Hypoglycemia is a common cause of altered mental status. Although classically associated with tachycardia, tremor, and diaphoresis, the predictive value of these manifestations is too low to be relied upon. As a result, all patients with altered consciousness require either rapid point-of-care testing of their glucose concentrations or empiric treatment for presumed hypoglycemia. When rapidly diagnosed and treated, hypoglycemic patients typically recover without sequelae. Delayed or incomplete therapy may lead to permanent neurologic dysfunction.
Adenosine triphosphate (ATP) provides the metabolic energy that fuels all critical cellular processes in all organs. In the adult brain, the anaerobic and aerobic metabolism of glucose through glycolysis and the citric acid cycle, respectively, are the primary sources of ATP (see Chap. 12). Although the adult brain can use fatty acids, amino acids, and ketones as alternate substrates for ATP synthesis, these are not adequate to sustain normal cerebral function in the setting of glucose deprivation. In the brain of fetuses and neonates, glucose is the only substrate for ATP production.81,99 Hypoglycemia is defined by organ dysfunction in the setting of inadequate concentrations of glucose; it cannot be safely defined by strict numerical values. The onset of hypoglycemia in both adults and children is followed rapidly by global cerebral dysfunction. In individuals with diabetes, the density of neuronal insulin receptors varies as a function of glycemic control so that diabetics with poor glycemic control have fewer neuronal glucose receptors and may experience hypoglycemic symptoms at much higher concentrations of glucose than those who are normally euglycemic. An important study of diabetics demonstrated that the mean blood glucose concentration for symptomatic hypoglycemia in poorly controlled diabetics was 78 ± 5 mg/dL compared with 53 ± mg/dL in normal control subjects.11 Hypoglycemia may cause neuropsychiatric sequelae effects that are clinically indistinguishable from those of other toxic-metabolic and structural brain injuries, which may include focal stroke syndromes, movement disorders, seizures, irritability, confusion, delirium, coma, and irreversible encephalopathy.3,33,59,67,69,70,85,103,108 The heart is partially dependent on glucose for energy production. Hypoglycemia causes myocardial stress that may manifest as angina and or dysrhythmias. This is aggravated by the systemic catecholamine response to hypoglycemia.34,62,68,71,72
The history and physical examination do not reliably detect patients who are hypoglycemic.47 Tachycardia, diaphoresis, pallor, hypertension, tremors, hunger, and restlessness tend to predominate when the decline in blood glucose concentration is rapid. These signs and symptoms may be blunted or absent from the use of β-adrenergic antagonists. Central nervous system signs of neuroglycopenia are nonspecific. They include visual disturbances, psychiatric disturbances, confusion, stupor, coma, seizures, and focal neurologic findings.67,86 In children, the only sign of neuroglycopenia may be lethargy or irritability.110
In most cases, the rapid correction of hypoglycemia by the administration of 0.5 to 1.0 g/kg of concentrated intravenous (IV) dextrose (6536232) immediately reverses these neurologic and ...