Nephrology Clinical guideline

Hypernatremia in Children - Complete Reference

Definitions & Classifications

  • Defined as serum sodium > 145 mEq/L.
  • Severity: Mild (146-149 mEq/L), Moderate (150-159 mEq/L), Severe (≥ 160 mEq/L).
  • Chronicity: Acute (< 48 hours) versus Chronic (> 48 hours). Default to Chronic if duration is unknown to prevent over-rapid correction risk.
  • High mortality rate (up to 15%) in neonates/infants due to massive fluid shifting.
  • Primarily a deficit of free water relative to body sodium levels, heavily driven by poor thirst mechanism, inability to access water (infants), or severe secretory losses.

Etiology (Volume Status Based)

  • Hypovolemic Hypernatremia (Water loss > Sodium loss): Severe watery diarrhea, vomiting, excessive sweating, osmotic diuresis (DKA/Hyperglycemia), burn injuries.
  • Euvolemic Hypernatremia (Pure water loss): Diabetes Insipidus (Central vs. Nephrogenic), inadequate free water intake, massive insensible losses (fever, radiant warmers in extremely preterm infants).
  • Hypervolemic Hypernatremia (Sodium gain > Water gain): Improperly mixed/concentrated formula, massive sodium bicarbonate resuscitation, severe salt poisoning, drowning in hypertonic sea water.

Clinical Presentation

  • Neurologic symptoms dominate due to cellular dehydration: Irritability, high-pitched cry, paradoxical lethargy with hyperreflexia, muscle twitching / spasticity.
  • Severe Complications (>160 mEq/L): Profound brain shrinkage pulling on meninges, leading to tearing of delicate bridging veins -> Subarachnoid Hemorrhage, Subdural Hematoma, and cerebral venous sinus thrombosis.
  • Skin/Extremities: 'Doughy' or velvety skin texture feeling (hallmark of severe hypernatremic dehydration), dry mucous membranes, sunken fontanelle.
  • Hemodynamic: Shock, tachycardia, delayed capillary refill (though intravascular volume is often better preserved than in isotonic dehydration due to osmotic fluid pull from intracellular space).

Diagnostic Pathway

  • 1. Assess overall volume status (Hypovolemic vs Euvolemic vs Hypervolemic).
  • 2. Check Urine Osmolality (U_Osm): Determines if kidneys are actively trying to conserve water.
  • U_Osm > 800 mOsm/kg (Appropriately conserved): Suggests extra-renal water loss (GI/Skin) or excess sodium intake.
  • U_Osm < 300 mOsm/kg (Inappropriately dilute): Diabetes Insipidus. Water deprivation test + exogenous DDAVP required to differentiate Central (responds) vs Nephrogenic (no response).
  • U_Osm 300-800 mOsm/kg: Suggests profound osmotic diuresis (measure urine glucose/urea) or partial DI.
  • Urine Sodium: U_Na < 20 mEq/L indicates hypovolemia/extrarenal loss. U_Na > 20 mEq/L indicates renal concentrating defect.

Management & Absolute Correction Limits

  • 1. HEMODYNAMIC RESUSCITATION: If the child is in hypotensive shock, RESUSCITATE FIRST with normal isotonic fluid (0.9% NaCl or LR) at 10-20 mL/kg bolus. DO NOT use hypotonic fluids for initial resuscitation even if Na is extremely high. Volume restoration supersedes correction curves.
  • 2. CALCULATE FREE WATER DEFICIT: FWD (Liters) = Total Body Water (TBW) * ((Current Na / Desired Na) - 1).
  • 3. CORRECTION RATE (CRITICAL): Brain cells form idiogenic osmoles (taurine, glutamine) to protect against shrinkage. Rapidly lowering serum Na causes massive water shift INTO brain cells -> CEREBRAL EDEMA & HERNIATION.
  • Rate Limit: Lower serum sodium by strictly MAXIMUM 0.5 mEq/L/hour (or exactly 10-12 mEq/L per 24 hours). If initial Na >170, safely correcting may take 72-96 continuous hours.
  • Acute Exceptions: Only if hypernatremia resulted from acute (<24hr) salt poisoning (no idiogenic osmoles formed yet), correction can be up to 1 mEq/L/hr.
  • 4. INFUSATE SELECTION: Typically use 0.45% NaCl + 5% Dextrose. Do NOT administer pure sterile/free water intravenously (causes catastrophic RBC hemolysis).
  • Monitor serum Sodium EXACTLY every 2 to 4 hours to titrate fluid rates based on the changing slope.

Diagnostic & Management Algorithm

  • Hypernatremia SLOW Correction: [START] Na > 150 -> [ACTION] Calculate free water deficit -> [MONITOR] Reduce Na by STRICTLY < 0.5 mEq/L/hour -> [GOAL] Prevent cerebral edema

References for this guideline are being added; see the methodology for our source hierarchy.

Medical disclaimer: This page is for qualified healthcare professionals and is a decision-support aid only. It does not replace clinical judgement, local protocols or product information. Verify every dose and threshold before use. See the full Medical Disclaimer.