Anticoagulation Management and Heparin Resistance During Cardiopulmonary Bypass: A Survey of Society of Cardiovascular Anesthesiologists Members

Finding a common definition of heparin resistance in adult cardiac surgery: communication from the ISTH SSC subcommittee on perioperative and critical care thrombosis and hemostasis

Ensuring adequate anticoagulation for patients requiring cardiac surgery and cardiopulmonary bypass (CPB) is important due to the adverse consequences of inadequate anticoagulation with respect to bleeding and thrombosis. When target anticoagulation is not achieved with typical doses, the term heparin resistance is routinely used despite the lack of uniform diagnostic criteria. Prior reports and guidance documents that define heparin resistance in patients requiring CPB and guidance documents remain variable based on the lack of standardized criteria. As a result, we conducted a review of clinical trials and reports to evaluate the various heparin resistance definitions employed in this clinical setting and to identify potential standards for future clinical trials and clinical management. In addition, we also aimed to characterize the differences in the reported incidence of heparin resistance in the adult cardiac surgical literature based on the variability of both target-activated clotting (ACT) values and unfractionated heparin doses. Our findings suggest that the most extensively reported ACT target for CPB is 480 seconds or higher. Although most publications define heparin resistance as a failure to achieve this target after a weight-based dose of either 400 U/kg or 500 U/kg of heparin, a standardized definition would be useful to guide future clinical trials and help improve clinical management. We propose the inability to obtain an ACT target for CPB of 480 seconds or more after 500 U/kg as a standardized definition for heparin resistance in this setting.

Contributing factors to heparin resistance during cardiopulmonary bypass

Since the risk factors for heparin resistance (HR) before cardiopulmonary bypass (CPB) have not been fully clarified, this study investigated the contributing factors for HR after the initial unfractionated heparin (UFH) dose of 500 IU/kg. We retrospectively analyzed the data of 371 patients who underwent CPB surgery, with the initial UFH dose of 500 IU/kg, between May 2017 and December 2021. We defined HR as the failure to achieve activated clotting time (ACT) of > 480 s after the initial UFH dose of 500 IU/kg. HR was observed in 36 patients (9.7%) (HR group), while HR was not observed in 335 patients (control group). The HR group included significantly more patients with preoperative use of UFH, with significantly higher white blood cell counts, fibrinogen, fibrinogen degradation products, D-dimer, and C-reactive protein, and lower hemoglobin and albumin. The multivariable logistic regression analysis identified albumin (OR: 3.09, 95% CI 1.3504-7.0845, p = 0.0075) and fibrinogen (OR: 0.99, 95% CI 0.9869-0.9963, p = 0.0003) as independent predictors for HR. Using the Youden index, the cutoffs of albumin and fibrinogen were calculated as 3.8 g/dL and 303 mg/dL, respectively. The receiver operating characteristic curves showed the predictive performance of albumin (area under the curve (AUC): 0.78, sensitivity: 65%, specificity: 81%) and fibrinogen (AUC: 0.77, sensitivity: 56%, specificity: 88%). The incidence of HR after the initial UFH dose of 500 IU/kg was 9.7%. The preoperative albumin < 3.8 g/dL and fibrinogen > 303 mg/dL were independent predictors for HR.

Investigation of real-world heparin resistance and anticoagulation management prior to cardiopulmonary bypass: report from a nationwide survey by the Japanese Association for Thoracic Surgery heparin resistance working group

OBJECTIVE

Heparin resistance is often encountered during cardiopulmonary bypass. Heparin dose and activated clotting time target values for the initiation of cardiopulmonary bypass are not yet universally standardized; further no consensus exists on the management of heparin resistance. This study aimed to investigate the current real-world practice on heparin management and anticoagulant treatment for heparin resistance in Japan.

METHODS

A questionnaire survey was conducted at medical institutions nationwide with which The Japanese Society of Extra-Corporeal Technology in Medicine members are affiliated, targeting surgical cases with cardiopulmonary bypass performed from January 2019 through December 2019.

RESULTS

Among 69% (230/332) of the participating institutions, the criterion for heparin resistance was defined as "the target activated clotting time value not reached even with an additional dose of heparin administration". Cases of heparin resistance were reported in 89.8% (202/225) of the responded institutions. Of note, 75% (106/141) of the responded institutions reported heparin resistance associated with antithrombin activity ≥ 80%. Antithrombin concentrate was used in 38.4% (238/619 responses) or third dose of heparin in 37.8% (234/619 responses) for advanced heparin resistance treatment. Antithrombin concentrate was found to be effective in resolving heparin resistance in patients having normal, as well as lower antithrombin activity.

