A reevaluation of heparin requirements for cardiopulmonary bypass

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

Monitoring anticoagulation and hemostasis in cardiac surgery

The need to monitor anticoagulation and hemostasis during and after cardiac surgery has led to recognition of the importance of evaluation and use of hemostasis monitors in this setting. Consequently, rapid and accurate identification of abnormal hemostasis has been the major impetus for the development of point-of-care tests and their use in transfusion algorithms for cardiac surgical and other critically ill patients.

Heparin-coated extracorporeal circulation with full and low dose heparinization: comparison of thrombin related coagulatory effects

Thrombin related coagulatory effects of a heparin-coated cardiopulmonary bypass system combined with full and low dose systemic heparinization were investigated in a prospective, randomized study in coronary bypass surgery patients. One hundred nineteen patients were divided into 3 groups. Group A (n = 39) had a standard uncoated extracorporeal circulation (ECC) set, and systemic heparin was administered in an initial dose of 400 IU/kg body weight. During ECC activated clotting time (ACT) was maintained at > or =480 s. Group B (n = 42) had the same ECC set completely coated with low molecular weight heparin. Intravenous heparin was given in the same dose as in Group A, and ACT was kept at the same level. Group C (n = 38) had the same coated ECC set as Group B, but intravenous heparin was reduced to 150 IU/kg, and during ECC, ACT was set to be > or =240 s. The same ECC components were used in all 3 groups including roller pumps, coronary suction, and an open cardiotomy reservoir. Thrombin generation as indicated by F1/F2 was significantly elevated at an ECC duration >60 min if heparin-coated ECC combined with low dose systemic heparinization was employed. Complexed thrombin (TAT) was significantly elevated after administration of protamine. Release of D-dimers indicating fibrinolysis was not significantly different between groups. Signs of clinical thromboembolism, i.e., postoperative neurological deficit, occurred in 2 patients in Group A and 1 patient in Group C. We conclude that heparin-coated extracorporeal circulation combined with reduced systemic heparinization intraoperatively leads to significantly increased thrombin generation, but not to increased fibrinolysis.

Heparin-bonded circuits: clinical outcomes and costs

The aim of this study was to use meta-analysis to combine the results of numerous studies and examine the impact of heparin-bonded circuits on clinical outcomes and the resulting costs. Heparin-bonded circuits, both ionically and covalently bonded, are examined separately. The results of the study provide evidence that heparin-bonded circuits result in improved clinical outcomes when compared to the identical nonheparin-bonded circuits. These improved clinical outcomes result in subsequent lower costs per patient with their use. However, differences are apparent in the significance and magnitude of these outcomes between ionically and covalently bonded circuits. Covalently bonded circuits provide a greater magnitude and significance of improvement in clinical outcomes than ionically bonded circuits. Total cost savings can be expected to be three times greater with covalently bonded circuits ($3231 versus $1068). It was concluded that the choice regarding the use of a heparin-bonded circuits and the type of heparin-bonded circuit used has the potential to alter clinical outcomes and subsequent costs. Cost consideration cannot be ignored, but clinical benefits should be the main rationale for the choice of cardiopulmonary bypass circuit. This analysis provides evidence that clinical benefits and cost savings can both be derived from use of the same technology-covalently bonded circuits.

Heparin-bonded circuits improve clinical outcomes in emergency coronary artery bypass grafting

