Pathophysiology of acute brain dysfunction: what's the cause of all this confusion?

PURPOSE OF REVIEW: To survey the recent medical literature examining the pathophysiology of acute brain dysfunction (delirium and coma) in the ICU. RECENT
FINDINGS: Clinical risk factors for brain dysfunction in the ICU continue to be elucidated and prediction models developed. Multiple studies have identified sedatives, especially benzodiazepines, as modifiable risk factors for delirium. Imaging studies examining global brain disorders have demonstrated white matter lesions and brain atrophy to be associated with delirium. Endothelial dysfunction, increased blood-brain barrier permeability, and reduced blood flow have also been implicated in cerebral perfusion abnormalities associated with brain dysfunction. The response of the brain to inflammation, including activation of microglia and neuronal apoptosis, leads to synaptic and neurochemical disturbances. Decreased availability of acetylcholine during critical illness leads to decreased counter-regulatory activity in response to inflammatory disease states, likely causing additional injury and further neurotransmitter imbalances. Dopamine, norepinephrine, and serotonin excess and their respective amino acid precursors have also been associated with brain dysfunction.
SUMMARY: The multifactorial pathophysiology of acute brain dysfunction remains incompletely understood. Multiple clinical risk factors have been identified and numerous pathophysiologic pathways have been hypothesized. Future research is required to investigate the roles of these pathways on differing clinical presentations, potential therapeutic options, and patient outcomes.