Residency · Residency · Emergency Medicine

Hemorrhagic Shock and Massive Transfusion

Pathophysiology of Hemorrhagic Shock

Stages of Hemorrhage

Hemorrhagic shock progresses through four classes based on blood volume loss. Class I (less than 750 mL, below 15 percent) produces minimal symptoms with normal vitals — the body fully compensates. Class II (750-1500 mL, 15-30 percent) produces tachycardia, narrowed pulse pressure, and anxiety, though the patient may still appear clinically well. Class III (1500-2000 mL, 30-40 percent) produces tachycardia, hypotension, altered mental status, and tachypnea. Class IV (more than 2000 mL, above 40 percent) produces severe hypotension, lethargy or obtundation, minimal urine output, and imminent arrest.

Compensatory Mechanisms

The body's compensatory response to hemorrhage includes sympathetic activation (producing tachycardia, peripheral vasoconstriction, cool extremities, and delayed capillary refill), renin-angiotensin-aldosterone system activation, ADH release promoting fluid retention, and transcapillary refill as interstitial fluid shifts into the vascular space. Young, healthy patients can maintain these compensatory mechanisms until 30 to 40 percent of blood volume is lost — then they decompensate rapidly and catastrophically.

The Lethal Triad

Three physiologic derangements — hypothermia, acidosis, and coagulopathy — form the lethal triad. Hypothermia impairs coagulation enzyme function and platelet aggregation. Lactic acidosis from tissue hypoperfusion impairs coagulation factor activity. Coagulopathy develops from consumption, dilution (particularly from crystalloid resuscitation), and trauma-induced coagulopathy (TIC). These three elements are mutually reinforcing — each worsens the others, creating a death spiral. Prevention and early reversal are the cornerstones of damage control resuscitation.

Trauma-Induced Coagulopathy (TIC)

TIC is a distinct entity that occurs within minutes of injury, before any fluid resuscitation. It is mediated by tissue injury combined with hypoperfusion, which activates the protein C pathway and leads to systemic anticoagulation, hyperfibrinolysis, and endothelial dysfunction. TIC is present in 25 to 30 percent of severely injured patients on arrival and is associated with a fourfold increase in mortality.

Recognition of Occult Hemorrhage

Clinical Assessment

Tachycardia may be the only early sign of significant hemorrhage — but patients on beta-blockers will not mount tachycardia. Base deficit and lactate are more sensitive markers of tissue hypoperfusion than vital signs: a lactate above 4 mmol/L indicates significant hemorrhagic shock, and a base deficit worse than -6 indicates severe shock. The shock index (heart rate divided by systolic blood pressure) provides a quick assessment: values above 0.9 suggest significant hemorrhage, and above 1.4 predict the need for massive transfusion. Serial hemoglobin is unreliable in acute hemorrhage because equilibration takes hours — the initial hemoglobin can be completely normal despite massive blood loss.

Sources of Occult Hemorrhage

The mnemonic "blood on the floor and four more" identifies the major sources: external hemorrhage (visible on the floor), thorax (each hemithorax can hold 2-3 liters), abdomen (hemoperitoneum, solid organ injury), retroperitoneum (pelvic fracture or retroperitoneal hemorrhage, where the entire blood volume can be lost), and thigh (each femur fracture can lose 1-1.5 liters). In children, the scalp is an additional significant source due to its high vascularity.

Damage Control Resuscitation

Principles

Damage control resuscitation has five core principles: minimizing crystalloid to avoid dilutional coagulopathy, early blood product administration in balanced ratios, permissive hypotension until surgical hemorrhage control is achieved, correction of the lethal triad, and early surgical or interventional hemorrhage control (damage control surgery).

Permissive Hypotension

The target is SBP 80 to 90 mmHg (MAP 50-60) until hemorrhage control is achieved. The rationale is that aggressive fluid resuscitation before hemorrhage control dislodges clots, dilutes coagulation factors, and worsens hypothermia. Three critical exceptions exist where permissive hypotension must not be used: traumatic brain injury (target SBP above 100, MAP above 80 to maintain cerebral perfusion), spinal cord injury (target MAP above 85), and elderly patients with poor baseline autoregulation.

