A disorder of consciousness, or impaired consciousness, is a state where consciousness has been affected by damage to the brain.

Consciousness requires both wakefulness and awareness.

Wakefulness is the ability to open your eyes and have basic reflexes such as coughing, swallowing and sucking.

Awareness is associated with more complex thought processes and is more difficult to assess. Currently, the assessment of awareness relies on physical responses being detected during an examination.

The main disorders of consciousness are:

• coma
• vegetative state
• minimally conscious state

Coma

A coma is when a person shows no signs of being awake and no signs of being aware. A person in a coma lies with their eyes closed and doesn't respond to their environment, voices or pain.

A coma usually lasts for less than two to four weeks, during which time a person may wake up or progress into a vegetative state or minimally conscious state.

Read more about comas.

Vegetative state

A vegetative state is when a person is awake but is showing no signs of awareness.

A person in a vegetative state may open their eyes, wake up and fall asleep at regular intervals and have basic reflexes, such as blinking when they're startled by a loud noise, or withdrawing their hand when it's squeezed hard. They're also able to regulate their heartbeat and breathing without assistance.

However, a person in a vegetative state doesn't show any meaningful responses, such as following an object with their eyes or responding to voices. They also show no signs of experiencing emotions.

If a person is in a vegetative state for a long time, it may be considered to be:

• a continuing vegetative state – when it's been longer than four weeks
• a permanent vegetative state – when it's been more than six months if caused by a non-traumatic brain injury, or more than 12 months if caused by a traumatic brain injury

If a person is diagnosed as being in a permanent vegetative state, recovery is extremely unlikely but not impossible.

Minimally conscious state

A person who shows clear but minimal or inconsistent awareness is classified as being in a minimally conscious state. They may have periods where they can communicate or respond to commands, such as moving a finger when asked.

A person may enter a minimally conscious state after being in a coma or vegetative state. In some cases a minimally conscious state is a stage on the route to recovery, but in others it's permanent.

As with vegetative state, a continuing minimally conscious state means it has lasted longer than four weeks. However, it's more difficult to diagnose a permanent minimally conscious state because it depends on things such as:

• the type of brain injury
• how severe the injury is
• how responsive the person is

In most cases, a minimally conscious state isn't usually considered to be permanent until it's lasted several years.

Why they happen

Disorders of consciousness can occur if the parts of the brain involved with consciousness are damaged. These types of brain injury can be divided into:

• traumatic brain injury – the result of a severe head injury, such as an injury sustained during a car accident or a fall from a great height
• non-traumatic brain injury – where the injury to the brain is caused by a health condition, such as a stroke
• progressive brain damage – where the brain is gradually damaged over time; for example, because of Alzheimer's disease

Read more about the causes of disorders of consciousness.

Making a diagnosis

A disorder of consciousness will only be confirmed after extensive testing to determine the person's level of wakefulness and awareness.

These examinations need to be carried out by someone experienced in disorders of consciousness, although the views of other healthcare professionals and family members should also be taken into consideration.

For some states of impaired consciousness, such as vegetative state and minimally conscious state, there are recommended criteria to help confirm a diagnosis.

Read more about diagnosing disorders of consciousness.

Treatment and care

Treatment can't ensure recovery from a state of impaired consciousness. Instead, supportive treatment is used to give the best chance of natural improvement. This can involve:

• providing nutrition through a feeding tube 
• making sure the person is moved regularly so they don't develop pressure ulcers
• gently exercising their joints to prevent them becoming tight
• keeping their skin clean
• managing their bowel and bladder – for example, using a tube known as a catheter to drain the bladder
• keeping their teeth and mouth clean
• offering opportunities for periods of meaningful activity – such as listening to music or watching television, being shown pictures or hearing family members talking

Sensory stimulation

In some cases, a treatment called sensory stimulation may be used in an attempt to increase responsiveness. This involves stimulating the main senses, such as vision, hearing and smell.

It's usually carried out by a trained specialist, but family members are often encouraged to be involved.

Some examples of sensory stimulation include:

• visual – showing photos of friends and family, or a favourite film
• hearing – talking or playing a favourite song
• smell – putting flowers in the room or spraying a favourite perfume
• touch – holding their hand or stroking their skin with different fabrics

It's not entirely clear how effective sensory stimulation is, but it's sometimes considered worthwhile. 

Recovery

It's impossible to predict the chances of someone in a state of impaired consciousness improving. It largely depends on:

• the type of brain injury
• how severe the injury is
• the person's age
• how long they've been in the state for

Some people improve gradually, whereas others stay in a state of impaired consciousness for years. Many people never recover consciousness.

There are only isolated cases of people recovering consciousness after several years. The few people who do regain consciousness after this time often have severe disabilities caused by the damage to their brain.

