INTRODUCTION
This chapter provides a basic a guide to parenteral rehydration, maintenance fluids, and management of common electrolyte abnormalities in children.
The most common cause of fluid and electrolyte abnormalities in children is dehydration.1 Dehydration results from a negative fluid balance due to decreased intake, increased output (renal, GI, or insensible losses from the skin or respiratory tract), or disease states such as burns, sepsis, or diabetes. Negative fluid balance can occur in the intracellular fluid or extracellular fluid compartments and may be accompanied by derangements in electrolytes. Table 129-1 lists some of the common causes of dehydration. Common signs of dehydration are listed in Table 129-2, and a validated clinical scoring system predicting the need for parenteral rehydration is provided in Table 129-7 of chapter 128, “Vomiting, Diarrhea, and Dehydration in Infants and Children.”
Decreased Intake: Voluntary or involuntary Anatomic or pathologic diseases (pharyngitis, stomatitis, cleft lip/palate, facial dysmorphism, airway obstruction) Neurologic diseases (meningitis, encephalitis, brain tumor, seizures) Febrile illnesses Increased Output: Insensible losses (fever, heat, respiratory diseases, diaphoresis, thyroid disease, cystic fibrosis) GI losses (vomiting, diarrhea) Renal losses: Osmotic (DKA, acute tubular necrosis) Nonosmotic (renal diseases, electrolyte disturbance, diabetes insipidus) Sodium losing (adrenal disease, diuretics, kidney disease, pseudohypoaldosteronism) Systemic Diseases: Moderate to severe burns Ascites Respiratory disease Peritonitis: medical or surgical with third spacing Anaphylaxis |
| None to Minimal Dehydration (<3% loss of body weight) | Some (mild to moderate) Dehydration (3% to 9% loss of body weight) | Severe Dehydration (>9% loss of body weight) | |
|---|---|---|---|
| Mental status | Well, alert | Fatigued, restless, irritable | Apathetic, lethargic, unconscious |
| Thirst | Normal, slight increase, or refusing fluids | Increased, eager to drink | Very thirsty or too lethargic to indicate |
| Heart rate | Normal | Normal to increased | Tachycardic with bradycardia in severe cases |
| Blood pressure | Normal | Normal | Normal to reduced |
| Pulse quality | Normal | Normal to reduced | Weak, thready |
| Breathing | Normal | Normal to tachypneic | Deep |
| Eyes | Normal | Slightly sunken orbits | Deeply sunken orbits |
| Tears | Present | Decreased | Absent |
| Mucous membranes | Moist | Dry | Parched |
| Anterior fontanelle | Normal | Sunken | Sunken |
| Skin turgor | Instant recoil | Recoil in <2 s | Recoil in >2 s |
| Capillary refill | Normal | Prolonged 1–2 s | Prolonged >2 s |
| Extremities | Warm | Cool | Cold, mottled, cyanotic |
| Urine output | Normal to decreased | Decreased (<1 mL/kg/h) | Minimal (<0.5 mL/kg/h) |
PATHOPHYSIOLOGY
Infants and children are particularly susceptible to dehydration for a number of developmental and physiologic reasons. They are dependent on caretakers to provide oral fluids and therefore cannot regulate their intake. In addition, young children and infants have increased fluid requirements and are at risk of increased fluid losses compared to adults and older children. Basal metabolic rates are highest in young children, peaking at 12 months of age and gradually decreasing starting at 3 years of age.2 Infants also have a higher turnover rate for water. Total body water as a percentage of body weight decreases from 75% in a term infant to 60% at 1 year of age, remaining at this percentage until puberty.3 The high percentage of total body water, coupled with a decreased ability to control water loss (e.g., insensible losses from larger surface area–to–body ratio and faster respiratory rate) and a decreased ability to concentrate the urine, predispose infants to dehydration. Furthermore, young children are more prone to hypermetabolic states, such as high fever, which also increase the need for free water. Fever increases the basal metabolic rate by 13% for each degree above 37.8°C.4
Because sodium and water are tightly regulated together, dehydration is often described in relation to serum sodium concentrations. Children can develop isonatremic (isotonic) dehydration (sodium level of 135 to 145 mEq/L), hyponatremic (hypotonic) dehydration (sodium level of <135 mEq/L), or hypernatremic (hypertonic) dehydration (sodium level of >145 mEq/L). Isonatremic dehydration is the most common form of dehydration. Isonatremic (isotonic) dehydration occurs when the fluid sodium losses are proportionate in the intracellular fluid and extracellular fluid compartments. Hyponatremic (hypotonic) dehydration occurs when fluid that is lost contains proportionately more sodium than blood, which leads to osmotic shifts of free water from the intracellular fluid to the extracellular fluid compartments. Hypernatremic (hypertonic) dehydration occurs when the fluid lost contains less sodium than the blood, which causes extracellular fluid free water to move into the intracellular fluid space.