CONCLUSION

Heparin resistance has occurred in many cardiovascular centers, even among patients with normal antithrombin activities. Interestingly, the administration of antithrombin concentrate resolved heparin resistance, regardless of the baseline antithrombin activity value.

Relationship between estimated and observed heparin sensitivity indices in cardiac and thoracic aortic surgery

BACKGROUND

Little evidence exists on the relationship between the estimated heparin sensitivity index (HSI) based on commonly available clinical and laboratory data and observed HSI in the adult population. This retrospective study assessed the relationship between the observed and estimated HSIs.

METHODS

This study was conducted in an academic, single-institution setting. Patients aged ≥ 20 years who underwent cardiac and thoracic aortic surgery and requiring cardiopulmonary bypass were included. Clinical and laboratory data, including age, sex, and platelet count, were collected. The fibrinogen-albumin ratio index was calculated by dividing the fibrinogen value by the albumin value, multiplied by 10.The HSI was calculated using the formula: (activated clotting time after initial heparin administration-baseline activated clotting time)/initial heparin dose (IU/kg). The estimated HSI was based on the results of multiple regression analysis that included clinically relevant factors. The intraclass correlation coefficient between the observed and estimated HSIs was used to assess.

RESULTS

In total, 560 patients with valid activated clotting time (ACT) values after initial heparin administration were included in the final analysis to explore associated factors using the estimated HSI. Multiple regression analysis revealed that hemodialysis, platelet count, fibrinogen-to-albumin ratio index, baseline activated clotting time, and initial heparin dose were significantly associated with the HSI. The mean (standard deviation) observed and estimated HSIs were 1.38 (0.43) and 1.55 (0.13), respectively, with an intra-class correlation coefficient of 0.10.

CONCLUSIONS

The correlation between the observed and estimated HSIs was low, and a formula with high accuracy for estimating the HSI is needed.

Minimum protamine dose required to neutralize heparin in cardiac surgery: a single-centre, prospective, observational cohort study

PURPOSE

Excess protamine contributes to coagulopathy following cardiopulmonary bypass (CPB) and may increase blood loss and transfusion requirements. The primary aim of this study was to find the least amount of protamine necessary to neutralize residual heparin following CPB using the gold standard assays of anti-IIa and anti-Xa activity. Secondary objectives were to evaluate whether the post-CPB activated clotting time could be used as a surrogate marker for quantifying heparin neutralization.

METHODS

Twenty-eight consecutive patients undergoing elective cardiac surgery were enrolled. Protamine administration was standardized through an infusion pump at 25 mg·min-1. Blood samples were withdrawn prior to and following administration of 150, 200, 250, and 300 mg protamine and analyzed for activated clotting time and anti-IIa and -Xa activity.

RESULTS

Following a mean (standard deviation) cumulative heparin dose of 67,700 (19,400) units and a CPB duration of 113 (71) min, protamine requirements varied widely. Eight out of 25 (32%) patients showed complete neutralization of anti-IIa and -Xa activity at the first sampling point (150 mg protamine; protamine:heparin ratio, 0.3 [0.1]). A protamine:heparin ratio of 0.5 (0.2) was sufficient for heparin neutralization in > 90% of patients. After CPB, a low to mid-range activated clotting time correlated well with anti-IIa and -Xa activity.

CONCLUSIONS

The protamine:heparin ratio required to neutralize residual unfractionated heparin (UFH) following CPB is variable. A protamine:heparin ratio of 0.3 was sufficient to neutralize UFH in some patients, while a ratio of 0.5 is sufficient to neutralize both residual anti-IIa and -Xa activity in most patients. Larger studies are necessary to confirm these findings and evaluate their clinical implications.

STUDY REGISTRATION

ClinicalTrials.gov (NCT03787641); registered 26 December 2018.

