Abstract
Background
Perioperative red blood cell transfusions (RBC) are associated with increased morbidity and mortality after cardiac surgery. Acute normovolemic hemodilution (ANH) is recommended to reduce perioperative transfusions; however, supporting data are limited and conflicting. We describe the relationship between ANH and RBC transfusions after cardiac surgery using a multi-center registry.
Methods
We analyzed 13,534 patients undergoing cardiac surgery between 2010 and 2014 at any of the 26 hospitals participating in a prospective cardiovascular perfusion database. The volume of ANH (no ANH, <400mL, 400–799mL, ≥800mL) was recorded and linked to each center’s surgical data. We report adjusted relative risks reflecting the association between the use and amount of ANH and the risk of perioperative RBC transfusion. Results were adjusted for preoperative risk factors, procedure, BSA, preoperative HCT, and center.
Results
ANH was used in 17% of the patients. ANH was associated with a reduction in RBC transfusions (RRadj 0.74, p <0.001). Patients having ≥800mL of ANH had the most profound reduction in RBC transfusions (RRadj 0.57, p<0.001). Platelet and plasma transfusions were also significantly lower with ANH. The ANH population had superior postoperative morbidity and mortality compared to the no ANH population.
Conclusions
There is a significant association between ANH and reduced perioperative RBC transfusion in cardiac surgery. Transfusion reduction is most profound with larger volumes of ANH. Our findings suggest the volume of ANH, rather than just its use, may be an important feature of a center’s blood conservation strategy.
Keywords: coronary artery bypass grafts, CABG, outcomes, Blood management, conservation, consequences
Introduction
Numerous publications have demonstrated an association between perioperative red blood cell transfusions (RBC) and higher risk of morbidity (e.g. renal failure, respiratory failure, stroke, infections) and mortality after cardiac surgery.1,2, 3 Indeed, single and multi-center studies have demonstrated safety and decreased morbidity and mortality associated with blood conservation measures.4 As a result, numerous blood conservation strategies are recommended, including acute normovolemic hemodilution (ANH).4
As practiced in cardiac surgery, ANH is the process by which whole blood is removed, collected, and stored from a patient after induction of anesthesia and prior to heparinization for cardiopulmonary bypass (CPB). ANH volume is replaced with sufficient volumes of colloid or crystalloid solutions to maintain hemodynamic stability. The autologous stored whole blood serves as a “blood bank” for the patient to receive non-diluted, fresh, whole blood containing red blood cells and critical clotting factors. Despite its theoretical benefits in reducing RBC transfusions, single center reports and meta-analyses have demonstrated mixed results regarding the effectiveness of ANH to reduce RBC transfusions.5.6–9,10–12 In its most recent blood management guidelines, the Society of Thoracic Surgeons and Society of Cardiovascular Anesthesiologists endorse ANH as a potential mechanism for blood conservation, but acknowledged the disparate data supporting its practice.4
We undertook a multi-center, observational study to identify the association between ANH use and RBC transfusions among patients undergoing cardiac surgery using a voluntary, multi-institutional registry of merged perfusion and cardiac surgical data. We hypothesized that patients exposed to ANH (and increased volume of ANH) would have lower rates of RBC transfusions.
Patients and Methods
This study was approved by the Institutional Review Board (IRB) of the University of Michigan Health System (IRB HUM00053934, Notice of Determination of “Not Regulated” Status).
Patient Population
The PERFusion measures and outcomes (PERForm) registry was established in 2010 as a voluntary database. Current efforts are focused on identifying perfusion practices associated with improved outcomes and providing benchmarking opportunities to support local and multi-institutional quality improvement initiatives. It is organizationally structured within the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative (MSTCVS-QC). At the time of this publication, 27 of 33 hospitals participating in the MSTCVS-QC contributed data to the PERForm registry, with an additional 8 centers located outside of Michigan (7, 8). The MSTCVS-QC began in 2001 as a cardiac surgeon-led quality collaborative embedded in the Michigan Society of Thoracic and Cardiovascular Surgeons, and in 2005 it became partially funded by the Blue Cross/Blue Shield of Michigan. The Collaborative meets quarterly to review various processes and outcomes and to facilitate and evaluate quality improvement studies.
