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Eur J Cardiothorac Surg 1999;16:206-210
© 1999 Elsevier Science NL

Transfusion after coronary artery bypass surgery: the impact of heparin-bonded circuits

Chris Brown Mahoneya, Gerald M. Lemoleb

a Carlson School of Management, University of Minnesota, 3-285 CSOM Building, 321-19th Avenue S, Minneapolis, MN 55455, USA
b Christiana Care Health Services, Newark, DE, USA

Corresponding author. Tel.: +1-612-6249013 or 6465296; fax: +1-651-6446506
e-mail: cmahoney{at}csom.umn.edu


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 Appendix A
 References
 
Objective: To identify the impact of heparin bonded (Carmeda®) circuits on the need for transfusion of packed red blood cells (PRBC) after CABG independent of the influence of patient, procedural, and surgical experience variables. Methods: A prospective, randomized trial examined the impact of heparin-bonded circuits in 210 patients undergoing coronary artery bypass surgery at Medical Center of Delaware (Christiana Care Health Services). Patients were randomized to either non-bonded circuits or heparin-bonded (Carmeda®) circuits. There were no significant differences in patient characteristics between the treatment and control group. A multivariate analysis was performed to identify the independent predictors of both the need for transfusion (logistic) and number of units of PRBC transfused (OLS). Results: The only significant (P<0.05) independent predictors of need for transfusion were gender (odds ratio (OR)=0.35 for males), use of anticoagulants prior to surgery (OR=2.09), cross-clamp time (OR=1.03 for each extra minute), and use of heparin-bonded circuits (OR=0.50 for patients in the heparin-bonded; Carmeda®, circuit group). The only significant independent predictors of number of PRBCs were anticoagulants prior to surgery, cross-clamp time, catheterization procedure on the same day, body surface area, and use of heparin-bonded circuits. Other patient demographic variables, comorbidities, and surgical variables were not significant independent predictors of the need for transfusion or the number of units transfused. Conclusions: Several factors influence the probability of transfusion that patients face following coronary artery bypass surgery. The probability of transfusion is 50% less and the number of PRBCs transfused are 1.42 units less when heparin-bonded (Carmeda®) circuits are used, adjusted for patient demographics, comorbidities, or surgical variables.

Key Words: Cardiopulmonary bypass • Heparin bonded circuit • Blood transfusion • Clinical outcomes


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 Appendix A
 References
 
Patients undergoing cardiac bypass surgery (CPB) today are different in many ways that challenge those providing surgical management: age, gender, cardiac condition, and especially comorbidities [1–3]. Surgeons also see a greater number of patients undergoing cardiac surgery for a second time. At the same time, management of patient outcomes following open-heart surgery with CPB is becoming increasingly more important. This is, at least in part, because any increase in perioperative complications will result in higher costs. Hospital costs are only part of the costs incurred when patients experience an increased number of adverse outcomes. An increase in adverse outcomes most frequently results in a decreased quality of life for the patient, a more extensive loss of work productivity, and additional costs of providing care beyond the hospitalization period. While these post-hospitalization costs are extremely difficult to track, any decrease in adverse outcomes patients experience during their hospitalization is likely to result in lower these costs as well.

CPB surgery on the multimorbid patient is more difficult to manage. CPB is a significant stress for the patient, completely separate from the surgical procedure itself. Numerous comorbidities may require additional therapeutic or technological interventions to maximize positive outcomes following CPB. Given the increasing number of multimorbid patients, further advances in this technology may improve overall patient outcome in times of limited resources.

One technological advance designed to decrease the stress to which the patient is subjected is heparin-bonded circuits. Their purpose is to limit the blood-material reaction, enhance biocompatibility and thromboresistance, and limit the post-perfusion syndrome [4]. Heparin-bonded surfaces change the blood-surface interface, resulting in reduced activations of neutrophils, platelets, and complement [5–10].

Heparin is bonded to the surfaces of the cardiopulmonary bypass circuit to increase biocompatibility. Surgical procedures requiring use of a cardiopulmonary bypass circuit have been compromised in their success by the clotting of blood in the extracorporeal circuit [11,12]. As the blood contacts a foreign surface, numerous reactions occur that initiates complement activation and may result in the ‘whole body inflammatory response’ [13]. The purpose of bonding heparin to all surfaces the blood comes in contact with is to limit the blood-material reaction that occurs and thereby reduce the incidence of postperfusion syndrome.

