized during the hospitalization into patients who did or did not receive an RBC transfusion; however, the subgroup analysis presented suggests that clinicians should strive to prevent crossing a threshold of 6 units RBC if clinically possible during the hospitalization to prevent worse midterm survival. Similarly, in a recent report by Ad and colleagues,
number of RBC units transfused in cardiac surgery patients exponentially correlated with predicted 30-day mortality, with an obvious inflection point at 5 units RBC.
Figure 3After matching for observed preoperative and postoperative characteristics, RBC transfusion is associated with more frequent postoperative complications such as prolonged ventilation, new hemodialysis, and prolonged ICU and hospital LOS in addition to reduced midterm survival. RBC, Red blood cell; CI, confidence interval; ICU, intensive care unit; LOS, length of stay; pRBC, packed red blood cells.
investigated blood transfusions in first-time, elective aortic root replacements reported in the STS Adult Cardiac Surgery Database from 2014 to 2017. More than 60% of the aortic root replacement operations required a blood transfusion with an operative mortality across all cohorts of 2.57%. Similar to our findings, transfusion was associated with reoperation for hemorrhage, prolonged ventilation, new hemodialysis, and longer hospital length of stay. However, the exclusion criteria in this study, including nonelective, reoperative surgery, total arch replacements, or unplanned revision of the original planned operation, limit the generalizability and translatability. Despite a smaller study cohort, our study supplements the findings by Hemli and colleagues
by broadening the inclusion criteria and rigorously controlling for baseline and operative characteristics that are known to impact postoperative survival.
A similar matching analysis was performed by Sultan and colleagues
to study the effect of blood transfusion during aortic surgery requiring deep hypothermic circulatory arrest. In a matched cohort of 224 patients who did or did not receive a blood transfusion, nearly a 4-fold increase was observed in 5-year mortality in patients who received a blood transfusion. In addition, prolonged ventilation, pneumonia, sepsis, stroke, and renal failure were also more frequently observed in patients who received a blood transfusion, strengthening our conclusion that perioperative blood transfusion significantly hinders postoperative morbidity and mortality. However, unlike in our study, cardiopulmonary bypass duration was longer in the blood transfusion group, which is well known to be associated with platelet dysfunction and coagulopathy due to a systemic inflammatory reaction and contact of platelets with the synthetic surface of the cardiopulmonary bypass tubing and oxygenator membrane, potentially complicating hemostasis.
As an institution, we implement multiple blood-conservation strategies to reduce the preponderance of perioperative RBC transfusion. Patients with anemia preoperatively will receive iron and erythropoietin to stimulate RBC production, thus reducing the likelihood that the patient will require an RBC transfusion perioperatively for critical low blood oxygen carrying capacity. Precautionary efforts between the surgical team, anesthesia, and the perfusionist further protect against RBC transfusion by whole-blood sequestration before cardiopulmonary bypass, autologous priming of the cardiopulmonary bypass circuit, RBC salvage with cell saver, meticulous surgical hemostasis via surgical technique and topical hemostatics, and early recognition and correction of coagulopathies with aminocaproic acid or tranexamic acid, factor VII, or FEIBA (factor eight inhibitor bypassing activity). We strive to uphold a static postoperative hemoglobin threshold of 7 to 8 g/dL for initiation of RBC transfusion therapy based on the STS/Society of Cardiovascular Anesthesiologists/American Society of Extracorporeal Technology/Society for the Advancement of Blood Management guideline; however, RBC transfusion is a multifactorial clinical decision made by the surgical, anesthesia, and the ICU care team.
We are investigating an individualized transfusion algorithm based on percent change from baseline hemoglobin to prevent overtransfusion of certain populations.
Blood product conservation not only provides a survival benefit for the patient but also reduces a financial burden on the health care system. The mean acquisition per unit of RBCs purchased from a supplier in the United States is more than $200, with additional costs for mandated onsite screening, storage, and retrieval.
In addition to the raw price of blood products, we have shown that a perioperative RBC transfusion for an aortic root replacement increases the ICU and hospital length of stay, resulting in greater health care prices. Dialysis and prolonged ventilation further financially burden the health care system by requiring specialized equipment and personnel. Stringent transfusion of RBCs in aortic root operations has the potential to reduce these costs and allow the hospital system to reallocate resources.
Limitations
This study is a single-center, retrospective study, limiting the generalizability of the findings across all cardiac surgery centers nationally. The population included patients with many different indications for aortic root surgery, urgency, and type of aortic root replacement, which has the potential for introducing confounding factors despite our attempts to limit this with propensity score matching. As such, we can only compare and draw conclusions from patients who were matched. Blood transfusion threshold at our institution follows national guidelines for a restrictive transfusion approach; however, transfusion decision-making ultimately is multifactorial and dependent on the medical care team.
Conclusions
Aortic root replacement frequently requires RBC transfusion during and after the operation secondary to longer cardiopulmonary bypass duration, lower cooling temperatures, and often multiple suture lines. After matching for observed preoperative and operative characteristics, we demonstrate RBC transfusion is associated with more frequent postoperative complications such as prolonged ventilation, new hemodialysis, and prolonged ICU and hospital length of stay. In addition, blood transfusion is associated with reduced midterm survival, most specifically in patients who received 6 or more units of blood. To further understand the effect of RBC transfusion in aortic root operations, studies accounting for potential confounding unobserved characteristics are needed.
Conflict of Interest Statement
The authors reported no conflicts of interest.
The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they may have a conflict of interest. The editors and reviewers of this article have no conflicts of interest.
Appendix E1
Figure E1Common support graph showing the propensity score overlap of RBC versus no RBC transfused cohorts before matching. RBC, Red blood cell.
Figure E2Covariate balance plot before and after propensity score matching for all 24 matched variables. Red indicates unadjusted SMD; blue indicates adjusted SMD.
Society of Thoracic Surgeons Blood Conservation Guideline Task Force
Ferraris V.A.
Ferraris S.P.
Saha S.P.
Hessel E.A.
Haan C.K.
et al.
Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesiologists clinical practice guideline.
The authors acknowledge research funding from the National Institutes of Health F32HL160058 (to A.R.D.), F32HL154681 (to A.J.P.), and R01HL157949 (to M.P.F.).
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