Children with acute gastroenteritis and dehydration are commonly treated in the emergency department (ED). Almost all children will have had rotavirus gastroenteritis, the most common etiology of acute gastroenteritis, by the age of 5 years. Morbidity and mortality are related to the acute loss of circulating fluid volume, ultimately resulting in diminished tissue perfusion, metabolic acidosis, and, in extreme cases, shock. The goals of therapy are the rapid restoration of circulating intravascular volume (water and electrolytes), the correction of acid-base disturbances, and the reduction of stool output and vomiting (1).

Oral rehydration therapy (ORT) is the administration of small volumes of an appropriate oral rehydration solution on a regular schedule (Fig. 89.1). For children with mild to moderate dehydration, ORT is recommended as the initial therapy of choice by the American Academy of Pediatrics, the World Health Organization, and the Centers for Disease Control (2,3,4). ORT can also be used for severely dehydrated children. Although ORT has been shown to be effective for treating moderately dehydrated children in an ED setting, its use in the United States has been limited (5). The most frequent obstacles to successful oral rehydration in the ED are false perceptions that oral rehydration is too slow or is not a definitive procedure. Physicians and nurses hold these beliefs as frequently as parents. Generally, 5 minutes spent preparing for and describing ORT to the family will reduce or eliminate these obstacles. ORT spares the child the pain of an intravenous line, promotes more direct parental involvement in the management of the child’s dehydration, and teaches the parents a skill that can be used the next time the child becomes dehydrated.

Acute gastroenteritis is caused by a variety of viral and bacterial pathogens. Fluid losses from gastroenteritis often have an electrolyte composition similar to that of plasma. Most of the fluid deficit during the early stages of dehydration is from the extracellular space, but with time the fluid losses equilibrate and fluid leaves the intracellular space. During the recovery phase, fluid administered to the patient enters the extracellular space initially and then gradually re-equilibrates with the intracellular space.

Vomiting is controlled by the emetic center in the central nervous system in the area postrema. Of note, this center contains 85% of the body’s 5HT-3 receptors. Diarrhea results when gastrointestinal fluid secretion exceeds fluid absorption. Regardless of the etiology, once fluid losses begin, a specific sequence of physiologic processes follow. Metabolic acidosis from decreased tissue perfusion causes further decline in end-organ function, such as decreased myocardial contractility, which may exacerbate the effects of shock. Reduced renal perfusion triggers the renin-angiotensin-aldosterone system, resulting in sodium and water retention at the expense of increased urinary potassium losses. Ultimately, hypokalemia results in decreased bowel motility, with the potential for further third-space fluid losses (6).

ORT can safely and rapidly restore circulating volume. Oral rehydration solutions consist of balanced mixtures of simple or complex carbohydrates and sodium. Small carbohydrate molecules promote absorption of sodium by “facilitated cotransport” (7), which in turn promotes water absorption. In the intestinal lining, this is most commonly glucose sodium cotransport, with an ideal stoichiometric ratio of one molecule of glucose to one molecule of sodium. Of note, when juice
is added to oral rehydration solutions to make it “taste better,” it alters the glucose-sodium ratio and disturbs the facilitated cotransport mechanism. ORT has been demonstrated to provide rehydration as rapidly as intravenous solutions and with equally good correction of electrolyte and acid-base disturbances.

ORT may be used in any conscious infant, child, or adolescent with acute gastroenteritis. It should be considered the initial therapy for children with mild to moderate dehydration and can be used as a temporizing measure for children with severe dehydration. Patients with signs of shock should receive aggressive intravascular fluid replacement in the early stages. The fluid deficit should be replaced in the ED over the first 4 hours. The maintenance phase consists of the remaining time the child is symptomatic from acute gastroenteritis and is being managed with feeding and fluids at home.

Vomiting is not a contraindication to ORT but requires modification of the technique (e.g., decreasing the volume with each syringe feed). Ondansetron, a 5HT-3 receptor antagonist, is an effective antiemetic for children and can be used to facilitate ORT. In fact, one dose of oral ondansetron in the ED is often sufficient to stop the emesis caused by gastroenteritis and allow for successful treatment with ORT. Alternatively, vomiting children or those refusing to drink may receive fluid via a nasogastric tube (see Chapter 84), provided they have intact airway protective reflexes. Absolute contraindications to ORT include the suspicion of an acute surgical abdomen, obtundation, and loss of airway protective reflexes. Relative contraindications include severe dehydration, mental status changes that preclude tolerating oral feeds, and parents unwilling to assist in the process.

Specific equipment used depends on the child’s age.

Fluids with high concentrations of sugars such as soft drinks, fruit juices, and fruit punch will actually exacerbate diarrhea by an osmotic effect. For purposes of discussion, the terms “physiologically appropriate solution” and “oral rehydration solution” refer to solutions containing no more than 3% glucose, 50 to 90 mEq/L of sodium, and potassium and base to correct losses. Although Pedialyte and Ricelyte are generally referred to as “oral maintenance” solutions, some authorities do not commonly differentiate between the oral maintenance and oral rehydration solutions. For practical purposes in the industrialized world, solutions containing 50 to 90 mEq/L of sodium provide adequate restoration of circulating volume in children with mild to moderate dehydration. Children with severe dehydration (more than 10%) or cholera should be given a true rehydration solution containing a sodium concentration of 70 to 90 mEq/L (Rehydralyte or WHO solution).

The compositions of various solutions commonly used in children with acute gastroenteritis are listed in Table 89.1. Of note, the high osmolality and low sodium content of cola, apple juice, and sports drinks make these products inappropriate for ORT. WHO has recently formulated a second oral rehydration solution that can be used for dehydration due to etiologies other than cholera.

An algorithm for management of children with dehydration caused by gastroenteritis is shown in Figure 89.2. ORT works best when the clinician incorporates the child’s parents into the process. The specific procedure undertaken will depend on parental and clinician preferences. The overriding principle is that continuous small quantities of oral rehydration solution must be provided. Giving an 8-kg infant 8 oz of fluid ad lib usually results in a messy and discouraging episode of vomiting. Most parents will not be able to restrict a thirsty infant to an ounce every few minutes unless they are given careful and explicit procedural instructions. The goal of ORT is to replace the entire deficit in 4 hours or less.