# Coagulopathy and Blood Management in Cardiac Surgery

## Introduction

Coagulopathy is an inherent consequence of cardiac surgery and cardiopulmonary bypass, arising from hemodilution, platelet dysfunction, fibrinolysis, and consumption of coagulation factors. Bleeding complications increase morbidity, mortality, and resource utilization. A systematic approach to patient blood management encompassing preoperative optimization, intraoperative conservation, and goal-directed transfusion reduces bleeding and improves outcomes.

## Pathophysiology of CPB-Related Coagulopathy

### Hemodilution

Circuit priming volume of 1000-1500 mL dilutes coagulation factors and platelets by 20-30%. Fibrinogen concentration falls disproportionately, and levels below 200 mg/dL impair clot formation.

### Platelet Dysfunction

CPB causes platelet activation, degranulation, and consumption on circuit surfaces. Platelet count decreases by 30-50%, and the remaining platelets have impaired aggregation. Hypothermia further inhibits platelet function. Platelet dysfunction is the most common cause of post-CPB microvascular bleeding.

### Coagulation Factor Consumption

Contact activation of the intrinsic pathway by circuit surfaces leads to consumption of factors V, VIII, and fibrinogen. Thrombin generation occurs throughout CPB despite heparin anticoagulation.

### Fibrinolysis

CPB activates fibrinolysis through release of tissue plasminogen activator (tPA) from the endothelium. Unopposed fibrinolysis contributes to diffuse microvascular bleeding and is most pronounced in prolonged bypass runs and reoperative surgery.

### Residual Heparin Effect

Inadequate protamine reversal leaves residual heparinization. Heparin rebound occurs when heparin redistributes from tissue stores after protamine clearance.

![Diagram of the coagulation cascade showing CPB-related disruption points](/images/cardiac-surgery-coagulopathy-cascade.png)

## Preoperative Assessment and Optimization

### Risk Assessment

Bleeding risk factors include reoperative surgery, prolonged CPB time, advanced age, low BMI, chronic kidney disease, and preoperative anemia. All anticoagulant and antiplatelet medications should be reviewed.

### Medication Management

Aspirin is continued or held per institutional protocol; the Society of Thoracic Surgeons recommends continuation for CABG. Clopidogrel and ticagrelor should be held 5-7 days before elective surgery when possible. Warfarin is discontinued 5 days preoperatively with bridging using heparin if the thrombotic risk is high. Direct oral anticoagulants (DOACs) are held 2-3 days (longer for renal impairment); idarucizumab reverses dabigatran and andexanet alfa reverses factor Xa inhibitors. Preoperative anemia should be identified and treated with iron deficiency correction, considering IV iron or erythropoietin in elective cases.

### Baseline Testing

Baseline testing includes complete blood count, PT/INR, aPTT, fibrinogen level, and thromboelastography (TEG) or rotational thromboelastometry (ROTEM) if available.

## Intraoperative Blood Conservation

### Antifibrinolytic Therapy

Tranexamic acid (TXA) is a lysine analogue that inhibits plasmin. A loading dose of 30 mg/kg is followed by a 15 mg/kg/hr infusion, with 2 mg/kg added to the CPB prime. TXA reduces blood loss by 25-30% and transfusion by 30-40%. Seizure risk exists with high doses, so maintaining the dose within the recommended range is important. Aminocaproic acid is an alternative but less potent antifibrinolytic, given as a 10 g loading dose with a 2 g/hr infusion.

### Cell Salvage

Intraoperative autotransfusion using cell saver devices washes, concentrates, and returns the patient's own red blood cells, reducing allogeneic transfusion. It is standard practice in cardiac surgery.

### Ultrafiltration

Modified ultrafiltration (MUF) concentrates blood after bypass termination and is most beneficial in pediatric surgery. Conventional ultrafiltration during CPB removes excess fluid and raises hematocrit.

### Surgical Hemostasis

Meticulous surgical technique is the first line of defense against bleeding. Systematic inspection of all suture lines, cannulation sites, and the mediastinum is performed before closing. Topical hemostatic agents including fibrin sealant, oxidized cellulose, and thrombin-soaked gelatin supplement surgical hemostasis.

## Point-of-Care Coagulation Testing

### Viscoelastic Testing

TEG and ROTEM provide rapid assessment of clot formation, strength, and lysis. Specific parameters guide targeted component therapy: a prolonged R-time or CT indicates coagulation factor deficiency treatable with FFP or prothrombin complex concentrate; low maximum amplitude or MCF suggests platelet or fibrinogen deficiency; a low alpha angle with low fibrinogen contribution calls for cryoprecipitate or fibrinogen concentrate; and evidence of fibrinolysis (LY30 above 3%) warrants antifibrinolytic therapy. Algorithm-driven transfusion based on viscoelastic testing reduces transfusion by 20-30% compared to empiric therapy.