Antithrombin Therapy: Current State and Future Outlook

Antithrombin (AT) is a natural anticoagulant pivotal in inactivating serine protease enzymes in the coagulation cascade, making it a potent inhibitor of blood clot formation. AT also possesses anti-inflammatory properties by influencing anticoagulation and directly interacting with endothelial cells. Hereditary AT deficiency is one of the most severe inherited thrombophilias, with up to 85% lifetime risk of venous thromboembolism. Acquired AT deficiency arises during heparin therapy or states of hypercoagulability like sepsis and premature infancy. Optimization of AT levels in individuals with AT deficiency is an important treatment consideration, particularly during high-risk situations such as surgery, trauma, pregnancy, and postpartum. Here, we integrate the existing evidence surrounding the approved uses of AT therapy, as well as potential additional patient populations where AT therapy has been considered by the medical community, including any available consensus statements and guidelines. We also describe current knowledge regarding cost-effectiveness of AT concentrate in different contexts. Future work should seek to identify specific patient populations for whom targeted AT therapy is likely to provide the strongest clinical benefit.

Heparin Resistance During Cardiopulmonary Bypass in Adult Cardiac Surgery

The use of heparin for anticoagulation has changed the face of cardiac surgery by allowing a bloodless and motionless surgical field throughout the introduction of cardiopulmonary bypass (CPB). However, heparin is a drug with complex pharmacologic properties that can cause significant interpatient differences in terms of responsiveness. Heparin resistance during CPB is a weighty issue due to the catastrophic consequences stemming from inadequate anticoagulation, and the treatment of it necessitates a rationalized stepwise approach due to the multifactorial contributions toward this entity. The widespread use of activated clotting time (ACT) as a measurement of anticoagulation during CPB is examined, as it may be a false indicator of heparin resistance. Heparin resistance also has been repeatedly reported in patients infected with COVID-19, which deserves further exploration in this pandemic era. This review aims to examine the variability in heparin potency, underlying mechanisms, and limitations of using ACT for monitoring, as well as provide a framework towards the current management of heparin resistance.

The addition of Tirofiban infusion to heparin for intraoperative heparin resistance associated with Marfan Syndrome

Marfan syndrome classically presents with aortic root aneurysms. Aortic ectasia causes diverse blood flow alterations, influencing the behavior of coagulation factors and platelet activity. Heparin resistance has also been reported associated with Marfan Syndrome in a small number of patients, probably due to antithrombin III (ATIII) deficiency or various mutations. The ascending aorta and the aortic valve are replaced with prosthetic material during Bentall- de Bonno procedures. Resistance to anticoagulation during extracorporeal circulation, represents a significant challenge for both anesthesiologists and the surgical team. Resistance to heparin was observed in a patient with Marfan syndrome undergoing a Bentall procedure. ATIII concentrate was not available, and ACT did not increase despite high doses of heparin. An alternate anticoagulation approach was used successfully.

Anesthesia Considerations in Infective Endocarditis

The management of infective endocarditis is complex and inherently requires multidisciplinary cooperation. About half of all patients diagnosed with infective endocarditis will meet the criteria to undergo cardiac surgery, which regularly takes place in urgent or emergency settings. The pathophysiology and clinical presentation of infective endocarditis make it a unique disorder within cardiac surgery that warrants a thorough understanding of specific characteristics in the perioperative period. This includes, among others, echocardiography, coagulation, bleeding management, or treatment of organ dysfunction. In this narrative review article, the authors summarize the current knowledge on infective endocarditis relevant for the clinical anesthesiologist in perioperative management of respective patients. Furthermore, the authors advocate for the anesthesiologist to become a structural member of the endocarditis team.

Management of heparin resistance due to antithrombin deficiency in a Chinese pregnant woman: a case report

Untreated individuals with antithrombin (AT) deficiency are at higher risk of thrombosis and adverse pregnancy outcomes. The present recommendations are mostly empirical for treating patients with AT deficiency during pregnancy because of the absence of guidelines. We report a rare case of heparin resistance due to AT deficiency in a pregnant 32-year-old Chinese woman. We also reviewed the English medical literature for AT deficiency and its association with thromboembolism and treatment. This patient suffered two early miscarriages because of thrombosis due to AT deficiency. The patient was administered the combination of adequate low molecular weight heparin with fresh frozen plasma and warfarin because of her heparin resistance. She delivered a healthy female newborn without any adverse effects of the anticoagulation therapy. Our findings suggest that the combination of adequate low molecular weight heparin with fresh frozen plasma and warfarin is effective for preventing thrombus during pregnancy.

