MCQs In Electrolyte Disorders

Q1 

You are evaluating a 2-week-old breastfed infant who is 15% below his birthweight and has been

lethargic and fed poorly over the past 4 days. You administer a normal saline fluid bolus.

Laboratory results include:

· Blood glucose of 126.0 mg/dl (7.0 mmol/L)

· Serum sodium of 170.0 mEq/L (170.0 mmol/L)

· Serum potassium of 5.0 mEq/L (5.0 mmol/L)

· Blood urea nitrogen of 31.0 mg/dL (11.1 mmol/L)

· Serum creatinine of 2.9 mg/dL (256.4 mcmol/L)

Of the following, the MOST appropriate initial fluid for correction is a solution containing 5%

dextrose and\

A. NaCl (%): 0.20

KCl (mEq/L): 40

Duration of Infusion(hr): 12 to 24

B. NaCl (%): 0.45

KCl (mEq/L): 0

Duration of Infusion(hr): 48 to 72

C. NaCl (%): 0.45

KCl (mEq/L): 40

Duration of Infusion(hr): 12 to 24

D. NaCl (%): 0.9

KCl (mEq/L): 0

Duration of Infusion(hr): 12 to 24

E. NaCl (%): 0.9

KCl (mEq/L): 40

Duration of Infusion(hr): 48 to 72

Answer:

B

 Hypernatremia results from excessive sodium administration (incorrectly mixed formula, sodium bicarbonate, hypertonic saline) or a deficit of water in relation to sodium. Such a deficit may occur from decreased water intake (inadequate breastfeeding, fluid restriction, lack of access to fluids), fluid losses (nephrogenic and central diabetes insipidus, increased insensible losses), or fluid losses in greater proportion than sodium losses (diarrhea, vomiting, diuretic use, burns).

Treatment of hypernatremia is directed at correction of both the serum sodium
concentration and the circulatory volume. Initially, some children may require isotonic fluid
boluses to restore circulation. It is important to note that children who have hypernatremia often
appear less dehydrated than they actually are due to preservation of the extracellular volume.
The following equation can be used to estimate the free water deficit:
Water deficit (mL)= 4 mL x ideal body weight (kg) x desired change in serum sodium
concentration

Hypernatremia, especially if chronic, should be corrected slowly, with a desired goal of
decreasing the serum sodium by 0.5 mEq/L per hour to avoid cerebral edema. Severe
hypernatremia (serum sodium >170.0 mEq/L [170.0 mmol/L]), as described for the child in the
vignette, should be corrected over 48 to 72 hours. Fluid administration generally consists of 1/4
to 1/2 normal saline solutions. Symptoms of overcorrection, such as changes in mental status or
onset of seizures, suggest the development of cerebral edema and should be treated with
hypertonic saline and slowing of the sodium correction. In general, potassium administration
should be withheld in cases of severe hypernatremic dehydration until adequate urine output is
assured

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