Definition and epidemiology
Coma is defined as a sustained pathological state of unconsciousness in which the eyes remain closed, there is no response to verbal stimuli, and no purposeful motor response to pain. It is operationally captured by a Glasgow Coma Scale (GCS) score of 8 or less, though GCS is a severity scale rather than a strict definition.
Coma itself is not a disease but a common final pathway for many conditions, so true population prevalence is not well defined. It is encountered frequently in emergency departments and intensive care units; traumatic brain injury, drug overdose, and cardiac arrest with hypoxic-ischemic encephalopathy are among the leading causes worldwide. Mortality and functional outcome depend heavily on the underlying etiology and duration.
- GCS ≤8 defines coma and is the threshold for airway protection/intubation
- Always check fingerstick glucose immediately in any comatose patient
- Unilateral fixed dilated pupil = uncal herniation compressing CN III
- Pinpoint pupils with respiratory depression suggests opioid overdose
- Noncontrast CT head is the first imaging study in undifferentiated coma
- Give thiamine before/with glucose in suspected alcoholics to prevent precipitating Wernicke encephalopathy
- Absent pupillary/corneal reflexes at 72 hours post-arrest predict poor prognosis
- Locked-in syndrome preserves consciousness with intact vertical eye movements, unlike true coma
Etiology and risk factors
Causes are broadly structural (focal brain lesion) or diffuse/toxic-metabolic (bilateral cortical or brainstem dysfunction without a discrete lesion).
Structural causes
- Traumatic brain injury (epidural, subdural, intraparenchymal hemorrhage, diffuse axonal injury)
- Ischemic or hemorrhagic stroke, especially brainstem or bilateral thalamic
- Subarachnoid hemorrhage
- Brain tumor with mass effect or herniation
- Cerebral abscess or other mass lesion
Toxic-metabolic and diffuse causes
- Hypoglycemia or severe hyperglycemia (DKA, HHS)
- Hypoxia and hypercapnia
- Drug or toxin overdose (opioids, sedative-hypnotics, alcohol, carbon monoxide)
- Electrolyte derangements (severe hyponatremia, hypercalcemia)
- Hepatic encephalopathy, uremic encephalopathy
- Sepsis and septic encephalopathy
- Status epilepticus or prolonged postictal state
- Hypothermia or hyperthermia
- Hypoxic-ischemic encephalopathy after cardiac arrest
Risk factors include substance use disorder, chronic liver or kidney disease, diabetes, uncontrolled hypertension, anticoagulant use, and recent head trauma.
Pathophysiology
Consciousness requires two intact components: the ascending reticular activating system (ARAS) in the brainstem and thalamus, which maintains arousal (wakefulness), and the bilateral cerebral cortex, which generates awareness (content of consciousness).
Coma results when either the ARAS is damaged (brainstem stroke, compressive herniation, diffuse axonal injury) or when both hemispheres are diffusely dysfunctional (toxic-metabolic insult, bilateral cortical injury, severe diffuse axonal injury). A focal unilateral cortical lesion alone does not cause coma unless it compresses the brainstem or opposite hemisphere.
Secondary injury mechanisms, including raised intracranial pressure, herniation syndromes, cerebral edema, and impaired cerebral perfusion, can convert a focal lesion into global dysfunction and deepen coma.
Clinical features
By definition the patient does not open eyes, does not follow commands, and does not produce comprehensible speech. Assessment focuses on identifying localizing versus non-localizing signs to distinguish structural from toxic-metabolic coma.
Key exam elements
- Glasgow Coma Scale: eye opening, verbal response, motor response (range 3-15)
- Pupillary responses: symmetric reactive pupils favor toxic-metabolic cause; unilateral fixed dilated pupil suggests uncal herniation (CN III compression); pinpoint pupils suggest opioid toxicity or pontine lesion
- Oculocephalic/oculovestibular (doll's eyes, cold caloric) reflexes: test brainstem integrity
- Respiratory pattern: Cheyne-Stokes, central neurogenic hyperventilation, or ataxic breathing localize to different brainstem levels
- Motor response to pain: localizing, withdrawal, decorticate (flexor) posturing, decerebrate (extensor) posturing, or flaccid
- Signs of trauma: Battle sign, raccoon eyes, scalp hematoma
- Fever, meningismus: suggest CNS infection
- Needle marks, pinpoint pupils, specific odors: suggest toxic ingestion
Diagnosis
Coma is a medical emergency; diagnostic workup proceeds simultaneously with stabilization.
Immediate steps
- Finger-stick glucose (treat hypoglycemia immediately)
- Airway, breathing, circulation assessment; protect airway if GCS ≤8
- Naloxone trial if opioid toxicity suspected
Laboratory workup
- Complete blood count, electrolytes, glucose, calcium
- Liver and renal function tests, ammonia if hepatic encephalopathy suspected
- Arterial blood gas, carboxyhemoglobin level if indicated
- Toxicology screen, blood alcohol level
- Blood cultures if infection suspected
Imaging and other studies
- Noncontrast CT head is the first-line imaging study to identify structural lesions, hemorrhage, mass effect, or herniation
- MRI brain if CT is nondiagnostic and suspicion remains high (e.g., brainstem stroke, diffuse axonal injury)
- Lumbar puncture if meningitis or encephalitis suspected and no contraindication (mass effect) on imaging
- Electroencephalogram if nonconvulsive status epilepticus is suspected
A structured approach (such as assessing pupils, eye movements, motor response, and breathing pattern) helps localize the lesion before imaging is available.