The use of heparin-bonded circuits to improve patient's experience during and outcomes after cardiopulmonary bypass has been well documented [4,5,7–10,14–18]. Many of these studies have either addressed one particular outcome such as need for transfusion or concentrated on the mechanisms by which changes in patient outcomes occur, e.g. reduced complement activation [5]. Other studies have addressed changing heparin protocol during CPB with the use of heparin-bonded circuits [4,17]. Few published studies [19,20] have examined several of the numerous patient endpoint outcomes, let alone cost savings resulting from improved patient outcomes. Rather than focusing on the physiologic changes, this study examined patient outcomes regarding blood transfusion during and after cardiac surgery resulting from use of heparin-bonded circuits (Carmeda®).


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Results
 4. Discussion
 5. Conclusion
 Appendix A
 References
 
A prospective, randomized study was carried out covering 210 patients undergoing routine open-heart surgery with CPB between July 1995 and October 1995. All patients were randomly assigned to either a heparin-bonded (Carmeda®) circuit or a non-bonded circuit. All data pre and post-operative, as well as surgical parameters, were collected using the Society for Thoracic Surgeons database guidelines and protocol.

Patients included were coronary artery bypass grafting (CABG), valve replacements, and other combined procedures. No patients were excluded. Patients were randomly assigned to either study group. Extracorporeal circuits used were identical in both groups except for the heparin-bonding and the oxygenator. The heparin-bonded group (n=102) had a Medtronic Maxima® oxygenator and the control (n=108) had an Avecor® oxygenator. Cannulas in the heparin-bonded group were also heparin-bonded as were the cardioplegia systems. Both circuits contained a BioPump® Centrifugal Pump (Medtronic Bio-Medicus, Eden Prairie, MN) as the arterial pump. A hollow filter hemoconcentrator was used if hemoglobin became too low.

Preoperative medication and anesthetic management was consistent during the study. The protocol for postoperative care was identical for both groups. All patients received 40 mg/kg body weight heparin. Additional doses were administered at ACT levels of less than 550 s. Protamine was given at a ratio of 2.5 mg/kg initial dose. in open heart procedures was performed with hypothermia between 27 and 29°C and additional cold crystalloid high volume cardioplegia. All CABG cases were done under intermittent aortic cross clamping with mild hypothermia (27–29°C) to provide myocardial protection. Trigger for intra-operative blood product use was a hematocrit of 17%. Postoperatively, a hemoglobin of 9.5 mg/dl was accepted without the need for transfusions. The routine antibiotic treatment was Cephazolin, with Vancomycin as an alternative for those allergic.

2.1. Statistical analysis
Patient demographics (means and SDs) and the outcome variables used in this study are presented in Table 1. Much additional data, as per the Society of Thoracic Surgeons data base collection protocol, was collected that is not included in this study. No pre-operative risk factors demonstrated significant differences.


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  		Table 1. Patient demographics and risk factors. P-values are for two sample t-tests

 
Statistical analysis was performed using ordinary (nonweighted) least squares and logistic multiple regression analysis. The effect of independent variables on the continuous dependent outcome variable (e.g. units of blood) was determined using a multiple linear regression model. Dichotomous dependent outcome variables’ effect (e.g. need for homologous transfusion) was determined using a logistic regression model. Only those variables having a P value less than 0.05 were considered to contribute significantly to predicting outcome variables.


   3. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
4. Discussion
 5. Conclusion
 Appendix A
 References
 
Table 1 presents variables of interest from patient profiles for both the heparin-bonded and non-bonded group. Both preoperative and intraoperative risk factors were similar; no significant differences existed between the heparin-bonded and the non-bonded groups. No patients were excluded during the study period.

Independent predictors of the need for homologous transfusion were identified with multivariate logistic analyses to ascertain that differences in patient profiles did not account for the differences seen between the heparin-bonded and the non-bonded group. These significant (P<0.05) independent predictors were gender, anticoagulant therapy pre-operatively, cross clamp time, and use of a heparin-bonded circuit. Odds ratios were 0.37 for male gender, 2.09 for the use of anticoagulant therapy pre-operatively, 1.03 for minutes of cross-clamp time, and 0.50 for use of the heparin-bonded (Carmeda®) circuit. Age, diabetes, previous MI, hypertension, left main disease, body surface area, prior CVA, chronic obstructive pulmonary disease, ejection fraction, operative status (elective versus urgent), intravenous nitroglycerin, or total pump time were not independent predictors of the need for non-autologous transfusion in this study (Table 2). The odds-ratio (Table 2) for heparin-bonded circuits is 0.50; those patients in the heparin-bonded (Carmeda®) circuit group were 50% less likely to require transfusion independent of anticoagulant use, cross clamp time, and gender.


