Coma

Coma is a state of prolonged unconsciousness where a person cannot be awakened or respond to their surroundings. It requires immediate medical attention and can result from various causes, including head injuries, stroke, infections, or complications from conditions like diabetes.

Table of contents

• What is a coma?
• Signs and symptoms
• What causes a coma?
• How doctors diagnose a coma
• Treatment and medical care
• Recovery and outlook
• Possible complications

What is a coma?

A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, and lacks a normal sleep-wake cycle^[1]. The person appears to be asleep, but no amount of external stimulation—such as sounds, sensations, or even pain—can prompt them to become awake and alert^[2].

During a coma, the person’s eyes remain closed and they show no signs of being aware of their environment^[3]. They cannot consciously feel, speak, hear, or move voluntarily^[4]. A coma is different from sleep because the person cannot be woken up by any means.

The term ‘coma’ comes from the Greek word κῶμα (koma), meaning deep sleep. It was already used in ancient medical texts, including the Hippocratic writings and later by Galen in the second century AD^[5].

A coma is a medical emergency that requires immediate attention^[6]. Quick action is needed to preserve life and brain function. Coma occurs when there is a serious problem with the brain’s arousal system (the reticular activating system), which is responsible for keeping you awake, or with communications between different brain areas^[7].

Comas typically don’t last longer than several weeks^[8]. However, the duration can vary from a few days to several weeks, and in rare cases, longer^[9]. People who are unconscious for a longer time might transition to a lasting vegetative state, known as a persistent vegetative state, or experience brain death^[10].

Signs and symptoms

The symptoms of a coma are relatively consistent and help medical professionals identify this serious condition. The most common signs include closed eyes, with the person appearing to be in a deep sleep^[11].

A person in a coma shows no voluntary response to their environment. They cannot open their eyes voluntarily, even when called by name or touched^[12]. There is no response to painful stimuli except for possible reflex movements, which are automatic reactions that don’t involve conscious thought^[13].

The person’s brainstem reflexes are often depressed. For example, their pupils may not respond normally to light. In some cases, one pupil may be larger than the other, or both pupils may be constricted^[14].

Breathing patterns may be irregular or unusual. The person might breathe slowly, irregularly, or show gasping breathing patterns^[15]. Some people in a coma may be able to breathe on their own, although others require a machine to help them breathe^[16].

The person will have very reduced basic reflexes such as coughing and swallowing^[17]. They show a complete absence of wakefulness and are unable to consciously feel, speak, or move^[18]. There is no speech, communication, or awareness of what is happening around them^[19].

What causes a coma?

A coma is caused by an injury to the brain. This injury can result from increased pressure, bleeding, loss of oxygen, or buildup of toxins in the brain^[20]. The injury can be temporary and reversible, or it can be permanent. Many types of problems can cause a coma, and more than 50% of comas are related to head trauma or disturbances in the brain’s circulatory system^[21].

Traumatic brain injuries are one of the most common causes. These are often caused by traffic collisions, falls, or acts of violence^[22]. When the brain swells as a result of trauma, the fluid pushes up against the skull, potentially causing damage to the brainstem and the reticular activating system, which is responsible for arousal and awareness^[23].

Stroke can lead to coma when there is reduced or stopped blood supply to the brain. This can result from blocked arteries or a burst blood vessel^[24]. When there is no blood flow to a major part of the brain or bleeding accompanied by swelling, a coma can occur^[25].

Lack of oxygen to the brain, known as anoxic brain injury, can cause a coma. People who have been rescued from drowning, revived after a heart attack, or experienced cardiac arrest might not awaken due to lack of oxygen to the brain^[26]. Oxygen deprivation can also occur with choking^[27].

Diabetes can cause coma when blood sugar levels become too high or too low^[1]. In people with diabetes, a coma can occur when blood sugar levels stay very high (hyperglycemia) or drop too low (hypoglycemia)^[9]. This type of coma is usually reversible once blood sugar is corrected, although prolonged hypoglycemia can lead to permanent brain damage^[9].

Infections of the central nervous system can cause coma. These include encephalitis (inflammation of the brain) and meningitis (inflammation of the membranes covering the brain and spinal cord), which cause swelling of the brain, spinal cord, or surrounding tissues^[1].

Brain tumors in the brain or brainstem can cause a coma by creating pressure or affecting brain function^[1]. Similarly, seizures, particularly continuous seizures called status epilepticus, can lead to coma by preventing the brain from recovering between seizures^[9].

Drug or alcohol intoxication, including overdoses of prescription or illegal drugs, can disrupt neuron functioning in the brain and lead to coma^[8]. Toxins and poisons, such as carbon monoxide poisoning, can also cause coma^[7].

Other causes include extreme body temperatures (very high or very low), kidney or liver failure, and metabolic abnormalities where substances that are normally found in the body accumulate to toxic levels^[9]. In some cases, doctors may deliberately induce a coma using medications to protect a person from intense pain during a healing process or to preserve brain function after a traumatic brain injury^[8].

How doctors diagnose a coma

A coma is a medical emergency, and quick diagnosis can be life-saving^[5]. If you’re unconscious, medical providers will immediately check your vital signs, which include your breathing, heart rate, and blood pressure^[12]. They may offer immediate treatment, such as glucose for low blood sugar or medication to reverse an opioid overdose if they suspect an overdose^[12].

Because people in comas can’t express themselves, healthcare professionals must rely on physical clues and information provided by family members and friends^[10]. Family members should be prepared to provide information about events leading up to the coma, such as vomiting or headaches, details about how the person lost consciousness, medical history, recent changes in health or behavior, and any drug use^[10].