CLINICAL FEATURES
Suspicion of fluid or electrolyte disorders can often be raised through a properly taken history. Questions to be asked on history include symptoms (what they are, when they started, where they started; e.g., was the child in a hot environment), whether fever is present, whether the child is tachypneic, and prior treatment. Prior treatment is of utmost importance beause this will demonstrate if intake has matched output and if appropriate (or more importantly, inappropriate) fluid replacement has occurred. For breastfeeding infants, inquire about frequency of feeds, whether the mother feels she has a good milk production, and whether the infant is feeding or engaged in nonnutrient sucking for comfort. If not breastfeeding, ask what type of fluid has been given, because hypotonic fluids (e.g., water or other hypotonic solutions) that increase the risk of hyponatremia are often used during illnesses. If the infant is bottle-fed, ask whether the formula is premixed or made from powder; hypernatremia or hyponatremia can result from inappropriately prepared formula. Questions surrounding output aid in assessing whether replacement of losses has been adequate; excess output results from vomiting or diarrhea (quantify the frequency and volume if possible). Assess urine output by asking how often the child is urinating or the number of wet diapers if the child is not yet toilet trained. Inquire about volume status by asking about tear production, the presence or absence of sweat, and the child’s general appearance and mental status: Is the child increasingly irritable or lethargic? Has the parent noticed a change in the skin (cyanotic, pale, mottled)? Most important, if known, is a change in weight, because weight loss is the gold standard for assessment of volume status.5 In addition to the specific questions, ask about signs or symptoms of infection, recent travel, sick contacts, and underlying chronic disease, which may point to a specific cause of dehydration. Children are at risk for accidental ingestion of toxins or plants, many of which can cause vomiting and lead to electrolyte disturbances, so such exposure should be specifically assessed.
Physical findings related to individual electrolyte disorders are discussed in relation to specific electrolyte disorder below. In general, children with dehydration demonstrate a spectrum of physical findings ranging from a normal exam if dehydration is mild, to hypovolemic shock if dehydration is severe. Table 129-2 lists common signs and symptoms, and Table 128-6 presents a simplified clinical scoring system for dehydration. Tachycardia is an early sign of dehydration as the body compensates for a decreased circulatory volume. Tachycardia can present with normal blood pressure with or without signs of shock (compensated shock), but may be accompanied by hypotension (uncompensated shock) in severe dehydration. Tachypnea may also be noted as metabolic acidosis develops in moderate to severe dehydration. Note the mental status and the presence of lethargy or hypotonia, because these suggest severe dehydration or electrolyte abnormalities. In infants, the quality of the fontanelle (flat or sunken) may aid in assessment of hydration status, along with the presence or absence of tears when crying; assess the mucous membranes for cracked, dry lips, or decreased saliva in mouth, and the temperature, color, and turgor of the skin (cool, mottled, cyanotic, decreased elasticity), as well as capillary refill time, which should be <2 seconds when normal. Finally, note the character of the pulses because diminished pulses may also reflect significant dehydration.
Laboratory testing for individual electrolyte disorders is discussed individually below. Routine laboratory testing for assessing dehydration alone is generally not required, because numerous studies have found a lack of correlation between laboratory values and degree of dehydration based on percent weight lost. Measure serum electrolytes if IV insertion is required for rehydration and signs of electrolyte disturbance are present,5,6 or if electrolyte abnormalities are expected due to certain underlying medical condition (e.g., diabetic ketoacidosis or congenital adrenal hyperplasia). Perform a bedside glucose test in any child presenting with altered sensorium, and rapidly correct hypoglycemia (see chapter 144, “Metabolic Emergencies in Infants and Children”).
INITIAL TREATMENT OF DEHYDRATION
Three main modalities exist for rehydration in children: oral, nasogastric, and parenteral. Treatment at each level of dehydration is discussed below and summarized in Table 129-3.
| Mild | Moderate | Severe | |
|---|---|---|---|
| Primary phase | PO* | PO* | IV†, IO, NG IO Central line |
| Secondary phase (if primary phase fails) | NG/IV | NG/IV‡ | |
| Tertiary phase (after rehydration to ensure ability to maintain oral intake—optional) | PO* | PO* | ± PO* after initial IV/IO rehydration |
| Laboratory studies | None | Optional# | Electrolytes, BUN, creatinine, calcium, glucose levels; urinalysis |
| Discharge criteria | Appears clinically well, alert, and orientated Vital signs within normal limits for age Urine output during hydrating period Intake is equal or greater to ongoing losses | ||
| Treatment failure | Admit or place in observation unit | ||
Mild and moderate dehydration can be successfully managed with oral or nasogastric rehydration. Oral rehydration therapy and the role of antiemetics for vomiting patients are discussed in detail in chapter 128. Nasogastric hydration is effective, even in vomiting patients.7,8 In a large study comparing nasogastric hydration versus IV hydration over 3 hours, subjects in the nasogastric-treated group had fewer complications, achieved resolution of ketonuria more often, and had greater reduction in specific gravity than IV-treated subjects. Nasogastric treatment is more cost effective than IV treatment.8
The child unable to tolerate oral/nasogastric rehydration therapy or with severe dehydration requires prompt fluid resuscitation with large volumes of fluid over a short period of time9,10 (Table 129-4). Give 20 mL/kg boluses over 5 to 10 minutes repetitively until hemodynamics stabilize. Up to 60 mL/kg or more may be required in the first hour, unless contraindicated based on underlying disease.11 Use an isotonic solution such as 0.9% saline or a lactated Ringer’s solution during this resuscitation phase.12
| Degree of Dehydration | IV Rehydration | Replacement of Ongoing Losses after Initial Rehydration |
|---|---|---|
| Severe with uncompensated shock | 20 mL/kg 0.9% saline bolus over 5 min, repeated until hemodynamically stable | 5–10 mL/kg 0.9% saline or 5% dextrose in 0.9% saline for each watery diarrheal stool and 2 mL/kg 0.9% saline or 5% dextrose in 0.9% saline for each emesis |
| Moderate to severe without signs of shock | 20 mL/kg 0.9% saline bolus over 1 h followed by 5% dextrose in 0.9% saline at 1–2× maintenance rate for 1 h |
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