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  		Table 2. Multivariate analyses of need for non-autologous blood (logit)a

 
Independent predictors of the number of units of homologous blood transfused were identified with multivariate least squares analyses to ascertain that differences in patient profiles did not account for the differences seen between the heparin-bonded and the non-bonded group. These significant independent predictors were body surface area, anticoagulant therapy pre-operatively, cross clamp time, cathed the same day as surgery, and use of a heparin-bonded (Carmeda®) circuit. Values of the coefficients on the number of units of blood transfused were a decrease of 2.79 units of blood when body surface area decreased by one full unit, 0.86 more units of blood for patients on anticoagulant therapy pre-operatively, an increase of 0.05 units of blood for each minute of cross-clamp time, an increase of 1.20 units of blood for patients who were cathed the same day as surgery, and a decrease of 1.42 units of blood for patients in the heparin-bonded (Carmeda®) circuit group. Age, diabetes, previous MI, hypertension, left main disease, body surface area, prior CVA, chronic obstructive pulmonary disease, ejection fraction, operative status (elective versus urgent), intravenous nitroglycerin, or total pump time were not independent predictors of the need for non-autologous transfusion in this study (Table 3). Heparin-bonded circuits decreased the number of units of blood by 1.4, adjusted for anticoagulant use, cross clamp time, cathed the same day, and body surface area.


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  		Table 3. Multivariate analyses of units of non-autologous blood (ols)a

 
Patient outcomes showed improved clinical results (Table 4). Significant differences between the heparin-bonded and the non-bonded group were found in incidence of non-autologous blood transfusion (57% vs. 70%; P=0.02), units of red blood cells transfused (2.35±2.73 vs. 3.42±4.02; P=0.0164), extended intubation (61% vs. 76%; P=0.02), and length of stay (7.05±3.1 vs. 9.94±13.5; P=0.0152). Numerous other clinical results exhibited a trend of improved outcomes in the heparin-bonded (Carmeda®) group but did not achieve statistically significant levels. These outcomes were pulmonary complications, renal complications, reoperation for bleeding, and extended need for intubation. Mortality and operative mortality were almost identical, showing no significant differences.


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  		Table 4. Clinical outcomes

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
5. Conclusion
 Appendix A
 References
 
The artificial surface of cardiopulmonary bypass circuits is a potent stimulus for platelet activation [13]. This inflammatory reaction is thought to be responsible for much of the morbidity following cardiopulmonary bypass. Bonding heparin to all surfaces that come into contact with blood during CPB was developed in an attempt to limit the blood-material reaction, enhance biocompatibility and thromboresistance, and limit the post-perfusion syndrome [17]. Heparin-bonded circuits are generally viewed to improve biocompatibility and thromboresisitance as the heparin layer mimics the native endothelium [13]. Many studies address platelet activation and the impact on other blood components [5,7,9,14–16,18]. However, as Aldea [4] points out, the clinical importance of heparin-bonded circuits is not agreed on. Clinical results of this study are important as they confirm some published research findings [4,17,21,22] and refute others [6] resulting from use of heparin-bonded circuits. Numerous differences in experimental designs (patient populations, circuit types varying, etc.) as well as varying definitions of complications, changing treatment thresholds, and inconsistent statistical analysis of data could also account for some of these different findings.

The results of the multivariate analyses, both in terms of need for non-autologous blood transfusion and the number of units of red blood cells given, showed a significant (P<0.05) positive impact resulting from the use of the heparin-bonded circuit (Carmeda®).

Patients in this study exhibited improvement in terms of adverse outcomes. Not only did the incidence of non-autologous transfusion decrease significantly (P<0.05), the magnitude decreased significantly, as well. Heparin-bonded (Carmeda®) circuits had a significant, positive impact on the need for transfusion of non-autologous blood and on the magnitude of transfusion when it was necessary. Significant findings also favored the heparin-bonded (Carmeda®) group for length of stay (day of surgery to discharge) and need for extended intubation. These results are in concurrence with those from other studies [13,17,23].


   5. Conclusion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
Appendix A
 References
 
The use of heparin-bonded circuits improved the clinical results of CPB for these patients, adjusted for other factors. These results, which corroborate those in other recent studies [8,15,17,20,22,23], demonstrate that patients benefit from the use of heparin-bonded (Carmeda®) circuits. Results such as these suggest careful consideration of the type of circuit used for CPB. The opportunity to positively impact patient clinical outcomes should not be ignored. Further study on the impact these improved clinical results have on costs during and after hospitalization would prove beneficial to decision-makers.


   Footnotes
 
Presented at the 12th Annual Meeting of the European Association for Cardio-thoracic Surgery, Brussels, Belgium, September 20–23, 1998.


   Appendix A
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 Appendix A
References
 
Conference discussion
Dr L. von Segesser (Lausanne, Switzerland): Can you tell us something about cost?