Evaluation of heparin infusion rates in patients with intravenous drug misuse

To evaluate the hypothesis that patients with a history of intravenous drug misuse (IVDM) initiated on weight-based heparin infusions require higher than expected infusion rates to achieve therapeutic activated partial thromboplastin time (aPTT). This study is a multicenter, retrospective chart review of patients with a history of IVDM who were admitted to an acute care site between 10/1/2015 and 9/30/2020 and treated with continuous heparin infusions. Patients were identified using ICD9 and ICD10 codes and included if they had a documented history of IVDM within the past six months. Variables of particular interest included: median heparin infusion rates to maintain therapeutic aPTT, average time to reach therapeutic aPTT, and International Society of Thrombosis and Haemostasis Criteria for moderate to severe bleeding. Of the 41 patients who met the inclusion and exclusion criteria, 39 achieved therapeutic aPTT while on a weight-based heparin infusion. All heparin infusions were initiated at a rate of 18 units/kg/hr then titrated per institutional heparin infusion protocols. The mean time to therapeutic aPTT was 38.48 h ± 26.4 h with a mean infusion rate of 27.64 ± 7.14 units/kg/hr. To maintain therapeutic anticoagulation, infusion rates 150% higher than the initial rate were required. Of the 39 patients who achieved therapeutic aPTT, 85% (33) met criteria for heparin resistance, defined as greater than 35,000 units of heparin daily. No statistical significance could be derived from this retrospective chart review as therapeutic heparin rates were evaluated in comparison to initial infusion rate, rather than a control group. The findings in this study demonstrate a possible clinical association of the reduced antithrombin activity previously described in opiate misusers. To efficiently achieve therapeutic anticoagulation, it may be appropriate to consider use of heparin antiXa monitoring in place of aPTT or utilization of increased initial heparin infusion rates.

Anticoagulation Monitoring for Perioperative Physicians

From preoperative medications to intraoperative needs to postoperative thromboprophylaxis, anticoagulants are encountered throughout the perioperative period. This review focuses on coagulation testing clinicians utilize to monitor the effects of these medications.

Joint EAPCI/ACVC expert consensus document on percutaneous ventricular assist devices

There has been a significant increase in the use of short-term percutaneous ventricular assist devices (pVADs) as acute circulatory support in cardiogenic shock and to provide haemodynamic support during interventional procedures, including high-risk percutaneous coronary interventions. Although frequently considered together, pVADs differ in their haemodynamic effects, management, indications, insertion techniques, and monitoring requirements. This consensus document summarizes the views of an expert panel by the European Association of Percutaneous Cardiovascular Interventions (EAPCI) and the Association for Acute Cardiovascular Care (ACVC) and appraises the value of short-term pVAD. It reviews the pathophysiological context and possible indications for pVAD in different clinical settings and provides guidance regarding the management of pVAD based on existing evidence and best current practice.

Potential Renoprotective Strategies in Adult Cardiac Surgery: A Survey of Society of Cardiovascular Anesthesiologists Members to Explore the Rationale and Beliefs Driving Current Clinical Decision-Making

OBJECTIVES

The authors sought to (1) characterize the rationale underpinning anesthesiologists' use of various perioperative strategies hypothesized to affect renal function in adult patients undergoing cardiac surgery, (2) characterize existing belief about the quality of evidence addressing the renal impact of these strategies, and (3) identify potentially renoprotective strategies for which anesthesiologists would most value a detailed, evidence-based review.

DESIGN

Survey of perioperative practice in adult patients undergoing cardiac surgery.

SETTING

Online survey.

PARTICIPANTS

Members of the Society of Cardiovascular Anesthesiologists (SCA).

INTERVENTIONS

None.

MEASUREMENTS & MAIN RESULTS

The survey was distributed to more than 2,000 SCA members and completed in whole or in part by 202 respondents. Selection of target intraoperative blood pressure (and relative hypotension avoidance) was the strategy most frequently reported to reflect belief about its potential renal effect (79%; 95% CI: 72-85). Most respondents believed the evidence supporting an effect on renal injury of intraoperative target blood pressure during cardiac surgery was of high or moderate quality. Other factors, including a specific nonrenal rationale, surgeon preference, department- or institution-level decisions, tradition, or habit, also frequently were reported to affect decision making across queried strategies. Potential renoprotective strategies most frequently requested for inclusion in a subsequent detailed, evidence-based review were intraoperative target blood pressure and choice of vasopressor agent to achieve target pressure.

