Robert C. Groom

Optimal Perfusion During Cardiopulmonary Bypass: An Evidence-Based Approach

In this review, we summarize the best available evidence to guide the conduct of adult cardiopulmonary bypass (CPB) to achieve “optimal” perfusion. At the present time, there is considerable controversy relating to appropriate management of physiologic variables during CPB. Low-risk patients tolerate mean arterial blood pressures of 50–60 mm Hg without apparent complications, although limited data suggest that higher-risk patients may benefit from mean arterial blood pressures >70 mm Hg. The optimal hematocrit on CPB has not been defined, with large data-based investigations demonstrating that both severe hemodilution and transfusion of packed red blood cells increase the risk of adverse postoperative outcomes. Oxygen delivery is determined by the pump flow rate and the arterial oxygen content and organ injury may be prevented during more severe hemodilutional anemia by increasing pump flow rates. Furthermore, the optimal temperature during CPB likely varies with physiologic goals, and recent data suggest that aggressive rewarming practices may contribute to neurologic injury. The design of components of the CPB circuit may also influence tissue perfusion and outcomes. Although there are theoretical advantages to centrifugal blood pumps over roller pumps, it has been difficult to demonstrate that the use of centrifugal pumps improves clinical outcomes. Heparin coating of the CPB circuit may attenuate inflammatory and coagulation pathways, but has not been clearly demonstrated to reduce major morbidity and mortality. Similarly, no distinct clinical benefits have been observed when open venous reservoirs have been compared to closed systems. In conclusion, there are currently limited data upon which to confidently make strong recommendations regarding how to conduct optimal CPB. There is a critical need for randomized trials assessing clinically significant outcomes, particularly in high-risk patients.

Intraoperative Red Blood Cell Transfusion During Coronary Artery Bypass Graft Surgery Increases the Risk of Postoperative Low-Output Heart Failure

Background— Hemodilutional anemia during cardiopulmonary bypass (CPB) is associated with increased mortality during coronary artery bypass graft (CABG) surgery. The impact of intraoperative red blood cell (RBC) transfusion to treat anemia during surgery is less understood. We examined the relationship between anemia during CPB, RBC transfusion, and risk of low-output heart failure (LOF). Methods and Results— Data were collected on 8004 isolated CABG patients in northern New England between 1996 and 2004. Patients were excluded if they experienced postoperative bleeding or received ≥3 units of transfused RBCs. LOF was defined as need for intraoperative or postoperative intra-aortic balloon pump, return to CPB, or ≥2 inotropes at 48 hours. Having a lower nadir HCT was also associated with an increased risk of developing LOF (adjusted odds ratio, 0.90; 95% CI, 0.82 to 0.92; P=0.016), and that risk was further increased when patients received RBC transfusion. When adjusted for nadir hematocrit, exposure to RBC transfusion was a significant, independent predictor of LOF (adjusted odds ratio, 1.27; 95% CI, 1.00 to 1.61; P=0.047). Conclusions— In this study, we observed that exposure to both hemodilutional anemia and RBC transfusion during surgery are associated with increased risk of LOF, defined as placement of an intraoperative or postoperative intra-aortic balloon pump, return to CPB after initial separation, or treatment with ≥2 inotropes at 48 hours postoperatively, after CABG. The risk of LOF is greater among patients exposed to intraoperative RBCs versus anemia alone.

Effect of the Perioperative Blood Transfusion and Blood Conservation in Cardiac Surgery Clinical Practice Guidelines of the Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesiologists upon Clinical Practices

BACKGROUND: The 2007 Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesiologists Clinical Practice Guideline for Perioperative Blood Transfusion and Blood Conservation in Cardiac Surgery was recently promulgated and has received much attention. Using a survey of cardiac anesthesiologists and perfusionists’ clinical practice, we aimed to assess the current practices of perfusion, anesthesia, and surgery, as recommended by the Guidelines, and to also determine the role the Guidelines had in changing these practices. METHODS: Nontrainee members of the Society of Cardiovascular Anesthesiologists, the American Academy of Cardiovascular Perfusion, the Canadian Society of Clinical Perfusion, and the American Society of ExtraCorporeal Technology were surveyed using a standardized survey instrument that examined clinical practices and responses to the Guidelines. RESULTS: A total of 1402 surveys from 1061 institutions principally in the United States (677 institutions) and Canada (34 institutions) were returned, a 32% response rate. There was wide distribution of the Guidelines with 78% of anesthesiologists and 67% of perfusionists reporting having read all, part, or a summary of the Guidelines. However, only 20% of respondents reported that an institutional discussion had taken place as a result of the Guidelines, and only 14% of respondents reported that an institutional monitoring group had been formed. There was wide variability in current preoperative testing, perfusion, surgical, and pharmacological practices reported by respondents. Twenty-six percent of respondents reported 1 or more practice changes in response to the Guidelines. The changes made were reported to be highly (9%) or somewhat (31%) effective in reducing overall transfusion rates. Only 4 of 38 Guideline recommendations were reported by >5% of respondents to have been changed in response to the Guidelines. CONCLUSIONS: Wide variation in clinical practices of cardiac surgery was reported. Little change in clinical practices was attributed to the Society of Thoracic Surgeons/Society of Cardiovascular Anesthesiologists Guidelines.

