Low blood sugar
HYPOGLYCEMIA, also known as low blood sugar, is defined as a blood glucose level less than 3mmol/L or approximately 50mg/dl.
Typically, the person with that blood sugar level on finger stick measurement from capillary blood has signs and symptoms of hypoglycemia and returns to normal after glucose is administered.
In a normal individual, blood sugar levels are constant throughout the day irrespective of meals and activity and tend to vary between 3mmol/L and 9mmol/L. This constant level is regulated through complex processes in the body that produce and utilise glucose.
The incidence of hypoglycemia varies and can be classified as: severe hypoglycemia, where the person becomes unconscious and needs to be revived with glucose or other drugs; low blood sugar levels without symptoms; symptoms suggestive of low blood sugar but the levels are normal and are becoming low for that individual; symptoms suggesting low blood sugar levels confirmed by measuring plasma glucose; and in persons in whom an event had occurred where the glucose levels are presumed to have been low.
Low blood sugar levels occur commonly in patients with diabetes mellitus, especially those who use insulin and certain blood sugar-lowering drugs such as the sulphonylureas, but may also occur in people who do not have diabetes mellitus.
Risk factors for low blood sugar in a diabetic include taking medication, such as insulin or blood sugar-lowering drugs and not eating adequately or missing meals as well as taking too much medication, and persons who have a problem absorbing meals due to intestinal diseases or complications after surgery such as gastric bypass. Other causes of low blood sugar can be due to liver or kidney failure, hormonal diseases, infections, drugs such as alcohol, foods such as ackee, tumours, and malnutrition.
SIGN AND SYMPTOMS
The signs and symptoms of hypoglycemia are usually nonspecific. Sometimes they are more obvious to the bystander than the patient and some diabetics may be unaware that they are having low blood sugar levels. It may even occur while they are sleeping.
The symptoms range from tremors, sweating, irritability, heart beating fast, headache, mood changes, problems concentrating, tiredness, and weakness in the body and limbs, to dizziness, blurred vision, slurred speech, seizures, and coma.
The brain uses an enormous amount of energy and glucose is its major fuel. In the absence of adequate glucose it uses other processes to form compounds such as ketone bodies, but these are limited in their use and brain function is soon severely impaired. The patient then becomes disoriented, sleepy, and may start to behave strangely. They can be combative and have seizures and later coma and death.
Low blood sugar can also affect the heart and cause abnormal rhythms, heart attacks and strokes. It can also cause eye changes and result in complications such as aspiration pneumonitis or pneumonia, where contents of the mouth and stomach go down the airway owing to the hypoglycemic patient becoming unconscious. Multiple episodes of hypoglycemia can cause impairment of brain function over time.
Treatment involves restoring blood sugar levels to normal, finding the cause, managing the complications and preventing further recurrences.
If the patient is conscious and can drink and eat, a meal high in carbohydrates or glucose paste in the mouth can be given to reverse the low blood sugar. If the patient is unconscious, nothing must be given to eat or drink as this can cause food to accidentally go down the airway. In these instances the patient should be taken to the emergency department for resuscitation and for glucose to be administered through the veins. An alternative is to give glucagon, which can be given through an injection in the muscle, if the patient has adequate stores of glycogen in the liver. It is not for patients who are malnourished, with poor liver stores or have liver failure. The blood glucose levels would be rechecked to ensure it returns to normal.
Patients are usually admitted to hospital if they are on oral diabetic drugs that have a long duration of action, such as the long-acting sulphonylureas, as the patient is at risk of becoming hypoglycemic again soon, if they have liver or kidney failure, if no cause of the low blood sugar can be found so further investigation is needed, if the patient has severe infection or does not respond to therapy.
Diabetics who took too much insulin or missed a meal whose blood sugar levels have returned to normal having got glucose intravenously and the sugar levels remain normal and are otherwise without illnesses are educated and discharged from hospital for follow-up at their general practitioner or endocrinologist.
Dr Romayne Edwards is a consultant emergency physician at the University Hospital of the West Indies and an associate lecturer at the University of the West Indies.