Version July 2025
INTRODUCTION —
Blood and coagulation management are key components of anesthesia care for cardiac surgical procedures that require cardiopulmonary bypass (CPB).
This topic reviews anticoagulation, anticoagulation reversal, and transfusion in individuals undergoing cardiac surgery with CPB.
Separate topics discuss:
●General principles for perioperative blood management – (See "Perioperative blood management: Strategies to minimize transfusions" and "Intraoperative transfusion and administration of clotting factors".)
●Reversal of heparin systemic anticoagulation with protamine after CPB – (See "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Protamine administration after cardiopulmonary bypass'.)
●Achieving hemostasis after CPB – (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass".)
BACKGROUND
Effects of cardiopulmonary bypass on hemostasis — Cardiopulmonary bypass (CPB) induces several hemostatic changes (figure 1) [1-4].
●Full systemic anticoagulation required for CPB blocks normal hemostatic processes. Protamine neutralization of heparin after the procedure rapidly stops its anticoagulation effect.
●Contact of blood with nonendothelial surfaces of the CPB circuit induces an intense inflammatory response. This results in procoagulant and anticoagulant effects [5-7]:
•Platelet activation and dysfunction.
•Initiation of the coagulation cascade.
•Decreased levels of circulating coagulation factors.
●Thrombin generation and activation of fibrinolytic pathways result in [8-11]:
•Platelet consumption.
•Reduction of procoagulant and anticoagulant proteins (especially fibrinogen and antithrombin).
●The priming solution for the CPB circuit (typically 1 to 1.5 L of a balanced crystalloid solution) causes hemodilution that exacerbates anemia and may also worsen coagulopathy and bleeding. (See 'Minimize further hemodilution during CPB' below.)
●Postbypass hypothermia may worsen coagulopathy. (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass", section on 'Maintenance of normothermia'.)
●Surgical blood loss increases the risk for requiring transfusions.
●Typical laboratory findings immediately after CPB include:
•Thrombocytopenia
•Low fibrinogen
•Prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT)
•Increased D-dimer
Overview of blood management for cardiac surgery — Blood management strategies have been developed to manage the effects of CPB on hemostasis and reduce transfusions [3,4,12-17].
In 2024, updated guidelines for multidisciplinary perioperative strategies to minimize blood loss and need for transfusion during adult cardiac surgery were jointly developed by the European Association of Cardio-Thoracic Surgery (EACTS), the European Association of Cardiothoracic Anaesthesiology and Intensive Care (EACTAIC), and the European Board of Cardiovascular Perfusion (EBCP) [3]. We generally agree with these guidelines and perioperative strategies, as discussed below and in other UpToDate topics:
●Pre-admission and preoperative strategies:
•Timely management of preoperative anemia – (See "Overview of preoperative evaluation and management for cardiac surgery in adults", section on 'Anemia' and "Perioperative blood management: Strategies to minimize transfusions", section on 'Treatment of anemia and iron deficiency'.)
•Management of medications affecting hemostasis – (See "Overview of preoperative evaluation and management for cardiac surgery in adults", section on 'Medications affecting hemostasis'.)
●Intraoperative strategies for each stage of the cardiac surgical procedure:
•Blood conservation strategies such as acute normovolemic hemodilution before CPB and intraoperative blood salvage before and after CPB – (See 'Blood conservation strategies' below.)
•Antifibrinolytic administration before, during, and after CPB – (See "Intraoperative use of antifibrinolytic agents", section on 'Use of antifibrinolytic agents in cardiac surgery'.)
•Avoiding excessive hemodilution before and during CPB – (See 'Avoid excessive fluid administration' below and 'Minimize further hemodilution during CPB' below.)
•Hemoconcentration and avoiding unnecessary transfusions during CPB – (See 'Hemoconcentration' below.)
•Implementation of transfusion guidelines to avoid unnecessary transfusions during or after CPB – (See 'Thresholds for RBC transfusion' below and "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass", section on 'Use of transfusion algorithms'.)
•Adequate hemostasis after CPB – (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass".)
●Postoperative strategies:
•Reducing residual coagulopathy – (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass", section on 'Management of bleeding and coagulopathy'.)
•Reducing postoperative anemia – (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass", section on 'Management of anemia'.)
