Disorders of consciousness: Clinical

One of the many higher-order functions of our brains is maintaining consciousness.

Consciousness includes both arousal or wakefulness, as well as awareness.

Now, arousal is maintained by a network of neurons in the pons and midbrain that form the ascending reticular activating system, or ARAS.

The ARAS sends out neuronal connections to both cerebral cortices, which are responsible for producing awareness.

So damage to the ARAS in the brainstem, both cerebral hemispheres, or damage to the tracts connecting them can affect a person’s consciousness.

Now, a coma is a state of profoundly decreased arousal resembling sleep, however, a comatose individual cannot be aroused by external stimuli.

“Stupor”, “obtundation”, and “lethargy” are terms that reflect states that fall between normal arousal and a coma, but individuals in these states can be aroused by external stimuli.

Arousability is assessed by noise stimulation, such as shouting in the individual’s ear, or somatosensory stimulation, like pressing on the supraorbital ridge or squeezing the trapezius muscle.

Now, the differential diagnosis for coma is large, but they fall into 4 broad categories: toxic, such as opioid toxicity, infectious, such as sepsis or meningitis and encephalitis, metabolic, which includes electrolyte imbalances or organ dysfunction, and structural, such as a stroke or subdural hemorrhage.

When a person is found to already be in a comatose state, it’s helpful to get information from witnesses, family members, friends, and paramedics, as well as from medical alert bracelets.