All programs in the MSTCVS-QC utilize the Society of Thoracic Surgeons (STS) data collection form and submit data on a quarterly basis to both the STS database and the MSTCVS-QC data warehouse. The PERForm registry contains information related to the care and conduct of cardiovascular perfusion practices. (A list of fields and definitions may be found at http://www.mstcvsqualitycollaborative.org/perform-registry.) Each surgical record is merged with a record from the PERForm registry (9). Participating sites are routinely audited for data validity and accuracy as part of the MSTCVS-QC audit system.
We included all patients ≥ 18 years of age operated on at one of 27 participating medical centers between the second quarter of 2010 through the second quarter of 2014 who underwent one of the following operations: isolated coronary artery bypass grafting (CABG), isolated aortic valve (AVR), AVR+CABG, mitral valve (MV) Repair, MV Replacement, CABG+ MV Repair or Replacement, totaling 19, 434 patients. Our final dataset included 13,534 patients; we excluded patients whose procedures do not have a STS predicted risk of mortality (STS PROM), those with missing information on ANH use, patients undergoing off-pump surgery, or surgery for endocarditis. ANH use and volume removed was dictated by clinicians at each institution.
Measures
The primary outcome for this analysis was any perioperative RBC transfusion defined as occurring during the intra- or post-operative stay. We additionally report crude rates of plasma and platelet transfusions as well as 30-day mortality, re-operation for bleeding, post-operative stroke, renal dysfunction and failure, and prolonged (>12 day) length of stay. Indications for red blood cell transfusions were determined by the clinical team caring for the patient. There was not a uniform transfusion protocol across all participating centers. We define ANH as the practice of removing autologous whole blood prior to systemic heparinization for CPB with the express purpose of reinfusion after protamine reversal. Hemodynamic stability was maintained by vasopressor support and the administration of sufficient volumes of colloid or crystalloid solutions per institutional protocol. We categorized the volume of harvested ANH based on the estimated volume contained in an autologous blood collection bag (i.e. <400mL=1 bag, 400–799=2 bags, >=800 = 3+ bags).
Statistical Analyses
Standard statistical tests were used, including chi-square tests for categorical data and two-sided Wilcoxon rank-sum tests for non-normally distributed continuous variables. Trends in patient characteristics, processes of care, and clinical outcomes were tested using non-parametric tests of trend.
Analysis of the ANH cohort was divided into 4 groups: all ANH recipients, those who had <400 mL removed, those with had 400–799 mL removed, and those who had ≥800 mL removed. We explored indexing ANH volume removed to patient body surface area (BSA), body mass index and estimated blood volume, but found no impact on results; thus, we chose to stratify simply by volume removed. Baseline demographic variables were reported on all patients, as well as pre-operative comorbidities. We report crude and adjusted relative risks for RBC transfusions using Poisson regression. We adjusted for each patient’s STS PROM, BSA, pre-operative hematocrit, medical center, net prime volume, cell salvage utilization, cell salvage volume, and procedure. Adjusted rates for post-operative outcomes are also reported.
Statistical analyses were performed using Stata 13.0 (College Station, TX). The tests were considered significant at p<0.05.
Results
A total of 13,534 patients were analyzed of whom 2,337 (17%) underwent ANH. Among ANH patients, 308 (13.2%) had <400 mL removed, 958 (41.9%) had 400–799 mL removed and 1071 (45.8%) had ≥800mL removed. ANH was utilized in 21 of the 26 (81%) centers contributing data to the database with most centers (62%) using it in less than 20% of cases, 4 (16%) using it between 20–59% of cases, and 4 (16%) using it in ≥ 60% of cases. ANH was employed in all types of identified procedures (isolated CABG, AVR-CABG, MV Repair-CABG, MV Replacement-CABG, AVR, MV Repair, and MV Replacement) regardless of center level of usage.