MANAGEMENT BEFORE CARDIOPULMONARY BYPASS
Evaluation and treatment of anemia — Evaluation and treatment of anemia prior to elective cardiac surgery with CPB can result in improved hemoglobin at the time of surgery. Details are discussed separately. Generally, this would occur at least 10 days prior to surgery for treatment of iron deficiency or other conditions to be effective. (See "Overview of preoperative evaluation and management for cardiac surgery in adults", section on 'Anemia' and "Perioperative blood management: Strategies to minimize transfusions", section on 'Treatment of anemia and iron deficiency'.)
Blood conservation strategies
Intraoperative blood salvage — Intraoperative blood salvage is used immediately before and after CPB for most cardiac surgical procedures due to the high likelihood of significant blood loss (>1000 mL). This is based on evidence that allogeneic blood transfusion and its associated complications can be avoided with a very low incidence of adverse events. Details and supporting evidence are discussed separately. (See "Surgical blood conservation: Intraoperative blood salvage".)
Intraoperative blood salvage with modifications of the circuit may be acceptable to some Jehovah's Witnesses who will not accept allogeneic blood [3,4]. For example, it may be necessary to modify the CPB circuit to maintain a continuous fluid path connected to the patient’s native circulation. (See "Approach to the patient who declines blood transfusion", section on 'Be clear about the patient's wishes regarding consent'.)
Acute normovolemic hemodilution — Acute normovolemic hemodilution (ANH) involves removal of blood from a patient shortly after induction of anesthesia, with maintenance of normovolemia using crystalloid and/or colloid replacement, followed by reinfusion of the patient's own (autologous) fresh whole blood when needed. Details of the technique are discussed separately. (See "Surgical blood conservation: Acute normovolemic hemodilution".)
●Indications – ANH is used before CPB in selected patients [3,16].
Factors that favor use of ANH include:
•Preoperative hemoglobin >13 g/dL
•Larger patient size
•Hemodynamic stability during the prebypass period
•Absence of coagulopathy or significant prebypass bleeding (eg, due to redo sternotomy)
The technique is usually avoided or used with extreme caution in patients who are particularly sensitive to hypovolemic hypotension. Examples include those with left main coronary artery disease (CAD) or severe multivessel CAD and those with obstructive lesions such as aortic stenosis, mitral stenosis, or hypertrophic obstructive cardiomyopathy (HOCM).
ANH is a good option for Jehovah's Witnesses, since many will consent to ANH if their blood is maintained in a closed circuit continuous fluid system [18]. (See "Approach to the patient who declines blood transfusion", section on 'Be clear about the patient's wishes regarding consent'.)
●Blood volumes – The amount of blood removed during ANH typically varies between 1 unit (equivalent to 450 to 500 mL) and 3 units (equivalent to 1350 to 1500 mL). Blood removal volume is calculated based on the patient's estimated blood volume, initial hemoglobin level, and desired hemoglobin level after withdrawal of blood with hemodilution (See "Surgical blood conservation: Acute normovolemic hemodilution", section on 'Amount of blood to withdraw'.)
●Rationale and supporting evidence – ANH decreases hemoglobin concentration during the period when most surgical blood loss is occurring, thereby minimizing the effects of loss of red blood cell (RBC) mass, while allowing reinfusion of the patient's own fresh whole blood (which includes RBCs, viable platelets, and normal levels of clotting factors) during or shortly after the surgical procedure.
•A 2017 meta-analysis of 29 randomized trials that included more than 2400 cardiac surgical patients noted a lower incidence of allogeneic transfusion in the ANH group (42 versus 56 percent), with the number of transfused units reduced by nearly 1 unit compared with usual care [19].
•In a national registry that included more than 18,000 adult cardiac surgical patients, use of ANH resulted in lower intraoperative transfusion rates (10 percent with an autologous priming [AP] blood conservation technique or 8 percent without an AP technique) relative to patients who had no blood conservation technique (27 percent were transfused) or those who had only an AP technique without ANH (20 percent were transfused) [20]. (See 'Autologous priming techniques' below.)
Avoid excessive fluid administration — In patients who do not undergo ANH, fluid administration prior to CPB is typically restricted to the relatively small volumes necessary to administer intravenous (IV) medications because hemodilution will occur at onset of CPB as the patient's blood volume intermixes with 1.0 to 1.5 L crystalloid CPB prime. (See "Anesthesia for cardiac surgery: General principles", section on 'Prebypass fluid management'.)
