Acute care must always start with basic life support: a patent airway, ventilation, and circulation. An easily reversible cause of coma, if treated sufficiently rapidly, is hypoxia secondary to airway obstruction or pulmonary disease. However, central nervous system lesions can also cause abnormal respiratory patterns. Quickly observing the patient's respiratory pattern may help with localization as described above.

Comatose patients are frequently intubated for one of two reasons: ventilatory failure or airway protection. Airway protective reflexes of gagging and coughing may be lost in coma, increasing the risk of aspiration. Also, the tongue and oropharynx relax, increasing the chance of airway obstruction. The aspiration risk is increased if gastric lavage is used for suspected toxic ingestion without a cuffed endotracheal tube in place.

Prior to intubation, the stability of the cervical spine must be assessed, particularly in patients with trauma. Also, patients who lose consciousness acutely may fall and injure their cervical spine. Because patients with altered mental status may be unable to tell the examiner about neck pain, all comatose patients should be treated as if their neck is injured unless a reliable witness can attest to the absence of a fall or other potential for neck injury.

A patient in a hard cervical collar may be difficult to intubate orally as neck extension cannot and should not be attempted; therefore nasotracheal intubation may be preferred. The one exception to nasal intubation would be if there is a suspected basilar skull fracture. If raised intracranial pressure is at all possible, 100 mg lidocaine (lignocaine) or 300 mg thiopental (thiopentone) should be administered intravenously 1 min prior to intubation to blunt the rise in intracranial pressure normally associated with intubation.

A key part of the immediate evaluation is the patient's vital signs, which may themselves help to decide the cause of unconsciousness. Severe hypotension can be sufficient to cause symptomatic central nervous system hypoperfusion and should be corrected urgently with fluids and/or vasopressors. Conversely, a severely elevated blood pressure may cause hypertensive encephalopathy, which is a neurological emergency requiring rapid treatment.

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