Alteration of consciousness involves reduced awareness initially of self, then of environment, and then the inability to be aroused. Different terms are used to describe alterations in consciousness. Confusion represents a loss of clear thinking and impaired cognition and decision making. Disorientation accompanies confusion. Delirium is a disturbed ability to focus, sustain, or shift attention, and children often have extreme mental or motor excitement. Lethargy resembles slumber with some arousal with moderate stimulation but also with quick return to the sleep state. Stupor is a condition of deep sleep or unresponsiveness except to repetitive vigorous stimuli. A coma is a state in which a person is unresponsive to all stimuli, including pain, and is the most profound degree of altered consciousness.

Arousal depends on intact communication between the reticular activating system (RAS) and its targets in the hypothalamus, thalamus, and cerebral cortex. The RAS is located within the brainstem and functions to regulate arousal in response to signals from the environment. Consciousness can be altered by dysfunction within the brainstem, impairment of both cerebral hemispheres, or by insults that globally depress neuronal activity. In children, there are many causes of altered consciousness, with the differentiation being between structural and nonstructural or medical conditions. A mnemonic exists that is helpful for remembering general categories: AEIOU TIPS. A- alcohol, abuse of substance; E-epilepsy, encephalopathy, electrolyte abnormalities, endocrine; I-insulin, intussusception; O-overdose, oxygen deficiency; U-uremia; T-trauma, temperature abnormality, tumor; I-infection; P-poisoning, psychiatric condition; S-shock, stroke. Table 85.1 provides a list of differential diagnoses.