Exceptions include patients with signs of hypovolemia and those who are undergoing ANH. (See 'Acute normovolemic hemodilution' above.)
Systemic anticoagulation — Systemic anticoagulation is necessary before initiation of CPB. Typically, this is accomplished with a bolus dose of heparin administered before aortic cannulation [3,21]. (See "Initiation of cardiopulmonary bypass", section on 'Aortic cannulation'.)
Heparin administration and monitoring
●Dose – The dose of heparin administered in preparation for CPB is typically 300 to 400 units/kg IV.
In patients with obesity undergoing CPB, basing the initial heparin dose on ideal rather than total body weight is reasonable, as long as adequate anticoagulation is verified [22,23].
●Monitoring adequacy of anticoagulation – Confirming adequacy of systemic anticoagulation is essential to prevent clot formation in the CPB circuit [3,4,24,25]. Blood sampling is performed approximately three minutes after heparin administration.
Adequacy of heparin anticoagulation is measured using a point-of-care (POC) test of the activated whole blood clotting time (ACT) to achieve a targeted value. A minimum post-heparin ACT value ≥400 to 480 seconds is targeted before initiation of CPB, although evidence defining optimal ACT is lacking [24,26-29].
Plasma heparin concentrations determined by POC heparin-protamine titration assays are also obtained, if available [3,24]. (See "Clinical use of coagulation tests", section on 'Monitoring heparins'.)
●Rationale – Advantages of heparin anticoagulation include:
•Ability to rapidly titrate its anticoagulant effect.
•Ability to rapidly reverse anticoagulation with protamine sulfate.
•Clinician familiarity due to decades of use.
•Low cost compared with alternatives such as direct thrombin inhibitors.
However, a non-heparin agent may be required in patients with heparin resistance or heparin-induced thrombocytopenia (HIT), as discussed below. (See 'Heparin resistance' below and 'Heparin-induced thrombocytopenia (HIT)' below.)
Special circumstances
Heparin resistance
●Definition – There is no standardized and validated definition of "heparin resistance"; the term is used when the desired preset anticoagulation target (typically an ACT ≥400 to 480 seconds) is not reached after initial heparin dosing [28,30-32] (see 'Heparin administration and monitoring' above).
The International Society of Haemostasis and Thrombosis has proposed a definition of not reaching an ACT value of 480 seconds after administration of a total dose of unfractionated heparin (UFH) of 500 U/kg [32]. This definition was based on available evidence and considers multiple practice patterns.
●Prevalence – The range of cardiac surgical patients who have heparin resistance has been reported to be 3 to 34 percent, depending on the definition of heparin resistance that is used [32].
●Causes – Causes and risk factors for heparin resistance are poorly understood [32,33].
Since heparin acts by binding to its cofactor antithrombin (AT), AT deficiency is one likely cause of heparin resistance [3,16,28,32,34,35]. (See "Antithrombin deficiency", section on 'Acquired deficiency'.)
AT levels <50 percent are often observed in cardiac surgical patients [36,37]. However, unless AT concentration was measured in the preoperative period, the diagnosis of AT deficiency as the cause of unanticipated heparin resistance cannot be certain.
Factors such as prior heparin therapy, liver insufficiency, thrombocytosis, elevated fibrinogen, or elevated von Willebrand factor (VWF) or factor VIII (FVIII) levels may also play a role. Further discussion is available in a separate topic. (See "Heparin and LMW heparin: Dosing and adverse effects", section on 'Heparin resistance/antithrombin deficiency'.)
●Management strategies – The following management strategies are reasonable (algorithm 1):
•Administer additional heparin – If heparin resistance due to AT deficiency or other factors is suspected, it is reasonable to first administer additional heparin doses. ACT measurements are then repeated. The maximum dose of heparin may be as high as 600 units/kg, although institutional protocols vary, and there is no validated upper limit [32].
It is important to be aware that large doses of heparin will accumulate in body tissues. Subsequently, gradual release of heparin into the intravascular space may occur, typically after CPB has been terminated and initial protamine administration to neutralize heparin effect has been completed. In such cases, it is usually necessary to administer additional doses of protamine, as discussed in a separate topic. (See "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Dosing for continued bleeding after initial protamine administration' and "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Avoiding heparin rebound'.)
