• An unconscious patient cannot communicate, is unarousable and does not obey commands.
• Unconsciousness is provoked by a bilateral hemispheric dysfunction or a disturbance of the reticular activating system at the brain stem.
• There are several causes of unconsciousness, many of which are life threatening (table T2). The diagnosis and treatment should therefore progress simultaneously.
• Immediate intervention will give extra time to discover the cause of unconsciousness and for the initiation of appropriate treatment.

• Resuscitation: See (Treatment of cardiac arrest in primary health care)

1. Check ABC (airway, breathing, circulation).
2. Prevent aspiration.
3. Exclude or treat hypoglycaemia.

• Immediate interventions include also, when deemed appropriate, the administration of thiamine (before glucose in alcoholics) and antidotes to poisons (naloxone, flumazenil).
• When the patient’s condition is stabilised, the cause of unconsciousness should be sought. Eyewitness accounts of the events leading to the loss of consciousness are of utmost importance (“the disease reveals its nature in the very beginning”) as are any available data regarding the patient’s past medical history and medication.

• The MIDAS mnemonic is a useful reminder of important and treatable causes of unconsciousness: Meningitis – Intoxication – Diabetes – Anoxia – Subdural haematoma.
• See also chart (Angiofibromas ("Adenoma sebaceum") on the facial skin).

The most common causes of unconsciousness

• In clinical practice, the causes of unconsciousness may be divided into four main categories:

1. A structural intracranial cause
   • For example, cerebral infarction, cerebral haemorrhage, cerebral contusion, brain tumour, cerebral abscess or other space occupying lesion
   • A supratentorial cause should be considered in the presence of dysphasia, hemiparesis, conjugate gaze deviation (”the patient looks towards the lesion, away from the hemiparesis”) and a positive Babinski sign on the side of the hemiparesis.
   • An infratentorial cause should be considered in the presence of disconjugation of the eyes, nystagmus, dysphagia, dysarthria, ataxia, hemiparesis, gaze deviation towards the paresis (”the patient looks away from the lesion”), tetraplegia, bilateral positive Babinski sign, occipital headache and vomiting.
   • Diagnosis is based on a neurological examination and neuroradiological investigations. Computed tomography (CT) of the head is the investigation of choice.
2. A systemic or diffuse cause of cerebral origin, for example metabolic, toxic, hypoxic or septic aetiology (60–70% of cases)
   • No neurological focal findings, signs and symptoms are principally ”symmetrical” (no unilateral symptoms). Typical findings include confusion, drowsiness, myoclonic twitching, asterixis (flapping tremor of the hands), tremor and, for example, pinpoint pupils (opioid intoxication).
   • In addition to clinical examination, laboratory investigations form the cornerstone of diagnosis.
3. Infection of the central nervous system (meningoencephalitis, encephalitis)
   • The patient’s condition is suggestive of meningeal irritation, i.e. fever, nuchal rigidity and confusion before loss of consciousness.
   • Diagnosis is based on the results of a cerebrospinal fluid sample and blood cultures.
4. Epileptic or other seizures and postictal states
   • Diagnosis is based on eyewitness accounts of the seizure, history of susceptibility to seizures and an electroencephalogram (EEG). Bite marks in the edge of the tongue suggest a post-seizure condition.

General status

• The patient’s general status is noted, including the head, neck, tongue, skin, body temperature, smell of breath, type of breathing, cardiovascular state, lung auscultation, abdomen and limbs.
• The patient should be observed for signs of trauma, infection, nuchal rigidity, hypertension, hypotension, chronic illness (malignancy, lungs, liver, kidneys, heart, immunodeficiency), intoxication (e.g. needlestick marks).

Neurological examination

• The aim of a neurological examination should be to either locate or exclude a brain injury as the cause of the unconsciousness.

1. The assessment of the level of consciousness should progress systematically.
   • Opening of the eyes (it may be necessary to shout into the patient’s ear), best motor response (if necessary, response to pain; for example to supraorbital, nail bed or sternal pressure) and best response to speech.
   • These variables form the Glasgow Coma Scale (GCS, table T1). The patient’s reactions are recorded in the medical notes.
2. Neuro-ophthalmologic status
   • The brain centres responsible for consciousness and mental alertness are situated close to the brainstem structures associated with eye movements. An examination of the eyes is therefore particularly important.
   • The following should be checked: pupillary responses (size, symmetry, reaction to light), optic discs of the fundi of the eyes (venous pulsation, papilloedema, haemorrhages; in practice it may be difficult to obtain a clear view on the papillae) and eye movements (the resting position, spontaneous movements and the oculocephalic reflex if necessary).
     • The oculocephalic reflex: the patient's head is turned quickly from one side to the other: the gaze should remain fixed on the same point.
     • The doll’s eye reflex: the gaze follows with the turning of the head = sign of brainstem injury.
3. Brain stem reflexes
   • The eyelash and corneal reflexes test the function of the upper pons.
   • The cough reflex (e.g. response to tracheal suctioning) tests the function of the lower pons.
   • The oculocephalic reflex is also a brain stem reflex and is an indicator of the functioning of the lower pons.
4. Neurological unilateral symptoms
   • Any side differences should be noted as regards spontaneous movements, responses to pain, limb tone and reflexes as well as the Babinski sign.

Urgent cases

• Certain causes of unconsciousness will quickly lead to death if left untreated. A clinical examination of the patient should therefore aim to immediately identify or exclude these conditions. See table T2.

Laboratory investigations

• The initial investigations should include:
  • ECG and chest x-ray
  • blood glucose and arterial blood gases
  • basic blood count with platelets, CRP
  • CK, TnT
  • creatinine, GFR (calculator ) urea, sodium, potassium, calcium
  • ALT, gamma-GT
  • APTT, INR
  • chemical urinalysis + urine culture
  • serum ethanol and intoxication samples at discretion.

Neuroradiological investigations

• CT scanning of the head
  • Usually the first imaging study to be carried out in an unconscious patient
  • Finds intracranial haemorrhages well.
• MRI scanning of the brain
  • Usually considered as a further investigation after the CT scan
  • Increases accuracy in the examination of the posterior cranial fossa, brain stem and the white matter of the brain.
  • Suspicion of herpes encephalitis is a special indication for MRI.
• CT angiography, MRI angiography
  • Necessary if any vascular findings would affect the treatment choices, for example in cases of suspected subarachnoid haemorrhage, basilar thrombosis, sinus thrombosis, cerebral vasculitis or dissection of the carotid artery.

Other investigations

• EEG
  • After consideration if the unconsciousness was preceded by a seizure, or if non-convulsive status epilepticus is suspected.
  • An EEG may also yield information of metabolic disturbances (e.g. hepatic coma) or infections (e.g. herpes encephalitis).
• Cerebrospinal fluid (CSF) (Lumbar puncture, examination of cerebrospinal fluid and findings)
  • A sample should always be obtained if an infection (or an inflammatory illness of the central nervous system) is suspected, or if the aetiology of unconsciousness remains unresolved.
  • The CSF investigations should include the appearance of the fluid (xanthochromia), cells, protein, glucose and bacterial staining + culture (suspicion of an infection). Two spare tubes should be provided and follow-up investigations carried out as appropriate.