Table 1 details baseline demographic descriptors and preoperative comorbidities of the studied patients. There are numerous differences between the ANH and non-ANH populations. Overall, ANH patients tend to be younger, male, and have a larger BSA. Furthermore, ANH patients tend to be less anemic with slightly higher estimated blood volumes. ANH patients had fewer comorbidities reflected in a lower STS risk of mortality (1.1% vs. 1.4%, p <0.001). When stratified by ANH volume removed, there are numerous noteworthy differences between cohorts. Compared to patients who had smaller volumes removed, patients who had ≥800 mL removed tended to be younger, male, and have a larger BSA with higher baseline HCT and larger estimated blood volumes. With the exception of severe aortic stenosis, patients who had ANH volumes ≥800 mL had lower comorbidity profiles and a lower STS PROM. Severe aortic stenosis was significantly higher in the ANH population with the ≥800 mL cohort.
Table 1.
Pre-operative Characteristics by Use and Volume of Acute Normovolemic Hemodilution
| ANH Volume | |||||||
|---|---|---|---|---|---|---|---|
| Variables | No ANH | ANH | <400ml | 400–799ml | >=800ml | p-valuea | p-valueb |
| Observations | 11,197 | 2,337 | 308 | 958 | 1,071 | ||
| 83% | 17% | 2% | 7% | 8% | |||
| Patient Age (%) | |||||||
| <60 | 27.2 | 33.5 | 34.1 | 29.4 | 37.0 | ||
| 60–69 | 32.6 | 32.5 | 27.9 | 35.0 | 31.7 | ||
| 70+ | 40.2 | 34.0 | 38.0 | 35.6 | 31.4 | <0.001 | <0.001 |
| Female (%) | 31.0 | 24.9 | 23.1 | 27.2 | 23.3 | <0.001 | <0.001 |
| Body Surface Area (m2) (%) | |||||||
| <1.6 | 4.7 | 4.4 | 3.6 | 6.7 | 2.5 | ||
| 1.6–1.79 | 14.4 | 11.9 | 13.0 | 14.6 | 9.1 | ||
| 1.8–1.99 | 25.2 | 25.1 | 27.0 | 23.6 | 26.0 | ||
| 2+ | 55.7 | 58.7 | 56.5 | 55.1 | 62.5 | <0.001 | <0.001 |
| Estimated Blood Volume (L) | |||||||
| Mean | 4.7 | 4.8 | 4.8 | 4.7 | 4.9 | <0.001 | <0.001 |
| Median | 4.7 | 4.8 | 4.8 | 4.7 | 4.9 | <0.001 | <0.001 |
| Hct, last preop (%) | |||||||
| <36 | 30.6 | 16.2 | 19.0 | 20.9 | 11.1 | ||
| 36–39 | 28.8 | 29.0 | 32.1 | 30.3 | 26.8 | ||
| 40–42 | 24.0 | 32.1 | 28.6 | 28.1 | 36.9 | ||
| 43+ | 16.5 | 22.7 | 20.3 | 20.6 | 25.3 | <0.001 | <0.001 |
| Predicted Risk of Mortality | |||||||
| Median | 1.4% | 1.1% | 1.1% | 1.2% | 0.9% | <0.001 | <0.001 |
| <1% | 37.5 | 47.7 | 43.8 | 43.8 | 52.2 | ||