Doctors perform a physical and neurological examination. The exam includes checking the person’s movements and reflexes, response to painful stimuli, and pupil size^[10]. They observe breathing patterns to help diagnose the cause of the coma and check the skin for signs of bruises due to trauma^[10].

Healthcare professionals use the Glasgow Coma Scale (GCS) to assess the severity of the coma^[12]. The GCS is a 15-point screening that evaluates eye, verbal, and motor responses to check a person’s level of consciousness. The lower the score, the more severe the coma^[7].

Blood samples are typically taken to check for various conditions, including a complete blood count, electrolytes and glucose levels, thyroid, kidney and liver functions, carbon monoxide poisoning, and drug or alcohol overdose^[10]. A spinal tap, also known as lumbar puncture, can check for signs of infections in the nervous system^[10].

Imaging tests are crucial for diagnosis. A CT scan of the head can reveal head injuries, bleeding in the brain, blood clots, or tumors. An MRI scan of the brain can detect damaged brain tissue and help diagnose the cause of the coma^[10]. An electroencephalogram (EEG) may be used to assess the electrical activity of the brain, which would be severely suppressed in a comatose patient^[19].

Treatment and medical care

The first goal in managing a comatose patient is to stabilize the patient and diagnose any rapidly reversible causes of coma^[3]. Treatment depends on the cause of the coma and is directed at preventing further damage to the brain^[4].

In the short term, a person in a coma will normally be looked after in an intensive care unit (ICU)^[4]. Supporting the patient’s vital signs remains the most crucial aspect of management^[13]. If the patient is having difficulty breathing, they may be placed on a ventilator (breathing machine) while the underlying cause is treated^[4].

The patient’s respiration and circulation must be monitored and maintained. This may require mechanical ventilation and medications to support blood pressure^[4]. Intravenous fluids or blood and other supportive care must be provided as needed^[3].

Treatment is tailored to the underlying cause. After a head injury, surgery may be required to stop bleeding and reduce swelling in the brain^[4]. If there is an underlying illness or poisoning, treatment will be directed at the underlying cause^[4]. For example, immediate treatment is crucial if a person with diabetes has dangerously lowered their blood sugar levels^[5].

During a coma, a person cannot care for themselves and needs around-the-clock medical support^[12]. They might need tube feeding to provide nutrition, a urinary catheter to collect urine, and assistance with all basic bodily functions^[12].

Once stable and no longer in immediate danger, further treatment focuses on supporting recovery and preventing complications^[4]. Healthcare professionals typically order a series of tests to learn what’s causing the coma so that proper treatment can begin^[1].

Recovery and outlook

Recovery from a coma is a long and often complex process^[18]. The outcome depends on the cause and severity of the damage a person has sustained^[8]. Brain damage can range from mild to severe, making it difficult to predict recovery time as well as the severity of the effects^[18].

A coma doesn’t usually last longer than several weeks^[1]. Some people will wake up after a few days or weeks, while others may go into a vegetative state or minimally conscious state^[4]. Over time, the person may start to gradually regain consciousness and become more aware^[4].

Coming out of a coma typically follows a pattern of stages. In the vegetative state, the person is unresponsive to stimuli with closed eyes. In the minimally conscious state, they have slow or inconsistent responses to sound, touch, or sight, including opening their eyes. This stage is one of the early signs of coming out of a coma^[7].

The confusional state follows, where the person responds more consistently but may be confused, agitated, and have memory problems. Eventually, with full consciousness, the person can complete most routine tasks but may need assistance. There may be personality changes that impact their judgment and decisions^[7].

It usually takes several months for people to come out of a coma. During this time, they regain consciousness and respond to what is happening. After another period, some people can fully recover their cognitive abilities^[18].

The body may need physical rehabilitation therapy to restore strength and reflexes lost during the coma^[18]. If clinical experts determine a potentially recoverable cause of brain injury, recovery from a coma can still be a long process. These patients may require a feeding tube and breathing tube with a ventilator for a prolonged time as the brain recovers^[19].

During the recovery period, family members must be prepared to provide emotional support and help guide necessary medical recovery^[18]. Recovery from a coma can sometimes be discouraging, but with proper care and support, patients can make significant progress and return to everyday life^[18].

In severe cases, a person’s condition may not change after an extended period. A person in a persistent vegetative state has damage to the areas of the brain responsible for consciousness, self-awareness, and personality but retains involuntary functions such as breathing and swallowing, heart rate, and blood pressure^[5]. This state can be permanent, though it’s possible to wake. Those that do wake usually don’t recover brain function^[7].

Possible complications

If you’re in a coma, you can’t care for yourself, which puts you at risk for several complications^[12]. People in a coma require extensive medical care to maintain their health and prevent complications such as pneumonia or blood clots^[2].

Complications from being in a coma or receiving coma-related care may include bedsores (pressure sores from lying in one position), blood clots in the legs, and infections^[12]. Common infections include pneumonia from a ventilator and urinary tract infections (UTIs) from a catheter^[12].

Muscle loss and weakness can occur from prolonged immobility^[12]. The person may experience respiratory and circulatory problems due to the body’s inability to maintain normal bodily functions^[2].

During a coma, there are several complications that could develop, such as urinary tract infections, blood clots in the legs, and pneumonia^[7]. Delaying treatment may lead to serious complications or life-threatening outcomes^[12].

Depending on the cause and the extent of damage, long-term effects can vary significantly. Some people make a full recovery with minimal long-term effects, while others may have lasting disabilities affecting movement, thinking, memory, or behavior^[19].

• Brain
• Brainstem
• Reticular activating system
• Cerebral hemispheres
• Cerebral cortex