Compared to patients undergoing elective or urgent coronary artery bypass grafting (CABG), those undergoing emergency CABG (EM-CABG) have a higher morbidity and mortality. The use of heparin-bonded circuits (HBC) has been shown to improve clinical outcomes in nonemergent CABG patients. It is not known, however, whether the improved hemostasis and attenuation of the inflammatory response to cardiopulmonary bypass, conferred by HBC, can overcome the high incidence of comorbid risk factors in (EM-CABG) patients and improve their outcomes. A retrospective analysis of 206 consecutive patients undergoing EM-CABG over 4 years (1993-1997) at one institution was performed. Eighty-one patients were treated with conventional non-heparin-bonded circuits (NHBC) with full anticoagulation protocol (FAP, activated clotting time [ACT] > 480 sec); 125 patients were treated with HBC and a lower anticoagulation protocol (LAP, ACT > 280 seconds). Outcomes and results were collected prospectively and are presented as mean +/- SD. Preoperative risk profiles were similar in both treatment groups. Postoperatively, compared with the NHBC group, patients treated with HBC/LAP required fewer homologous donor units (4.1 +/- 10.7 vs 8.2 +/- 13.6 units, p = 0.005), were less likely to require inotropic support (18.6% vs 38.3%, p = 0.005), and had a lower incidence of perioperative myocardial infarction (MI, 3.2% vs 12.3%, p = 0.04) and pulmonary complications (4.0% vs 12.3%, p = 0.04). The use of HBC/LAP resulted in a decreased incidence of postoperative complications (12.8% vs 28.4%, p = 0.01, odds ratio 0.37 with 95% confidence interval [CI] 0.18-0.76). This resulted in a shorter duration of ventilatory support (30.5 +/- 54.0 vs 72.8 +/- 16.7 hours, p = 0.009), ICU stay (38.2 +/- 36.5 vs 91.5 +/- 68.7 hours, p = 0.009), hospital stay (8.0 +/- 7.1 vs 11.0 +/- 8.9 days, p = 0.008), and therefore cost. In conclusion, the use of HBC/LAP in EM-CABG resulted in a reduction of homologous transfusion and postoperative complications associated with decreased hospital stays and cost.

Enhanced blood conservation and improved clinical outcome after valve surgery using heparin-bonded cardiopulmonary bypass circuits

BACKGROUND

Recently, heparin-bonded (HBC) cardiopulmonary bypass circuits (CPB) were formed to be associated with improved outcome after coronary artery bypass grafting. There are very few reports on the efficacy and safety of these circuits in valve surgery.

METHODS

A retrospective cohort study of all patient populations undergoing first time valve surgery from 1992 to 1995 in a tertiary teaching hospital. Outcomes of 120 patients undergoing valve surgery using HBC and lower anticoagulation HBC were compared to 232 patients treated with conventional circuits and full heparinization (nonheparin-bonded-circuit [NHBC]).

RESULTS

Postoperative 24-hour chest tube drainage (558 +/- 466 mL vs 1054 +/- 911 mL, p < 0.00001), and reoperation for bleeding (2.5% vs 8.2%, p = 0.04) were lower in the HBC group. HBC patients required significantly less transfusions (total donor exposure of 6.9 +/- 13.0 units vs 18.6 +/- 26.2 units, p < 0.00001). Multiple linear regression analysis identified CPB time as a predictor of increased homologous blood transfusions, and the use of HBC, a large body surface area, and elective procedure as predictors of decreased transfusions. Perioperative mortality was similar (HBC 2.5%, NHBC 4.7%, p = 0.24). Overall complications were lower in the HBC group (42% vs 56.2%, p = 0.02). Perioperative myocardial infarction (0.8% vs 1.3%, p = 0.58) and cerebrovascular accident (3.3% vs 3.9%, p = 0.53) were similar. Two (1.7%) HBC patients had valve re-replacement compared to none in the NHBC (p = 0.22). Multiple logistic regression model revealed that age and CPB time were associated with increased complications, and the use of HBC with reduced complications.

CONCLUSION

Use of HBCs with lower anticoagulation in valve surgery resulted in a significant reduction of transfusion requirements and improved clinical outcome. Because of a potential for early mechanical valve thrombosis, until further data is available, conventional levels of systemic anticoagulation should be achieved when using HBC in valve surgery.

Neointimal thickening after severe coronary artery injury is limited by a short-term administration of a factor Xa inhibitor. Results in a porcine model

BACKGROUND

Fibrin- and platelet-rich thrombus formations occur as the initial event after percutaneous transluminal coronary angioplasty. We therefore tested the hypothesis that short-term administration of the recombinant tick anticoagulant peptide (rTAP), a factor Xa inhibitor, would reduce the thickness of neointima at 28 days after injury in a porcine coronary balloon angioplasty model.