CONCLUSIONS

A large number of perioperative strategies are believed to variably affect renal injury in adult patients undergoing cardiac surgery, with wide variation in perceived quality of evidence for a renal effect of these strategies.

Joint EAPCI/ACVC expert consensus document on percutaneous ventricular assist devices

There has been a significant increase in the use of short-term percutaneous ventricular assist devices (pVADs) as acute circulatory support in cardiogenic shock and to provide haemodynamic support during interventional procedures, including high-risk percutaneous coronary interventions. Although frequently considered together, pVADs differ in their haemodynamic effects, management, indications, insertion techniques, and monitoring requirements. This consensus document summarizes the views of an expert panel by the European Association of Percutaneous Cardiovascular Interventions (EAPCI) and the Association for Acute Cardiovascular Care (ACVC) and appraises the value of short-term pVAD. It reviews the pathophysiological context and possible indications for pVAD in different clinical settings and provides guidance regarding the management of pVAD based on existing evidence and best current practice.

Infective Endocarditis Is a Risk Factor for Heparin Resistance in Adult Cardiovascular Surgical Procedures: A Retrospective Study

OBJECTIVES

Heparin resistance (HR), defined as a decrease in heparin responsiveness, can result in adverse events with prolonged duration of surgery. Although some clinical risk factors have been suggested, the relationship with the surgical diagnosis is unclear. The aim of present study was to elucidate the clinical predictors of HR including the surgical diagnosis.

DESIGN

This retrospective cohort study determined the incidence of HR (defined as activated clotting time [ACT] <400 seconds after 250-350 IU/kg of heparin administration) and heparin sensitivity index (HSI) was calculated from the rate of change in ACT per heparin dose. Preoperative demographic data, medication history, and laboratory data also were analyzed.

SETTING

Single institution, tertiary care hospital.

PARTICIPANTS

Adult patients who underwent cardiovascular surgery with cardiopulmonary bypass between January 2012 and September 2018.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 287 patients, 88 (30.7%) were classified as HR. In univariate analysis, infective endocarditis (IE), platelet count, and serum fibrinogen and albumin levels were associated with HR. After adjustment for baseline ACT and initial heparin dose, IE (odds ratio 4.57, [95% CI: 1.10-19.1]; p = 0.037) and albumin ≤3.5 g/dL (3.17, [1.46-6.93]; p = 0.004) were associated independently with HR. Patients with IE had significantly lower HSI than those with other diseases. All HR patients were treated with additional heparin, and 17 of them received human antithrombin-III concentrate.

CONCLUSIONS

Infective endocarditis and preoperative hypoalbuminemia were associated independently with HR. The optimal anticoagulation strategy for patients with these risk factors requires further investigations based on the authors' findings.

Antiphospholipid Syndrome and Cardiac Bypass: The Careful Balance between Clotting and Bleeding

Antiphospholipid syndrome (APS) is an acquired autoimmune condition characterized by the presence of antiphospholipid antibodies (lupus anticoagulant, anticardiolipin antibody, and anti-β₂ glycoprotein-I antibody) which leads to clinical thrombosis via a multifactorial mechanism of action. Despite the propensity to form clot in vivo, these antibodies interfere with the assembly of the prothrombinase complex on phospholipids in in vitro assays, leading to prolongation of activated clotting time and activated partial thromboplastin time. This disconnect between what occurs in vivo and in vitro makes monitoring anticoagulation during cardiac surgery particularly complex. We present a patient with APS undergoing coronary artery bypass grafting with cardiopulmonary bypass. We delineate our strategy for managing anticoagulation in the presence of this syndrome using the Hepcon Hemostasis Management System Plus (Medtronic, Inc. Minneapolis, MN) device by targeting whole blood heparin concentration to monitor anticoagulation.

Correlation between activated clotting time monitoring and heparin concentration measurement in a patient with antiphospholipid syndrome during cardiac valve surgery: a case report

Background

Anticoagulation management of patients with antiphospholipid syndrome (APS) undergoing cardiac surgery is challenging due to the prolongation of activated clotting time (ACT). Currently, no study has compared the utility of ACT monitoring using the Hemochron Jr. Signature+ and that of heparin concentration management using the Hemostasis Management System (HMS) Plus in patients with APS.

