Perfusion / MSTCVS-QC Publications
Determinants of hospital variability in perioperative red blood cell transfusions during coronary artery bypass graft surgery
To identify to what extent distinguishing patient and procedural characteristics can explain center-level transfusion variation during coronary artery bypass grafting surgery.
Observational cohort study using the Perfusion Measures and Outcomes Registry from 43 adult cardiac surgical programs from July 1, 2011, to July 1, 2017. Iterative multilevel logistic regression models were constructed using patient demographic characteristics, preoperative risk factors, and intraoperative conservation strategies to progressively explain center-level transfusion variation.
Of the 22,272 adult patients undergoing isolated coronary artery bypass surgery using cardiopulmonary bypass, 7241 (32.5%) received at least 1 U allogeneic red blood cells (range, 10.9%-59.9%). When compared with patients who were not transfused, patients who received at least 1 U red blood cells were older (68 vs 64 years; P < .001), were women (41.5% vs 15.9%; P < .001), and had a lower body surface area (1.93 m2 vs 2.07 m2; P < .001), respectively. Among the models explaining center-level transfusion variability, the intraclass correlation coefficients were 0.07 for model 1 (random intercepts), 0.12 for model 2 (patient factors), 0.14 for model 3 (intraoperative factors), and 0.11 for model 4 (combined). The coefficient of variation for center-level transfusion rates were 0.31, 0.29, 0.40, and 0.30 for models 1 through 4, respectively. The majority of center-level variation could not be explained through models containing both patient and intraoperative factors.
The results suggest that variation in center-level red blood cells transfusion cannot be explained by patient and procedural factors alone. Investigating organizational culture and programmatic infrastructure may be necessary to better understand variation in transfusion practices.
The Role of Race on Acute Kidney Injury After Cardiac Surgery
Acute kidney injury (AKI) frequently complicates cardiac surgery and is more common among Black patients. We evaluated determinants of race-based differences in AKI rates.
Serum creatinine-based criteria were used to identify adult cardiac surgical patients having postoperative AKI in the Perfusion Measures and Outcomes (PERForm) Registry (July 1, 2014, to June 30, 2019). Patient characteristics, operative details, and outcomes were compared by race (Black vs White) after excluding patients with preoperative dialysis, missing preoperative or postoperative creatinine, or other races. A mixed effects model (adjusting for demographics, comorbidities, surgical factors) used hospital as a random effect to predict postoperative stage 2 or 3 AKI. Propensity score analyses were conducted to evaluate robustness of the primary analyses.
The study cohort included 34 520 patients (8% Black). More Black patients than White patients were female (43% vs 27%, P < .001), and had hypertension (93% vs 87%, P < .001) and diabetes mellitus (51% vs 41%, P < .001). Acute kidney injury of stage 2 or greater occurred in 1697 patients (5%), more often among Black than White patients (8% vs 5%, P < .001). Intraoperatively, Black patients had lower nadir hematocrits (23 vs 26, P < .001), and were more likely to be given transfusions (22% vs 14%, P < .001). After adjustment, Black race (compared with White) independently predicted odds for postoperative AKI (adjusted odds ratio 1.50; 95% confidence interval, 1.26 to 1.78). The multivariable findings were similar in propensity score analyses.
Despite accounting for differences in risk factors and intraoperative practices, Black patients had a 50% increased odds for having moderate-severe postoperative AKI compared with White patients. Additional evaluations are warranted to identify potential targets to address racial disparities in AKI outcomes.
Evaluating Changes in del Nido Cardioplegia Practices in Adult Cardiac Surge
Abstract: There has been a rapid adoption of the use of del Nido cardioplegia (DC) among adults undergoing cardiac surgery. We leveraged a multicenter database to evaluate differences over time in the choice and impact of cardioplegia type (DC vs. blood) among patients undergoing cardiac surgery. We evaluated 26,373 patients undergoing non-emergent coronary artery bypass and/or valve surgery between 2014-2015 (early period) and 2017-2018 (late period) at 31 centers. DC was compared with blood-based cardioplegia (BC: 1:1, 2:1, 4:1, 8:1, and variable ratio). We evaluated whether treatment choice differed across prespecified patient characteristics, procedure type, and perfusion practices by time period. We evaluated increased DC use with clinical outcomes (major morbidity and mortality, prolonged intubation, and renal failure), after adjusting for baseline characteristics, procedure type, center, and year. DC use increased from 19.6% in 2014-2015 to 41.5% in 2017-2018, p < .001. Increased DC use occurred among coronary artery bypass grafting (CABG), valve, and CABG + valve procedures, all p < .001. Differences in median procedural duration increased over time (DC vs. BC): 1) bypass duration was 11.0 minutes shorter with DC in the early period and 27.0 minutes shorter in the late period, and 2) cross-clamp duration was 7.0 minutes shorter with DC in the early period and 17.0 minutes shorter in the late period, all p < .001. There were no statistical differences in adjusted odds of major morbidity and mortality (odds ratio [OR]adj: 1.01), prolonged intubation (ORadj: .99), or renal failure (ORadj: .80) by DC use (p > .05). In this large multicenter experience, DC use increased over time and was associated with reduced bypass and ischemic time absent any significant differences in adjusted outcomes. The Journal of ExtraCorporeal Technology
Prediction of Transfusions After Isolated Coronary Artery Bypass Grafting Surgical Procedures
Background: Although blood transfusions are common and have been associated with adverse sequelae after cardiac surgical procedures, few contemporaneous models exist to support clinical decision making. This study developed a preoperative clinical decision support tool to predict perioperative red blood cell transfusions in the setting of isolated coronary artery bypass grafting.
