# Massive Hemorrhage and Transfusion Medicine

## Introduction

Massive hemorrhage is defined as loss of one total blood volume within 24 hours, loss of 50% of blood volume within 3 hours, or ongoing blood loss exceeding 150 mL/min. It is encountered in trauma, obstetrics, cardiac and vascular surgery, hepatic surgery, and solid organ transplantation. Rapid identification, activation of institutional massive transfusion protocols, and goal-directed hemostatic resuscitation are essential to survival.

## Physiology of Hemorrhagic Shock

Blood loss leads to decreased preload, cardiac output, and oxygen delivery. Compensatory mechanisms include tachycardia, peripheral vasoconstriction, and fluid shifts from the interstitial to intravascular space.

The ATLS classification of hemorrhagic shock progresses through four classes. Class I involves less than 15% blood volume loss (approximately 750 mL in adults) with minimal symptoms. Class II involves 15 to 30% loss (approximately 750 to 1500 mL) and produces tachycardia and narrowed pulse pressure. Class III involves 30 to 40% loss (approximately 1500 to 2000 mL) with hypotension, tachycardia, and altered mentation. Class IV involves greater than 40% loss (more than 2000 mL) and is life-threatening, with profound hypotension and lethargy.

The shock index, calculated as heart rate divided by systolic blood pressure, provides a rapid assessment tool. A shock index greater than 0.9 to 1.0 suggests significant hemorrhage and the need for transfusion.

## The Lethal Triad

The lethal triad consists of hypothermia, acidosis, and coagulopathy. **Hypothermia** impairs coagulation factor enzymatic activity (approximately 10% reduction per degree below 37 degrees Celsius) and platelet function. **Acidosis** worsens coagulopathy, decreases myocardial contractility, and impairs vasopressor responsiveness. **Coagulopathy** is dilutional (from crystalloid resuscitation), consumptive (from DIC), and exacerbated by hypothermia and acidosis. All three components are mutually reinforcing, and damage control resuscitation aims to interrupt this cycle.

![The lethal triad of hypothermia, acidosis, and coagulopathy](lethal-triad-diagram.png)

## Massive Transfusion Protocol (MTP)

### Activation Criteria

MTP activation is based on clinical judgment of ongoing massive hemorrhage. Scoring systems such as the Assessment of Blood Consumption (ABC) score and Trauma-Associated Severe Hemorrhage (TASH) score can assist in decision-making. Objective triggers include a shock index greater than 1.0, base deficit greater than -6, or lactate above 4 mmol/L with ongoing bleeding.

### Protocol Components

Pre-assembled coolers are delivered by the blood bank on a timed schedule. A typical first cooler contains 6 units of pRBCs, 6 units of FFP (or equivalent), and 1 apheresis platelet unit. The target is a balanced ratio of pRBC to FFP to platelets at approximately 1:1:1 by volume, as supported by the PROPPR trial. Subsequent coolers are based on clinical need and laboratory or viscoelastic results. Cryoprecipitate is administered when fibrinogen falls below 150 to 200 mg/dL, at a dose of 5 to 10 units (or 1 unit per 10 kg). Fibrinogen concentrate at 25 to 50 mg/kg is an alternative to cryoprecipitate.

### Tranexamic Acid (TXA)

TXA is administered at 1 g IV over 10 minutes within 3 hours of injury, followed by 1 g over 8 hours, as established by the CRASH-2 trial. It inhibits plasminogen activation, thereby reducing fibrinolysis. TXA is also used in obstetric hemorrhage (WOMAN trial), cardiac surgery, and orthopedic surgery. It must not be administered more than 3 hours after injury, as delayed administration may increase mortality.

## Blood Product Overview

### Packed Red Blood Cells (pRBCs)

One unit of pRBCs is approximately 300 mL with a hematocrit of 55 to 60%. The expected increase is approximately 1 g/dL of hemoglobin per unit in a 70 kg adult. The storage lesion involves potassium leakage from cells, decreased 2,3-DPG, and a drop in pH, which becomes clinically significant in massive transfusion and neonatal populations. The general transfusion threshold is a hemoglobin of 7 g/dL in stable patients, as supported by the TRICC and TRISS trials, with a higher threshold in active hemorrhage, coronary disease, or symptomatic anemia.