Crystalloid Limitation

Crystalloid should be limited to a maximum of 1 to 2 liters before transitioning to blood products. Balanced crystalloids (lactated Ringer's) are preferred over normal saline to reduce hyperchloremic acidosis. Excessive crystalloid worsens acidosis, hypothermia, and dilutional coagulopathy.

Massive Transfusion Protocol (MTP)

Activation Criteria

Clinical judgment is the most important factor in activating the MTP. Scoring systems such as the ABC score and TASH score assist the decision. General triggers include SBP below 90 despite initial resuscitation, active hemorrhage requiring surgical control, and clinical assessment of ongoing massive bleeding. Activation triggers a pre-packaged cooler of blood products from the blood bank.

Balanced Resuscitation Ratios

The target is a 1:1:1 ratio of packed RBCs to fresh frozen plasma to platelets. The PROPPR trial (2015) showed that a 1:1:1 ratio was associated with improved hemostasis and reduced death from exsanguination in the first 24 hours, though there was no overall 28-day mortality difference compared to 1:1:2. In practice, products are transfused as they become available — RBCs should not be delayed while waiting for plasma. Cryoprecipitate should be considered early if fibrinogen falls below 150 to 200 mg/dL.

Whole Blood Resuscitation

Low-titer group O whole blood provides RBCs, plasma, platelets, and coagulation factors in a single unit. It is logistically simpler than component therapy and offers a more physiologically balanced product. Its use is growing in both military and civilian trauma, though supply and logistics limit widespread adoption.

Uncrossmatched Blood

Type O RBCs are used for emergent transfusion — O-negative for women of reproductive age, and O-positive is acceptable for males and postmenopausal women. Type AB plasma is the universal donor plasma but is in limited supply. Crossmatched blood should be used as soon as available, typically within 30 to 60 minutes.

Tranexamic Acid (TXA)

Mechanism

TXA is an antifibrinolytic that inhibits plasminogen activation, preventing breakdown of existing clots. It does not promote new clot formation — it stabilizes clots that are already forming.

CRASH-2 Trial (2010)

The CRASH-2 trial randomized more than 20,000 trauma patients to TXA versus placebo. TXA reduced all-cause mortality (14.5 versus 16.0 percent) when given within 3 hours of injury. The greatest benefit was seen when given within 1 hour. Critically, TXA given more than 3 hours after injury was associated with increased mortality. The dose is 1 g IV over 10 minutes, followed by 1 g IV over 8 hours.

Current Practice

TXA should be administered within 3 hours of injury for significant hemorrhage or anticipated need for transfusion. Prehospital TXA is increasingly adopted. The PATCH trial, however, did not show a benefit from prehospital TXA in a well-developed trauma system, adding nuance to the debate about optimal timing and setting.

Viscoelastic Testing

TEG and ROTEM

Thromboelastography (TEG) and rotational thromboelastometry (ROTEM) provide point-of-care assessment of the entire coagulation cascade — clot initiation, clot strength, and fibrinolysis — with results available in 10 to 15 minutes (faster than conventional coagulation studies). They guide targeted component therapy: a prolonged R-time or CT (clotting time) indicates the need for FFP; a low MA or MCF (clot firmness) calls for platelets; a low alpha angle or CFT (clot formation) calls for cryoprecipitate to boost fibrinogen; and high LY30 or ML (fibrinolysis) calls for TXA.

Adjuncts and Hemorrhage Control

Tourniquets

Tourniquets are first-line for life-threatening extremity hemorrhage. They should be applied high and tight on the extremity using commercial windlass devices (CAT, SOFT-T). Ischemia time is generally safe for up to 2 hours, with conversion to alternative hemostasis when possible. Two tourniquets may be needed for large or proximal wounds.

Hemostatic Agents

Kaolin-impregnated gauze (QuikClot Combat Gauze) is packed deep into wounds. Wound packing with hemostatic gauze is used for junctional hemorrhage at the axilla, groin, and neck where tourniquets cannot be applied.

Pelvic Binder

A pelvic binder is applied for suspected unstable pelvic fracture with hemorrhage. It reduces pelvic volume and tamponades venous bleeding. It is placed at the level of the greater trochanters, using a sheet or commercial device (T-POD, SAM Pelvic Sling). Definitive management involves angioembolization or preperitoneal packing.

