What Is the Difference Between Brain Death and Being in a Coma?

When someone is on a ventilator and unresponsive, families are often told they are in a coma, or that they are brain dead. These are very different. This article explains the terms in plain language. It is general information, not medical advice.

What is a coma?

A state of unconsciousness without waking. According to a National Institute of Neurological Disorders and Stroke summary, in a coma the person is totally unconscious, unresponsive, unaware, and cannot be aroused, and their eyes are closed. Brain & Life, from the American Academy of Neurology, says the person cannot be awakened, does not respond to pain, sound, or touch, and has no sleep-wake cycles. If the lower brainstem is also damaged, the person often needs a ventilator to breathe.

How long does a coma last?

Not long. The Model Systems Knowledge Translation Center says coma rarely lasts more than four weeks. Some people move from coma to a vegetative state, and others to partial awareness. Healthtalk notes that after a few days or weeks in a coma, a person who does not die usually “wakes up” in the sense that their eyes open.

What are the vegetative and minimally conscious states?

Stages after coma. In the vegetative state, which is also called unresponsive wakefulness syndrome, the person’s eyes open and they have sleep-wake cycles, but they show no awareness. It is called persistent after 30 days, and a PubMed Central table says it is called permanent after three months. In the minimally conscious state, the Model Systems center says, a person may follow simple instructions or respond some of the time, but not consistently.

What is brain death?

The permanent loss of all brain function. The NINDS summary describes brain death as the lack of measurable brain function due to diffuse damage to the cerebral hemispheres and the brainstem, and says it is irreversible. In the United States, it is legally death; see How Does a Doctor Know Someone Is Dead?. StatPearls says the exam finds coma, no brainstem reflexes, and no attempt to breathe.

Why can they look alike?

Because of machines. StatPearls explains that the Uniform Determination of Death Act was written in response to life support, which can keep circulation and breathing going even when the whole brain has stopped working. A body on a ventilator may be warm and have a heartbeat. This can be very hard for families, and doctors will explain the tests.

Can someone wake from brain death?

No. The NINDS summary says brain death is irreversible, unlike coma. The Brain & Life article explains that some people who are comatose or in a vegetative state can recover to different degrees. For related decisions, see Advance Directives and Organ and Tissue Donation After Death.