Chapter 126 Insulin.: Insulin receptors on the beta cells of the pancreas sense elevations in blood glucose concentration and trigger insulin release into the blood. For incompletely understood reasons, glucose taken by mouth evokes more insulin release than parenteral glucose does. Certain amino acids induce insulin release and even cause hypoglycemia in some patients. Sulfonylurea oral hypoglycemic agents work, in part, by stimulating the release of insulin from the pancreas. Glucose Regulatory Mechanisms.: Maintenance of the normal plasma glucose concentration requires precise matching of glucose use and endogenous glucose production or dietary glucose delivery. The regulatory mechanisms that maintain systemic glucose balance involve hormonal, neurohumoral, and autoregulatory factors. Glucose regulatory hormones include insulin, glucagon, epinephrine, cortisol, and growth hormone. Insulin is the main glucose-lowering hormone. Insulin suppresses endogenous glucose production and stimulates glucose use. Insulin is secreted from the beta cells of the pancreatic islets into the hepatic portal circulation and has important actions on the liver and the peripheral tissues. Insulin stimulates glucose uptake, storage, and use by other insulin-sensitive tissues, such as fat and muscle. The American Diabetes Association (ADA) defines four major types of diabetes mellitus: type 1 diabetes mellitus, type 2 diabetes mellitus, gestational diabetes, and diabetes due to secondary disease processes or drugs. The 1997 National Diabetes Data Group report discontinued the use of the terms insulin-dependent diabetes mellitus and non–insulin-dependent diabetes mellitus because they are confusing and clinically inaccurate. In addition, use of Arabic numerals (1 and 2) instead of Roman numerals is the standard. The most recent update to the standards of care for diabetes was published in January 2011.1 The diagnostic criteria for diagnosis of diabetes were changed in 2010 from the previous standards of elevated fasting glucose concentration and abnormal result of the 2-hour oral glucose tolerance test (OGTT) to use of the hemoglobin A1c (HbA1c) value as the preferred confirmatory test.1 An HbA1c value above 6.5% is now considered diagnostic of diabetes. However, the fasting plasma glucose concentration and 2-hour OGTT are still considered valid, as is the presence of a random glucose measurement of more than 200 mg/dL in a nonfasting patient. In addition, the use of fasting plasma glucose concentration may help identify patients at risk for diabetes (if their glucose concentration is elevated but not crossing the threshold for diagnosis of diabetes). Type 1 Diabetes Mellitus.: Type 1 diabetes is characterized by abrupt failure of production of insulin with a tendency to ketosis even in the basal state. Parenteral insulin is required to sustain life. From 85 to 90% of patients with type 1 diabetes demonstrate evidence of one or more autoantibodies implicated in the cell-mediated autoimmune destruction of the beta cells of the pancreas. Strong human leukocyte antigen (HLA) associations are also found in type 1 diabetes. The autoimmune destruction has multiple genetic predispositions and may be related to undefined environmental insults. Type 2 Diabetes Mellitus.: Patients with type 2 diabetes may remain asymptomatic for long periods and show low, normal, or elevated levels of insulin because of insulin resistance. Ketosis is rare in type 2 disease. Patients have a high incidence of obesity. Hypertriglyceridemia is also frequently noted. No association exists with viral infections, islet cell autoantibodies, or HLA expression. Hyperinsulinemia may be related to peripheral tissue resistance to insulin because of defects in the insulin receptor. Defects in muscle glycogen synthesis have an important role in the insulin resistance that occurs in type 2. Gestational Diabetes.: Gestational diabetes “mellitus” is characterized by an abnormal OGTT result that occurs during pregnancy and either reverts to normal during the postpartum period or remains abnormal. The clinical pathogenesis is thought to be similar to that of type 2. The clinical presentation is usually nonketotic hyperglycemia during pregnancy. Screening is performed around the 24th to 28th week with a 75-g oral glucose load in a woman with no prior history of diabetes. Diabetes due to Other Causes.: Myriad other causes of diabetes have been identified; these include chronic pancreatitis, cystic fibrosis, genetic defects in the beta cell or in insulin receptors, and chemical induced (such as Vacor and chemotherapeutic, antipsychotic, or antiretroviral medications). The management of diabetes due to these conditions is cause specific and depends on whether the underlying pathophysiologic process more closely resembles type 1 or type 2 diabetes. Impaired Glucose Tolerance.: Impaired glucose tolerance (IGT) and its analogue, impaired fasting glucose (IFG), are considered to identify individuals at high risk for development of diabetes. This group is composed of persons whose plasma glucose levels are between normal and diabetic and who are at increased risk for the development of diabetes and cardiovascular disease. The pathogenesis is thought to be related to insulin resistance. Presentations of IGT/IFG include nonketotic hyperglycemia, insulin resistance, hyperinsulinism, and often obesity. IGT/IFG differs from the other classes in that it is not associated with the same degree of complications of diabetes mellitus. Many of these patients even spontaneously have normal glucose tolerance. One should not be complacent about the patient with IGT because the decompensation of this group into the category of diabetes