| 1–1.9% | 23.9 | 23.5 | 26.0 | 23.1 | 23.3 | ||
| 2–2.9% | 12.3 | 11.7 | 9.4 | 12.9 | 11.2 | ||
| 3%+ | 26.4 | 17.1 | 20.8 | 20.2 | 13.4 | <0.001 | <0.001 |
| Comorbid Disease (%) | |||||||
| Myocardial Infarction | |||||||
| None | 58.6 | 72.53 | 65.6 | 67.8 | 78.8 | ||
| Within 7days | 19.2 | 9.2 | 12.7 | 13.1 | 4.8 | ||
| >= 7 days | 22.2 | 18.3 | 21.8 | 19.2 | 16.4 | <0.001 | <0.001 |
| CHF | 22.3 | 17.0 | 18.2 | 19.7 | 14.3 | <0.001 | <0.001 |
| NY Heart Assoc Class III/IV | 16.8 | 11.7 | 14.3 | 14.2 | 8.8 | <0.001 | <0.001 |
| Aortic Stenosis, Severe | 13.5 | 17.9 | 16.6 | 15.6 | 20.4 | <0.001 | <0.001 |
| Diabetes Mellitus (%) | 41.0 | 32.1 | 40.3 | 37.0 | 25.5 | <0.001 | <0.001 |
| Hemoglobin A1c (median) | 5.9 | 5.9 | 5.9 | 6.0 | 5.8 | 0.17 | <0.001 |
| Periperhal Arterial Disease (%) | 14.9 | 9.0 | 14.0 | 11.9 | 5.0 | <0.001 | <0.001 |
| EGFR | |||||||
| >=90 | 43.8 | 49.6 | 51.6 | 46.6 | 51.6 | ||
| 60–89 | 33.5 | 33.1 | 30.5 | 32.7 | 34.2 | ||
| 30–59 | 18.6 | 15.1 | 15.9 | 17.8 | 12.4 | ||
| <30 or Kidney Failure | 4.1 | 2.3 | 2.0 | 2.9 | 1.8 | <0.001 | <0.001 |
| Ejection Fraction (%) | |||||||
| <40% | 15.1 | 11.1 | 16.3 | 10.9 | 9.9 | ||
| 40–9% | 14.2 | 9.1 | 12.8 | 10.1 | 7.2 | ||
| 50–9% | 31.8 | 25.0 | 33.0 | 29.3 | 19.0 | ||
| 60+ | 39.0 | 54.7 | 37.9 | 49.7 | 63.9 | <0.001 | <0.001 |
| Previous operation (%) | 6.3 | 10.4 | 3.9 | 9.0 | 13.6 | <0.001 | <0.001 |
| Urgent/Emergent (%) | 50.0 | 31.8 | 47.1 | 38.9 | 21.0 | <0.001 | <0.001 |
for the comparison of ANH use
for the comparison across ANH volume categories
Operative data from the analyzed patients are detailed in Table 2. Retrograde autologous priming (RAP) of the CPB circuit was used more frequently (82.8% vs. 71.4%, p <0.001) and at greater volumes in ANH patients. Over 60% of patients who had ≥ 800 mL of ANH volume had ≥ 500 mL of RAP volume. As a consequence of increased RAP among ANH patients, smaller crystalloid CPB prime volumes were used as well. Overall, ANH patients received more crystalloid volume, with increasing volume administered to patients with greater ANH volume removed. There was no difference in nadir HCT between ANH and no-ANH patients, including those patients with a nadir HCT <21 (p=0.5). ANH patients received less cell salvage volume (455 ml vs. 658 mL, p<0.001).
Table 2.