•Check plasma heparin concentration – If available, plasma heparin concentration measured by POC assays such as heparin-protamine titration is also obtained to provide supplemental information [3,24,38,39]. If a total dose of 600 units/kg of heparin has been administered and the plasma heparin concentration is ≥4 units/mL with an ACT ≥350 seconds, it may be reasonable to initiate CPB after discussion among the cardiac surgeon, perfusionist, and anesthesiologist. A heparin concentration ≥4 units/mL is considered to be the critical concentration of heparin required to prevent thrombosis during CPB [3,24,28,34,38,39].
•Administer AT concentrate or Fresh Frozen Plasma (FFP) – Any individual with ACT <400 seconds or plasma heparin concentration <4 units/mL after receiving 600 units/kg of heparin may be suspected of having AT deficiency, although other potential causes are considered. In such cases, we administer a source of AT, preferably AT concentrate 500 to 1000 units [3,16,31,34,40-45]. If AT concentrate is not available, administration of 2 to 4 units of FFP is an alternative [24,25,28]. AT concentrate is preferred over FFP because AT concentrate does not cause volume overload and there is less risk of infection transmission and other complications of blood transfusion [3,16,40,41,46]. (See "Antithrombin deficiency", section on 'Available AT products and dosing'.)
ACT measurements are repeated five minutes after completion of administration of AT concentrate or FFP. If ACT is still <400 seconds, an additional 500 units of AT concentrate or two additional units of FFP may be considered, particularly if the patient is large (eg, weight >100 kg). Also, an additional dose of heparin may be administered, particularly if some time has elapsed (eg, >30 minutes) while AT concentrate or FFP is obtained and administered. Then the ACT value is rechecked.
However, there is no evidence that the use of AT supplementation attenuates adverse postoperative outcomes in adult patients [47], although normalization of AT level reduced coagulopathy and bleeding in pediatric patients undergoing cardiac surgery with CPB [48].
We avoid preemptive preoperative or postoperative administration of AT concentrate. Observational studies of AT supplementation in cardiac surgery demonstrated no clinical benefits of AT supplementation as a preemptive preoperative strategy or as a treatment for postoperative low AT values [49,50]. Furthermore, randomized trials in patients receiving AT supplementation reported a higher incidence of acute kidney injury (AKI; pooled odds ratio [OR] 4.41, 95% CI 1.90-10.23; four trials with 651 patients) [49].
●Other options – Decision-making regarding other options is complex, and requires consultation among the cardiac surgeon, perfusionist, and anesthesiologist. As noted above, it may be reasonable to initiate CPB after administration of a total heparin dose of 600 units/kg if plasma heparin concentration is determined to be ≥4 units/mL by POC assays such as heparin-protamine titration and the ACT is ≥350 seconds.
Initiation of CPB has also been reported after administration of a total heparin dose of 600 units/kg with an ACT value ≥350 seconds when no POC heparin-protamine assay was available [26]. Additional heparin was administered after initiation of CPB, using a fixed dosing regimen (eg, heparin 100 to 150 units/kg per hour, or 50 units/kg every 30 minutes if the duration of CPB will be brief). Failure to maintain therapeutic heparin levels has been associated with coagulopathic bleeding due to consumption of clotting factors by a process analogous to low grade disseminated intravascular coagulation (DIC) [28]. Fortunately, risks of thrombosis in patients with heparin resistance due to causes other than AT deficiency will often be mitigated by the hemodilution that occurs after the onset of CPB. (See 'Minimize further hemodilution during CPB' below.)
In all cases, adequacy of heparinization is monitored every 30 minutes throughout the duration of CPB, with the goal of maintaining ACT ≥400 seconds (and/or heparin concentration ≥4 units/mL). (See 'Maintenance of anticoagulation' below.)
Heparin-induced thrombocytopenia (HIT) — Occasionally, a patient presents for cardiac surgery with a current or remote history of HIT (algorithm 2). Management of these patients is discussed in detail in a separate topic. (See "Management of heparin-induced thrombocytopenia (HIT) during cardiac or vascular surgery".)
Antiphospholipid syndrome (APS) — APS is an autoimmune multisystem disorder, most commonly associated with systemic lupus erythematosus (SLE), that is characterized by arterial, venous, or small vessel thromboembolic events due to persistent antiphospholipid antibodies. (See "Clinical manifestations of antiphospholipid syndrome".)
