Delirium is an acute confusional state on the spectrum of acute brain dysfunction that is suspected to be precipitated by an underlying medical etiology. Current research in delirium suggests 2 distinct, but sometimes coexisting, etiologies: (1) Direct brain insults such as hypotension, hypoxia, trauma, and toxins; or (2) aberrant stress responses induced by physiologic insults such as infections or surgery.26 While both categories represent end-organ damage of the brain, there is overlap between the physiologic underpinnings of the 2 groups, and this dichotomy serves as a framework for understanding delirium.27 Direct brain insults are defined as entities that affect the energy supply or consumption of the brain or have otherwise disruptive effects on the brain architecture and pathways. Aberrant stress response more closely describes the cellular response to systemic insults. The current belief is that stressors and the ensuing sympathetic surge are associated with a preponderance of inflammatory cytokines, resulting in an imbalance of neurotransmitters. There is an increase in the dopaminergic tone and a decrease in acetylcholine in the central nervous system; however, there is some thought that the different psychomotor subtypes each have a unique mix of neurotransmitter dysregulation, and delirium represents the final common pathway of multiple pathologic neurotransmitter pathways.7,28,29
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