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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. However, delayed or incomplete therapy may lead to permanent neurologic dysfunction (Chap. 53).
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In 1891, Fisher performed the unbelievable feat of identifying the 16 possible different spatial configurations of aldohexose (C6H12O6), the most prominent member being dextrose or d-glucose.38 This discovery won him the 1902 Nobel Prize in chemistry. The diverse manifestations of hypoglycemia and the treatment of severe cases with intravenous (IV) dextrose have been appreciated for decades.68
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Sugar is the general term used for sweet carbohydrates that are used as food. Simple sugars are called monosaccharides and include glucose (also known as dextrose, or d-glucose, as the l-isomer is hardly found in nature), fructose (also known as fruit sugar, the sweetest), and galactose. The disaccharides include maltose, lactose, and sucrose (sucrose is also known as table or granulated sugar).
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Sugars are found in the tissues of most plants, but are only present in sufficient concentrations for efficient extraction in sugarcane and sugar beet. Commercially, glucose is produced from the hydrolysis of starch. Several crops serve as the starch source, with maize being the most common in the United States.
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In humans, carbohydrates are absorbed and transported via two main systems. Sodium-dependent glucose transporters (SGLT1-6) are responsible for the intestinal glucose absorption.13 Their discovery represented the first description of the mechanism of “flux coupling” or cotransporting, in which transporting one substrate down its concentration gradient creates energy that can then be used to transport a second substrate against a concentration gradient. Other facilitative sugar transporters include GLUT1 to GLUT14 and HMIT.107 GLUT4 is expressed in insulin-sensitive tissues and regulates whole-body glucose homeostasis.78 GLUT3 is found in neurons and in the placenta and has a high affinity for glucose, allowing for transport even in low substrate conditions.7 GLUT5 is responsible for the absorption of fructose in the small intestine.9 The GLUT5 transporter has wide variability and is dependent on the amount of glucose ingested relative to the fructose. Decreased fructose absorption can lead to abdominal bloating and osmotic diarrhea in susceptible individuals.55 Binding of glucose to one of the GLUT receptors causes a conformational change that results in glucose translocation across the membrane.54
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Besides the mono and disaccharides mentioned above, sugars are also found in ...