APS is a prothrombotic, proinflammatory state that may be exacerbated by contact of blood with nonendothelial surfaces in the CPB circuit [51-55]. This may worsen complement activation, platelet activation, and clotting. (See 'Effects of cardiopulmonary bypass on hemostasis' above.)
Guidelines developed by the American Society of Extracorporeal Technology (AMSECT) and others suggest the following modifications from usual care for patients with known APS [54,55]:
●Administer supra-therapeutic doses of heparin to achieve systemic anticoagulation before initiating CPB, with target ACT value of >800 seconds (rather than the typical ACT target of ≥400 to 480 seconds). After initial anticoagulation, ACT is checked every 20 minutes. If available, heparin-normalized anti-factor Xa levels are also monitored. (See 'Heparin administration and monitoring' above.)
●Avoid administering antifibrinolytic agents (epsilon-aminocaproic acid [EACA] or tranexamic acid [TXA]). (See "Intraoperative use of antifibrinolytic agents", section on 'Use of antifibrinolytic agents in cardiac surgery'.)
●Administer only one quarter of the usual dose of protamine to neutralize heparin and reverse anticoagulation after CPB. (See "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Initial protamine dosing strategies'.)
Additional small doses of protamine may be administered if necessary to control persistent bleeding. (See "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Dosing for continued bleeding after initial protamine administration'.)
●Avoid using cell salvage, or closely monitor the equipment, as clots are likely to form in the tubing or basin. (See "Surgical blood conservation: Intraoperative blood salvage".)
●Although patients with APS may have thrombocytopenia, particular care is necessary if platelet transfusions are administered after CPB, to avoid a thrombotic event. If needed, less than the typical number of platelet units are administered slowly with careful monitoring for evidence of clotting. (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass", section on 'Platelets'.)
Antifibrinolytic administration — Since fibrinolysis is a major contributor to coagulopathy and bleeding during cardiac surgery with CPB, we recommend prophylactic antifibrinolytic therapy (either EACA or TXA) (figure 1) [3,56].
The antifibrinolytic agent is typically administered after anesthetic induction and always before initiation of CPB. We withhold the antifibrinolytic agent until after heparin has been administered [57]; however, institutional protocols for precise timing of initial administration vary. Details regarding dosing, timing of administration, and efficacy are presented in a separate topic. (See "Intraoperative use of antifibrinolytic agents", section on 'Use of antifibrinolytic agents in cardiac surgery'.)
Antifibrinolytic agents are avoided in patients with APS. (See 'Antiphospholipid syndrome (APS)' above.)
MANAGEMENT DURING CARDIOPULMONARY BYPASS
Maintenance of anticoagulation — Adequacy of heparin anticoagulation is measured with a point-of-care (POC) test such as the activated whole blood clotting time (ACT) every 30 minutes throughout CPB to maintain a targeted value (≥400 to 480 seconds) [4,25].
If available, plasma heparin concentrations may also be determined by POC assays such as heparin-protamine titration, with target heparin concentration ≥4 units/mL [3,4,25,28,58]. (See 'Heparin administration and monitoring' above.)
Protocols in some institutions emphasize administration of additional heparin if the heparin concentration is <4 units/mL, if measured, even if ACT values are adequate.
Minimize further hemodilution during CPB — During onset of CPB, further hemodilution occurs as the patient's own blood volume intermixes with a crystalloid priming solution for the CPB circuit that is typically 1.0 to 1.5 L and typically reduces hemoglobin concentration by 1 to 2 g/dL [3,59]. Minimizing hemodilution during CPB may aid in maintaining hemoglobin levels above transfusion thresholds and avoid the need for transfusion during CPB. However, safe use of the techniques discussed below requires adequate prebypass oxygen carrying capacity and intravascular volume status. (See 'Management of anemia' below.)
Use a CPB circuit of appropriate size — Excessive hemodilution is particularly likely if the CPB circuit volume is large or if patient blood volume is limited by small patient size. Minimizing circuit priming volume (eg, by selecting a CPB oxygenator of appropriate size and using shorter tubing lengths) reduces risk for the excessive hemodilution with the required crystalloid priming volume [3,4,16].