Same Admission Cardiac Catheterization and Cardiac Surgery: Is There an Increased Incidence of Acute Kidney Injury?

BACKGROUND Acute kidney injury (AKI) is predictive of increased long-term mortality after cardiac surgery. Patients often undergo surgery after cardiac catheterization during the same admission for reasons of instability and threatening anatomy as well as nonurgent reasons such as patient convenience. We hypothesized that patients undergoing cardiac catheterization and cardiac surgery during the same admission are more likely to develop AKI after cardiac surgery than patients for whom surgery is performed on a later admission. METHODS We prospectively enrolled 668 nonemergent adult cardiac surgical cases. Patients having heart catheterization were divided into two groups: cardiac catheterization followed by cardiac surgery during the same hospital admission (same admission) or catheterization followed by surgery during a later admission (later admission). The AKI was defined by an increase in serum creatinine from baseline by 50% or greater or 0.3 (mg/dL) or greater. Univariable and multivariable logistic regression and propensity-matched analyses were conducted. RESULTS The incidence of AKI was significantly higher in the patients who had same admission cardiac catheterization and surgery (50.2%) compared with patients who had surgery on a later admission (33.7%, p = 0.009). The adjusted odds ratio for surgery on a later admission was 1.54 (95% confidence interval: 1.11 to 2.13) suggesting a 54% increased risk of AKI. Propensity-matched results were similar with 1.58 (95% confidence interval: 1.13 to 2.22). CONCLUSIONS When cardiac catheterization and cardiac surgery occur during the same hospitalization, there is an increased risk for postoperative AKI. After cardiac catheterization, discharge and readmission for nonurgent surgery should be considered as such an approach might reduce the risk of AKI.

Size makes a difference: use of a low-prime cardiopulmonary bypass circuit and autologous priming in small adults

Low hematocrit (Hct < 20) during cardiopulmonary bypass (CPB) is associated with higher mortality and other adverse outcomes. More frequently, low Hct is encountered in patients with small body size and women patients. This prompted us to take an aggressive approach in our care of these patients, involving a strategy for predicting patients at risk of low Hct, with the aid of an electronic worksheet that accurately predicts CPB Hct, and two prevention strategies: use of a low-prime CPB circuit (LP) for all adult patients with a body surface area (BSA) <1.7 m2 and use of autologous circuit priming (AP), in addition to the low-circuit volume in some patients. The two cohorts of patients in whom these techniques were employed were compared to a group matched for body size where our standard adult circuit (STD) was used. There were 233 patients in the standard group, 139 in the LP group, and 68 in the LP/AP group. The CPB circuit prime volume was 1710 ml for the STD group and 1110 ml for the LP group. Use of autologous priming techniques further reduced the prime volume by 545 ± 139 ml. The incidence of low Hct (<20%) during CPB was thus reduced from 70% to 15% (p = 0.001) when using both techniques together without increasing red blood cell (RBC) transfusions. These changes in perfusion management resulted in a reduction in the incidence of renal complications (STD = 9.4%, LP = 6.5% (ns) and LP/AP = 0%, p = 0.008) and a decrease in hospital mortality (STD = 9.8%, LP = 4.3, p = 0.05 and LP/AP = 0%, p=. 007). Matching the CPB circuit to the patient’s size and use of other prime-reduction strategies can increase Hct levels during CPB and improve outcomes in smaller patients, who are susceptible to increased risk.

Paediatric perfusion practice in North America: an update

In August 1994, an updated survey questionnaire was mailed to each paediatric open-heart surgery programme in North America as a follow-up to the 1989 paediatric survey. The survey requested demographic data, equipment selection criteria and specific perfusion techniques for paediatric patients. The earlier survey revealed a wide range of clinical practice. Data from the recent survey were compared with the 1989 survey to identify current programme demographics and trends in equipment use and techniques. Responses were received from 125 hospitals (110 active programmes and 15 programmes that do not perform paediatric open-heart surgery) for a response rate of 74%. Of the 110 active centres, 77 perform both adult and paediatric cardiac surgery, and 33 perform paediatric surgery exclusively. Forty-three centres reported that they perform paediatric cardiac transplantation, an increase from 35 centres in 1989. Total caseload increased by more than 8% per year from 1988 to 1994. In 1994, 18% of the patients were operated upon during the first month of life (versus 15% in 1989), and 46% were operated on during the first year of life (versus 45% in 1989) While the 1989 survey was characterized by a high degree of heterogeneity in equipment and techniques, the recent survey reveals a trend toward homogeneity among respondents. The use of membrane oxygenation and arterial line filtration has become universal, and there was an increase in the use of all types of safety devices in the cardiopulmonary bypass circuit.