Differential diagnosis
Several conditions can mimic coma or must be distinguished from it clinically.
| Condition | Distinguishing feature |
|---|---|
| Locked-in syndrome | Preserved consciousness and vertical eye movements/blinking; quadriplegia and anarthria from ventral pons lesion |
| Persistent vegetative state | Eyes open, sleep-wake cycles present, but no awareness; follows prolonged coma |
| Minimally conscious state | Inconsistent but reproducible evidence of awareness |
| Brain death | No brainstem reflexes, no respiratory drive, confirmed by formal clinical/apnea testing |
| Psychogenic unresponsiveness | Normal neurologic exam, resistance to passive eyelid opening, normal imaging/EEG |
| Catatonia | Waxy flexibility, mutism, may respond to benzodiazepines |
| Severe depression/akinetic mutism | Preserved arousal on exam despite profound apparent unresponsiveness |
Management
Management follows emergency stabilization first, then targeted treatment of the underlying cause.
Initial stabilization (ABC approach)
- Secure airway (intubation if GCS ≤8 or inadequate airway protection)
- Ensure adequate oxygenation and ventilation
- Establish IV access, treat hypotension
- Correct hypoglycemia immediately with dextrose
- Administer thiamine before or with glucose if Wernicke encephalopathy is a concern (chronic alcohol use)
- Naloxone for suspected opioid overdose; flumazenil is used cautiously and selectively for benzodiazepine overdose given seizure risk
Cause-directed therapy
- Evacuate mass lesions (hematoma) neurosurgically when indicated
- Treat raised intracranial pressure (head elevation, osmotic therapy with mannitol or hypertonic saline, hyperventilation as temporizing measure, neurosurgical decompression if needed)
- Antibiotics/antivirals empirically for suspected CNS infection, pending or alongside LP results
- Antiepileptic therapy for status epilepticus
- Correct electrolyte and metabolic derangements gradually to avoid overcorrection (especially sodium)
- Targeted temperature management after cardiac arrest, per resuscitation guidelines (international consensus has shifted toward strict normothermia or mild hypothermia depending on recent trial evidence; practice varies by institution)
- Supportive ICU care: eye and skin care, DVT and stress ulcer prophylaxis, nutrition
Serial neurologic examinations and reassessment of GCS guide prognosis and the need for escalation of care.
Complications and prognosis
Complications include aspiration pneumonia, pressure injuries, venous thromboembolism, nosocomial infections, and secondary brain injury from raised intracranial pressure or herniation.
Prognosis depends heavily on etiology, duration, and findings on neurologic examination. Coma from reversible toxic-metabolic causes (e.g., hypoglycemia, drug overdose) generally has a better outcome once the derangement is corrected, whereas coma from severe structural injury or prolonged hypoxic-ischemic encephalopathy carries higher mortality and risk of persistent vegetative state or severe disability. Absent pupillary and corneal reflexes at 72 hours after cardiac arrest are strong predictors of poor neurologic outcome. Patients who do not progress beyond coma may evolve into a vegetative state, minimally conscious state, or brain death; formal brain death determination requires a defined clinical protocol including apnea testing.
AEIOU TIPS for causes of altered consciousness/coma: Alcohol/Acidosis, Epilepsy/Electrolytes, Insulin (hypo/hyperglycemia), Overdose/Oxygen (hypoxia), Uremia; Trauma/Temperature, Infection, Psychiatric, Stroke/Space-occupying lesion.
Practice questions
1. A 54-year-old man is brought to the emergency department unresponsive. He has pinpoint pupils, a respiratory rate of 6/min, and track marks on his arms. Which of the following is the most appropriate immediate step?
2. A 68-year-old woman with a history of hypertension develops sudden coma. Examination reveals a fixed, dilated left pupil and right hemiparesis. What is the most likely underlying mechanism?
3. A 45-year-old man with chronic alcohol use disorder is found unresponsive. Fingerstick glucose is 40 mg/dL. Which of the following should be administered together with or before dextrose to avoid precipitating a complication?
Frequently asked questions
What causes coma?
Coma results from either diffuse dysfunction of both cerebral hemispheres or damage to the brainstem's reticular activating system. Common causes include traumatic brain injury, stroke, hypoxic-ischemic injury after cardiac arrest, drug or alcohol overdose, hypoglycemia, severe infections, and metabolic derangements like liver or kidney failure. Structural lesions and toxic-metabolic causes are the two broad categories clinicians distinguish on exam and imaging.
What are the first signs before someone goes into a coma?
Warning signs often include progressive confusion, drowsiness, slurred speech, and decreasing responsiveness to voice or touch before complete unresponsiveness develops. Depending on the cause, there may be preceding headache, vomiting, seizure activity, focal weakness, or signs of intoxication. In metabolic causes like hypoglycemia, sweating and confusion typically precede loss of consciousness.
How is coma diagnosed?
Coma is diagnosed clinically using the Glasgow Coma Scale, with a score of 8 or less indicating coma, combined with assessment of pupillary response, eye movements, and motor response to pain. Workup then includes immediate glucose check, laboratory tests, and a noncontrast CT scan of the head to identify structural causes. Further tests like MRI, EEG, or lumbar puncture are used based on initial findings.
Is coma reversible?
Yes, coma can be reversible if the underlying cause is identified and treated promptly, such as correcting hypoglycemia, reversing drug overdose, or draining a hematoma. Reversibility depends heavily on the cause and duration; toxic-metabolic coma often resolves fully with treatment, while prolonged structural or hypoxic brain injury carries a higher risk of permanent disability or progression to a vegetative state.
Coma vs vegetative state — what is the difference?
In coma, the eyes remain closed and there are no sleep-wake cycles, whereas in a vegetative state the eyes open and sleep-wake cycles return, but there is still no awareness of self or environment. A vegetative state often develops after a patient survives beyond the initial coma stage. Neither state involves purposeful responses, distinguishing both from a minimally conscious state.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: R40.2
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.