### Standard Tests

The ACT monitors heparin anticoagulation and protamine reversal. The anti-Xa assay provides more accurate heparin monitoring than ACT, especially with aprotinin or hypothermia. Platelet count and fibrinogen level are also routinely assessed.

![Thromboelastography tracing showing normal pattern and common abnormalities in cardiac surgery](/images/cardiac-surgery-teg-patterns.png)

## Transfusion Therapy

| Blood Product | Transfusion Trigger | Dose | Expected Effect | Key Considerations |
|--------------|--------------------|----- |----------------|-------------------|
| Packed RBCs | Hgb <7 g/dL (stable); <8 g/dL (active bleeding) | 1 unit | ↑ Hgb ~1 g/dL | Independently associated with infection, AKI, mortality |
| Platelets | <100,000/mcL with bleeding or functional deficiency (TEG/ROTEM) | 1 apheresis unit | ↑ Plt 30,000-50,000/mcL | Platelet dysfunction more important than count after CPB |
| FFP | INR >1.5 with active bleeding | 10-15 mL/kg | Replaces all coagulation factors | PCC is a low-volume alternative |
| Cryoprecipitate | Fibrinogen <200 mg/dL with bleeding | 10 units (pooled) | ↑ Fibrinogen ~70 mg/dL | Rich in fibrinogen, factor VIII, XIII, vWF |
| Fibrinogen concentrate (RiaSTAP) | Fibrinogen <200 mg/dL | 70 mg/kg | Standardized fibrinogen replacement | Reduced infection risk vs. cryoprecipitate |

### Red Blood Cells

A restrictive threshold of hemoglobin below 7 g/dL is used for stable patients, with a threshold below 8 g/dL for active bleeding or high-risk patients. Each RBC unit increases hemoglobin by approximately 1 g/dL. Transfusion is independently associated with infection, acute kidney injury, and mortality.

### Platelets

Platelet transfusion is indicated for a count below 100,000/mcL with active bleeding or functional platelet deficiency on viscoelastic testing. One apheresis unit typically raises the platelet count by 30,000-50,000/mcL.

### Fresh Frozen Plasma (FFP)

FFP contains all coagulation factors and is indicated when the INR exceeds 1.5 with active bleeding, dosed at 10-15 mL/kg. Prothrombin complex concentrate (PCC) is a low-volume alternative for factor replacement.

### Cryoprecipitate and Fibrinogen Concentrate

Cryoprecipitate is rich in fibrinogen, factor VIII, factor XIII, and von Willebrand factor. It is indicated when fibrinogen falls below 200 mg/dL with ongoing bleeding. Fibrinogen concentrate (RiaSTAP) at a 70 mg/kg dose offers standardized dosing and reduced infection risk compared to cryoprecipitate.

## Management of Refractory Bleeding

The first step is surgical re-exploration, as surgical bleeding must be excluded before treating coagulopathy. Recombinant factor VIIa (rFVIIa) is used off-label as rescue therapy for refractory coagulopathic bleeding, though it carries thrombotic risk. DDAVP (desmopressin) at 0.3 mcg/kg IV releases vWF and factor VIII and is useful for uremia-related platelet dysfunction. Protamine re-dosing may be appropriate if heparin rebound is suspected, guided by ACT or anti-Xa levels. Hypothermia, acidosis, and hypocalcemia must be checked and corrected, as all impair coagulation.

![Algorithm for goal-directed blood management in cardiac surgery using viscoelastic testing](/images/cardiac-surgery-blood-management-algorithm.png)

## Key Clinical Pearls

Tranexamic acid should be administered in every cardiac surgical case requiring CPB unless contraindicated. Viscoelastic testing (TEG/ROTEM) with algorithm-driven transfusion significantly reduces unnecessary blood product use. Always exclude surgical bleeding before attributing hemorrhage to coagulopathy; return to the operating room early if chest tube output exceeds 200 mL/hr for 2 hours. Fibrinogen is the first coagulation factor to reach critically low levels after CPB, and the target should be above 200 mg/dL. The "lethal triad" of hypothermia, acidosis, and coagulopathy is mutually reinforcing, and all three must be corrected simultaneously.

## References

1. Raphael J, Mazer CD, Subramani S, et al. Society of Cardiovascular Anesthesiologists clinical practice improvement advisory for management of perioperative bleeding and hemostasis in cardiac surgery patients. *Anesth Analg*. 2019;129(5):1209-1221.
2. Myles PS, Smith JA, Forbes A, et al. Tranexamic acid in patients undergoing coronary-artery surgery. *N Engl J Med*. 2017;376(2):136-148.
3. Karkouti K, Wijeysundera DN, Yau TM, et al. Platelet transfusions are not associated with increased morbidity or mortality in cardiac surgery. *Can J Anesth*. 2006;53(3):279-287.
4. Weber CF, Gorlinger K, Meininger D, et al. Point-of-care testing: a prospective, randomized clinical trial of efficacy in coagulopathic cardiac surgery patients. *Anesthesiology*. 2012;117(3):531-547.