Altered States of Consciousness

Key Features

Essentials of Diagnosis

• Reduction or alteration in cognitive and affective mental functioning and in arousability or attentiveness

• Acute onset

General Considerations

• The neurologic substrate for consciousness is the ascending reticular activating system in the brainstem, which extends the thalamus and paraventricular nucleus of the hypothalamus

• Large lesions of the cortex, especially bilateral lesions, can also cause coma

Clinical Findings

Symptoms and Signs

• Many terms, including obtundation, lethargy, somnolence, stupor, light coma, and deep coma, are used to describe the continuum from fully alert and aware to complete unresponsiveness

• Persistent vegetative state

  • Denotes a chronic condition in which there is preservation of the sleep-wake cycle

  • However, there is no awareness of self or the environment

  • No recovery of mental function

• Minimally conscious state

  • Denotes patients who do not meet criteria for persistent vegetative state

  • These patients occasionally may have purposeful movements

• Brain death refers to patients in coma without brainstem reflexes or spontaneous respirations

Differential Diagnosis

• Locked-in syndrome

  • Describes patients who are conscious but have no access to motor or verbal expression because of massive loss of motor function of the pontine portion of the brainstem

  • Vertical eye movements may be preserved

• Akinetic-mutism

  • Patient is aware, but does not initiate movement or follow commands

  • Caused by lesions of the frontal lobes

• Catatonia

  • Refers to patients with psychiatric illness

  • Patients retain ability to maintain trunk and limb postures

Diagnosis

Laboratory Findings and Diagnostic Procedures

• If the cause of the coma is not obvious, emergency laboratory tests must be obtained

• Initial tests include

  • An immediate blood glucose

  • Complete blood cell count

  • Urine obtained by catheterization if necessary

  • pH and electrolytes (including bicarbonate)

  • Serum urea nitrogen

  • Aspartate aminotransferase

  • Ammonia

• Urine, blood, and even gastric contents must be saved for toxin screen if the underlying cause is not obvious

• Blood culture and lumbar puncture often are necessary to rule out CNS infection

  • Papilledema is a relative contraindication to lumbar puncture prior to imaging

  • Often, a blood culture is obtained, antibiotics started, and imaging study of the brain done prior to a diagnostic lumbar puncture

  • If meningitis is suspected and a lumbar puncture is delayed or believed to be hazardous, antimicrobials should be started and the diagnostic lumbar puncture done later

• Tests that are helpful in obscure cases of coma include

  • Oxygen and carbon dioxide partial pressures

  • Serum and urine osmolality

  • Porphyrins

  • Lead levels

  • General toxicology screen

  • Serum amino acids

  • Urine organic acids

• Rarely, an emergency EEG aids in diagnosing the cause of coma

  • May correlate with the stage of coma and add prognostic information

  • Should be ordered if seizures are suspected

Imaging

• If severe head trauma or increased pressure is ...