Level of consciousness

The Glasgow Coma Scale8 provides the most useful hierarchical assessment of the level of consciousness. The responses to commands, calling the patient's name, and painful stimuli are observed for eye opening, limb movement, and voice. Painful stimuli such as supraorbital pressure for central stimulation and nail bed pressure for peripheral stimulation are useful and reproducible. Eye opening is relatively easy to assess, though the fixed and unresponsive opening of the eyes sometimes seen in deep coma must not be confused with the volitional or reflex opening of the eyes from a closed position in response to stimuli. All four limbs are tested individually for movement and the best response is recorded in assessing the Glasgow Coma Scale. An asymmetry between the responses may be of importance in the overall assessment (see below). Patients in lighter grades of coma still retain the ability to vocalise and may grimace and withdraw their limbs from pain. These responses are progressively lost as the coma deepens. It is important to test pain bilaterally in the periphery and cranially as patients may only vocalise or respond to painful stimuli on one side, raising the possibility of hemi-anaesthesia and providing evidence for a focal lesion. A grimace response to painful stimulation is believed to indicate intact cortical bulbar function,2 but there are patients in coma, particularly after hypoxic-ischaemic insults, who show grimace in response to minor peripheral stimulation yet have no associated peripheral motor response. When this situation is seen it always raises the question of a ventral pontine lesion or a cervical cord injury, but more commonly it evolves into a vegetative state and is, generally, a poor prognostic sign.

The level of coma should be documented serially and is one of the most important indicators of the need for further investigation. When the level of consciousness can be seen to be improving there is no need to make urgent decisions. When deterioration occurs then management decisions must be made. It may of course be correct, when the prognosis is recognised to be hopeless, to make the decision not to undertake further investigation or therapy.

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