TABLE 17-1. PROCESSES LEADING TO PATHOLOGIC DEPRESSION OF CONSCIOUSNESS

  1. Reticular formation involvement (less common cause of depressed consciousness)
    1. Supratentorial mass lesions that secondarily compress brain stem (e.g., neoplasm, abscess, herpes simplex encephalitis, infarction with swelling, and hemorrhage) (See Fig 24-2)
    2. Subtentorial mass or destructive lesions that compress or directly destroy brain stem (e.g., infarction, hemorrhage [brain stem or cerebellar], tumor, abscess)
  2. Bilateral hemispheric and reticular formation depression (most common cause of depressed consciousness) (see also Table 16-3), almost always metabolic depression
    1. Oxygen, substrate, or metabolic cofactor deficiencies (e.g., ischemia, hypoxia, hypoglycemia, vitamin deficiency)
    2. Toxic
      • Endogenous - renal failure, hepatic failure, pulmonary failure (carbon dioxide narcosis), endocrine hyper- or hypofunction
      • Exogenous (most often diagnosed cause of coma) - sedative drug overdose (e.g., barbiturates, alcohol, tranquilizers, opiates, etc.); acid poisons (e.g., methyl alcohol, paraldehyde, ethylene glycol); enzyme inhibitors (e.g., arsenic, lead and other heavy metals, insecticides, cyanide, salicylates), carbon monoxide.
      • CNS infection (meningitis, encephalitis)
    3. Acid-base or ionic abnormalities in CNS environment (including hyper- and hyponatrimia, hyperecalcemia, hypermagnesemia)
    4. Postictal (epileptic) diffuse depression
    5. Traumatic dysfunction without histologic structural change (concussion, diffuse axonal injury)
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