For detailed guidance, see Chapters 1, 59, 112 (airway management), 11 and 113 (management of respiratory failure) and 2 (management of hypotension and shock).

• If blood glucose is <4.0 mmol/L, give 100 mL of 20% glucose or 200 mL of 10% glucose over 15–30 min IV, or glucagon 1 mg IV/IM/SC.
• Recheck blood glucose after 10 min, if still below 4.0 mmol/L, repeat the above IV glucose treatment.
• In patients with malnourishment or alcohol-use disorder, there is a remote risk of precipitating Wernicke's encephalopathy by a glucose load: prevent this by giving thiamine 100 mg IV before or shortly after glucose administration. See Chapter 81 for further management of hypoglycaemia.

• Take into account prehospital treatment. Give lorazepam (which is less likely to cause respiratory suppression) 0.1 mg/kg (typically 4–8 mg) IV over 5–10 min (Table 16.2), midazolam 10 mg buccally (NICE-recommended, but only licensed in patients <18 years), or diazepam 10–20 mg IV at a rate of <2.5 mg/min (faster injection rates carry the risk of sudden apnoea).
• If the seizure does not terminate, give a second dose, to a maximum total dose of lorazepam 8 mg or diazepam 40 mg.
• See Chapter 16 for further management of seizures/status epilepticus.

• If the respiratory rate is <12/min, or the pupils are pinpoint, or there is other reason to suspect opioid poisoning, give naloxone 800μgm IV every 2–3 min up to a total dose of 3200μgm or until the respiratory rate is >15/min.
• If there is a response to bolus naloxone, start an IV infusion: add naloxone 2000μgm to 500 mL glucose 5% or normal saline (4μgm/mL) and titrate against the respiratory rate and conscious level. The plasma half-life of naloxone is 1h, shorter than that of most opioids.
• In patients who have taken partial opioid agonists such as buprenorphine, methadone and tramadol, repeated large (1200μgm) doses of naloxone may be required to achieve a satisfactory response.
• If there is no response to naloxone, opioid poisoning is excluded.

Give flumazenil 200μgm IV over 15s; if needed, further doses of 100μgm can be given at 1-min intervals up to a total dose of 2 mg.

• Document the level of consciousness in objective terms, using the Glasgow Coma Scale (see Figure 3.2).
• Examine for signs of head injury (e.g. scalp laceration, bruising, bleeding from an external auditory meatus or from the nose). If there are signs of head injury, assume additional cervical spine injury until proved otherwise: the neck must be immobilized in a collar and X-rayed before you check for neck stiffness and the oculocephalic response.
• Check for neck stiffness.
• Record the size of pupils and their response to bright light (Figure 3.3). Examine the fundi.
• Check the oculocephalic response. This is a simple but important test of an intact brainstem. Rotate the head to left and right. In an unconscious patient with an intact brainstem, both eyes rotate in the opposite direction from movement of the head.
• Examine the limbs: tone, response to a painful stimulus (nailbed pressure), tendon reflexes and plantar responses.

The differential diagnosis for reduced consciousness can be split into three groups on the basis of the presence or absence of focal signs and meningism (Table 3.1).

• If bacterial meningitis or viral meningo-encephalitis are possible (because of fever and meningism), empirical anti-microbial therapy (with cefotaxime (plus ampicillin in patients over 55 or at increased risk of listeria infection) and aciclovir) should be started immediately, after taking blood for culture. See Chapters 68 and 69.
• If acute adrenal insufficiency is possible (Chapter 90) give hydrocortisone 200 mg IV. Fludrocortisone is not required in addition as this dose of hydrocortisone has sufficient mineralocorticoid action.
• If CT shows a mass lesion or hydrocephalus, seek urgent advice from a neurosurgeon