Hypoglycaemia is a condition in which the blood glucose (blood sugar) level falls below the normal range, typically defined as below 4.0 mmol/L in adults. Glucose is the primary fuel source for the brain; when blood glucose falls too low, the brain is deprived of energy and neurological symptoms develop rapidly. The severity of symptoms increases with the degree and duration of hypoglycaemia.
Symptoms progress in stages. Early symptoms are driven by adrenaline release (the body’s attempt to raise blood glucose) and include sweating, trembling, palpitations, pallor, anxiety, and hunger. As blood glucose falls further, neuroglycopaenic symptoms develop: confusion, difficulty concentrating, slurred speech, visual disturbances, and abnormal behaviour. Severe hypoglycaemia can cause loss of consciousness, seizures, and, in extreme cases, cardiac arrest.
In the intensive care unit following cardiac arrest, tight control of blood glucose is an important element of post-resuscitation management. Both hypoglycaemia and hyperglycaemia (high blood glucose) are harmful to the injured brain and are associated with worse neurological outcomes. Current guidance recommends maintaining blood glucose between 6 and 10 mmol/L in post-arrest patients, with regular monitoring and insulin infusions used to achieve this target.
Hypoglycaemia most commonly occurs as a complication of diabetes treatment (insulin or sulphonylurea medications). People with diabetes who take insulin should carry fast-acting glucose (tablets, sugary drink, or gel) at all times and be aware of their personal warning symptoms. Family members and carers should know how to recognise and treat hypoglycaemia and when to call an ambulance.
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