Altered level of Conciousness

Overview

Altered Level of Consciousness (ALOC) refers to an acute or subacute impairment in arousal (wakefulness, mediated by the ascending reticular activating system [ARAS]) and/or awareness (cognition, mediated by the cerebral cortex). It spans a spectrum from confusion/delirium to lethargy, obtundation, stupor, and coma.¹

Core Pathophysiology: ALOC results from either:

Diffuse bihemispheric cortical dysfunction (metabolic, toxic, infectious, or hypoxic states).
Focal brainstem lesion directly disrupting the ARAS.

Hypoglycaemia and hypoxia are immediately reversible, life-threatening causes of ALOC. Check point-of-care blood glucose and oxygen saturation during the initial assessment, alongside airway, breathing and circulation.¹

Approach

Step 1: Primary Survey & Immediate Resuscitation (ABCDE)

Airway: Assess patency, ventilation and airway protection. A GCS score of 8 or less warrants early involvement of an appropriately trained clinician for advanced airway assessment; the decision to intubate also depends on respiratory and clinical findings.^1,2
Breathing: Oxygenation/ventilation check (SpO2, ABG/VBG for pCO2 retention).
Circulation: IV access, monitor BP and HR (hypotension/shock vs. Cushing’s triad [bradycardia, severe hypertension, irregular respirations] indicating elevated intracranial pressure).
Disability: GCS score, pupil size/reactivity, bedside glucose check (DON’T EVER FORGET GLUCOSE – “DEFG”).
Exposure: Temperature (hypothermia vs. hyperthermia/sepsis), toxidrome clues, trauma marks.

Step 2: Rapid Empiric Reversals (If Indicated)

Hypoglycemia: 50 mL D50W IV (or 100 mL D10W).
Opioid Overdose (Pinpoint pupils + respiratory depression): Naloxone 0.4–2 mg IV/IM/IN.
Wernicke Encephalopathy / Alcohol Use: Thiamine 100–500 mg IV (give before or alongside glucose).

Step 3: Clinical Decision Branching (AEIOU TIPS Mnemonic)

Focal Neurological Deficits / Asymmetry: -> Immediate Non-Contrast Head CT +/- CTA (Rule out ischemic stroke, ICH, mass effect, herniation).
Fever / Meningismus / Rash: Assess for meningitis or encephalitis. Perform lumbar puncture promptly when safe; defer it for features suggesting raised intracranial pressure or other contraindications. Give empiric treatment promptly if lumbar puncture or imaging would cause a clinically significant delay.³
Diffuse Symmetrical Non-Focal Exam: -> Metabolic/Toxicology/Sepsis workup.

A low GCS should prompt urgent airway assessment. Consider protective reflexes, oxygenation, ventilation, vomiting, seizures and the underlying cause rather than using the score alone as an automatic intubation rule.^1,2

Differential Diagnosis

Use the “AEIOU TIPS” Mnemonic for Etiologies:

A – Alcohol / Acidosis: Acute intoxication, withdrawal, DKA, AKA, uremic acidosis.
E – Epilepsy / Encephalopathy / Endocrine: Post-ictal state, non-convulsive status epilepticus (NCSE), hepatic encephalopathy, thyroid storm / myxedema coma, adrenal crisis.
I – Infection: Meningitis, encephalitis, sepsis, UTI/pneumonia in elderly.
O – Oxygenation / Opiates: Hypoxia, hypercapnia (CO2 narcosis), opioid/sedative toxicity.
U – Uremia: Severe acute kidney injury or end-stage renal disease.
T – Trauma / Temperature / Tumor: TBI (epidural/subdural hematoma, contusion), heat stroke, hypothermia, intracranial mass.
I – Insulin (Hypoglycemia): Absolute emergency; mimics stroke/focal deficits.
P – Poisoning / Psychogenic: Toxidromes (anticholinergics, sympathomimetics, TCAs), catatonia, conversion disorder.
S – Stroke / Space-Occupying Lesion: Ischemic stroke (especially basilar artery occlusion), ICH, SAH, venous sinus thrombosis.