Intra-operative Practices by Use and Volume of Acute Normovolemic Hemodilution
| ANH Volume | |||||||
|---|---|---|---|---|---|---|---|
| Variables | No ANH | ANH | <400ml | 400–799ml | >=800ml | p-valuea | p-valueb |
| Observations | 11,197 | 2,337 | 308 | 958 | 1,071 | ||
| CPB Time (median) | 97 | 111 | 116 | 112.5 | 108 | <0.001 | <0.001 |
| Clamp Time (median) | 74 | 85 | 87 | 87 | 81 | <0.001 | <0.001 |
| Retrograde Autologous Prime (%) | |||||||
| No RAP | 28.6 | 17.2 | 14.0 | 12.6 | 22.3 | ||
| <500ml | 20.7 | 20.2 | 14.9 | 30.4 | 12.5 | ||
| 500–699ml | 26.5 | 21.1 | 9.1 | 22.7 | 23.2 | ||
| ≥700ml | 24.2 | 41.5 | 62.0 | 34.3 | 42.0 | <0.001 | <0.001 |
| Net Prime Volume (%) | |||||||
| ≤500ml | 14.8 | 26.1 | 52.6 | 29.8 | 15.2 | ||
| 500–999ml | 41.8 | 46.4 | 40.9 | 46.7 | 47.8 | ||
| 1–1.49ml | 23.8 | 20.3 | 5.2 | 17.6 | 27.1 | ||
| ≥1.5L | 19.5 | 7.1 | 1.3 | 6.0 | 9.9 | <0.001 | <0.001 |
| Net Fluid Volume Administered on Bypass (%)! | |||||||
| <500ml | 46.4 | 43.9 | 61.1 | 46.1 | 37.1 | ||
| 500–999ml | 21.5 | 22.0 | 21.3 | 23.4 | 21.0 | ||
| ≥1L | 32.1 | 34.1 | 17.6 | 30.6 | 41.9 | 0.02 | 0.00 |
| Nadir Hct (%) | |||||||
| <21 | 16.6 | 14.2 | 15.3 | 16.6 | 11.5 | ||
| 21–23 | 20.6 | 23.7 | 30.6 | 23.1 | 22.0 | ||
| 24–25 | 13.8 | 17.8 | 15.6 | 19.1 | 17.3 | ||
| 26+ | 49.0 | 44.4 | 38.4 | 41.2 | 49.1 | <0.001 | 0.50 |
| Cell Salvage Volume Transfused (ml), median |
658.0 | 455.0 | 405.0 | 440.0 | 500.0 | <0.001 | <0.001 |
| Ultrafiltration (%) | 26.6 | 23.7 | 30.1 | 25.2 | 20.6 | <0.001 | <0.001 |
for the comparison of ANH use
for the comparison across ANH volume categories
We collected information concerning the 1st post-operative Hct in the intensive care unit (ICU). The mean 1st post-operative Hct in the ICU was not appreciably different by ANH use: 30.9 (ANH) vs. 30.5 (no ANH), p<0.001. The mean 1st post-operative Hct in the ICU by ANH volume: 30.5 (no ANH), 30.1 (<400mL), 30.5 (400–799mL), 31.6 (>=800mL), p<0.001.
Table 3 reports adjusted outcomes associated with ANH utilization. RBC transfusion rates were significantly lower among patients in whom ANH was used (33.5% vs. 40.3%, p <0.001). Increased ANH volume was significantly associated with progressively fewer RBC transfusions (p<0.001), although did not impact the rate of transfusions given solely in the operating room (p=0.78). ANH use remained significantly associated with fewer RBC transfusions (RRadj 0.74 p <0.001), even after adjusting for pre-operative risk, procedure, BSA, preoperative HCT, net prime volume, cell salvage utilization, cell salvage volume and center, Figure 1. While protective at each volume threshold, the protective effect of RBC transfusion was most pronounced when ≥800mL of ANH volume is removed (RRadj 0.57, p<0.001). There was a significantly lower rate of plasma (4.9% vs. 8.5%, p <0.001) and platelet transfusions (5.2% vs. 8.5%, p<0.001) among those with ANH use. As with RBC transfusions, patients having ≥800mL of ANH had the lowest transfusion rates of plasma 3.3%) and platelets (3.4%), p<0.001.
Table 3.