Case presentation

A 71-year-old woman with APS was scheduled to undergo an aortic valve replacement for aortic regurgitation. The ACT was measured using the Hemochron Jr. Signature+, and the heparin concentration was measured concurrently using the HMS Plus. ACT over 480 s corresponded to an adequate heparin concentration during cardiopulmonary bypass. The clinical course was uneventful, and no thrombotic or hemorrhagic complications were observed.

Conclusion

In the present patient with APS, the Hemochron Jr. Signature+ was useful as an anticoagulation management during cardiac valve surgery.

Current Neurologic Assessment and Neuroprotective Strategies in Cardiac Anesthesia: A Survey to the Membership of the Society of Cardiovascular Anesthesiologists

BACKGROUND

Neurologic injury and cognitive disorder after cardiac surgery are associated with morbidity and mortality. Variability in the application of neuroprotective strategies likely exists during cardiac surgery. The Society of Cardiovascular Anesthesiologists (SCA) conducted a survey among its members on common perioperative neuroprotective strategies: assessment of aortic atheromatous burden, management of intraoperative blood pressure, and use of cerebral oximetry.

METHODS

A 15-item survey was developed by 3 members of the SCA Continuous Practice Improvement - Cerebral Protection Working Group. The questionnaire was then circulated among all working group members, adapted, and tested for face validity. On March 26, 2018, the survey was sent to members of the SCA via e-mail using the Research Electronic Data Capture system. Responses were recorded until April 16, 2018.

RESULTS

Of the 3645 surveys e-mailed, 526 members responded (14.4%). Most responders worked in academic institutions (58.3%), followed by private practices (38.7%). Epiaortic ultrasound for the assessment of aortic atheromatous burden was most commonly utilized at the surgeon's request (46.5%). Cerebral oximetry was most commonly used in patients with increased perioperative risk of cerebral injury (41.4%). Epiaortic ultrasound (1.9%) and cerebral oximetry (5.2%) were rarely part of a standardized monitoring approach. A majority of respondents (52.0%) reported no standardized management strategies for neuroprotection during cardiac surgery at their institution. A total of 55.3% stated that no standardized institutional guidelines were in place for managing a patient's blood pressure intraoperatively or during cardiopulmonary bypass. When asked about patients at risk for postoperative cerebral injury, 41.3% targeted a blood pressure goal >65 mmHg during cardiopulmonary bypass. The majority of responders (60.4%) who had access to institutional rates of postoperative stroke/cerebral injury had standard neuroprotective strategies in place.

CONCLUSIONS

Our data indicate that approximately half of the respondents to this SCA survey do not use standardized guidelines/standard operating procedures for perioperative cerebral protection. The lack of standardized neuroprotective strategies during cardiac surgery may impact postoperative neurologic outcomes. Further investigations are warranted and should assess the association of standardized neuroprotective approaches and postoperative neurological outcomes.

Massive atrial myxoma requiring emergency cardiopulmonary bypass in a patient with heparin resistance

Heparin exhibits complex pharmacology with a wide variation in individual response. Despite this, heparin is the most commonly used anticoagulant during cardiopulmonary bypass. Heparin resistance in the context of a patient with severe cardiovascular compromise presents a potentially life-threatening challenge. A 31-year-old woman was listed for emergency excision of a massive left atrial myxoma. On induction of anaesthesia, she developed marked cardiovascular instability secondary to mitral inflow obstruction. An initial heparin dose of 600 units.kg^-1 produced an activated clotting time of 360 s; however, immediate cardiopulmonary bypass was required. Heparin resistance remained problematic throughout the procedure, with an inadequate response to antithrombin three supplementation. Despite a total dose of 120,000 units of heparin, anticoagulation was fully reversed with 500 mg protamine and there was no subsequent re-heparinisation. Heparin resistance, when coinciding with profound cardiovascular instability, requires a pragmatic response to expedite establishment of cardiopulmonary bypass whilst minimising potential harm. In this case, successful cardiopulmonary bypass was achieved with additional heparin boluses from an alternative batch administered both intravenously and via the bypass circuit. We therefore advocate consideration of this approach as one possible solution to achieving safe entry onto cardiopulmonary bypass in a crisis scenario.