How to Cite This Chapter: Panju M, Masoom H, Gundy S, Cheung J, Patel A, Jankowski M, Zwolińska G. Coma. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed May 22, 2024.
Last Updated: June 6, 2019
Last Reviewed: July 3, 2022
Chapter Information

Definition and CausesTop

Coma is a prolonged loss of consciousness with reduced response to external stimuli. Causes: Table 1.


1. Assess the patient (see Loss of Consciousness).

2. Assess consciousness (depth of coma): Check responsiveness (to voice, touch, and pain) using the Glasgow Coma Scale (GCS) (see Table: Glasgow Coma Scale). Reevaluate the GCS score often to monitor for any fluctuation in the patient’s mental status.

3. Perform a complete head-to-toe assessment:

1) Vital signs: Tachycardia, bradycardia, hyperthermia, hypothermia, hyperventilation, hypoventilation, hypertension, hypotension.

2) Eyes: Pupil size and reactivity, nystagmus, gaze deviation, scleral icterus; fundoscopy for papilledema.

3) Head and neck: Meningismus, tongue biting (especially the lateral aspects of the tongue), Battle sign.

4) Neurologic examination: Ability to follow commands, tone, deep tendon reflexes, Babinski reflex, asterixis, posturing (decerebrate/extensor or decorticate/flexor), convulsions, myoclonus.

5) Cardiovascular examination: Murmurs, arrhythmias, volume status.

6) Respiratory examination: Pattern of breathing (Cheyne-Stokes, Kussmaul), decreased breath sounds, wheezes, crackles.

7) Abdominal examination: Distension, ascites, peritoneal signs, distended bladder.

8) Dermatologic examination: Cellulitis, sacral or heel ulceration, signs of IV drug use.

4. Initiate universal and specific antidotes (as applicable):

1) Thiamine 100 mg IM or IV (administer before glucose [dextrose]).

2) Glucose (1 ampoule of 50% dextrose in water).

3) Naloxone 0.4 mg IV (if opioid overdose is suspected).

4) Supplemental oxygen (100% fraction of inspired oxygen [FiO2] if carbon monoxide poisoning is suspected).

5. Order diagnostic tests:

1) Electrocardiography (ECG).

2) Laboratory tests:

a) Complete blood count (CBC): An elevated white blood cell count may indicate a central nervous system infection.

b) Serum biochemistry tests: Serum levels of glucose (low or elevated in hyperosmolar hyperglycemic nonketotic coma and diabetic ketoacidosis), sodium, potassium, ammonia (usually elevated in hepatic coma), urea/blood urea nitrogen (BUN) and creatinine (elevated in uremia), lactate (elevated in hypoxia and shock), calcium (elevated in hypercalcemic crisis), phosphate, magnesium.

c) Arterial blood gas analysis may reveal hypercapnia, hypoxemia, and acidosis.

d) Serum and urine osmolality (elevated in toxic alcohol ingestions).

e) Toxicology screen if ingestion suspected.

f) Levels of acetylsalicylic acid (ASA) and paracetamol (INN acetaminophen) (in all patients with suspected overdose, as ingestion is common).

g) Thyroid-stimulating hormone (TSH) levels (high in myxedema coma).

h) Urinalysis: Elevated ketone bodies (and sometimes glucose) in ketoacidosis.

i) Lumbar puncture and cerebrospinal fluid examination if meningitis or encephalitis are suspected.

3) Imaging studies: Computed tomography (CT) of the head with no contrast enhancement allows visualization of intracranial bleeding and cerebral edema. Chest radiographs are used to assess for atelectasis due to aspiration (perform a therapeutic bronchoscopy if necessary).

6. Perform a differential diagnosis of coma (Table 1), determine the cause, and treat the underlying condition, if possible.


Table 1.3-1. Typical manifestations of coma based on etiology



Typical manifestations


Subarachnoid or intracranial hemorrhage

Sudden onset, headache, vomiting, focal neurologic signs, signs suggestive of meningitis

Extensive stroke affecting bilateral cerebral hemispheres or brainstem

Sudden onset, focal neurologic signs, progressive clinical deterioration


Direct brain injury or accumulating subdural hematoma

History of trauma, lacerations or other signs of head trauma, bleeding from ears or CSF leakage from nose or ears

Increased intracranial pressure

Brain tumor or abscess, subdural hematoma

History of escalating headache, progressive impairment of mental status, papilledema, focal neurologic signs



History of headache and fever, subacute course, signs suggestive of meningitis


As above plus signs of disseminated encephalopathy, seizures, involuntary movements



Hyperhidrosis, dilated pupils, seizures, hyporeflexia, Babinski sign, sometimes focal neurologic signs


Hyperventilation, Kussmaul breathing


Progressive apathy, progressive obtundation, tremor, seizures

Liver disease

Coma preceded by memory impairment, confusion, and somnolence with subsequent development of pyramidal, extrapyramidal, and cerebellar signs and low frequency tremor


Signs of hypercalcemia


Cerebral edema caused by changes in CSF and cell tonicity, can also be provoked by overly rapid correction in patient with chronic derangement


Signs of hypernatremia


History of hypothyroidism, gradual deterioration over weeks, common hypercapnia



Sudden abnormalities in behavior or mental status, seizures, sometimes extremity paresis


Cardiac and respiratory arrest

Sudden onset, decortication or decerebration, myoclonus, epileptic seizures


Carbon dioxide retention in patients with respiratory insufficiency

Gradual deterioration of mental status, prior headache, shallow respiration, conjunctival injection

Extreme body temperatures


Signs of hypothermia


Signs of hyperthermia


Toxic alcohols, ethanol

Signs of alcohol intoxication

Anticholinergics, sedative hypnotics, antipsychotics, opioids, carbon monoxide poisoning

Signs of poisoning and intoxication


Catatonia, pseudocoma

History of psychiatric diagnosis and deterioration, normal cold caloric testing

CSF, cerebrospinal fluid.

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