This chapter serves as a quick reference for fluid and electrolyte abnormalities in children, focusing on definitions, differential diagnosis, common presentations, and basic approach to management.
FLUID MAINTENANCE
Maintenance fluid needs are based on insensible losses from the skin and respiratory tract and sensible losses from urine and stool.
Maintenance intravenous fluids (IVF) are provided when patients cannot or will not take fluid orally. They are not a substitute for fluids already lost; repletion fluids should be provided in addition to maintenance fluids for this purpose. The clinician should also consider ongoing fluid losses when providing supplemental IVF.
This is usually provided with IVF containing 5% dextrose and 77 mEq/L of sodium (which is 0.45% sodium chloride or ½ normal saline).
DEHYDRATION AND HYPOVOLEMIA
Dehydration is common in children, and is most commonly due to gastroenteritis, with losses in excess of retained intake.
Dehydration may be isotonic, hyponatremic, or hypernatremic, and the history will suggest the etiology. The following section discusses isotonic dehydration.
Assessment of dehydration
Percent dehydration = (preillness weight – current weight)/preillness weight
Preillness weight is often not accurately known. Table 3-1 gives physical examination findings that allow estimation of the degree of dehydration.
Management
Mild dehydration: 3%-5%
Oral rehydration therapy (ORT): 50 mL/kg plus replacement of ongoing losses with oral rehydration solution (ORS) over 4 hours
If vomiting, give small frequent amounts (5-10 mL) every 1-2 minutes to give total volume of ORS calculated over 4 hours.
Reassess hydration status and ongoing losses every 2 hours.
Serum electrolyte measurement is not necessary for mild and moderate dehydration when isotonic dehydration is suspected.
Moderate dehydration: 6%-9%
Attempt ORT with 100 mL/kg plus replacement of ongoing losses with ORS over 4 hours.
If ORT fails, then begin intravenous (IV) rehydration with normal saline (NS), with a goal of replacing the fluid deficit over 4 hours.
Severe dehydration: ≥10%
Severe dehydration is a medical emergency and results in shock.
Obtain serum electrolytes and glucose.
Treat hypoglycemia (glucose < 60 mg/dL) and electrolyte abnormalities.
Give a rapid IV bolus of 20 mL/kg normal saline and repeat as necessary to improve perfusion.
Once pulse, perfusion, and mental status return to normal, ORT can begin, with a goal of replacing the remaining deficit over 2-4 hours.
Replacement of ongoing losses
Consider the patient’s underlying source of fluid loss when choosing the composition of replacement fluids. For example, fecal losses contain more water than sodium (35-60 mEq Na/L), so ½ NS would be an appropriate replacement fluid.
Inpatient management indications include: intolerance of ORS (intractable vomiting, refusal, or inadequate intake), inability to provide adequate care at home, acute bloody diarrhea, concern for complicating illnesses, severe dehydration, lack of follow-up, progressive symptoms, young age, or diagnostic uncertainty.
See Table 3-2 for the composition of common oral fluids compared with the WHO recommendations for the composition of ORS.
TABLE 3-1 Symptoms Associated with Dehydration
Symptom
Minimal or no dehydration (<3% loss of body weight)
Mild-to-moderate dehydration (3%-9% loss of body weight)
Severe dehydration (>9% loss of body weight)
Mental status
Well; alert
Normal, fatigued or restless, irritable
Apathetic, lethargic, unconscious
Thirst
Drinks normally; might refuse liquids
Thirsty; eager to drink
Drinks poorly; unable to drink
Heart rate
Normal
Normal to increased
Tachycardia, with bradycardia in most severe cases
Quality of pulses
Normal
Normal to decreased
Weak, thread, or impalpable
Breathing
Normal
Normal; fast
Deep
Eyes
Normal
Slightly sunken
Deeply sunken
Tears
Present
Decreased
Absent
Mouth and tongue
Moist
Dry
Parched
Skin fold
Instant recoil
Recoil in <2 sec
Recoil in >2 sec
Capillary refill
Normal
Prolonged
Prolonged; minimal
Extremities
Warm
Cool
Cold; mottled; cyanotic
Urine output
Normal to decreased
Decreased
Minimal
Source: Adapted from Duggan C, Santosham M, Glass RI. The management of acute diarrhea in children: oral rehydration, maintenance, and nutritional therapy. Morb Mortal Wkly Rep 1992;41(No. RR-16):1-20; World Health Organization. The Treatment of Diarrhea: A Manual for Physicians and Other Senior Health Workers. Geneva, Switzerland: World Health Organization, 1995. Available at http://www.who.int/childadolescent-health/New_Publications/CHILD_HEALTH/WHO.CDR.95.3.htm.
TABLE 3-2 Composition of ORS Compared with Common Oral Fluids
ORS
Carbohydrate (mmol/L)
Sodium (mmol/L)
Potassium (mmol/L)
Chloride (mmol/L)
Osmolarity (mOsm/L)
WHO recommendations
Should equal Na, but not > 110
60-90
15-25
50-80
200-310
WHO ORS (2002, reduced osmolarity)
75
75
20
65
245
WHO ORS (1975)
111
90
20
80
311
Pedialyte
139
45
20
35
250
Apple juice
667
0.4
44
45
730
Gatorade
323
20
3.2
11
299
Soda
622
1.6
N/A
N/A
650
Adapted from MMWR Recommendations and Reports: Managing acute gastroenteritis among children: oral rehydration, maintenance, and nutritional therapy.
ELECTROLYTE ABNORMALITIES
Hypernatremia
Definition
Hypernatremia is defined as a serum sodium >150 mEq/L.
Etiology
Etiology of hypernatremia can be divided into categories:
Excess sodium intake, for example, incorrectly prepared formula, sea water or sodium chloride ingestion, and iatrogenic causes such as sodium bicarbonate or hypertonic (3%) saline administration.
Dehydrated states (hypernatremic dehydration)
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