Causes of a Fall in GCS – Intra and Extra Cranial 

A decreasing GCS always needs urgent assessment. Think broadly: brain causes (intracranial) and systemic causes (extracranial). 

INTRACRANIAL CAUSES 
(Primary brain pathology or raised intracranial pressure) 

1. Expanding Intracranial Lesions 
Epidural haematoma 
Subdural haematoma 
Intracerebral haemorrhage 
Brain tumour with bleed 
Clues: 
Head injury history 
Worsening headache 
Vomiting 
Unequal pupils 
Rapid GCS decline 

2. Raised Intracranial Pressure (ICP) 
Causes: 
Cerebral oedema 
Hydrocephalus 
Space-occupying lesions 
Clues: 
Reduced consciousness 
Headache worse lying flat 
Vomiting 
Papilloedema (late) 
Cushing’s triad (late): ↓HR, ↑BP, irregular breathing 

3. Cerebral Ischaemia or Stroke 
Large territory infarct 
Brainstem stroke 
Haemorrhagic stroke 
Clues: 
Sudden onset 
Focal neurological deficits 
Gaze deviation 
Dysarthria 

4. Post-Traumatic Brain Injury 
Diffuse axonal injury 
Cerebral contusions 
Secondary injury (hypoxia, hypotension) 
Clues: 
Trauma history 
Initially normal GCS that later deteriorates 

5. Seizure-Related 
Ongoing seizure 
Post-ictal state 
Non-convulsive status epilepticus 
Clues: 
Witnessed seizure 
Tongue biting 
Incontinence 
Prolonged confusion 

6. CNS Infection 
Meningitis 
Encephalitis 
Brain abscess 
Clues: 
Fever 
Neck stiffness 
Photophobia 
Rash (meningococcal) 

EXTRACRANIAL CAUSES 
(Systemic or metabolic causes affecting brain function) 
1. Hypoxia 
Airway obstruction 
Respiratory failure 
Pneumonia 
Pulmonary embolism 
Clues: 
Low SpO₂ 
Cyanosis 
Tachypnoea 
Hypoxia is one of the most common reversible causes 
2. Hypotension / Shock 
Sepsis 
Haemorrhage 
Cardiac causes 
Clues: 
Low BP 
Tachycardia 
Cool peripheries 
Reduced urine output 

3. Metabolic Disturbances 
Hypoglycaemia / hyperglycaemia 
Hyponatraemia / hypernatraemia 
Hepatic or uraemic encephalopathy 
Clues: 
Abnormal blood results 
Confusion without focal neurology 

4. Drugs and Toxins 
Opioids 
Benzodiazepines 
Alcohol 
Sedatives 
Overdose 
Clues: 
Pinpoint pupils (opioids) 
Smell of alcohol 
Medication history 

5. Sepsis 
Any source (UTI, chest, abdomen) 
Clues: 
Fever or hypothermia 
Tachycardia 
Hypotension 
Raised lactate 

6. Hypercapnia 
COPD exacerbation 
Respiratory depression 
Clues: 
Drowsiness 
Flushed skin 
Raised CO₂ on ABG 

Clinical Approach 

When GCS drops, think: “ABCDE first – CT second” 

Airway – protect if GCS ≤8 
Breathing – oxygenation, CO₂ 
Circulation – BP, glucose 
Disability – GCS, pupils, glucose 
Exposure – fever, infection, trauma 

Red Flags Requiring Immediate Escalation 
Drop in GCS ≥2 points 
Unequal or fixed pupils 
GCS ≤8 
New focal neurological deficit 
Signs of raised ICP 

Key Points 

Not all low GCS = head injury. Always exclude hypoxia and hypoglycaemia. 

Time is critical; refer to Stroke Unit if stroke suspected and arrange urgent transfer (in accordance with local policy) 

Mnemonic for Causes of Falling GCS 

Primary mnemonic: “HEADS & TABS” 
H – Hypoxia 
Low oxygen, airway obstruction, respiratory failure 
E – Electrolytes / Endocrine 
Glucose, sodium, calcium, liver or renal failure 
A – Alcohol / Drugs 
Opioids, benzodiazepines, overdose, intoxication 
D – Damage (Intracranial) 
Bleed, stroke, tumour, raised ICP, trauma 
S – Sepsis / Seizures 
Infection, meningitis, post-ictal state 
 
T – Trauma 
Head injury, secondary brain injury 
A – Acidosis / CO₂ retention 
Hypercapnia, respiratory failure 
B – Blood pressure (Low) 
Shock, haemorrhage, sepsis 
S – Sugar 
Hypoglycaemia (always check early!) 
 
Ultra-Fast Emergency Mnemonic 
“O2 – Sugar – Brain – Drugs – Sepsis” 
Use this when someone suddenly deteriorates. 
 
Intracranial-Only Mnemonic 
“BETS” 
Bleed 
OEdema / raised ICP 
Tumour / trauma 
Stroke / seizure 
 
Extracranial-Only Mnemonic 
“SHAMPOO” (sounds silly — sticks forever) 
Sepsis 
Hypoxia 
Alcohol / drugs 
Metabolic 
Pressure (low BP) 
Oxygen/CO₂ issues 
Overdose