Coma

Eye response

Eyelids remain closed with pain

Eyelids closed but open to pain

Eyelids closed but open to loud voice

Eyelids open but not tracking

Eyelids open or opened, tracking or blinking to command

Motor response

No response to pain or generalized myoclonus status

Extension response to pain

Flexion response to pain

Localizing to pain

Thumbs up, fist or peace sign

Brainstem reflex

Absent pupil, corneal and cough reflex

Pupil and corneal reflexes absent

Pupil or corneal reflexes absent

One pupil wide and fixed

Pupil and corneal reflexes present

Respiration

Breathes at ventilator rate or apnea

Breathes above ventilator rate

Not intubated, irregular breathing

Not intubated, Cheyne-Stokes breathing pattern

Not intubated, regular breathing pattern

Total score is the sum points for all four parameters. Minimum score = 0, maximum score = 16. the lower the score, the deeper the coma

An U score on ACDU, a P score on AVPU, or a GCS score ≤8 indicates coma.

5.3 Diagnostic Markers

History regarding the circumstances of coma occurrence should be obtained from bystanders.

Similarly, the patient’s previous clinical history should be obtained.

The basic neurological examination provided by the aforementioned coma scales should be extended to better evaluate cranial nerve function, somatic motor and sensory function, and respiration patterns.

General clinical examination and appropriate blood and urine analyses are mandatory to rule out some causes of coma and to provide baseline assessment of patients.

Noncontrast computed tomography (CT) – Is the examination of choice to detect structural lesions and intracerebral bleeding. CT angiography: intracerebral vessel stenosis. Perfusion CT: cerebral areas of hypoperfusion.

MR – Is not always readily available, is time-consuming; should be reserved to hemodynamically stable patients.

Cerebral angiography – To determine the source of subarachnoid hemorrhages or thrombosis.

Lumbar puncture: meningitis or subarachnoid hemorrhage. Should be performed after CT scan to avoid its ominous side effects.

Electroencephalogram (EEG) for seizures (see Chap. 2). Its routine use in comatose patients in the ICU has been advocated to rule out subclinical status epilepticus.

5.4 Differential Diagnosis

The diagnostic tools described in the previous paragraph are essential in the work-up of the differential diagnosis of the causes of coma. Appropriate treatment of the underlying causes is mandatory to improve the prognosis of comatose patients.

Another differential diagnosis challenge may be the differentiation of coma from another state mimicking it, such as the following:

The locked-in syndrome. Locked-in patients are de-efferented and tetraplegic; not unconscious. Vertical eye movements and eyelid opening are preserved. EEG reactive alpha rhythm is preserved (alpha coma).
Guillain-Barré syndrome. In rare cases, it can lead to complete de-efferentation.
Status epilepticus and post-critical state.
Psychiatric states. Some severe psychiatric conditions may mimic coma.

5.5 Prognosis

No comprehensive multifactorial model for outcome prognosis in comatose patients is available. Basically, the prognosis of coma depends not only upon its severity and duration, but also upon its underlying etiology. Coma is not a disease, but the expression of an underlying pathology.

Coma produced by hypoxia-anoxia due to cardiac arrest (CA) is considered a paradigm for non-traumatic coma. Moreover, it should be kept in mind that CA may occur as a consequence of any event per se causing unconsciousness: in these cases, the prognostic burden is carried both by CA-related hypoxia-anoxia and by the original triggering event.

Neurological outcome after coma is usually measured with the Cerebral Performance Category scale (CPC – see Table 5.2) [6] or the Modified Ranking scale (see Table 5.3) [7]. For coma ensuing after traumatic brain injury, specific scales such as the Glasgow Outcome Scale and the extended Glasgow Outcome Scale have been devised (see Chap. 2).

Table 5.2

Cerebral Performance Category (CPC)

1	Good cerebral performance: conscious, alert, able to work, might have mild neurological or psychological deficit
2	Moderate cerebral disability: conscious, alert, sufficient cerebral function for independent activities of daily life. Able to work in sheltered environment	Good outcome
3	Severe cerebral disability: conscious, dependent on other for daily support because of impaired brain function. Ranges from ambulatory state to severe dementia or paralysis
4	Coma or vegetative state: any degree of coma without the presence of all brain death criteria. Unawareness, even if appears awake (vegetative state) without interaction with environment; may have spontaneous eye opening and sleep/awake cycles. Cerebral unresponsiveness	Poor outcome
5	Brain death