Final answer:
Direct pressure is used for severe arterial or venous bleeding, and a tourniquet is used if the bleeding is from a major artery and is life-threatening. Emergency transfusions in a critical situation use O negative blood, the universal donor, to avoid adverse reactions.
Step-by-step explanation:
The type of bleeding that requires direct pressure is typically arterial or venous bleeding that is severe but not severe enough to warrant a tourniquet. This kind of hemorrhage involves a significant amount of blood loss that cannot be controlled by the body's hemostatic mechanisms alone. When a blood vessel is severed, and blood components are leaking out, applying direct pressure to the wound can help to control the bleeding. If the bleeding is particularly severe, such as in the case of a major artery being cut, a tourniquet may be necessary. This would help to constrict the flow of blood to the area, preventing blood loss until medical help can be provided.
Regarding the question of what type of blood is transfused during a medical emergency when the patient's blood type is unknown, the answer is type O negative blood, commonly referred to as the universal donor. This is because O negative blood can be safely given to patients of any blood type without the risk of agglutination or adverse reactions.