Dr Mahoney: In terms of costs, with the information that's available until the surgeon and perfusionist go back and code some of the complications more specifically, there's about $2200 of difference between these two groups due to the incidence of transfusion, length of stay and number of units of red blood cells. This does not include pulmonary or renal complications.

Dr von Segesser: And what is the added cost of the devices used?

Dr Mahoney: That is somewhat difficult for me to comment on because the device cost is not the same for all institutions. People negotiate different prices and I am not sure what the exact cost of the device is. However, the cost is definitely less than the $2200 difference from just transfusion costs and length of stay costs.

Dr A. Nasri (Zalaegerszeg, Hungary): I have noticed that there are pulmonary complications and the difference was significant. Can you tell us what kind of complications you had and why there is a significant differentiation between the two types?

Dr Mahoney: For pulmonary complications, I am having them go back and code exactly what type they are. Some of them I know were respiratory failure, there was an increased incidence of respiratory failure in the non-bonded group, and I think this is a very interesting question. I have looked at and worked with analyzing the data from about seven different medical centers now, looking at use of heparin-bonded circuits, some of them also vary heparin protocol. But I haven't seen anyone publish or present on exactly what this difference in pulmonary complications results from. This is a trend that you see across all studies. I have seen data on children, neonates who are having surgery on congenital heart defects, and this difference in pulmonary complications is more pronounced. I don't know the mechanism, I haven't seen anybody specify the mechanism, but it is very clear that this occurs repeatedly. The difference in the pulmonary complications is consistent across different institutions and patient populations.


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 Appendix A
 References
 

  1. Stump D.A., Rogers A.T., Hammon J.W., Newman S.P. Cerebral emboli and cognitive outcome after cardiac surgery. J Cardiothorac Vas Anes 1996;10(1):113-119.
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  6. Gorman R., Ziats N., Gikakis N., Edmunds H., et al. Surface-bound heparin fails to reduce thrombin formation during clinical cardiopulmonary bypass. J Thorac Cardiovasc Surg 1996;111:1-12.[Abstract/Free Full Text]
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  9. Ovrum E., Mollnes T., Fosse E., et al. High and low heparin dose with heparin-coated cardiopulmonary bypass circuits: activation of complement and granulocytes. Ann Thorac Surg 1995;60:1755-1761.[Abstract/Free Full Text]
  10. Pekna M., Hagman L., Halden E., et al. Complement activation during cardiopulmonary bypass: effects of immobilized heparin. Ann Thorac Surg 1994;58:421-424.[Abstract]
  11. Gibbon J., Jr Application of a mechanical heart and lung apparatus to cardiac surgery. Minn Med 1954;37:171-185.[Medline]
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  13. Kirklin J., Westaby S., Blackstone E., et al. Complement and the damaging effects of cardiopulmonary bypass. J Thorac Cardiovasc Surg 1983;86:845-857.[Abstract]
  14. Von Segessor L., Weiss B., Pasic M., et al. Risk and benefits of low systemic heparinization during open-heart operations. Ann Thorac Surg 1994;58:391-398.[Abstract]
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  16. Gu Y., van Oeveren W., van der Kamp K., Akkerman C., Boonstra P., Wildevuur R. Heparin-coating of extracorporeal circuits reduces thrombin formation in patients undergoing cardiopulmonary bypass. Perfusion 1991;6:221-225.
  17. Aldea G., Doursounian P., O'Gara P., et al. Heparin-bonded circuits with a reduced anticoagulation protocol in primary CABG: a prospective, randomized study. Ann Thorac Surg 1996;62:410-418.[Abstract/Free Full Text]
  18. Wendel H., Heller W., Hoffmeister H. Pathway of platelet protection in heparin-coated devices and its significance for cardiac surgery. Trans Soc Biomat 1995;21:28.
  19. Ferraris V.A., Berry W.R., Klingman R.R. Comparison of blood reinfusion techniques used during coronary artery bypass grafting. Ann Thorac Surg 1993;56:433-440.[Abstract]
  20. Mahoney C.B. Heparin bonded circuits: clinical outcomes and costs. Perfusion 1998;13:219-232.[Free Full Text]
  21. Ovrum E., Brosstad F., Am Holen E, et al. E.. Effect on coagulation and fibrinolysis with reduced vs. full systemic heparinization and heparin-coated cardiopulmonary bypass. Circulation 1995;92:2579-2584.[Abstract/Free Full Text]
  22. Svenmarker S., Sandstrom E., Karlsson T., Jansson E., Haggmark S., Lindholm R., Appelblad M., Aberg T. Clinical effects of the heparin coated surface in cardiopulmonary bypass. Eur J Cardiothorac Surg 1997;11:957-964.[Abstract]
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Received September 22, 1998; received in revised form April 27, 1999; accepted April 27, 1999.




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