mellitus is 1 to 5% per year.1 The prevalence of diabetes is difficult to determine because many standards have been used. Regardless, the most recent data estimate that 8.3% of Americans of all ages and 11.3% of all adults older than 20 years have diabetes.1 Approximately 215,000 Americans younger than 20 years have diabetes. Of these, 5 to 10% have type 1, and 90 to 95% have type 2; other types account for 1 to 5% of cases. The peak age at onset of type 1 diabetes is 10 to 14 years. Approximately 1 of every 600 schoolchildren has this disease. In the United States the prevalence of type 1 is approximately 0.26% by the age of 20 years, and the lifetime prevalence approaches 0.4%. The annual incidence among persons from birth to 16 years of age in the United States is 12 to 14 per 1 million population. The incidence is age dependent, increasing from near-absence during infancy to a peak occurrence at puberty and another small peak at midlife.1 As a rule, any random plasma glucose level above 200 mg/dL, HbA1c value above 6.5%, fasting plasma glucose concentration above 126 mg/dL, or 2-hour postload OGTT is sufficient to establish the diagnosis of diabetes. In the absence of hyperglycemia with metabolic decompensation, these criteria should be confirmed by repeated testing on a different day. Confirmation can be made by the same test or two different tests (fasting plasma glucose and HbA1c, for example). A value of 150 mg/dL is likely to distinguish diabetic from nondiabetic patients more accurately. Formal OGTTs are unnecessary except during pregnancy or in patients who are thought to have diabetes but who do not meet the criteria for a particular classification. The World Health Organization and ADA provide protocols for performance of the OGTT.1 Hypoglycemia is a common problem in patients with type 1 diabetes, especially if tight glycemic control is practiced; it may be the most dangerous acute complication of diabetes. The estimated incidence of hypoglycemia in diabetic patients is 9 to 120 episodes per 100 patient-years. As significant efforts continue to keep both fasting and postprandial glucose concentrations within the normal range, the incidence of hypoglycemia may increase. The most common cause of coma associated with diabetes is an excess of administered insulin with respect to glucose intake. Hypoglycemia may be associated with significant morbidity and mortality.2 Severe hypoglycemia is usually associated with a blood glucose level below 40 to 50 mg/dL and impaired cognitive function. Hypoglycemia without warning symptoms, or hypoglycemia unawareness, is a dangerous complication of type 1 diabetes probably caused by previous exposure to low blood glucose concentrations.2 Even a single hypoglycemic episode can reduce neurohumoral counter-regulatory responses to subsequent episodes. Other factors associated with recurrent hypoglycemic attacks include overaggressive or intensified insulin therapy, longer history of diabetes, autonomic neuropathy, and decreased epinephrine secretion or sensitivity. Treatment of hypoglycemia secondary to oral hypoglycemic agents depends on the agent. Metformin and the thiazolidinedione agents rarely cause significant or prolonged hypoglycemia, whereas sulfonylureas, which are insulin secretagogues, do cause hypoglycemia. Sulfonylurea oral hypoglycemic agents pose special problems because the hypoglycemia they induce tends to be prolonged and severe. Patients with an overdose of sulfonylurea hypoglycemic agents should have a minimum observation period of 24 hours if hypoglycemia is recurrent in the ED after management of the initial episode. Patients at risk for hypoglycemia from oral sulfonylureas include patients with impaired renal function, pediatric patients, and patients who are naïve to hypoglycemic agents. Although symptoms may occur after an overdose, several case reports in patients with renal failure and pediatric patients describe refractory hypoglycemia after ingestion of a single pill. One case series of pediatric patients presenting with sulfonylurea ingestion who were euglycemic initially demonstrated an average time to onset of 8 hours to the initial hypoglycemic episode.3 However, onset of symptoms was delayed up to 18 hours in some patients. As a result, we recommend 23 hours of observation for patients with known or suspected ingestion of hypoglycemic agents. A patient with hypoglycemia from sulfonylureas, in addition to standard glucose replacement, frequently requires treatment with an agent to inhibit further insulin release, such as octreotide, a somatostatin analogue. Several case series have described the use of octreotide in both adult and pediatric patients suffering from sulfonylurea-induced hypoglycemia, frequently reporting successful results with a significant decrease in the number of episodes of recurrent hypoglycemia. A randomized clinical trial concluded that patients receiving octreotide had a decreased glucose supplementation requirement.4 No single set protocol for use has been described; however, typical adult doses have ranged from 50 to 100 µg intravenously or subcutaneously every 12 hours, and pediatric dosages have ranged from 25 to 50 µg intravenously or subcutaneously. Whereas experience thus far with octreotide has been positive, it does not obviate the need for prolonged observation and serial glucose measurements.
Diabetes Mellitus and Disorders of Glucose Homeostasis
Diabetes Mellitus
Principles of Disease
Types of Diabetes
Epidemiology
Diagnostic Strategies
Hypoglycemia
Principles of Disease
Management
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Diabetes Mellitus and Disorders of Glucose Homeostasis
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