What is Coma ? Causes, Complications and Types

what happens when someone is in a coma

A coma is a state of prolonged unconsciousness which can be caused by many different problems, like alcohol intoxication, drug intoxication, brain tumor, stroke, head injury, or even an underlying illness, such as an infection or diabetes. The coma is a medical emergency. Swift action is needed to preserve life and brain function. Normally, doctors order a battery of blood tests and a brain CT scan to try to determine what the cause for coma is, so they can begin with the proper treatment. The coma seldom lasts longer than several weeks. It is noticed that those people, who are unconscious for a longer period of time may transition to a persistent vegetative state. It depends on the cause of coma, but people who are in a persistent vegetative state for more than one year are extremely unlikely to awaken.

induced coma

Symptoms of the coma

Here are the signs and symptoms of coma:

  • Irregular breathing
  • There is no a response to painful stimuli, except for reflex movements
  • Closed eyes
  • No response of limbs, except for reflex movements
  • Depressed brainstem reflexes, such as pupils nor responding to light

The coma is a medical emergency, so people must see doctor as soon as possible.

Causes of the coma

There are many different types of problems which can lead to coma. Some examples for coma include:

  • Drugs and alcohol: If you overdose with alcohol or drugs, then this could result in coma. [1,2]
  • Traumatic brain injuries: The traumatic types of the coma are often caused by traffic collisions or acts of violence and they are the most common causes for coma. [3]
  • Toxins: Toxins are substances which are normally found in the body and they can accumulate to toxic levels if the body fails to dispose of them correctly. The exposure to toxins, such as lead or carbon monoxide, can cause brain damage and a coma. Also, the ammonia due to liver disease, the urea from kidney failure or the carbon dioxide from a severe asthma attack can accumulate to toxic levels in the body. [4]
  • Bleeding: The bleeding in the layers of the brain can cause coma due to the compression and swelling on the injured side of the brain. This compression is causing the brain to shift, which is causing damage to the brainstem and the RAS. Tumors, cerebral aneurysms and high blood pressure are non – traumatic causes of bleeding in the brain. [5]
  • Stroke: The reduced or interrupted blood supply to the brain (stroke), which can be caused by a burst blood vessel or blocked arteries, can result in the coma. [6]
  • Tumors: The brainstem or tumors in the brain can cause a coma. [7]
  • Seizures: The single seizure can rarely produce coma. The ongoing seizures can lead to a coma. Continuous seizures are known as epilepticus. The repeated seizures can prevent the brain from recovering in between seizures and this will lead to prolonged unconsciousness and coma. [8]
  • Diabetes: Those people who have diabetes, the blood sugar levels can become too low (hypoglycemia) or too high (hyperglycemia) can cause a coma. [9]
  • Infections: Infections, such as meningitis and encephalitis, can cause swelling or inflammation of the spinal cord, brain or the tissues which surround the brain. The severe cases of these infections can result in brain damage or a coma.
  • Lack of oxygen: We know that the oxygen is essential for the brain function. Those people who have been rescued from drowning or those who have been resuscitated after a heart attack, may not awake due to the lack of oxygen to the brain. The cardiac arrest is causing sudden cutoff of blood flow and oxygen to the brain, which is known as anoxia or hypoxia. After CPR (cardiopulmonary resuscitation) survivors of cardiac arrest are often in comas. [10]


Many people gradually recover from a coma, but others enter a vegetative state or die. Some people who recover from coma can have minor or major disabilities. Here are complications which may develop during a coma:

  • Blood clots in the legs
  • Bladder infections
  • Pressure sores


Here are types of the coma:

  • Medically induced
  • Brain death
  • Locked – in syndrome
  • Persistent vegetative state
  • Anoxic brain injury
  • Toxic – metabolic encephalopathy


[1] Buylaert WA. Coma induced by intoxication. Acta Neurologica Belgica. 2000;100(4):221-4.

[2] Pereira FR, McMaster MTB, Polderman N, et al. Adverse effects of GHB-induced coma on long-term memory and related brain function. Drug and Alcohol Dependence. 2018;190:29-36.

[3] Firsching R. Coma after acute head injury. Deutsches Arzteblatt international. 2017;114(18):313–20.

[4] Stanca S, Ulmeanu CE, Stanca HT, Iovanescu G. Clinical features in toxic coma in children. Experimental and Therapeutic Medicine. 2019;18(6):5082-7.

[5] Bates D. The prognosis of medical coma.

[6] Li J, Wang D, Tao W, et al. Early consciousness disorder in acute ischemic stroke: incidence, risk factors and outcome. BMC Neurology. 2016; 16: 140.

[7] Ryu J, Jung W, Jung YJ, et al. Early prediction of neurological outcome after barbiturate coma therapy in patients undergoing brain tumor surgery. PLoS One. 2019;14(4):e0215280.

[8] Alvarez V, Lee JW, Westover B, et al. Therapeutic coma for status epilepticus: Differing practices in a prospective multicenter study. Neurology. 2016;87(16):1650–9.

[9] Ben-Ami H, Nagachandran P, Mendelson A, et al. Drug-induced hypoglycemic coma in 102 diabetic patients. Archives of Internal Medicine. 1999;159(3):281-4. doi:10.1001/archinte.159.3.281

[10] Johns Hopkins Medicine. Scientific statement on predicting survival for cardiac arrest survivors. 2019. Retrieved from www.hopkinsmedicine.org/news/newsroom/news-releases/scientific-statement-on-predicting-survival-for-cardiac-arrest-survivors


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.