Red Cell Transfusion in Acute Blood Loss and Shock

In acute haemorrhage, the aim is to stop bleeding, restore perfusion and replace oxygen carrying capacity and haemostatic capacity in time. Haemoglobin is a poor guide early, because it falls only after dilution or fluid resuscitation, so decisions rest on bleeding rate, haemodynamics and the likely trajectory.

Blood volume. Adults about 70 mL/kg, children about 80 mL/kg, and neonates about 85 to 90 mL/kg.

Classes of haemorrhage. Loss under 15% usually causes few signs, 15 to 30% causes tachycardia and narrowed pulse pressure, 30 to 40% causes hypotension, tachycardia and confusion, and over 40% is immediately life-threatening. Young adults and children compensate until late and then collapse suddenly.

Risk context. Delay in blood and control of bleeding causes death. Large volumes of crystalloid dilute clotting factors, worsen acidosis and hypothermia and raise bleeding. Over-transfusion leads to overload and wasted scarce units.

Special groups. Pregnancy (blood volume expanded, signs delayed, rapid deterioration), children (compensate then collapse), older adults and patients on anticoagulants or beta blockers (blunted tachycardia), and trauma with head injury.

Recognition. Heart rate, blood pressure, shock index (heart rate divided by systolic pressure, with a value of about 0.9 to 1 or more suggesting significant bleeding), capillary refill, lactate, base deficit, urine output and mental state. Identify the source: external, chest, abdomen, pelvis, long bones, retroperitoneum, gastrointestinal, uterus.

Triggers for red cell transfusion.

• Class III or IV haemorrhage, or haemodynamic instability not responding to a small volume of crystalloid.

• Continuing bleeding with a falling haemoglobin and rising lactate.

• Massive haemorrhage (loss of one blood volume in 24 hours, 50% in 3 hours, or bleeding over 150 mL/minute).

Where haemoglobin thresholds do not apply. In uncontrolled bleeding, do not wait for haemoglobin to fall. Once bleeding is controlled, the restrictive threshold of about 7 g/dL applies in most patients, with a higher value in myocardial ischaemia.

Blood pressure targets. Permissive hypotension (systolic about 80 to 90 mmHg) can be used until bleeding is controlled in penetrating trauma and similar situations, but not in head or spinal injury, and with attention to pregnancy and duration. The target varies by setting.

Differential considerations. Non-haemorrhagic shock (septic, cardiogenic, obstructive such as tension pneumothorax and cardiac tamponade, spinal), which does not need blood.

Red flags. Penetrating torso injury, pelvic fracture, ruptured ectopic pregnancy, placental abruption, uterine atony, oesophageal varices, aortic aneurysm rupture, and anticoagulant use.

Immediate actions.

1. Call for senior help and activate the massive haemorrhage plan if criteria are met.

2. Control the source: direct pressure, tourniquet, pelvic binder, surgery, interventional radiology, uterotonics and uterine procedures, endoscopy.

3. Two large bore intravenous or intraosseous lines.

4. Send samples for group, crossmatch, full blood count, coagulation, fibrinogen and blood gas, and start emergency uncrossmatched blood if needed.

5. Give tranexamic acid 1 g intravenously over 10 minutes within 3 hours of injury (or of birth in postpartum haemorrhage), then 1 g over 8 hours in trauma.

6. Keep the patient warm and correct calcium.

Component choice. Give red cells (or whole blood where available), and add plasma and platelets early in massive haemorrhage, in balanced proportions directed by clinical response and laboratory or viscoelastic results. Limit crystalloid to the minimum needed, with balanced solutions preferred.

Dose.

• Adults: unit by unit, reassessing perfusion and bleeding after every 1 to 2 units, with rapid infusion through a blood warmer in massive haemorrhage.

• Children: 10 to 20 mL/kg of red cells, or whole blood 20 mL/kg, repeated as needed.

• Do not apply a fixed ratio alone: integrate source control, calcium, temperature and serial results.

Special groups.

• Pregnancy: early obstetric intervention, tranexamic acid, fibrinogen replacement and plasma, with a left lateral tilt.

• Head injury: avoid hypotension.

• Anticoagulated patients: reversal with specific agents.

• Jehovah's Witnesses and others refusing blood: all non-blood measures and early senior input.

Monitoring. Continuous heart rate, blood pressure, oxygen saturation and urine output. Repeat haemoglobin, lactate, base deficit, ionised calcium, potassium, temperature, platelets, prothrombin time, activated partial thromboplastin time and fibrinogen every 30 to 60 minutes during active haemorrhage.

Complications. Hypothermia, acidosis, hypocalcaemia, hyperkalaemia, coagulopathy, overload, lung injury, haemolysis from emergency blood, and multi organ failure.

Referral and escalation. Surgeon, anaesthetist, intensivist, obstetrician and haematologist early. Blood bank medical lead to coordinate stock when many units are needed.

Disposition. After bleeding control, transfer to a high dependency or intensive care setting. Stop the massive haemorrhage plan once bleeding is controlled and return unused products. Replace iron and plan follow up of haemoglobin.