A Primer on Pediatric Dehydration

Dehydration is a common clinical presentation in pediatrics, and it can lead to significant morbidity and mortality. It is important to recognize the signs and symptoms of dehydration in order to prevent complications such as hypovolemic shock, end-organ failure and death.

Case 1

A 4-month-old boy presents with copious vomiting and diarrhea for the last 24 hours. His parents say it started shortly after he woke up yesterday. He has not tolerated formula since the previous evening and has not urinated all day. The parents describe the diarrhea as non-bloody and liquid brown. The emesis is non-bloody and non-bilious. The parents mention that their son attends daycare. His first set of vitals is temperature 37ºC, pulse 170, respiratory rate 34, blood pressure 80/42. On exam the baby is difficult to arouse, his eyes are sunken, his mucous membranes are dry, and his anterior fontanel is depressed. On skin examination, his capillary refill time is 4 seconds, and he has abnormal skin turgor. Upon stimulation he begins to cry, but does not produce any tears.

Case 2

A 4-year-old girl, previously healthy, presents with fever, headache and vomiting for two days. Her parents say she started feeling weak last night. She refused her dinner and skipped breakfast today. She has vomited three times and is complaining of a headache and neck pain. Her vitals on presentation are temperature 39.4ºC, pulse 110, respiratory rate 16, blood pressure 100/60. She appears ill and mildly lethargic, and has tacky mucous membranes, normal capillary refill and normal skin turgor. On pulmonary exam, her lungs are clear to auscultation, and she has no accessory muscle use.

Epidemiology and Pathophysiology

Dehydration is a frequent reason for emergency room visits and affects at least 2 million children annually.¹ Frequently caused by gastroenteritis, dehydration may result in serious morbidity and mortality. Gastroenteritis and dehydration account for 30% of all infant and toddler deaths worldwide, and approximately 300 deaths annually in the U.S.² Gastroenteritis alone results in 1.9 million pediatric deaths annually, or 19% of all deaths under the age of 5.³

Clinically significant dehydration, as used in this review, refers to extracellular fluid volume depletion. The body contains two major volume compartments, the extracellular fluid (ECF) and intracellular fluid (ICF). The ICF represents two-thirds of the body’s fluid, while the ECF accounts for the remaining third. The ECF can further be divided into the interstitial fluid (75%) and plasma (25%). When symptoms of dehydration occur, the intravascular volume, the plasma component of the ECF, is depleted. In infants (children under 1 year), the ECF and ICF comprise 70% of their total weight, while in adults they account for only 60%.⁴ An average 70-kg adult excretes 40 ml/kg of water per day, while a 5-kg infant excretes 100 ml/kg, and is therefore more susceptible to dehydration. ⁴ Infants and young children require greater volumes of water than adults to maintain a homeostatic fluid environment.

Clinical dehydration can be classified as mild (less than 3% change in body weight), moderate (3%–9% change in body weight) or severe (greater than 9% change in body weight).⁵ These are rough percentages and do not always correlate with clinical presentation.

Although the majority of children presenting with dehydration have associated acute gastroenteritis, it is important to consider the multiple other etiologies. Most pediatric dehydration is secondary to fluid losses from vomiting and diarrhea, but it can also be from severe bacterial infection such as pneumonia, meningitis or urinary tract problems. Other etiologies of dehydration include diabetic ketoacidosis, pyloric stenosis or anything causing increased intracranial pressure. Volume depletion can also occur secondary to trauma with associated hemorrhage.

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