Major Haemorrhage: Definition & Pathophysiology

• Major haemorrhage is a condition requiring careful understanding and management.

Blood Volume

• Circulating blood volume varies; females average 65ml/kg, while males average 75ml/kg.
• A drop in blood pressure typically occurs after losing about 40% of the total circulating blood volume.

Defining Major Haemorrhage

• Definitions vary, but generally includes: -Loss of more than one blood volume within 24 hours (around 70 mL/kg, >5 liters in a 70 kg adult). -50% of total blood volume lost in less than 3 hours. -Bleeding exceeding 150 mL/minute.
• Clinically, a heart rate above 110 bpm and systolic blood pressure below 90 mmHg indicates major hemorrhage.

Pathophysiology During Major Haemorrhage

• Blood pressure relies on stroke volume and heart rate, which combine to produce cardiac output.
• Cardiac output and systemic vascular resistance work to maintain blood pressure.
• Homeostasis tightly balances blood pressure for normal bodily function, relying on receptors, a control center, and effectors.
• Declining blood pressure stimulates baroreceptors, increasing heart rate and contractility and promoting vasoconstriction.

Blood Clotting Cascade

• The clotting cascade has two pathways: Intrinsic and Extrinsic
• The Intrinsic pathway is triggered by direct damage to blood vessels.
• Damage to blood vessels, plus collagen exposure, activates platelets in the Intrinsic pathway.
• The Extrinsic pathway is initiated by external trauma.
• Damage outside the blood vessels, hypoxia, sepsis, and inflammation can activate the extrinsic pathway.
• Both pathways activate Factor 10, leading to the common pathway.
• Fibrinogen, when activated, forms fibrin which is essential for clot formation.
• Losing blood results in loss of clotting factors and fibrinogen.
• Plasmin, made from thrombin-activated plasminogen, breaks down clots via thrombolysis.
• Citrate in donated blood bags binds to calcium to prevent clotting, so calcium levels needs to be monitored.

The Lethal Triad

• The lethal triad consists of coagulopathy, hypothermia, and metabolic acidosis, which together can lead to death.
• Coagulopathy involves loss of red blood cells and clotting factors.
• Hyperfibrinolysis, where the body breaks down clots, can occur.
• Tranexamic acid (antifibrinolytic) impairs enzymes that break down clots and should be given within 3 hours of trauma.
• Metabolic acidosis: pH is less than 7.35.
• In metabolic acidosis, low oxygen perfusion increases lactate from anaerobic metabolism.
• Metabolic acidosis impacts enzyme function and pharmacokinetics of drugs.
• Electrolyte imbalances like low calcium can occur during metabolic acidosis.
• Hypothermia: Peripheral vasoconstriction occurs.
• Cold temperatures impair enzyme function
• Blood carries oxygen and clotting factors, but these do not reach the peripheries
• Platelet dysfunction can occurs around 32°C (coagulopathy).
• Haemostasis is impaired in Hypothermia
• Treatment includes active warming measures and minimizing heat loss

Aim of Treatment

• The aim of treatment is linked to the lethal triad and involves controlling bleeding and preventing blood loss.
• Techniques of control include damage control surgery and direct/indirect pressure.
• Replace lost volume, ideally with "like for like" blood products.
• Avoid excess crystalloid use, to prevent diluting the blood.
• NICE (2016) advises against crystalloid use for active bleeding, recommending hypotensive resuscitation with palpable pulse.
• Testing methods and blood products are methods to correct coagulopathy.

Processes of Stabilization

• Tissue oxygenation, volume, fluids, and temperature should monitored.
• Rapid control of bleeding should be implemented.
• Initial management of bleeding and coagulopathy should be controlled.
• Maintain BP at a low target with crystalloid fluid-restricted volume replacement and vasopressors & inotropes for heart function.

Blood Products

• Packed Red Blood Cells: increase oxygen carrying capacity and tissue perfusion through Hb
• Fresh Frozen Plasma (FFP): Contains all clotting factors, including fibrinogen.
• Cryoprecipitate: Spun from FFP and contains a higher concentration of fibrinogen.
• Platelets: Valuable resource needed to start entire clotting process.

Clinical Assessment

• Systolic blood pressure below 90 mmHg is assessed; heart rate above 110 bpm is assessed.
• Blood on the floor and in four body areas (chest, abdomen, pelvis, and femurs) is a key sign.
• Activating the major haemorrhage protocol (2222) should be done.

Major Haemorrhage Protocol

• Protocols may vary locally, but generally follow national guidance from NICE (2016), AABGI (2016), and AA (2023).
• For uncontrolled bleeding, declare a major haemorrhage.
• Give a 1:1 ratio of red cells and FFP per NICE (2016) and AAGBI (2016) guidelines.
• Include 2 pools of cryoprecipitate and 1-unit of platelets in the transfusion.
• Aim for a return of central pulses and low target blood pressure.
• Group specific blood should be used when available as (O negative is used until then).
• Regular testing should be done to ensure accuracy of treatment therapy.

Clinical Management

• Start by calling for help and noting the time.
• Increase FiO2 and reduce inhalation/intravenous anaesthetics
• Check and expose intravenous access.
• Control any obvious bleeding.
• Call blood bank and assign someone to communicate and liaise with bank, activate protocol and communicate how quick needed.
• Discuss surgical, anaesthetic and nursing teams.
• Monitor progress.
• Plan on going care in an appropriate clinical area

Issues To Watch Out For

• Citrate in transfusion bags severely reduces calcium concentration (same for FFP).
• Regular ABG analysis and supplementary Calcium Chloride IV are needed.
• Massive red cell transfusion leads to an increase in potassium (hyperkalemia).
• Regular ABG are needed.
• Treat with calcium and dextrose-insulin infusion.
• Large-volume FFP transfusion has risks of circulatory overload (TACO), allergic reactions and transfusion-related acute lung injury.
• May even cause excess clotting if over-transfused, requiring heparinisation.

The Lethal Diamond

• Recent studies suggest adding hypocalcaemia to the Lethal Triad, making it the Lethal Diamond.
• Calcium is key in platelet aggregation and the activation of clotting factors.
• Calcium is an essential electrolyte for cardiac contraction and regulates arterial and venous constriction.
• Calcium plays an important role in regulating blood pH

Considerations for the ODP

• Rapid sequence induction and intubation should be preformed asap and in under 45 minutes of initial call for help.
• Anticipate surgical airway, depending on injury type
• Find major haemorrhage protocol location
• Locate and operate up to date training for blood fridge and blood products (especially out of hours!).
• Assist with the transfer of the patient.
• Multidisciplinary teamwork is required for effectively managing the patient.

Understand major haemorrhage, its definitions based on blood volume loss and bleeding rate, and differences in blood volume between genders. Learn the pathophysiology, including the roles of stroke volume, heart rate, cardiac output, and systemic vascular resistance in maintaining blood pressure.