Adjusted Post-operative Outcomes by Use and Volume of Acute Normovolemic Hemodilution
| ANH Volume | |||||||
|---|---|---|---|---|---|---|---|
| Variables | No ANH | ANH | <400ml | 400–799ml | >=800ml | p-valuea | p-valueb |
| Observations | 11,197 | 2,337 | 308 | 958 | 1,071 | ||
| Reoperation for Bleeding (%) | 2.3% | 1.9% | 2.5% | 2.0% | 1.0% | 0.30 | 0.09 |
| Stroke (%) | 1.8% | 1.3% | 1.8% | 1.4% | 1.0% | 0.22 | 0.14 |
| Acute Kidney Injury (%) | 28.2% | 24.1% | 28.3% | 25.6% | 20.9% | <0.001 | <0.001 |
| Renal Failure (%) | 2.9% | 1.3% | 2.8% | 1.4% | 1.1% | <0.001 | <0.001 |
| Intra-aortic balloon pump (%) | 8.2% | 4.9% | 7.5% | 5.3% | 3.3% | <0.001 | <0.001 |
| Red Blood Cells (%) | |||||||
| None | 59.7% | 66.5% | 66.1% | 63.1% | 70.7% | <0.001 | <0.001 |
| Intra-op Only | 8.5% | 7.7% | 3.5% | 9.4% | 7.1% | 0.78 | 0.81 |
| Post-op Only | 21.9% | 16.1% | 25.9% | 18.7% | 6.6% | <0.001 | <0.001 |
| Intra + Postop | 10.4% | 4.9% | 5.9% | 6.6% | 2.7% | <0.001 | <0.001 |
| Plasma (%) | 8.5% | 4.9% | 7.3% | 5.8% | 3.3% | <0.001 | <0.001 |
| Platelets (%) | 8.5% | 5.2% | 7.8% | 6.1% | 3.4% | <0.001 | <0.001 |
| Prolonged Length of Stay (%) | 15.9% | 12.4% | 18.2% | 13.0% | 10.5% | <0.001 | <0.001 |
| 30-d Mortality | 2.8% | 1.5% | 2.0% | 0.01% | 2.0% | <0.001 | 0.01 |
| Readmission (%) | 12.1% | 11.4% | 9.5% | 12.5% | 10.5% | 0.61 | 0.66 |
Adjusted for pre-operative hematocrit, body surface area, net prime volume, Cell Saver volume, center and procedure
for the comparison of ANH use
for the comparison across ANH volume categories
Figure 1.
Rate of Red Blood Cell Transfusions by Volume of Acute Normovolemic Hemodilution Removed. Relative risks are also presented after adjustment for each patient’s STS predicted risk of mortality, BSA, pre-operative hematocrit, medical center, and procedure.
Risk adjusted thirty-day mortality was lower among patients receiving ANH (1.5 vs. 2.8%, p < 0.001). Compared to the no-ANH cohort, patients receiving ANH had less acute kidney injury (28.2% vs. 24.1%, p < 0.001), renal failure (1.3% vs. 2.9%, p<0.001). Patients receiving ≥800mL of ANH had the lowest rates of acute kidney injury (20.9%), p<0.001. Use of ANH was associated with lower rates of prolonged length of stay (12.4% vs. 15.9%, p<0.001), and was lowest among patients having ≥800mL of ANH, p<0.001. The difference in stroke (1.3% vs. 1.8%, p=0.22) and readmission rates (11.4% vs. 12.1%, p=0.61) associated with ANH use did not reach statistical significance.
