Hyponatremic Dehydration MCQ | Diagnosis & Management

Clinical Scenario:

A 10-month-old infant is brought to the emergency department with a 4-day history of profuse diarrhea and vomiting. The mother reports that she has been giving the child plain water after each loose stool instead of ORS. On examination, the infant is lethargic, has sunken eyes, delayed capillary refill, and cool extremities. He develops a generalized tonic-clonic seizure shortly after arrival.

Laboratory investigations show:

Serum sodium: 118 mmol/L
Serum potassium: 3.8 mmol/L
Blood glucose: 92 mg/dL

What is the most appropriate initial treatment?

A. 0.9% normal saline
B. 3% hypertonic saline
C. 5% dextrose
D. Lactated Ringer’s solution
E. Oral rehydration solution

Correct answer & Explanation:

Correct Answer: B. 3% hypertonic saline

Explanation

This infant has symptomatic hyponatremia (hyponatremic dehydration), evidenced by:

Severe hyponatremia (Na⁺ 118 mmol/L)
Seizures
Lethargy

The immediate priority is to treat the neurological emergency by administering 3% hypertonic saline (2–3 mL/kg over 10–20 minutes), which rapidly raises the serum sodium by approximately 4–6 mmol/L and reduces cerebral edema. Once seizures have stopped and the child is stabilized, dehydration should be corrected with isotonic fluids.

Why the other options are incorrect

A. 0.9% Normal saline
Appropriate for volume resuscitation but does not correct symptomatic hyponatremia rapidly enough in a child with seizures.

C. 5% Dextrose
Hypotonic after metabolism and may worsen hyponatremia.

D. Lactated Ringer’s solution
Useful for dehydration but contains only 130 mmol/L sodium and is not the initial treatment for hyponatremic seizures.

E. Oral rehydration solution
Not appropriate in a child with seizures and severe dehydration.

Learning Point

In hyponatremic dehydration, the presence of neurological symptoms (seizures, coma, altered consciousness) is an indication for immediate treatment with 3% hypertonic saline, followed by careful correction of dehydration and gradual normalization of serum sodium to avoid osmotic demyelination syndrome.