Blood loss due to trauma is a leading cause of death in young people and is the result of the ‘lethal triad’ of hypothermia, acidosis and coagulopathy, which collectively reduce haemostasis. Emergency department nurses can help to reverse the triad through the timely and efficient use of blood products and fluids. This article briefly examines different blood groups, describes the elements of the lethal triad, and discusses the blood products used to transfuse patients with major haemorrhage.