Clinical Scenario:
A 7-month-old infant is brought to the emergency department with a 3-day history of profuse watery diarrhea and poor feeding. The parents report preparing infant formula with extra scoops of powder because they believed it would improve nutrition. On examination, the infant has lost 11% of body weight, is irritable with a high-pitched cry, has dry mucous membranes, a mildly sunken anterior fontanelle, and doughy skin. The heart rate is 168/min, peripheral pulses are well palpable, and capillary refill time is 2 seconds. Laboratory investigations reveal a serum sodium of 162 mmol/L, serum potassium of 4.2 mmol/L, and blood glucose of 92 mg/dL. Which of the following clinical findings is most characteristic of hypernatremic dehydration?
A. Delayed capillary refill disproportionate to the degree of dehydration
B. Doughy skin with marked irritability
C. Generalized edema
D. Hyperactive bowel sounds
E. Severe sunken eyes with absent peripheral pulses
Correct answer & Explanation:
Correct Answer: B. Doughy skin with marked irritability
Explanation
Hypernatremic dehydration occurs when water loss exceeds sodium loss or when excess sodium is administered, as may occur with incorrectly concentrated infant formula. The elevated extracellular osmolality draws water from intracellular spaces, including the brain, producing neurological manifestations.
Characteristic features include:
- Marked irritability
- High-pitched cry
- Doughy or “pasty” skin texture
- Hypertonia or increased muscle tone
- Seizures in severe cases
- Signs of dehydration that may appear less severe than the actual fluid deficit because intravascular volume is relatively preserved.
The serum sodium concentration of 162 mmol/L confirms hypernatremic dehydration.
Why the other options are incorrect
A. Delayed capillary refill disproportionate to the degree of dehydration
Incorrect. In hypernatremic dehydration, circulation is often relatively preserved initially, and capillary refill may remain near normal despite significant water loss.
B. Doughy skin with marked irritability
Correct. These are classic clinical features of hypernatremic dehydration.
C. Generalized edema
Incorrect. Edema is not a feature of hypernatremic dehydration.
D. Hyperactive bowel sounds
Incorrect. Bowel sounds are not specific for the type of dehydration.
E. Severe sunken eyes with absent peripheral pulses
Incorrect. These findings are more suggestive of advanced hypovolemic shock. In hypernatremic dehydration, dehydration may be underestimated clinically because tissue turgor is relatively preserved.
Learning Point
Hypernatremic dehydration should be suspected in infants with:
- Serum sodium ≥150 mmol/L
- Irritability or lethargy
- High-pitched cry
- Doughy skin
- Hypertonia
- Clinical signs of dehydration that appear less severe than the actual fluid deficit
Correction of hypernatremia must be slow, generally aiming to reduce the serum sodium by no more than 0.5 mmol/L/hour (approximately 10–12 mmol/L in 24 hours) to minimize the risk of cerebral edema.