Withdrawing nutritional support

If a person has been in a vegetative state for a minimum of 12 months, it may be recommended that nutritional support is withdrawn. This is because:

• there's almost no chance of a recovery by this point
• prolonging life would have no benefit for the person concerned
• prolonging treatment could offer false hope and cause unnecessary emotional distress for the friends and family of the person concerned

The medical team will discuss the issue with family members, but the decision has to be referred to the courts in England, Wales and Northern Ireland before any further action can be taken. In Scotland a court ruling isn't required, but is often sought.

If the court agrees with the decision, a palliative care team will usually be involved in planning the withdrawal. Once nutritional support is eventually withdrawn, the person will die within a few days or weeks.

Disorders of consciousness can occur if the parts of the brain responsible for consciousness are injured or damaged.

The main causes can generally be divided into:

• traumatic brain injury
• non-traumatic brain injury
• progressive brain damage

Common examples of these types of brain damage are outlined below.

Traumatic brain injury

Traumatic brain injury occurs when an object or outside force causes severe trauma to the brain. This is most often caused by:

• falls
• traffic accidents
• violent assault

See severe head injury for more information.

Non-traumatic brain injury

Non-traumatic brain damage is usually caused by a health condition, such as:

• a condition that deprives the brain of oxygen – without a continuous supply of oxygen, brain tissue begins to die
• a condition that directly attacks brain tissue

Specific causes of non-traumatic brain injury include:

• strokes
• heart attacks 
• severe brain infections – such as meningitis (an infection of the outer layer of the brain) or encephalitis (an infection of the brain itself)
• drug overdoses
• poisoning
• almost drowning or other types of suffocation, such as smoke inhalation
• a blood vessel bursting, leading to bleeding inside the brain – the medical term for this is a ruptured aneurysm

Progressive brain damage

In some cases brain damage can gradually occur over time. Examples of conditions that cause progressive brain damage include:

• Alzheimer's disease
• Parkinson's disease
• a brain tumour

It takes extensive testing to assess levels of wakefulness and awareness before a disorder of consciousness can be confirmed.

This may involve tests such as brain scans, but is largely based on the specific features a person displays, such as whether they can respond to commands.

The Glasgow Coma Scale

Doctors can score a person's level of consciousness using a tool called the Glasgow Coma Scale. This assesses three things:

• eye opening – a score of 1 means the eyes don't open at all, and 4 means opens eyes spontaneously
• verbal response to a command – 1 means no response, and 5 means a person is alert and talking
• voluntary movements in response to a command – 1 means no response, and 6 means a person can follow commands

A lower score indicates a more severely impaired consciousness, such as a coma, although this level will be monitored regularly to look for any changes.

The brain injury association Headway has more detailed information about the Glasgow Coma Scale.

Other scoring systems

There are also more specific scoring systems, which are based on more detailed observations of a person's behaviour.

One example is known as the JFK Coma Recovery Scale-Revised (CRS-R). This system uses 23 different items, each with individual scales to assess how a person is responding.

You can read more detailed information about the CRS-R on The Center for Outcome Measurement in Brain Injury (COMBI) website.

Brain scans

Brain scans are used to help assess the level of brain damage in someone with impaired consciousness. They can also check for signs of any complications, such as hydrocephalus, a build-up of fluid on the brain.

There are several types of scans that can assess brain structure. A CT scan or MRI scan are used if the person is able to tolerate it.

Research brain scans

There are separate scans that can show areas of brain activity as well as brain damage. These are only used in research settings at the moment, but may be useful if a person can't move or speak.

One example is a functional magnetic resonance (fMRI) scan. A fMRI scan is able to show changes if the brain is responding to lights and sound.

However, they don't necessarily show awareness because the brain is able to respond to stimulation even without the person actually being aware of it. Research is being carried out into ways brain scans can be used to show true awareness.

Criteria for a vegetative state

A vegetative state is when a person is awake but showing no signs of awareness. Doctors are particularly careful when diagnosing a permanent vegetative state, as there's a risk of misdiagnosis.

A confident diagnosis can only be made if the following criteria have been met:

• the cause of the brain injury has been established – for example, if a case of meningitis is suspected, a diagnosis can be confirmed by testing the fluid that surrounds the brain for infection
• it's been confirmed drugs or medication aren't responsible for the symptoms
• it's been confirmed treatable problems with the body's chemistry (a metabolic disorder) aren't responsible for the symptoms of loss of awareness – an example of a metabolic disorder is a diabetic coma, where people lose consciousness because their blood sugar levels are either dangerously high or dangerously low
• the possibility of a treatable cause in the brain, such as a brain tumour, has been ruled out by brain imaging scans
• examinations have been carried out by a trained assessor experienced in prolonged disorders of consciousness

For a permanent vegetative state to be confirmed, the above criteria must apply and either:

• six months must have passed since the start of symptoms after a non-traumatic brain injury
• 12 months must have passed since the start of symptoms after a traumatic brain injury