Autologous priming techniques — Techniques such retrograde autologous priming (RAP) and/or antegrade autologous priming (AAP) are used in many institutions to displace priming volume in the CPB circuit, thereby allowing reduction of the crystalloid priming volume and decreasing the degree of hemodilution [3,4,16,40,60-66]. Either a RAP or AAP technique allows 400 to 800 mL of crystalloid prime to be sequestered from the CPB circuit, thereby minimizing hemodilution. These techniques are a useful component of blood management in selected adults, particularly those with excessive intravascular volume [66]. (See "Initiation of cardiopulmonary bypass", section on 'Autologous priming'.)
In a 2021 meta-analysis that included 11 randomized trials (1337 patients) and 10 observational studies (2327 patients), RAP was associated with reduced intraoperative red blood cell (RBC) transfusions (odds ratio [OR] 0.34, 95% CI 0.22-0.55; 18 studies), as well as reduced RBC transfusions during the entire hospitalization (OR 0.28, 95% CI 0.19-0.41; 5 studies), compared with priming techniques not including RAP [60]. Incidences of stroke and acute kidney injury (AKI) were similar. However, the volume of RAP is limited if hypovolemia or hypotension are present, and RAP is not feasible due to safety concerns in some patients (eg, those with critical coronary or cardiac valve disease or cerebral comorbidities). Conversely, AAP can be applied safely under virtually any conditions because it occurs over a few seconds during initiation of CPB.
Ultrafiltration techniques — Conventional ultrafiltration (CUF) employs a hemofiltration filter in parallel to the CPB circuit that can continuously remove plasma-free solute and water from diverted blood, thereby concentrating blood, increasing hemoglobin, removing electrolytes such as potassium, and possibly removing inflammatory mediators and other small molecules [3,67,68].
CUF techniques can be used to prevent further hemodilution after the initial decrease in hemoglobin level at the onset of CPB, and it can subsequently remove additional accumulated volume after administration of cardioplegia solution [3,4,16]. However, we avoid inducing hypovolemia by avoiding use of large-volume CUF or routine use of negative balance ultrafiltration in an attempt to reverse hemodilution, particularly in patients at risk for AKI [4,69-72].
A 2021 systemic review and meta-analysis of >8000 patients did not show any increased risk for AKI with high-volume CUF [73]. Subgroup analysis of those with previous chronic kidney disease suggested no significant differences in incremental AKI development (risk ratio [RR] = 0.84, 95% CI 0.53-1.33, p = 0.47).
However, some retrospective studies have noted an association of CUF with AKI. In one retrospective study that included 6407 patients undergoing coronary artery bypass grafting (CABG), CUF during CPB increased risk of AKI compared with not using CUF [72]. Another retrospective analysis of >1600 patients with normal baseline kidney function suggested that high-volume CUF >32 mL/kg was associated with AKI [71]. These retrospective studies described the volume of fluid removed, rather than overall fluid balance. However, it is reasonable to limit the volume of fluid removed unless there is clinical evidence of hypervolemia.
Management of anemia
Hemoconcentration — For hemoglobin <7.5 g/dL (or hematocrit <22 percent), initial treatment during CPB is removal of fluid by ultrafiltration (hemoconcentration), if volume status allows, to account for hemodilution due to the CPB prime [74]. (See 'Ultrafiltration techniques' above.)
If the hemoglobin is <7 g/dL shortly before initiation of CPB, some packed RBCs would be used in the circuit prime. (See 'Management before cardiopulmonary bypass' above.)
Thresholds for RBC transfusion — When hemoconcentration is not possible or is ineffective, or if further treatment for severe anemia is necessary, available salvaged RBCs are returned first, followed by reinfusion of blood units harvested via normovolemic hemodilution, followed by allogeneic units. (See "Surgical blood conservation: Intraoperative blood salvage" and 'Acute normovolemic hemodilution' above.)
●Indications – Guidelines published by professional societies recommend RBC transfusion for hemoglobin <6 g/dL and avoiding RBC transfusion for hemoglobin >10 g/dL [3,4,40]. Transfusion of allogeneic RBCs is reasonable if hemoglobin remains <7.5 g/dL and neither salvaged nor harvested blood is available [3,75,76]. However, despite the randomized trials discussed below, the optimal hemoglobin level during cardiac surgery is not known. Thus, transfusion decisions are individualized, taking into account factors such as whether the patient is actively bleeding or has active myocardial ischemia or infarction, reduced cardiac function, significantly increased risk for critical end-organ ischemia, or clinical or laboratory evidence of hypoperfusion (eg, hypotension, metabolic acidosis, lactic acidosis, low mixed venous oxygen saturation [SvO2], or difficulty achieving higher CPB flows to counteract low hemoglobin) [17,40,77,78]. (See "Indications and hemoglobin thresholds for RBC transfusion in adults", section on 'Rationale for transfusion' and "Management of cardiopulmonary bypass", section on 'Pump flow and mixed venous oxygen saturation'.)
