Grading Hypernatremic Dehydration in Children
Hypernatremic dehydration in children is graded primarily by serum sodium concentration, with mild defined as 145-150 mmol/L, moderate as 150-157 mmol/L, and severe as >157 mmol/L, while clinical severity is assessed by percentage of body water loss: mild (3-5%), moderate (6-9%), and severe (≥10%) dehydration. 1
Classification by Serum Sodium Concentration
- Mild hypernatremia: 145-150 mmol/L – This represents the lower threshold where sodium elevation begins to cause clinical concern, though symptoms may be minimal 2
- Moderate hypernatremia: 150-157 mmol/L – At this level, neurological symptoms become more apparent and careful correction is required 1
- Severe hypernatremia: ≥157 mmol/L – This threshold is associated with significant morbidity and requires urgent intervention, with mean initial sodium in severe cases reported at 159-160 mmol/L 3, 1
The definition threshold varies slightly across sources, with some defining hypernatremia as serum sodium ≥150 mmol/L 3 while others use ≥145 mmol/L 2. For clinical purposes, sodium ≥150 mmol/L consistently indicates significant hypernatremic dehydration requiring active management 3, 1.
Clinical Assessment of Dehydration Severity
Beyond sodium levels, the percentage of body water loss determines clinical severity:
- Mild dehydration (3-5% body weight loss) – Minimal clinical signs, child may appear slightly dry 1
- Moderate dehydration (6-9% body weight loss) – Decreased skin turgor, dry mucous membranes, sunken fontanelle in infants 1
- Severe dehydration (≥10% body weight loss) – Shock, altered mental status, poor perfusion; present in 87.6% of hospitalized hypernatremic cases 1
Half of children with hypernatremic dehydration present in shock, and neurological signs occur in 77% of cases, making clinical assessment critical alongside laboratory values 1.
Associated Laboratory Findings
Hypernatremic dehydration typically presents with:
- Metabolic acidosis in 97.2% of cases – Reflects tissue hypoperfusion and lactic acid accumulation 1
- Acute renal failure in 76.2% of cases – Prerenal azotemia from severe volume depletion 1
- Elevated hematocrit and blood urea nitrogen – Markers of hemoconcentration and dehydration severity 4
Age-Specific Considerations
The mean age of children with hypernatremic dehydration is 6.5 months, with infants being particularly vulnerable due to higher insensible water losses and inability to access fluids independently 1. In neonates, especially those <34 weeks gestation, primary sodium depletion from deficient tubular reabsorption is a frequent cause 5.
Etiology and Risk Factors
Diarrhea accounts for 94.3% of hypernatremic dehydration cases in pediatric populations, making it the dominant cause 1. Other contributing factors include:
- Inadequate water intake relative to losses 6
- Excessive sodium intake (iatrogenic or dietary) 4
- Transepidermal water loss in neonates 4
- Nephrogenic diabetes insipidus (rare but important cause) 2
Correction Rate Guidelines
The serum sodium should be corrected at a maximum rate of 0.5 mmol/L per hour or 10-15 mmol/L per 24 hours to prevent cerebral edema, which is the most feared complication of overly rapid correction 2, 1. In practice, studies show that with appropriate fluid management, serum sodium normalizes within 72 hours in 84.1% of cases 1.
Corrections faster than 48-72 hours have been associated with increased risk of pontine myelinolysis, particularly in preterm infants 5.
Common Pitfalls
- Using isotonic saline (0.9% NaCl) as initial therapy worsens hypernatremia because it delivers excessive osmotic load – 3 liters of urine are required to excrete the osmotic load from just 1 liter of isotonic fluid 2
- Failing to recognize shock – 50% of children present with shock requiring immediate plasma expansion before definitive correction 1
- Correcting too rapidly – This causes cerebral edema, seizures, and permanent neurological injury 2, 4
- Inadequate monitoring – Serum sodium should be checked every 2-4 hours initially during active correction 2