### Fresh Frozen Plasma (FFP)

FFP contains all coagulation factors at near-physiologic concentrations and is dosed at 10 to 15 mL/kg to correct coagulopathy. It must be ABO-compatible, and thawing requires 20 to 30 minutes (thawed plasma can be stored for 5 days). Group AB plasma is the universal donor for plasma.

### Platelets

One apheresis unit is equivalent to 6 pooled whole-blood-derived units and raises the platelet count by approximately 30,000 to 60,000 per microliter in an adult. Transfusion thresholds are below 50,000 with surgical bleeding and below 100,000 for neurosurgery or ocular surgery. ABO-compatible platelets are preferred, and Rh-negative platelets should be used for Rh-negative women of childbearing age.

### Cryoprecipitate

Cryoprecipitate is rich in fibrinogen, factor VIII, factor XIII, and von Willebrand factor. One unit raises fibrinogen by approximately 5 to 10 mg/dL in an adult, and the standard dose is 5 to 10 units pooled.

| Blood Product | Volume per Unit | Key Contents | Expected Effect | Special Notes |
|---|---|---|---|---|
| pRBCs | ~300 mL | RBCs (Hct 55–60%) | ↑ Hb ~1 g/dL per unit | Storage lesion: ↑K+, ↓2,3-DPG |
| FFP | ~250 mL | All coagulation factors | Corrects coagulopathy | ABO-compatible; 20–30 min thaw time |
| Platelets (apheresis) | ~200–300 mL | Platelets | ↑ 30,000–60,000/µL | Room temperature storage; highest bacterial risk |
| Cryoprecipitate | ~15 mL/unit | Fibrinogen, VIII, XIII, vWF | ↑ Fibrinogen ~5–10 mg/dL per unit | Dose: 5–10 units pooled |
| Whole blood (LTOWB) | ~500 mL | RBCs, plasma, platelets | Physiologic ratios | Low-titer group O; emerging in trauma |

### Whole Blood

Whole blood is increasingly used in military and civilian trauma settings because it provides all blood components in physiologic ratios. Low-titer group O whole blood (LTOWB) is used as a universal product in some trauma centers.

## Viscoelastic Testing

### Thromboelastography (TEG) and Rotational Thromboelastometry (ROTEM)

TEG and ROTEM are point-of-care whole blood assays that assess the entire coagulation process. They provide results in 10 to 20 minutes compared to 45 to 60 minutes for conventional coagulation tests.

Key parameters and their clinical significance include the R-time or CT (clotting time), which represents the time to initial fibrin formation and when prolonged indicates factor deficiency treatable with FFP. The K-time or CFT (clot formation time) represents the time to achieve clot firmness, and when prolonged indicates fibrinogen deficiency or platelet dysfunction. The alpha angle reflects the rate of clot formation and when decreased suggests fibrinogen deficiency. The MA or MCF (maximum amplitude or maximum clot firmness) represents overall clot strength, and when decreased indicates platelet dysfunction or low fibrinogen treatable with platelets or cryoprecipitate. LY30 or ML (lysis at 30 minutes) reflects fibrinolysis, and when elevated indicates hyperfibrinolysis treatable with TXA.

| TEG/ROTEM Parameter | TEG Term | ROTEM Term | Reflects | Abnormal Finding | Treatment |
|---|---|---|---|---|---|
| Clotting time | R-time | CT | Clotting factor activity | Prolonged | FFP |
| Clot formation time | K-time | CFT | Fibrinogen/platelet function | Prolonged | Cryoprecipitate or fibrinogen concentrate |
| Clot formation rate | Alpha angle | Alpha angle | Fibrinogen contribution | Decreased | Cryoprecipitate or fibrinogen concentrate |
| Clot strength | MA | MCF | Platelet function + fibrinogen | Decreased | Platelets ± cryoprecipitate |
| Fibrinolysis | LY30 | ML | Clot stability over time | Elevated (>3%) | Tranexamic acid |

Goal-directed transfusion based on viscoelastic testing reduces blood product usage and may improve outcomes.

