context: The body is a complex machine. Many organs and systems constantly work to keep it healthy. Some functions are so crucial that you can't live if they stop. When they fail, special medical procedures, commonly called life support, can keep you alive until your body is ready to take over again. But sometimes the body isn't able to resume the work. If these systems stop working for any reason, you need life support: Lungs: In cases of near-drowning, pneumonia, drug overdose, a blood clot, and severe lung injury or disease, such as COPD and cystic fibrosis, and muscle or nerve diseases such as ALS and muscular dystrophy Heart: Sudden cardiac arrest or heart attack Brain: Stroke or a severe blow to the head When most people talk about a person being on life support, they're usually talking about a ventilator, which is a machine that helps someone breathe. A ventilator (or respirator) keeps oxygen flowing throughout the body by pushing air into the lungs. It's used temporarily for conditions like pneumonia, but it may be needed longer for someone with lung failure. One end of a tube goes into the windpipe through the nose or mouth. The other end attaches to the electric pump. Some people get medicine to make them more comfortable and sleepy while on a breathing machine. When a person's heart stops, doctors will try to restart it. These life support methods include CPR, which keeps blood and oxygen flowing throughout the body, electric shocks (called defibrillation) to get the heart beating again, and medication to help the heart work. Less urgent forms of life support include dialysis to filter toxins from the blood, and a feeding tube or an IV to give nutrition and water. Doctors, nurses, and other health care professionals will begin life support immediately unless: You decline it outright. You left written instructions saying you don't want it. Your medical power of attorney or closest family member, with the right to make decisions for you, turns it down on your behalf. Doctors usually advise stopping life support when there is no hope left for recovery. The organs are no longer able to function on their own. Keeping the treatment going at that point may draw out the process of dying and may also be costly. Choosing to remove life support usually means that the person will die within hours or days. The timing depends on what treatment is stopped. People tend to stop breathing and die soon after a ventilator shuts off, though some do start breathing again on their own. If he is not taking in any fluids, he will usually die within several days of a feeding tube removal, though he may survive for as long as a week or two. When someone is unconscious or not of sound mind, doctors and family members decide when life support measures should stop. It's a hard decision, especially if the sick person hasn't previously discussed his end-of-life wishes with his family. Doctors encourage family members to focus on what they think their loved one would want. It's important to remember that it's the underlying condition, not the removal of life support, that actually causes someone to die, and doctors will do all they can to keep your loved one comfortable.