Methods: We performed a multicenter, observational study of 20,377 patients undergoing isolated coronary artery bypass grafting among patients at 39 hospitals participating in the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative’s PERFusion measures and outcomes (PERForm) registry between 2011 and 2015. Candidates’ preoperative risk factors were identified based on previous work and clinical input. The study population was randomly divided into a 70% development sample and a 30% validation sample. A generalized linear mixed-effect model was developed to predict perioperative red blood cell transfusion. The model’s performance was assessed for calibration and discrimination. Sensitivity analysis was performed to assess the robustness of the model in different clinical subgroups.
Results: Transfusions occurred in 36.8% of patients. The final regression model included 16 preoperative variables. The correlation between the observed and expected transfusions was 1.0. The risk prediction model discriminated well (receiver operator characteristic [ROC]development, 0.81; ROCvalidation, 0.82) and had satisfactory calibration (correlation between observed and expected rates was r = 1.00). The model performance was confirmed across medical centers and clinical subgroups.
Conclusions: Our risk prediction model uses 16 readily obtainable preoperative variables. This model, which provides a patient-specific estimate of the need for transfusion, offers clinicians a guide for decision making and evaluating the effectiveness of blood management strategies.
The Relationship between Intra-Operative Transfusions and Nadir Hematocrit on Post-Operative Outcomes after Cardiac Surgery
Abstract: Uncertainty exists regarding the optimal strategy for the management of anemia in the setting of cardiac surgery. We sought to improve our understanding of the role of intra-operative hematocrit (HCT) and transfusions on peri-operative outcomes following cardiac surgery. A total of 18,886 patients undergoing on-pump cardiac surgery were identified from a multi-institutional registry including surgical and perfusion data. Patients were divided into four groups based on their intra-operative nadir HCT (<21 or ≥21) and whether or not they received intra-operative red blood cell (+RBC or −RBC) transfusions. Outcomes were adjusted for the Society of Thoracic Surgeons predicted risk of mortality (PROM), pre-operative HCT, and medical center. Regardless of nadir HCT cohort, those who received a transfusion had higher PROM relative to patients who did not receive a transfusion. The mean PROM was significantly higher among those HCT ≥21 + RBC (5.3%) vs. HCT ≥ 21 − RBC (1.9%), p < .001. Similarly, the PROM was significantly higher among HCT <21 + RBC (5.1%) vs. those HCT <21 − RBC (3.1%), p < .001. Adjusted outcomes demonstrated an increased impact of RBC transfusions on adverse outcomes irrespective of nadir HCT including stroke (p < .001), renal failure (p < .001), prolonged ventilation (p < .001), and mortality (p< .001). This study demonstrates that transfusions have a more profound effect on post-operative cardiac surgery outcomes than anemia.
Greater Volume of Acute Normovolemic Hemodilution May Aid in Reducing Blood Transfusions After Cardiac Surgery
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, <400 mL, 400 to 799 mL, ≥800 mL) 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, body surface area, preoperative hematocrit, and center.
Results: The ANH was used in 17% of the patients. ANH was associated with a reduction in RBC transfusions (RRadj [adjusted risk ratio] 0.74, p < 0.001). Patients having 800 mL or greater 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 with 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.
Nadir Hematocrit on Bypass and Rates of Acute Kidney Injury: Does Sex Matter?
Background: Reports have associated nadir hematocrit (Hct) on cardiopulmonary bypass with the occurrence of renal dysfunction. Recent literature has suggested that women, although more often exposed to lower nadir Hct, have a lower risk of postoperative renal dysfunction. We assessed whether this relationship held across a large multicenter registry.
Methods: We undertook a prospective, observational study of 15,221 nondialysis-dependent patients (10,376 male, 68.2%; 4,845 female, 31.8%) undergoing cardiac surgery between 2010 and 2014 across 26 institutions in Michigan. We calculated crude and adjusted OR between nadir Hct during cardiopulmonary bypass and stage 2 or 3 acute kidney injury (AKI), and tested the interaction of sex and nadir Hct. The predicted probability of AKI was plotted separately for men and women.
Results: Nadir Hct less than 21% occurred among 16.6% of patients, although less commonly among men (9.5%) than women (31.9%; p < 0.001). Acute kidney injury occurred among 2.7% of patients, with small absolute differences between men and women (2.6% versus 3.0%, p = 0.20). There was a significant interaction between sex and nadir Hct (p = 0.009). The effect of nadir Hct on AKI was stronger among male patients (adjusted odds ratio per 1 unit decrease in nadir Hct 1.10, 95% confidence interval: 1.05 to 1.13) than female patients (adjusted odds ratio 1.01, 95% CI: 0.96, 1.06).