High or low hematocrits during cardiopulmonary bypass for patients undergoing coronary artery bypass graft surgery? An evidence-based approach to the question

We have observed an inverse relationship between a CPB Hct <20% and the need for cardiac support and hospital mortality. These data call for an aggressive and concerted effort to avoid a CPB Hct of <20%. The focus should be directed at women and small men since this subset of patients are most likely to experience low CPB Hct. A comprehensive, multimodality blood-conservation plan that involves the use of erythropoietin, aprotinin, preoperative autologous donation, shed blood reinfusion, and minimal phlebotomy for blood testing was proposed by Rosengart and colleagues based on their experience in caring for 50 Jehovahs Witness patients. Efforts to conserve blood and ensure hemostasis should cover the entire spectrum of care, including preoperative phlebotomy (for blood tests), diagnostic and interventional procedures, and intraoperative and postoperative care. Further work is needed to understand the mechanism for the relationship between low Hct and adverse outcomes. Each open-heart center should consider the Hct question carefully, examining both the published literature and their own results related to CPB Hct and patient outcomes.

Detection and Elimination of Microemboli Related to Cardiopulmonary Bypass

Background—Neurobehavioral impairment is a common complication of coronary bypass surgery. Cerebral microemboli during cardiopulmonary bypass (CPB) are a principal mechanism of cognitive injury. The aim of this work was to study the occurrence of cerebral embolism during CPB and to evaluate the effectiveness of evidence-based CPB circuit component and process changes on the exposure of the patient to emboli. Methods and Results—M-Mode Doppler was used to detect emboli in the inflow and outflow of cardiopulmonary circuit and in the right and left middle cerebral arteries. Doppler signals were merged into a single display to allow real-time associations between discrete clinical techniques and emboli detection. One hundred sixty-nine isolated coronary artery bypass grafting (CABG) patients were studied between 2002 and 2008. There was no statistical difference in median microemboli detected in the inflow of the CPB circuit, (Phase I, 931; Phase II, 1214; Phase III, 1253; Phase IV, 1125; F [3,158]=0.8, P=0.96). Significant changes occurred in median microemboli detected in the outflow of the CPB circuit across phases, (Phase I, 702; Phase II, 572; Phase III, 596; Phase IV, 85; F [3,157]=13.1, P<0.001). Significant changes also occurred in median microemboli detected in the brain across phases, (Phase I, 604; Phase II, 429; Phase III, 407; Phase IV, 138; F [3,153]=14.4, P<0.001). Changes in the cardiopulmonary bypass circuit were associated with an 87.9% (702 versus 85) reduction in median microemboli in the outflow of the CPB circuit (P<0.001), and a 77.2% (604 versus 146) reduction in microemboli in the brain (P<0.001). Conclusions—Changes in CPB techniques and circuit components, including filter size and type of pump, resulted in a reduction in more than 75% of cerebral microemboli.

Glycemic Control and Reduction of Deep Sternal Wound Infection Rates: A Multidisciplinary Approach

OBJECTIVE To demonstrate the multidisciplinary interactions and tools required to effect changes in the processes of care to achieve tight glycemic control (TGC) and reduce deep sternal wound infection (DSWI) rates in patients undergoing cardiac surgery. DESIGN A retrospective cohort analysis comparing the rate of DSWI before and after implementing a multidisciplinary TGC initiative. SETTING A cardiac surgical program in a tertiary care community hospital in New England. PATIENTS A total of 3065 consecutive adult patients undergoing cardiac surgery who were operated on between January 1, 2004, and December 31, 2006. INTERVENTIONS Evidence demonstrating the relationship between hyperglycemia and DSWI was presented to the multidisciplinary group caring for patients undergoing cardiac surgery. In addition, special emphasis was placed on nursing feedback and in-service training. A cumbersome glycemic management text protocol was replaced with a novel color-coded bedside tool (nomogram) to guide the bedside management of hyperglycemia. Subsequently, an algorithm for the transition to a home regimen was developed, which further improved standardization of care and ease of management. MAIN OUTCOME MEASURES Hourly blood glucose level monitoring and the incidence of DSWI. RESULTS Eighteen months after the new program was initiated, the DSWI rate decreased by more than 60% from 2.6% to 1.0%, when compared with the preceding 18 months (P < .001). CONCLUSION A TGC program using a novel tool in a multidisciplinary setting was successfully and safely established, resulting in sustained improvement in the DSWI rate.

Aortic cannula velocimetry

Robert C Groom, Aaron G Hill The Virginia Heart Center at Fairfax Hospital, Falls Church, Virginia, Barry Kuban The Ohio State University Department of Biomedical Engineering, Columbus, Ohio, William Oneill 3M Cardiovascular, Incorporated, Ann Arbor, Michigan, Bechara F Akl, Alan M Speir, James Koningsberg, Gregory T Sprissler, Mohamed Shakoor, Paul S Massimiano, Nelson A Burton, Robert A Albus, Quentin Macmanus and Edward A Lefrak The Virginia Heart Center