●Preparation – Leukocyte-reduced blood is used to reduce the risk of febrile reactions and other complications [79]. (See "Practical aspects of red blood cell transfusion in adults: Storage, processing, modifications, and infusion", section on 'Pre-storage leukoreduction'.)
●Supporting evidence – Transfusion thresholds in cardiac surgery have been evaluated in multiple randomized trials [80-82]. A 2021 meta-analysis of data from these trials suggested that a restrictive transfusion strategy with a hemoglobin threshold of 7 to 8 g/dL (hematocrit 21 to 24 percent) is reasonable for patients undergoing cardiac surgery with CPB, compared with higher hemoglobin thresholds of 9 to 10 g/dL (hematocrit 27 to 30 percent) [82]. This is based on lower exposure to allogeneic blood with comparable outcomes such as mortality, cardiac events, infections, and other outcomes. Mortality at 30 days in cardiac surgery patients was not statistically different for a restrictive compared with a liberal transfusion strategy (risk ratio [RR] 0.99, 95% CI 0.74-1.33).
Both RBC transfusion and very low nadir hemoglobin levels (<6 to 7 g/dL) during CPB are associated with increased morbidity and mortality [17,74,83-87]. In particular, lower nadir hematocrit during CPB has been associated with postoperative AKI [78,86,88-96].
●Adverse effects of transfusion – Although decline in postoperative kidney function may be attributable to adverse effects of reduced oxygen delivery due to anemia during CPB, no critical hemoglobin threshold predicting AKI has been identified. RBC transfusion during cardiac surgery is also associated with AKI [88,93,96,97].
Furthermore, transfusions in patients may also have adverse consequences such as transfusion-associated circulatory overload (TACO), especially in individuals with cardiac or kidney dysfunction [98].
ACHIEVING HEMOSTASIS AFTER CARDIOPULMONARY BYPASS —
After weaning from CPB, protamine is administered to reverse systemic heparin anticoagulation, as discussed in a separate topic. (See "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Protamine administration after cardiopulmonary bypass'.)
Individuals who receive higher doses of heparin, such as those with heparin resistance, will have greater accumulation of heparin in body tissues and prolonged release of heparin into the intravascular space, resulting in the "heparin rebound" phenomenon. (See 'Heparin resistance' above.)
This heparin rebound may be treated preemptively by administering a protamine infusion at 25 mg/hour, beginning after the initial reversal of heparin anticoagulation and extended into the postoperative period over approximately four hours, as described in a separate topic [99]. (See "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Avoiding heparin rebound'.)
Achieving hemostasis and management of bleeding during the postbypass period, including indications for platelet transfusions, are discussed in a separate topic. (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass".)
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Transfusion and patient blood management" and "Society guideline links: Management of cardiopulmonary bypass".)
SUMMARY AND RECOMMENDATIONS
●Rationale – The cardiopulmonary bypass (CPB) circuit induces an intense inflammatory response resulting in coagulopathy due to multiple mechanisms (figure 1). Hemodilution and hypothermia may exacerbate coagulopathy after CPB. (See 'Effects of cardiopulmonary bypass on hemostasis' above.)
●Strategies to conserve blood before CPB – Blood conservation strategies often used in the prebypass period. These include aggressive reversal of preoperative anemia with iron supplementation at least 10 days in advance for elective procedures, and in the immediate pre-CPB period, priming the circuit with blood for severe anemia (hemoglobin <7 g/dL), use of blood salvage technology and, in selected patients, acute normovolemic hemodilution (ANH). (See 'Overview of blood management for cardiac surgery' above and "Surgical blood conservation: Intraoperative blood salvage" and "Surgical blood conservation: Acute normovolemic hemodilution".)
