Depressed fontanel

Specialty: Pediatrics.

• Sunken fountain
• sign of neonatal dehydration
• concave fontanelle

Why it occurs

• Moderate to severe dehydration (loss of fluid volume secondary to acute gastroenteritis, vomiting or insufficient intake)
• Chronic protein-calorie malnutrition (marasmus or weight atrophy with loss of the fat pad and tissue turgor)
• Hypovolemic shock (acute loss of body fluids with circulatory redistribution)
• Central or nephrogenic diabetes insipidus (massive loss of free water through the kidneys with hypernatremic dehydration)

Initial workup

Immediate determination of arterial or capillary gases to assess the acid-base balance (metabolic acidosis). Complete ionogram (sodium, potassium, chlorine, ionic calcium) to diagnose hypernatremic, hyponatremic or normonatremic dehydration. Kidney function with urea, creatinine and urinary density in fresh sample (if collection is possible). Capillary blood glucose to rule out diabetic ketoacidosis or reactive hypoglycemia. Complete blood count (elevated hematocrit due to hemoconcentration).

Standard management

• 0.9% physiological saline solution — isotonic crystalloid for emergency volume expansion in case of shock or severe dehydration; bolus dose of 10 to 20 ml/kg intravenously or intraosseous, to be administered in 10-20 minutes, repeatable according to clinical response
• 5% glucose serum with variable sodium intake — used for fluid maintenance and correction of the calculated deficit once the patient is stabilized, adjusting the infusion rate according to serum sodium levels to avoid cerebral edema
• Oral rehydration salts (of choice in mild to moderate dehydration without uncontrollable vomiting; fractional administration of 50-100 ml/kg over 4 hours in small doses of 5 ml every 2-3 minutes).