REBOA

REBOA serves as a temporizing measure for non-compressible torso hemorrhage. Zone I (descending thoracic aorta) is used for abdominal hemorrhage, and Zone III (infrarenal aorta) for pelvic hemorrhage. It bridges the patient to definitive surgical or interventional hemorrhage control.

Damage Control Surgery

Damage control surgery is an abbreviated surgical intervention focused exclusively on hemorrhage control and contamination control — the approach is to pack and plan, deferring definitive repair until physiology is corrected in the ICU. The ICU resuscitation phase focuses on correcting hypothermia, acidosis, and coagulopathy, after which the patient returns to the operating room for definitive repair in 24 to 48 hours. This approach reduces mortality compared to prolonged definitive surgery in the physiologically unstable patient.

<image>A clinical infographic illustrating the lethal triad of trauma with a triangular diagram at the center. Each vertex of the triangle represents one component: hypothermia (with a thermometer icon showing less than 35 degrees C), acidosis (with a pH less than 7.2 and lactate greater than 4), and coagulopathy (with an INR greater than 1.5 and low fibrinogen). Bidirectional arrows between each vertex show that each component worsens the others. Surrounding the triangle are intervention boxes: active warming measures, balanced transfusion with TXA, damage control surgery, and limited crystalloid use. A mortality curve shows dramatically increased death rates as more components of the triad are present.</image>

<image>A step-by-step visual protocol for massive transfusion activation and delivery in the ED. The timeline starts at time zero with MTP activation and shows cooler contents at each phase. Phase 1 (0-15 minutes): 6 units pRBCs, 6 units FFP, 1 apheresis platelet unit delivered in a cooler. Phase 2 (15-30 minutes): repeat same contents. Each phase includes a checklist of concurrent actions: calcium replacement (1 g calcium chloride per 4 units pRBCs), TXA administration, temperature monitoring, VBG for pH and lactate, TEG/ROTEM if available. A laboratory monitoring sidebar shows targets: fibrinogen greater than 150, pH greater than 7.2, ionized calcium greater than 1.0, platelets greater than 50,000.</image>

<image>A ROTEM/TEG tracing diagram showing four example tracings with interpretation. Tracing 1: normal clot formation and strength. Tracing 2: prolonged CT/R-time indicating factor deficiency (treat with FFP). Tracing 3: reduced MCF/MA indicating low platelet function or fibrinogen (treat with platelets or cryoprecipitate). Tracing 4: increased lysis at 30 minutes indicating hyperfibrinolysis (treat with TXA). Each tracing is annotated with the key measurement values and the recommended blood product intervention.</image>

Clinical Pearls

In acute trauma hemorrhage, tachycardia may be the only early sign — do not be reassured by a "normal" blood pressure in a tachycardic patient. Initial hemoglobin is unreliable in acute hemorrhage because equilibration takes hours; use clinical assessment, lactate, and base deficit instead. Limit crystalloid to 1 to 2 liters before transitioning to blood products — excessive crystalloid worsens the lethal triad. TXA must be given within 3 hours of injury — after 3 hours it may increase mortality per the CRASH-2 data. Calcium must be administered during massive transfusion (1 g calcium chloride per 4-6 units pRBCs) because citrate in stored blood chelates calcium, causing hypocalcemia-induced coagulopathy and myocardial depression. Permissive hypotension (SBP 80-90) is appropriate in hemorrhagic shock except in TBI (target SBP above 100) and spinal cord injury (target MAP above 85). A negative FAST does not exclude hemorrhage — retroperitoneal bleeding and early injury may not produce detectable free fluid. Damage control resuscitation and damage control surgery are complementary strategies — the goal is to break the lethal triad, not achieve definitive repair in the physiologically unstable patient.

References

• Holcomb JB, et al. PROPPR Trial: Transfusion of plasma, platelets, and red blood cells in a 1:1:1 vs. a 1:1:2 ratio. JAMA. 2015;313:471-482.
• CRASH-2 Trial Collaborators. Effects of tranexamic acid on death, vascular occlusive events, and blood transfusion in trauma patients. Lancet. 2010;376:23-32.
• Cannon JW. Hemorrhagic shock. NEJM. 2018;378:370-379.
• Bickell WH, et al. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. NEJM. 1994;331:1105-1109.
• Sperry JL, et al. Prehospital plasma during air medical transport in trauma patients at risk for hemorrhagic shock (PAMPer Trial). NEJM. 2018;379:315-326.

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