After a severe injury or illness that affects the brain, patients can fall into a persistently unconscious state, causing them to be unaware of themselves or their environment. Depending on their level of consciousness, patients are considered to be either comatose, in a minimally conscious state, experiencing unresponsive wakefulness syndrome, or brain death by neurological criteria. In the first three situations, these states can determine treatment as well as how to prepare family members for decisions regarding the patient's prognosis and quality of life.
Coma
In this state, either the thalamus, the brainstem, or both hemispheres of the brain are damaged. Patients cannot be awakened, are unresponsive to stimuli such as pain, sound, or touch, and do not experience sleep-wake cycles. If the lower part of the brainstem has also been damaged, the patient often requires a ventilator to breathe.
Coma is caused by a severe brain injury such as a traumatic head injury, brainstem stroke, or a brain hemorrhage that affects the surrounding tissue and brain structure, as well as severe hypothermia, drug overdose, drowning, and cardiac arrest. Regaining consciousness depends on the cause, severity of the injury, and how long the coma lasts. Patient care is individualized and includes physical therapy and constant nursing care.
Minimally conscious state
In minimally conscious state (MCS), patients are intermittently aware of their surroundings and may respond to commands. Although they are mostly drowsy and unresponsive, they may have moments where they mouth words, react to pain, hold an object, respond to commands, or track movement with their eyes. Patients may improve gradually, especially those who have some ability to speak. It is still difficult to predict, however, how much they can improve beyond a major disability.
There are two kinds of MCS: MCS-minus and MCS-plus.
- MCS-minus is low-level behaviors like tracking and localized response to pain.
- MCS-plus is higher-level behaviors that can include following commands, answering yes or no, or other forms of intentional communications.
A patient in MCS-plus has a better outcome than MCS-minus, but doctors agree that recovery is difficult to predict and a patient would likely still face long-term neurological disability.
Unresponsive wakefulness syndrome
Previously known as persistent vegetative state, unresponsive wakefulness syndrome is a state that lasts more than one month (known as persistent), more than three months if caused by a non-traumatic injury, or more than 12 months if caused by a traumatic injury.
In this state, patients do not show signs of self-awareness or can speak or hear. Because brainstem functions that affect breathing and involuntary movements remain intact, patients may be able to breathe on their own and open their eyes, unlike patients in coma who do not open their eyes. Patients with unresponsive wakefulness syndrome may also experience sleep-wake cycles, grind their teeth, thrash, or make facial movements. Patients may remain in this state for decades if all medical complications are treated quickly and thoroughly.
Brain death by neurological criteria
This is the legal and physiological definition of death and can be caused by severe injury or lack of oxygen to the brain. It involves these critical factors: coma, permanent inactivity in the brain and brainstem, and no ability to generate a breath without ventilation machines.
The permanent inactivity in the brain or brainstem must have an unknown case and no explanations. The inability to generate a breath without ventilation machines is determined by a formal apnea test, which is usually the final test to declare someone brain death by neurological criteria.
A patient who is brain death by neurological criteria may continue to have a beating heart, but removing supportive equipment will lead to cardiac arrest.
Dr. James Kelly is a professor emeritus of neurology at the University of Colorado School Anschutz.