●Initiation of anticoagulation
•Routine heparin dosing – Intravenous (IV) heparin is administered before aortic cannulation, typically 300 to 400 units/kg, and adequate systemic anticoagulation is confirmed to prevent clot formation in the CPB circuit using a point-of-care (POC) test such as activated whole blood clotting time (ACT) to achieve and maintain a targeted value, typically ≥400 to 480 seconds, before initiation of CPB. If available, plasma heparin concentrations may also be determined by a POC heparin-protamine titration, with target heparin concentration ≥4 units/mL. (See 'Systemic anticoagulation' above and 'Maintenance of anticoagulation' above.)
•Management of heparin resistance – For patients whose ACT value is not at target after initial dosing, it is reasonable to first administer additional heparin doses. For patients whose ACT value is not at target after additional heparin up to a total of 600 units/kg, we suggest administration of antithrombin (AT) concentrate (Grade 2B), at a dose of 500 to 1000 units, to treat suspected AT deficiency. For those who do not have access to AT concentrate, two to four units of Fresh Frozen Plasma (FFP) may be used as a source of AT. AT concentrate is preferred to FFP to avoid volume overload and decrease risks for infection transmission and other complications of blood transfusion.
Rarely, a lower ACT value of approximately 350 seconds may be accepted for initiation of CPB in a patient with heparin resistance, with administration of additional heparin by a fixed dosing regimen.
•Antifibrinolytic therapy – We administer prophylactic antifibrinolytic therapy (aminocaproic acid [EACA] or tranexamic acid [TXA]) before initiation of CPB, as discussed separately, with limited exceptions such as antiphospholipid syndrome (APS). (See "Intraoperative use of antifibrinolytic agents", section on 'Use of antifibrinolytic agents in cardiac surgery'.)
●Special populations – Special considerations apply to some individuals:
•HIT – Risks and management options for heparin-induced thrombocytopenia (HIT) are discussed separately. (See 'Heparin-induced thrombocytopenia (HIT)' above and "Management of heparin-induced thrombocytopenia (HIT) during cardiac or vascular surgery".)
•APS – For patients with antiphospholipid syndrome (APS), changes to the routine protocol include using higher heparin doses and avoiding certain prothrombotic interventions such as an antifibrinolytic agent and full-dose protamine reversal. (See 'Antiphospholipid syndrome (APS)' above.)
●Maintenance of anticoagulation – Adequacy of heparin anticoagulation is measured with POC tests such as ACT every 30 minutes to maintain a targeted value throughout CPB (typically above 480 seconds). If available, a heparin-protamine titration assay with a targeted plasma heparin concentration of ≥4 units/mL may also be employed. (See 'Maintenance of anticoagulation' above.)
●Strategies to minimize excessive hemodilution before and during CPB
•Prebypass – Restrict volume administration to small amounts necessary to administer IV medications in patients who are euvolemic and not undergoing ANH. (See 'Avoid excessive fluid administration' above.)
•During CPB – Use minimal CPB circuit prime volume, autologous priming techniques, shorter circuit tubing, and ultrafiltration (UF), while avoiding hypovolemia and hypotension. (See 'Minimize further hemodilution during CPB' above.)
●Management of anemia – During CPB, initial treatment of hemoglobin <7.5 g/dL (or hematocrit <22 percent) involves removal of fluid by hemoconcentration when possible.
For individuals with anemia during or after CPB despite hemoconcentration, we suggest using a restrictive transfusion strategy with transfusion of red blood cells (RBCs) for hemoglobin <7.5 g/dL (Grade 2B). However, some patients may benefit from transfusion when their hemoglobin is ≥7.5 g/dL. Examples include those who are actively bleeding or have active cardiac ischemia or infarction, reduced cardiac function, significantly increased risk for critical end-organ ischemia, or clinical or laboratory parameters indicating hypoperfusion (eg, hypotension caused by anemia, metabolic acidosis, lactic acidosis, low mixed venous oxygen saturation [SvO2], low tissue oxygen delivery during CPB). (See 'Management of anemia' above.)
●Reversing anticoagulation and achieving hemostasis after CPB
•After weaning from CPB, protamine is administered to reverse systemic heparin anticoagulation, as discussed separately. (See "Protamine reversal of heparin anticoagulation after cardiopulmonary bypass", section on 'Protamine administration after cardiopulmonary bypass'.)
•Management of bleeding in the postbypass period, including indications for platelet transfusion, is discussed separately. (See "Achieving hemostasis after cardiac surgery with cardiopulmonary bypass".)
