A blood transfusion is a medical procedure where blood is transferred from one person (the donor) to another person (the recipient).

Emergency medical services in the United Kingdom provide emergency care to people with acute illness or injury and are predominantly provided free at the point of use by the four National Health Services (NHS) of England, Scotland, Wales, and Northern Ireland.

Emergency medicine is the medical speciality concerned with the care of illnesses or injuries requiring immediate medical attention.

Intensive care medicine, also called critical care medicine, is a medical specialty that deals with seriously or critically ill patients who have, are at risk of, or are recovering from conditions that may be life-threatening.

Packed red blood cells, also known as packed cells, are red blood cells that have been separated for blood transfusion.