Pathophysiology
Clinical meaning
Consciousness requires two components: arousal (maintained by the ascending reticular activating system - ARAS - in the brainstem pons and midbrain projecting through the thalamus to the cortex) and awareness (mediated by the cerebral cortex, particularly the frontoparietal association areas). Altered mental status (AMS) results from dysfunction of either the ARAS (causing reduced arousal - obtundation, stupor, coma) or bilateral cortical hemispheres (causing impaired awareness - confusion, delirium). Unilateral cortical lesions typically produce focal deficits (aphasia, neglect) without impaired consciousness unless they cause mass effect compressing the contralateral hemisphere or brainstem. The AEIOU-TIPS mnemonic organizes the broad differential: A (Alcohol, Acidosis), E (Endocrine/Electrolytes, Encephalopathy, Epilepsy), I (Infection, Insulin/hypoglycemia), O (Oxygen/Overdose/Opiates), U (Uremia), T (Trauma, Temperature), I (Increased ICP, Intracranial pathology), P (Psychiatric, Poisoning), S (Stroke, Shock, Seizure). Delirium (acute confusional state) is the most common presentation of AMS in hospitalized patients: characterized by acute onset, fluctuating course, inattention, and disorganized thinking. It results from diffuse neurotransmitter imbalance (acetylcholine deficiency and dopamine excess in most cases) and is a medical emergency with increased mortality and long-term cognitive consequences if not promptly...