METHODS AND RESULTS

Continuous intravenous infusion of rTAP (average dose, 194 micrograms . kg-1 . min-1) or placebo (vehicle only) was given to the study pigs for 60 hours. The goal of anticoagulation was to maintain the activated clotting time at 200 seconds. A central venous catheter was inserted 2 days before the procedure. On the day of coronary injury, the animals were administered boluses of rTAP (6.5 mg) and then underwent injury with an oversized metallic coil by standard methods in the right, circumflex, or left anterior descending coronary artery. No significant difference in vascular injury between rTAP and vehicle control was observed after euthanasia at 28 days. Significantly less neointimal thickening occurred in the rTAP-treated animals (thickness, mean +/-SD: 0.30 +/-0.08 mm) compared with the control (0.48 +/- 0.12 mm, P< .001).

CONCLUSIONS

The specific factor Xa inhibitor rTAP, when given in fully anticoagulant doses for a short duration after coronary artery injury in the porcine model, resulted in a long-term decrease in neointimal thickness. These results implicate thrombin generation in neointimal formation and suggest that administration of a potent antithrombotic for several days immediately after the procedure may influence the long-term outcome of the coronary injury with a decrease in neointimal formation.

Enhanced blood conservation in primary coronary artery bypass surgery using heparin-bonded circuits with lower anticoagulation

BACKGROUND

Despite many advances in blood conservation techniques, a significant proportion of patients undergoing primary coronary revascularization still require homologous transfusions. A comprehensive strategy to diminish perioperative blood loss was developed by integrating many individual components to create an improved blood conservation environment and was prospectively applied to 557 patients undergoing primary coronary artery bypass grafting (CABG) procedures performed in our medical center over a 14-month period.

METHODS

The first 455 patients were treated with conventional, nonheparinbonded circuits (NHBCs) and full anticoagulation (activated clotting time [ACT] > 480 sec). We wanted to test the hypothesis of whether "tip-to-tip" heparin-bonded circuits (HBCs) used in conjunction with lower anticoagulation (ACT > 280 sec) when added to our current blood conservation environment can further enhance clinical outcomes. We prospectively applied this technique to a consecutive group of patients (n = 102).

RESULTS

Compared to patients treated with NHBCs, patients treated with HBCs had a significantly lower mediastinal and pleural chest tube output in the first 24 hours (683 +/- 561 mL vs 984 +/- 616 mL, p < 0.00001) were less likely to be transfused (52% vs 68.1%, p < 0.01) and had a lower exposure to different blood donor units (4.1 +/- 8.4 vs 9.3 +/- 10.3, p < 0.000003). There were no complications directly related to HBCs used in conjunction with lower anticoagulation. Morbidity and mortality rates were similar in both treatment groups.

CONCLUSION

In summary, HBCs in conjunction with lower anticoagulation were safely applied in patients undergoing primary CABG with marked improvement in blood conservation, and should be considered for broader clinical use.

The effect of the anticoagulation regimen on endothelial-related coagulation in cardiac surgery patients

Heparin is still the most commonly used anticoagulant in cardiac surgery necessitating cardiopulmonary bypass. In recent years, endothelial-related coagulation (e.g. thrombomodulin/protein C-system) has enlarged our knowledge of the regulation of haemostasis. In a controlled randomised study, the influence of different regimens of anticoagulation on the thrombomodulin/protein C-system was studied. Sixty patients undergoing elective coronary artery bypass grafting were randomly allocated into four groups (n = 15) to receive: 300 IU.kg-1 of heparin before bypass; 600 IU.kg-1 of heparin; 300 IU.kg-1 of heparin as bolus followed by a continuous infusion of 10 000 IU.h-1 until the end of bypass; or 600 IU.kg-1 of heparin plus 'high dose' aprotinin (2 million IU of aprotinin before bypass, 500 000 IU.h-1 until the end of the operation and 2 million IU added to the bypass pump prime). Grouping was blinded for the surgeon and the anaesthetist. Plasma concentrations of thrombomodulin, protein C and (free) protein S as well as thrombin/antithrombin III were measured by enzyme-linked-immunosorbent assays after induction of anaesthesia, during and after bypass, at the end of surgery, 5 h after bypass, and on the first postoperative day. Activated clotting time was significantly longer during bypass in group 2 (566 (60)s) and group 4 (655 (59)s), whereas standard coagulation parameters showed no differences between the four groups. Blood loss and use of homologous blood and blood products were highest in groups 2 and 3. Thrombomodulin plasma levels were similar (and normal) at baseline (< 40 ng.l-1), decreased during bypass and reached baseline values postoperatively without showing significant group differences. Protein C did not show any differences among the groups within the investigation period. 'Free' protein S plasma levels were most reduced in group 1 (from 68 (8)% to 48 (9)% after bypass). Thrombin/antithrombin III plasma concentrations increased most in groups 1 (to 69 (14) micrograms.l-1 after bypass) and 2 (to 48 (7) micrograms.l-1 after bypass), whereas they remained significantly lower in groups 3 and 4. The thrombomodulin/protein C-system was not significantly influenced by the regimen of anticoagulation. Administration of 'high-dose' heparin was associated with the highest blood loss, which could not be related to endothelial-associated coagulation.

