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The Bare Essentials
  1. Eelco F M Wijdicks
  1. Professor E F M Wijdicks, Consultant, Neurosciences Intensive Care Unit, St Mary’s Hospital, Mayo Clinic, 200 first Street SW, Rochester, MN 55905, USA; wijde{at}

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Comatose patients present to the neurologist in several ways, particularly in the emergency room or intensive care unit. Given the many causes of coma, the central focus is a comprehensive evaluation that starts with a detailed history, although this has to be an account—at least to begin with—from bystanders, paramedics or even the police. This is followed by a neurological and general examination, gathering of key findings, localisation of the involved brain structure, neuroimaging and other laboratory tests. Sorting out the cause of coma is what neurologists do best— compared with other specialists. Of course the relatively recent availability of MRI has helped tremendously in understanding some cases of coma but brain imaging can be normal. Indeed, unravelling the cause of coma remains in many circumstances a clinical judgement.

Once treated, comatose patients can recover suddenly (eg, after quick correction of hypoglycaemia) but many patients have significant structural brain injury and take days to awaken. About 25% of patients stay in a prolonged state of unconsciousness but even then slow awakening is to be expected; only a very small fraction survive but never emerge from coma.

Definitions of Altered States of Consciousness

Impaired consciousness has been traditionally regarded as a problem with alertness, awareness of self, or both.

  • A disturbance of arousal—mainly a function of the reticular formation in the brainstem— leads to diminished alertness.

  • A disturbance involving content—a function of multiple cortical areas—leads to diminished awareness, and failure to accurately integrate what is perceived.

These two components are interrelated but sometimes dissociated. One can be awake and aware, awake but not aware and not awake and not aware.

Coma is best defined as a completely unaware patient unresponsive to external stimuli with only eye opening to pain with no eye tracking or fixation, and limb withdrawal to a noxious stimulus at best (often with reflex …

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  • Competing interests None

  • Provenance and peer review Not commissioned; externally peer reviewed.

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