Conclusions: Lower nadir Hct was associated with an increased risk of AKI, and the effect appears to be stronger among men than women. Understanding of the mechanism underlying this association remains uncertain, although these results suggest the need to limit exposure to lower nadir Hct, especially for male patients.
Impact of Ultrafiltration on Kidney Injury After Cardiac Surgery: The Michigan Experience
Background: This study examines the relationship between the use and volume of conventional ultrafiltration (CUF) and the risk of acute kidney injury (AKI) after isolated on-pump coronary artery bypass graft surgery.
Methods: A total of 6,407 consecutive patients underwent isolated on-pump coronary artery bypass graft surgery between 2010 and 2013 at 21 medical centers participating in the PERFusion Measures and Outcomes (PERForm) registry. We assessed the effect of CUF use on AKI and other postoperative sequelae using a generalized linear mixed-effect model with a logit link. We also modeled the effect of increasing volume of CUF per weight on AKI, and tested for any modification by a patient’s preoperative kidney function.
Results: Patients having CUF were more likely to have diabetes, vascular disease, chronic obstructive pulmonary disease, congestive heart failure, history of a myocardial infarction, or an intraaortic balloon pump (p < 0.05). They had lower preoperative and nadir hematocrits, creatinine clearance, and ejection fraction (p < 0.05). Patients exposed to CUF had higher adjusted risk of AKI (adjusted odds ratio, 1.36; p = 0.002), although similar rates of death, stroke, and reoperation for bleeding (p > 0.05). The risk of AKI was modified by a patient’s preoperative kidney function (p < 0.0004). Among patients with a creatinine clearance of less than 99.6 mL/min (95% confidence interval, 67.6 to 137.5), increasing volume of CUF was associated with a higher risk of AKI.
Conclusions: Patients exposed to CUF had a higher adjusted risk of AKI. Clinical teams should consider lower volumes of CUF among patients with low creatinine clearance to minimize the risk of AKI.
Validation of a Perfusion Registry: Methodological Approach and Initial Findings
Abstract: Although regional and national registries exist to measure and report performance of cardiac surgical programs, few registries exist dedicated to the practice of cardiopulmonary bypass (CPB). We developed and implemented a cardiovascular perfusion registry (Perfusion Measures and outcomes [PERForm] Registry) within the structure of the Michigan Society of Thoracic and Cardiovascular Surgeons (MSTCVS) to improve our understanding of the practice of CPB. The PERForm Registry comprises data elements describing the practice of CPB. Fourteen medical centers within MSTCVS have voluntarily reported these data on procedures in which CPB is used. We validated the case count among procedures performed between January 1, 2011 to December 31, 2011, and validated the values among 20 fields at three medical centers. We queried database managers at all 14 medical centers to identify the infrastructure that contributed to best overall data collection performance. We found that 98% of all records submitted to the PERForm and 95% of those submitted to the Society of Thoracic Surgeons (STS) matched. We found quite favorable agreement in our audit of select fields (95.8%). Those centers with the most favorable performance in this validation study were more likely to use electronic data capture, have a perfusionist as the STS database manager, and have involvement of the STS database manager in the PERForm or STS databases. We successfully and accurately collected data concerning cardiovascular perfusion among 14 institutions in conjunction with the MSTCVS. Future efforts will focus on expanding data collection to all MSTCVS participating institutions as well as more broadly outside of Michigan.
Cardiac Surgeons and the Quality Movement: the Michigan Experience
The Michigan Society of Thoracic and Cardiovascular Surgeons (MSTCVS) was founded in 1965 during an era when many national, regional, and state speciality societies were beginning. The first meeting of what was initially called the Michigan Society of Thoracic Surgeons was held on September 21, 1965 in Detroit in conjunction with the Michigan State Medical Society (personal communication, Allen Silbergleit, MD, PhD, Historian, Michigan Society of Thoracic and Cardiovascular Surgeons, August 2008). The initial meeting was attended by 17 of the 60 board certified thoracic surgeons in Michigan. Dr Cameron Haight, Head of the Section of Thoracic Surgery at the University of Michigan in Ann Arbor, was the President of the society.
As one of the first state thoracic organizations, plans were implemented for an annual meeting, which in the initial years often occurred in conjunction with the American College of Surgeons Michigan Chapter meeting. In the mid-1980s the Michigan Society of Thoracic Surgeons created its own meeting time and moved the annual meeting to resort areas in northern Michigan in late summer. Recognizing the evolution of the speciality of Thoracic Surgery, in 1988 the name of the organization was changed from the Michigan Society of Thoracic Surgeons to the Michigan Society of Thoracic and Cardiovascular Surgeons. Today, the Society has over 100 board-certified thoracic surgeon members, as well as associate members, including data managers, physician assistants, and perfusionists.
Since its inception in 1965 the society has had yearly meetings with the initial focus of these meetings on case presentations, as well as providing an opportunity for house officers from Michigan programs in general surgery, and the two thoracic surgical residency programs to present scientific papers. Presentations from invited cardiac and thoracic surgeon guests with expertise in various areas have become a part of the meeting programs in recent years.