Discussion
In our analysis of 13,534 patients in a multicenter prospectively collected database we discovered a number of findings that further support the use of ANH as an effective blood conservation technique to prevent peri-operative RBC transfusions during cardiac surgery. First, the use of ANH was effective, as it was associated with fewer allogenic red blood cell transfusions, even after adjustment for pre-operative risk factors, medical center and procedure type. Second, ANH use was also associated with fewer platelet and plasma transfusions. Third, the reduction in allogeneic transfusions is most pronounced when ≥800 mL of ANH volume is removed. In addition, ANH was associated with improved risk adjusted outcomes, including prolonged length of stay, 30-day mortality, and renal failure. The safety of ANH combined with reduction in allogenic blood transfusions supports its use as a component of an overall blood conservation strategy in cardiac surgery. Our findings support those of previous studies reporting a reduction in allogenic transfusions with ANH utilization. New York Hospital - Cornell randomized 90 cardiac surgery patients to either ANH or no ANH and found a significant reduction in RBC, platelet and plasma transfusions.9 Similarly, 100 CABG patients randomized to ANH or no ANH by the Los Angeles Kaiser group experienced a 45% reduction in allogeneic transfusions with ANH usage.7 Furthermore, a meta-analysis of randomized trials of ANH use reported a 50% reduction in allogeneic transfusions in cardiac surgery patients.11 Our data conflicts with previous reports that have found no significant effect of ANH on post-operative RBC transfusions, including randomized trials by Casati (n=200)13 and Hohn (n= 80)10; both of these studies showed no significant reduction in allogeneic transfusions. While cardiac surgery patients were not analyzed separately, a meta-analysis of cardiac and vascular surgery patients found no reduction in transfusions with the use of ANH.12
Our study highlights a potentially critical point in the practice of ANH: the volume removed matters. We found the most profound reduction in transfusions occurred when ≥ 800mL of ANH volume is removed. Similarly, the Bryson meta-analysis11 observed the most significant blood conservation impact occurred when ANH volumes exceeded one liter, while Helm and Kochamba found a reduction in transfusions with removal of mean ANH volumes of 1540 mL and 866 mL, respectively.7, 9 Furthermore, studies demonstrating a null effect tended to remove smaller volumes of ANH.13,10 The null findings of these studies may be reflective of a sub-therapeutic volume of ANH rather than the lack of utility of ANH in general. Thus, ANH may be not only underutilized in frequency but also used insufficiently when employed. In addition, our data demonstrates a significant portion of patients who undergo ANH also undergo RAP, with the highest proportion in the ≥800 mL cohort (60% of which had ≥500 mL of RAP volume) which implies appropriately selected patients can tolerate relatively large shifts of their blood volume. While further research is needed to determine the dose response relationship of ANH on transfusion prevention, our large multi-institutional study shows that ANH is not only safe and effective at reducing RBC transfusions, but is most effective when removing ≥800mL of a patient’s blood volume. We recognize some limitations to our current study. First, we cannot rule out the effect of unmeasured confounding, including other institutional or physician-related practices.14, 15 We employed standard approaches, including risk adjustment, to address apparent differences in pre-operative characteristics. Second, we recognize that there are a number of clinical reasons and patient level factors that impact the clinical decision to use ANH. With that being said, we could not find evidence of adverse harm associated with the use of ANH, including among patients with EF <40%, those undergoing urgent/emergent operations, and those with STS predicted mortality risk of ≥ 3%.
This contemporaneous, multi-institutional study demonstrates the reduction in transfusions associated with the use of ANH. Furthermore, our findings suggest that a therapeutic ANH volume may be higher than that removed by many centers. While additional studies are needed to identify the optimal volume of ANH to remove in a given patient, clinicians should consider employing ANH as part of a larger blood management strategy.
Acknowledgments
We acknowledge the editorial review provided by Amanda Schuetz and Katie Wopinsky.
Disclosure
The MSTCVS Quality Collaborative recognizes the support of Blue Cross Blue Shield of Michigan and Blue Care Network. Dr. Likosky is supported in part by the following grants from the Agency for Healthcare Research and Quality (AHRQ), U.S. Department of Health and Human Services: R01HS022535 and R03HS022909. The opinions expressed in this document are those of the authors and do not reflect the official position of AHRQ or the U.S. Department of Health and Human Services. Dr. Sundt is a consultant for Thrasos Therapeutics.
Footnotes
Meeting presentation: Society of Thoracic Surgeons 51st Annual Meeting, San Diego, CA, January 24–28, 2015.
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