Heparin and antithrombin III levels during cardiopulmonary bypass: correlation with subclinical plasma coagulation

The anticoagulant effect of heparin in the milieu of altered antithrombin III levels was investigated in adult (n = 7) and pediatric (n = 14) patients undergoing open heart operations. The pediatric patients were subdivided into a control group (n = 8) and an antithrombin III group (n = 6), which received 1,000 units of antithrombin III. The reduction in antithrombin III levels during cardiopulmonary bypass was obvious in patients of all ages, showing a greater reduction (although not statistically significant) in the pediatric patients. However, the antithrombin III group patients maintained their preoperative levels of antithrombin III. The elevated fibrinopeptide A levels in pediatric and adult control group patients suggested that considerable subclinical plasma coagulation occurred during open heart operations, especially during the normothermic period of cardiopulmonary bypass and after the administration of protamine. Antithrombin III levels in the children were the most predictive (r = -0.58; p < 0.001) for production of fibrinopeptide A during moderate hypothermic cardiopulmonary bypass, but the heparin levels were most predictive (r = -0.57, p < 0.03) in the adults. This result may be related to the different actions of heparin when antithrombin III levels are reduced. Supplementation with antithrombin III succeeded in suppressing the activation of the coagulation cascade and resulted in no statistical change in fibrinopeptide A levels at any time. We conclude that heparin and (in some patients) antithrombin III levels are important variables for the inhibition of fibrin formation and the possible preservation of coagulation proteins.

Risk and benefit of low systemic heparinization during open heart operations

Heparin surface-coated perfusion equipment with improved thromboresistance was evaluated in 104 consecutive patients undergoing open heart operation in a prospective, randomized trial with low versus full systemic heparinization. Surgical procedures included coronary artery revascularization in 47 of 54 (87%) for low versus 44 of 50 patients (88%; not significant [NS]) for full, valve repair/replacement in 8 of 54 (15%) for low versus 5 of 50 patients (10%; NS) for full, left ventricular aneurysm repair in 1 of 54 (2%) for low versus 2 of 50 patients (4%; NS) for full, and other in 3 of 54 (6%) for low versus 3 of 50 patients (6%; NS) for full. Cross-clamp time was 39.2 +/- 10.7 minutes for low versus 39.5 +/- 10.5 minutes for full (NS). Cardiopulmonary bypass time was 68.6 +/- 20.1 minutes for low versus 69.3 +/- 16.6 minutes for full (NS). Lowest activated coagulation time during perfusion was 255 +/- 75 seconds for low versus 537 +/- 205 seconds for full (p < 0.0005). In the low group, the target activated coagulation time of more than 180 seconds was not reached during perfusion in 4 of 54 patients (7%), the lowest value being 164 seconds. No oxygenator failure occurred. Hospital mortality was 0 of 54 (0%) for low versus 1 of 50 patients (2%) for full (NS). Bleeding required surgical revision in 0 of 54 (0%) for low versus 4 of 50 patients (8%) for full (p = 0.05). Drainage (24 hours) was 790 +/- 393 mL for low versus 1,039 +/- 732 mL for full (p < 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)