Chapter 17

### INTRODUCTION

The management of fluid and electrolyte balance in children is an ever-present challenge in the practice of emergency medicine. The varying size of patients coupled with their dependency on others to provide alimentation, both during healthy times and illness, add to the challenge. The ambient environment and multiple organ systems, including the skin, alimentary tract, lungs, kidneys, heart, vasculature, and muscles, joined by multiple endocrine systems create the balance. Although most patients are in the emergency department for short periods of time, the diagnosis of the fluid and electrolyte status needs to have a wider scope. There are formulas for calculating the proper amounts of fluids and solute for patients, but the calculations have to be modified over time. The fluid status of a patient needs to be reassessed on a regular basis regardless of the calculations.

### DISORDERS OF VOLUME

#### GENERAL CONSIDERATIONS

Intravascular volume is crucial to homeostasis and survival. The pediatric population is a great deal more sensitive to derangements in volume than their adult counterparts. The volume status of a child is determined largely in part on the sodium concentration which is regulated by the kidney’s ability to alter the amount of sodium reabsorbed along the nephron. The kidneys have a remarkable ability to vary the amount of sodium resorption and thus regulate volume status. However, the renal system’s ability to compensate can be overcome by extreme volume loss, markedly decreased intake, volume redistribution, or disease in the kidney itself.

#### VOLUME DEPLETION

##### Clinical Findings

History and physical examination contribute significantly to the evaluation and the treatment of children with presumed volume depletion. Important historical elements involve the presence of gastrointestinal (GI) symptoms which are among the most common conditions requiring fluid therapy. Other conditions resulting in volume depletion are poor intake, sepsis, burns, cystic fibrosis, and conditions of the kidney or regulating hormones.

Knowing the severity or quantity of volume depletion is helpful in directing therapy as well as the urgency and duration of therapy. Dehydration is classified into < 5%, 5-10%, and > 10%. For many years a variety of physical findings and scales (collections of findings) have been proposed. None of these is as good as accurate weights.

Look for the presence of dry mucous membranes, absence of tears, tachycardia at rest, capillary refill greater than 3 seconds, abnormal respiratory pattern, and hypotension. In the absence of a documented baseline weight, which is generally not available to the emergency department physician, the patient with a history of poor intake and extra loss may be considered to be hydrated to less than 5% dehydrated. The presence of one or more of these signs would put the patient in the 5-10% range of dehydration. The patient who demonstrates all the signs is profoundly ill and in shock. Ultrasound measuring the ratio of the aorta and inferior vena ...

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