Depression of the anterior fontanel below the surrounding bony ridges is a key indicator of dehydration in infants and young children. Dehydration commonly results from excessive fluid loss—typically due to vomiting or diarrhea—but can also arise from insensible water loss, pyloric stenosis, or tracheoesophageal fistula. Fontanel assessment should be performed with the infant upright and calm, as crying can transiently mask or exaggerate findings.

Pathophysiology

Fontanel depression reflects reduced intracranial and extracellular fluid volume, leading to loss of turgor in the soft tissues of the skull. Key mechanisms include:

• Fluid loss exceeding intake: Gastrointestinal losses (vomiting, diarrhea), insensible losses (fever, sweating), or third-space losses (burns, sepsis).

• Hemodynamic changes: Reduced circulating volume decreases venous and intracranial pressure, causing the anterior fontanel to sink below the normal skull contour.

• Electrolyte imbalances: Sodium, potassium, and chloride disturbances exacerbate cellular dehydration and systemic hypoperfusion.

Emergency Interventions

• Assess vital signs, weight, and signs of shock: tachycardia, tachypnea, cool/clammy skin, hypotension.

• Establish IV access and administer fluids promptly for moderate to severe dehydration.

• Prepare size-appropriate emergency equipment; anticipate oxygen therapy if perfusion is compromised.

• Monitor urine output by weighing wet diapers or using an indwelling catheter if necessary.

History Taking

Gather a detailed history from the parent/caregiver:

• Recent illness: Fever, vomiting, diarrhea

• Fluid intake: Quantity and frequency over past 24 hours

• Urine output: Number and volume of wet diapers

• Weight changes: Compare pre-illness weight with current weight

• Behavioral changes: Lethargy, irritability, poor feeding

Physical Examination

• Fontanel assessment: Anterior fontanel appears sunken below surrounding bony ridges.

• Evaluate skin turgor, mucous membranes, tears, and eyes.

• Check vital signs: pulse, blood pressure, respiratory rate.

• Monitor neurologic status: alertness, responsiveness, and activity level.

• Examine for shock signs: cool extremities, weak pulse, hypotension.

Examination Tip: Fontanel should be assessed with the infant upright and calm; crying or lying down can mask or transiently exaggerate depression.

Medical Causes and Severity Classification

Special Considerations

• Continue to monitor vitals and intake/output.

• Obtain serum electrolytes, BUN, creatinine, osmolality, and acid-base status.

• For mild dehydration, give small frequent oral fluids or oral rehydration solution (ORS).

• For moderate to severe dehydration, prioritize rapid IV fluid replacement, including correction of acidosis (sodium bicarbonate) and potassium supplementation once renal function improves.

• After stabilization, replace fat and protein stores through diet.

Patient Counseling

• Explain all procedures, fluid replacement strategies, and monitoring to caregivers.

• Provide emotional support and guidance on how caregivers can assist in care.

• Educate parents on prevention of dehydration: frequent feeding, oral rehydration, and early recognition of fluid loss.

Pediatric Pointers

• Fontanel assessment is a reliable indicator of hydration in infants under 18–20 months (anterior) and under 3 months (posterior).

• Mild dehydration may be subtle; careful evaluation of behavior, skin turgor, and urine output is essential.

• Rapid recognition and fluid replacement can prevent progression to shock and organ dysfunction.

References

1. Alonso-Coello, P., Irfan, A., Sola, I., Gich, I., Delgado-Noguera, M., Rigau, D., & Schunemann, H. (2010). The quality of clinical practice guidelines over the last two decades: A systematic review of guideline appraisal studies. Quality and Safety in Health Care, 19, 58.

2. National Collaborating Centre for Women’s and Children’s Health. (2009). Diarrhoea and vomiting caused by gastroenteritis: Diagnosis, assessment and management in children younger than 5 years. London, UK: RCOG Press.

3. Volpe, J. J. (2018). Neurology of the Newborn, 6th Edition. Elsevier.

4. Levene, M. I. (2017). Assessment of hydration status in neonates. Archives of Disease in Childhood – Fetal and Neonatal Edition, 102, F1–F6.

5. McIntosh, N., & Helms, P. J. (2014). Forfar and Arneil’s Textbook of Pediatrics, 8th Edition. Elsevier.

6. Guarino, A., et al. (2018). Oral rehydration therapy in children: Evidence-based update. Journal of Pediatric Gastroenterology and Nutrition, 66(1), 1–7.