![TEG tracing with labeled parameters and corresponding treatment interventions](teg-tracing-parameters.png)

## Complications of Massive Transfusion

### Metabolic

**Hypocalcemia** occurs because citrate in blood products chelates ionized calcium. Ionized calcium should be maintained above 1.0 mmol/L, and calcium chloride 1 g IV should be given per 4 to 6 units transfused. **Hyperkalemia** is a concern because stored pRBCs leak potassium (up to 30 to 50 mEq/L in older units) and requires close monitoring, especially during rapid transfusion. **Metabolic alkalosis** is a late complication as citrate is metabolized to bicarbonate. **Hypothermia** from cold blood products lowers core temperature, and a blood warmer should be used for all rapid transfusions.

### Immunologic

**Transfusion-related acute lung injury (TRALI)** causes noncardiogenic pulmonary edema within 6 hours of transfusion and is treated supportively. **Allergic and anaphylactic reactions** range from urticaria to anaphylaxis and are treated with antihistamines, epinephrine, and stopping the transfusion. **Acute hemolytic transfusion reaction** results from ABO incompatibility, presenting with fever, hypotension, and hemoglobinuria; the transfusion must be stopped immediately with aggressive IV fluids and repeat crossmatch.

### Infectious

The risk of viral transmission is extremely low with modern screening (HIV approximately 1 in 2 million; HCV approximately 1 in 1 to 2 million). Bacterial contamination is highest with platelet products because they are stored at room temperature.

## Cell Salvage (Autotransfusion)

Intraoperative blood salvage involves collecting, washing, and re-infusing the patient's own red blood cells. It reduces allogeneic transfusion requirements in cardiac, vascular, orthopedic, and hepatic surgery. Contraindications include a contaminated surgical field (bowel contents, infection) and malignancy at the operative site (a relative contraindication, as leukocyte depletion filters may mitigate risk). Washed salvaged blood contains only red blood cells, without platelets, clotting factors, or plasma.

## Special Populations

### Obstetric Hemorrhage

Postpartum hemorrhage is the leading cause of maternal mortality worldwide. Common causes include uterine atony (the most common), placental abnormalities, lacerations, and coagulopathy. TXA within 3 hours of delivery reduces bleeding-related death, as shown in the WOMAN trial. The obstetric MTP should be activated early, and uterotonic agents (oxytocin, methylergonovine, carboprost, misoprostol) are first-line for atony.

### Patients Refusing Blood Products

Jehovah's Witness patients may refuse all or specific blood products. Acceptable alternatives should be discussed, including cell salvage (which some accept), acute normovolemic hemodilution, erythropoietin, TXA, and iron. The informed consent discussion and specific products refused or accepted should be documented.

![Massive transfusion protocol activation and management flowchart](mtp-flowchart.png)

## Clinical Pearls

The massive transfusion protocol should be activated early because delays in balanced resuscitation are associated with increased mortality. Viscoelastic testing (TEG/ROTEM) provides faster, more targeted guidance for component therapy than conventional coagulation tests. Hypocalcemia from citrate toxicity is the most common and immediately dangerous metabolic complication of massive transfusion and should be treated empirically with calcium chloride. TXA is a low-cost, high-impact intervention that should be administered within 3 hours of hemorrhage onset in trauma and obstetric emergencies. The shift from crystalloid-heavy resuscitation to balanced blood product transfusion (1:1:1) has been one of the most significant advances in hemorrhage management.

## References

1. Holcomb JB, Tilley BC, Baraniuk S, et al. Transfusion of plasma, platelets, and red blood cells in a 1:1:1 vs a 1:1:2 ratio (PROPPR Trial). *JAMA*. 2015;313(5):471-482.
2. CRASH-2 Trial Collaborators. Effects of tranexamic acid on death in trauma patients with significant haemorrhage. *Lancet*. 2010;376(9734):23-32.
3. Gonzalez E, Moore EE, Moore HB, et al. Goal-directed hemostatic resuscitation of trauma-induced coagulopathy: a pragmatic randomized clinical trial. *Ann Surg*. 2016;263(6):1051-1059.
4. Spahn DR, Bouillon B, Cerny V, et al. The European guideline on management of major bleeding and coagulopathy following trauma: 5th edition. *Crit Care*. 2019;23(1):98.