the comatose patient

introduction

coma or decreased conscious state is a common presentation or occurrence within the ED, and most are transient due to syncope / near syncope or post-ictal states.
decreased conscious state will reliably occur when cerebral perfusion falls to low (eg. hypotension or raised intracranial pressure (ICP)), there is a lack of cerebral oxygenation (eg. hypoxia), or there is a severe metabolic disturbance (eg. hypoglycaemia, severe acidosis, etc).
the cause of the decreased conscious state may be immediately life-threatening (eg. ventricular fibrillation (VF), choking / cardiac arrest / BLS / ALS / CPR, raised intracranial pressure, hypoglycaemia, hypoxia, head trauma or the shocked hypotensive patient)
persistent decreased conscious state in itself may be immediately life-threatening as patient may not be able to support their airway, prevent aspiration or ventilate spontaneously.

usual resuscitation measures addressing airway, breathing, circulation
- hypotension or weak pulse suggests shock as the cause:
  - trial of bolus iv fluids 10-20ml/kg unless C/I by clinical picture of cardiac failure or acute pulmonary oedema (APO)
  - consider tension pneumothorax, exsanguination, ectopic pregnancy, anaphylaxis, septic shock, cardiogenic shock, pulmonary embolism (PE)
check glucose level to exclude hypoglycaemia
if trauma possible, protect cervical spine
consider naloxone (Narcan) 0.1mg/kg (max 2mg) im/iv/intranasal in case opiate overdose, particularly if intravenous drug users (IVDU) or injection drug use (IDU) or pinpoint pupils
if evidence of seizures, Mx as per seizures, but be aware that hypoxia, shock, eclampsia and hypoglycaemia can all be the cause.
move to a resuscitation area as soon as possible for ongoing cardiorespiratory and neurologic monitoring
if persistent coma with GCS < 9 and no readily identifiable reversible cause, and no NFR status, consider intubation to protect airway and ensure adequate ventilation.

ECG
FBE
U&E
glucose
LFT
blood gas to exclude metabolic acidosis (eg. diabetic ketoacidosis (DKA) or toxicology) or alkalosis
coagulation screen - as there is a reasonable likelihood of need to do a lumbar puncture (LP)

if history of febrile illness, petechial/purpuric rash or neck stiffness consider:
- meningitis or meningoencephalitis - urgent empirical antibiotics +/- aciclovir
if history of febrile illness and hypotensive or clinically in shock, consider septic shock
if high temperature, consider also, heat illness and heat stroke, neuroleptic malignant syndrome or serotonin syndrome
if fever and young child with no sinister features, consider febrile convulsion
if recent international travel, consider:
- cerebral malaria
- typhus, yellow fever, trypanosomiasis, typhoid
NOTE: many of the conditions below also cause a raised temperature, and some are often precipitated by infections (eg. hepatic and Wernicke's encephalopathy)

if evidence of trauma, Mx as per trauma including urgent CT scan of brain and cervical spine
if history of sudden headache preceding collapse, consider subarachnoid haemorrhage (SAH), thus urgent CT scan
if focal neurology then consider stroke (CVA) or other intracranial pathology, thus urgent CT scan
if no focal neurology, consider toxicology cause
- eg. check blood alcohol level, paracetamol, blood gases, and consider salicylate levels
- gamma hydroxybutyrate (GHB), tricyclic antidepressant overdose, etc
if known alcoholic, see ethanol intoxication/poisoning
if hypothermic, see hypothermia
consider raised intracranial pressure (ICP)
if encephalopathic consider:
- Wernicke's encephalopathy
  - alcoholics or post-bariatric surgery patients, with infection or carbohydrate load while thiamine deficient ⇒ start iv thiamine high dose
- if hypertensive, consider hypertensive encephalopathy
- if PH liver disease, consider hepatic encephalopathy
- if infant, consider non-accidental injury, herpetic, blocked V-P shunts, etc.
other uncommon causes include:
- acute renal failure (ARF), hyponatraemia, hypercalcaemia, myxoedema, Addisonian crisis, etc.