Pediatric emergency medicine trisk 131

FIGURE 22.1 Suspected dehydration. BSA, body surface area; NS, normal saline; GI,
gastrointestinal; CNS, central nervous system; Hx, history; DKA, diabetic ketoacidosis; CAH,
congenital adrenal hyperplasia; ATN, acute tubular necrosis; DI, diabetes insipidus; CF, cystic
fibrosis.


TABLE 22.3
OTHER CONSIDERATIONS FOR VOMITING ALONE
Diabetic ketoacidosis
Increased intracranial pressure
Otitis media
Heart failure
Obstruction (e.g., pyloric stenosis)
Urinary tract infection
Ingestion
Age of the child, nutritional status, and type of dehydration may also affect
clinical assessment, which is critical to effective management of the acutely
dehydrated child. In general, older children show signs of dehydration sooner
than babies do because of their lower levels of extracellular water. Babies with
excess subcutaneous fat may look less dehydrated than they really are, whereas
severely malnourished babies may appear to be more dehydrated secondary to
wasted supporting tissues. Signs of dehydration may be less evident or appear
later in hypernatremic dehydration. Excessive irritability with increased muscle
tone, and doughy or smooth and velvety skin, often are noted with this type of
dehydration. Conversely, signs of dehydration may be more pronounced or appear
sooner in hyponatremic dehydration. Keeping these observations in mind,
particular attention should be paid to the overall appearance, mental status, eyes,
and skin on physical examination. Patients with obvious burns or diseases that
disrupt the integument in the same way (e.g., scalded skin syndrome) are
presumed to have become dehydrated through transudation of fluid through the
skin. Additional considerations are listed in Table 22.1 . The mildly dehydrated

child usually appears well or may be tired, have decreased tearing, and a slightly
dry mouth. Dry mucous membranes are an early sign of dehydration, but this
finding is affected by rapid breathing and ingestion of fluids. Conversely, the
severely dehydrated baby classically appears quite ill with lethargy or irritability,
a dry mouth, sunken fontanel, and absent tears. Moderate states of dehydration,
however, require careful evaluation. One of the more objective measures of
dehydration is assessment of skin perfusion by measuring capillary refill time.
Although the child’s body temperature does not predictably affect capillary refill
time, it may be falsely prolonged when measured on the foot or in a cool room.


Laboratory
In general, laboratory values are not helpful in diagnosing dehydration, rather the
history and physical examination should be used. However, in children who are
judged to have moderate to severe dehydration that requires intravenous (IV)
rehydration, laboratory tests of electrolytes, glucose, blood urea nitrogen, and
creatinine are usually obtained to determine osmolarity and renal function.
Approximately one-third of moderately to severely dehydrated children will have
hypoglycemia less than 60 mg/dL. Based on the initial serum sodium, most
children have isonatremic dehydration (also referred to as isotonic dehydration,
serum sodium 130 to 150 mEq/L), whereas others have hypernatremic
dehydration (hypertonic dehydration, serum sodium greater than 150 mEq/L) or
hyponatremic dehydration (hypotonic dehydration, serum sodium less than 130
mEq/L). The acid–base status may be assessed further with an arterial or venous
blood gas. Urine specific gravity and ketones cannot be reliably used as indicators
for dehydration. However, a history of polyuria and the presence of glucose and
ketones may indicate diabetic ketoacidosis, whereas a history of disorders of the
central nervous system (CNS) suggests diabetes insipidus.

Diagnostic Approach

In approaching the patient with presumed dehydration, the initial assessment
serves to determine whether compensated or uncompensated shock is present. If
the child appears to be in shock, resuscitation should begin and a number of lifethreatening disorders need to be considered, as discussed in Chapter 10 Shock . A
detailed history, including assessment of intake and output, aids in determining
the etiology of the patient’s dehydration. Together, the physical examination and
history usually allow the physician to establish a diagnosis and degree of
dehydration. Laboratory evaluation is not routinely needed to determine that a
patient is dehydrated, but may be collected to assess for suspected electrolyte
abnormalities, or to make a diagnosis of a disease at risk for dehydration (i.e.,
diabetes mellitus).

Initial Management
The dehydrated child must be examined immediately for the degree of
dehydration or state of hypovolemic shock. If there is severe dehydration or
uncompensated shock, the patient is treated acutely with isotonic fluids to restore
intravascular volume regardless of serum osmolarity or cause of the dehydration.
Normal saline or Ringer lactate is given via an IV or intraosseous line in 20
mL/kg aliquots over approximately 15 to 30 minutes, or as quickly as possible if
there is uncompensated shock. Reassessment is paramount after each fluid bolus


for the patient’s response to treatment. Careful reevaluation must be undertaken
as rapid infusion of IV fluids in a patient who is actually in heart failure will be
detrimental causing worsening of the condition. When blood pressure is restored,
heart rate returns to normal, distal pulses strengthen, and skin perfusion improves,
isotonic fluids may be safely discontinued. Careful attention should be paid to
ongoing losses. Urine output is the most important indicator of restored
intravascular volume in patients with intact renal and adrenal function, and
without diabetes mellitus or insipidus, and should be a minimum of 1 mL/kg/hr.
Hypoglycemia can often coexist in severe dehydration. Dextrose can be given via

IV. An initial bolus of 5 mL/kg of D10 can be given via peripheral IV or, if a
central line is present, 2 mL/kg of D25.

Oral Rehydration Therapy
If the child is determined to be mildly or moderately dehydrated, then oral
rehydration therapy (ORT) is the therapeutic option of choice. ORT is the
frequent administration of small volumes of an appropriate rehydration solution,
typically with an oral syringe. The use of ondansetron, a serotonin 5HT3 selective
receptor antagonist, has clearly been shown to improve the success of rehydration
with ORT in patients greater than 6 months of age ( Table 22.4 ). A one-time
dose has been shown to be sufficient and prescribing for home use has not been
shown to reduce return rates to the ED. Once given, ORT should be initiated in 15
to 30 minutes. An appropriate rehydration solution has the correct balance of
glucose and sodium, which enables the body to absorb the water passively via the
sodium glucose cotransport mechanism in the small intestine. The glucose-tosodium ratio is an important determinant in the acceptability of these solutions.
Optimal solutions have a 1:1 or a 2:1 glucose:sodium ratio. When additional
sweetener is added to the rehydration solution, the ratio of glucose to sodium is
distorted and may result in osmotic diarrhea or inappropriate absorption of
electrolytes. There are two categories of rehydration solutions: initial rehydration
solutions that contain 60 to 90 mEq/L of sodium (e.g., Rehydralyte, World Health
Organization oral rehydration solutions) and maintenance solutions that contain
40 to 60 mEq/L of sodium (e.g., Pedialyte). If the etiology of the dehydration is
presumed to be due to cholera, then the higher sodium concentration is
appropriate because there is a large sodium loss in the diarrhea stools of cholera
patients. However, if the etiology of the dehydration is presumed to be viral
gastroenteritis, then the lower sodium concentration solutions would be
appropriate and are more readily available. Both rehydration and maintenance
solutions have approximately 20 mEq/L of potassium and a low glucose