Consider non-convulsive seizures or status epilepticus in unexplained persistent impaired consciousness, particularly when the patient does not recover as expected after a clinical seizure. Arrange urgent EEG or continuous EEG according to the clinical setting.⁴

Investigations

First-Line / Bedside & Emergency Diagnostics:

Point-of-Care Blood Glucose: Immediate bedside test.
Venous / Arterial Blood Gas (VBG/ABG): Evaluate pH, pCO2 (hypercapnia), pO2, lactate, carbon monoxide (HbCO).
Basic Bloods: FBC, Electrolytes, Urea, Creatinine, LFTs, Calcium, Magnesium, Phosphate.
Toxicology Screen: Serum paracetamol, salicylate levels, ethanol; urine drug screen.
12-Lead ECG: Check for conduction delays (TCA overdose), ischemia, or arrhythmias.
Chest X-ray / Urinalysis: Screen for hidden infectious sources.

Targeted / Secondary Neuro-Diagnostic Workup:

Non-Contrast Head CT: Indicated in trauma, focal exam, papilledema, acute sudden onset, fever with altered mental status, or unexplained ALOC.
CT Angiography (CTA) Head/Neck: Rule out basilar artery thrombosis or arterial dissection.
Lumbar Puncture (CSF Analysis): Cell count, protein, glucose, Gram stain, bacterial/viral PCR (HSV, VZV, enterovirus) for suspected CNS infection.
Electroencephalogram (EEG): Rule out NCSE or subclinical seizures.
MRI Brain (Diffusion-Weighted Imaging): Superior detection for early ischemic stroke, brainstem lesions, encephalitis, or posterior reversible encephalopathy syndrome (PRES).

For suspected bacterial meningitis, obtain blood samples and perform lumbar puncture first when safe and practical, but do not allow imaging or lumbar puncture to cause a clinically significant delay to empiric antibiotics. Suspected encephalitis also warrants prompt specialist-directed assessment and treatment.³

Critical Management

Immediate Stabilization Targets:

Airway: Seek immediate advanced airway assessment for GCS 8 or less, inadequate ventilation, inability to protect the airway, recurrent vomiting, or other urgent indications; individualise the decision to intubate.^1,2
Hemodynamics: Maintain Mean Arterial Pressure (MAP) >= 65 mmHg (or higher if elevated ICP is suspected to ensure adequate Cerebral Perfusion Pressure [CPP = MAP – ICP]).
Glycemic Control: Treat hypoglycemia immediately with IV dextrose; avoid rapid overcorrection of severe hyperosmolar states.

Suspected Elevated Intracranial Pressure (ICP):

Positioning: Elevate the head of bed to approximately 30 degrees, when cerebral perfusion permits, and maintain a neutral midline head position.⁵
Hyperosmolar Therapy: Administer IV Hypertonic Saline (3%) or IV Mannitol (0.5–1 g/kg) if signs of brain herniation (unilateral dilated pupil, decerebrate posturing) are present.
Hyperventilation: Temporary bridging measure (target pCO2 30–35 mmHg) only during active herniation crises.

Give parenteral thiamine promptly when Wernicke encephalopathy is suspected, before or alongside glucose when feasible. Treat confirmed hypoglycaemia immediately; do not postpone glucose while obtaining thiamine.¹

References

Schiff N. Overview of coma and impaired consciousness [Internet]. Merck Manual Professional Edition; updated 2026 Jul [cited 2026 Oct 2]. Available from: https://www.merckmanuals.com/professional/neurologic-disorders/coma-and-impaired-consciousness/overview-of-coma-and-impaired-consciousness
National Institute for Health and Care Excellence. Head injury: assessment and early management [Internet]. NICE guideline NG232. London: NICE; 2023 [cited 2026 Oct 2]. Available from: https://www.nice.org.uk/guidance/ng232
National Institute for Health and Care Excellence. Meningitis (bacterial) and meningococcal disease: recognition, diagnosis and management [Internet]. NICE guideline NG240. London: NICE; 2024 [cited 2026 Oct 2]. Available from: https://www.nice.org.uk/guidance/ng240
Herman ST, Abend NS, Bleck TP, Chapman KE, Drislane FW, Emerson RG, et al. Consensus statement on continuous EEG in critically ill adults and children, part I: indications. J Clin Neurophysiol. 2015;32(2):87-95. doi:10.1097/WNP.0000000000000166
Cook AM, Morgan Jones G, Hawryluk GWJ, Mailloux P, McLaughlin D, Papangelou A, et al. Guidelines for the acute treatment of cerebral edema in neurocritical care patients. Neurocrit Care. 2020;32(3):647-666. doi:10.1007/s12028-020-00959-7