Hypoglycemia
Hypoglycemia: Excerpt from Handbook of Diseases
An abnormally low glucose level in the bloodstream, hypoglycemia occurs when glucose burns up too rapidly, when the glucose release rate falls behind tissue demands, or when excessive insulin enters the bloodstream.
Hypoglycemia is classified as reactive or fasting. Reactive hypoglycemia results from the reaction to the disposition of meals or the administration of excessive insulin. Fasting hypoglycemia causes discomfort during long periods of abstinence from food, for example, in the early morning hours before breakfast.
Although hypoglycemia is a specific endocrine imbalance, its symptoms are commonly vague and depend on how quickly the patient’s glucose levels drop. If not corrected, severe hypoglycemia may result in coma, irreversible brain damage, and death.
Causes
The two forms of hypoglycemia have different causes and occur in different types of patients.
Reactive hypoglycemia
Several forms of reactive hypoglycemia occur. In a diabetic patient, it may result from administration of too much insulin or, less commonly, too much oral antidiabetic medication. In a mildly diabetic patient (or one in the early stages of diabetes mellitus), reactive hypoglycemia may result from delayed and excessive insulin production after carbohydrate ingestion.
Similarly, a nondiabetic patient may suffer reactive hypoglycemia from a sharp increase in insulin output after a meal. Sometimes called postprandial hypoglycemia, this type of reactive hypoglycemia usually disappears when the patient eats something sweet.
In some patients, reactive hypoglycemia may have no known cause (idiopathic reactive) or may result from total parenteral nutrition due to gastric dumping syndrome or from impaired glucose tolerance.
Fasting hypoglycemia
Fasting hypoglycemia usually results from an excess of insulin or insulin-like substance or from a decrease in counterregulatory hormones. It can be exogenous, resulting from such external factors as alcohol or drug ingestion, or endogenous, resulting from organic problems.
Endogenous hypoglycemia may result from tumors or liver disease. Insulinomas, small islet cell tumors in the pancreas, secrete excessive amounts of insulin, which inhibits hepatic glucose production. They’re generally benign (in 90% of patients).
Extrapancreatic tumors, although uncommon, can also cause hypoglycemia by increasing glucose utilization and inhibiting glucose output. Such tumors occur primarily in the mesenchyma, liver, adrenal cortex, GI system, and lymphatic system. They may be benign or malignant.
Among nonendocrine causes of fasting hypoglycemia are severe liver diseases, including hepatitis, cancer, cirrhosis, and liver congestion associated with heart failure. All these conditions reduce the uptake and release of glycogen from the liver.
Some endocrine causes include destruction of pancreatic islet cells; adrenocortical insufficiency, which contributes to hypoglycemia by reducing the production of cortisol and cortisone needed for gluconeogenesis; and pituitary insufficiency, which reduces corticotropin and growth hormone levels.
Causes in infants and children
Hypoglycemia is at least as common in neonates and children as it’s in adults. Usually, infants develop hypoglycemia because of an increased number of cells per unit of body weight and because of increased demands on stored liver glycogen to support respirations, thermoregulation, and muscle activity.
In full-term neonates, hypoglycemia may occur 24 to 72 hours after birth and is usually transient. In neonates who are premature or small for gestational age, onset of hypoglycemia is much more rapid — it can occur as soon as 6 hours after birth — due to their small, immature livers, which produce much less glycogen. A rare cause of hypoglycemia in infants is nesidioblastosis, a benign condition of the insulin-producing islet cells. The treatment is surgical.
Maternal disorders that can produce hypoglycemia in infants within 24 hours after birth include diabetes mellitus, pregnancy-induced hypertension, erythroblastosis, and glycogen storage disease.
Signs and symptoms
Reactive hypoglycemia causes fatigue, malaise, nervousness, irritability, trembling, tension, headache, hunger, cold sweats, and rapid heart rate. The same clinical effects usually characterize fasting hypoglycemia.
In addition, fasting hypoglycemia may cause central nervous system (CNS) disturbances, for example, blurred or double vision, confusion, motor weakness, hemiplegia, seizures, and coma.
In infants and children, signs and symptoms of hypoglycemia are vague. A neonate’s refusal to feed may be the primary clue to underlying hypoglycemia. Associated CNS effects include tremors, twitching, weak or high-pitched cry, sweating, limpness, seizures, and coma.
Diagnosis
Reagent or glucose reagent strips provide quick screening methods for determining blood glucose level. A color change that corresponds to less than 45 mg/dl indicates the need for a venous blood sample.
Laboratory testing confirms the diagnosis by showing decreased blood glucose values. The following values indicate hypoglycemia:
❑ full-term neonates — less than 30 mg/dl before a feeding; less than 40 mg/dl after a feeding
❑ preterm neonates— less than 20 mg/dl before a feeding; less than 30 mg/dl after a feeding
❑ children and adults — less than 40 mg/dl before a meal; less than 50 mg/dl after a meal.
In addition, a 5-hour glucose tolerance test may be administered to provoke reactive hypoglycemia. After a 12-hour fast, laboratory testing to detect plasma insulin and plasma glucose levels may identify fasting hypoglycemia.
Treatment
Urgent treatment may be provided by glucose tablets, candy, or fluids if the patient is alert. Dextrose 50% solution is given for emergency treatment, followed by a constant infusion in children and adults. Reactive hypoglycemia and fasting hypoglycemia require different treatments.
Reactive hypoglycemia
Effective treatment of reactive hypoglycemia requires dietary modification to help delay glucose absorption and gastric emptying. Usually, this includes small, frequent meals; ingestion of complex carbohydrates, fiber, and fat; and avoidance of simple sugars, alcohol, and fruit drinks.
The patient may also receive anticholinergic drugs to slow gastric emptying and intestinal motility and to inhibit vagal stimulation of insulin release.
Fasting hypoglycemia
In fasting hypoglycemia, surgery and drug therapy are usually required. In patients with insulinoma, removal of the tumor is the treatment of choice. Drug therapy may include nondiuretic thiazides, such as diazoxide, to inhibit insulin secretion, streptozocin, and hormones, such as glucocorticoids and long-acting glycogen.
In neonates
Therapy for neonates who have hypoglycemia or who are at risk of developing it includes preventive measures. A hypertonic solution of dextrose 10%, calculated at 5 to 10 ml/kg of body weight administered I.V. over 10 minutes and followed by 4 to 8 mg/kg/minute for maintenance, should correct a severe hypoglycemic state in neonates.
To reduce the chance of hypoglycemia in high-risk neonates, they should receive feedings — either breast milk or a solution of dextrose 5% or 10% in water — as soon after birth as possible.
Special considerations
❑ Watch for signs of hypoglycemia (such as poor feeding) in high-risk neonates.
❑ Monitor infusion of hypertonic glucose in the neonate to avoid hyperglycemia, circulatory overload, and cellular dehydration. Terminate glucose solutions gradually to prevent hypoglycemia caused by hyperinsulinemia.
❑ Monitor the effects of drug therapy, and watch for the development of adverse effects.
❑ Teach the patient which foods to include in his diet (complex carbohydrates, fiber, and fat) and which foods to avoid (simple sugars and alcohol). Refer the patient and his family for dietary counseling as appropriate.
Book Source Details
- Book Title: Handbook of Diseases
- Author(s): Springhouse
- Year of Publication: 2003
- Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Handbook of Diseases
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2003
ISBN: 1-58255-266-5
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