Hyponatremic Dehydration MCQ | Diagnosis and 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), characterized by severe hyponatremia (Na⁺ 118 mmol/L) accompanied by seizures and lethargy.

Management of Hyponatremic Dehydration

The immediate priority is treatment of the neurological emergency with hypertonic saline. 3% sodium chloride can be administered intravenously as a bolus. Pediatric protocols commonly use approximately 2–3 mL/kg over 15–20 minutes, with the dose repeated if seizures or significant neurological symptoms persist and the sodium remains severely low.

The initial objective is to rapidly increase the serum sodium enough to control the neurological symptoms, rather than immediately normalize the sodium concentration. Once the acute neurological manifestations have improved, further correction should be carefully controlled to reduce the risk of osmotic demyelination.

Why the other options are incorrect

A. 0.9% Normal saline
Incorrect as the initial treatment for hyponatremic seizures. Isotonic saline is appropriate for volume resuscitation and subsequent correction of hypovolemic hyponatremia, but symptomatic hyponatremic encephalopathy requires hypertonic saline initially.

C. 5% Dextrose
Incorrect. After glucose is metabolized, dextrose-containing water behaves as free water and can worsen hyponatremia.

D. Lactated Ringer’s solution
Incorrect as the initial treatment for hyponatremic seizures. Although it can be used for volume replacement in some clinical situations, its sodium concentration is insufficient for rapid treatment of symptomatic severe hyponatremia.

E. Oral rehydration solution
Incorrect in a child with seizures and altered consciousness. Oral or enteral rehydration is inappropriate during an acute neurological emergency.

Learning Point for Pediatric FCPS, MRCPCH & MD.

Hyponatremia + neurological symptoms = emergency.

In a child with severe symptomatic hyponatremia, particularly seizures or impaired consciousness, administer hypertonic saline promptly. Sodium should initially be raised enough to control the neurological manifestations, followed by careful monitoring and controlled correction.

References

Royal Devon University Healthcare NHS Foundation Trust. Paediatric intravenous fluid prescription and the management of hyponatraemia and hypernatraemia [Internet]. Exeter: Royal Devon University Healthcare NHS Foundation Trust; 2024 [cited 2026 Sep 18].
Brighton and Sussex University Hospitals NHS Trust. Supportive Care Protocol: Management of fluid and electrolytes [Internet]. Brighton: BSUH; 2020 [cited 2026 Sep 18]. Available from: Pediatric hyponatremia protocol

You can also practice another MCQ on Hypernatremic Dehydration