Normal Serum Level: 135-145 mEq/L
Daily Sodium requirement: 3- 5mEq/kg

Hyponatremia (<135mEq/L)

Causes :

  • Euvolemia: (SIADH, Fluid overload, water
    intoxication)
  • Hypovolemia: (Dehydration, diarrhea, vomiting,
    diuresis)
  • Hypervolemia:(Congestive heart failure, Liver
    failure, Nephrotic syndrome, AKI, CKD)

Signs and Symptoms:

  • Mild
    • Headache, nausea, vomiting, lethargy and
      confusion
  • Severe
    • Refractory status epilepticus, coma, decorticate posturing, dilated pupil,
      anisocoria, papilledema, cardiac arryhtmia, cerebral edema (<125mEq/L)

Pathophysiology:
Hypo-osmolality causes influx of water into the intracellular space, which results in cytotoxic cerbral edema and increased intracranial pressure and can lead to brain ischemia, herniation and death. Brain cell adpats by extrusion of intracellular electrolytes and organic osmolytes such as glutamate and aspartate that can produce seizure

Note: Too rapid correction may result in osmotic demyelination or central pontine myelinolysis.

Treatment:

  • Check the volume status
    • Hypovolemia
      • Correct the hypovolemia first with NS or RL
      • WHO ORS rehydration solution is preferable for patients who are able toaccept orally
    • Isovolemia/Hypervolemia
      • Fluid restriction and diuresis
  • Is patient symptomatic or asymptomatic?
    • Symptomatic
      • Rapid correction: 3% NS @ 4-6 ml/kg over 30 minutes followed by slow correction
        • Each ml/kg of 3% NS raises serum Na by
          approximately 1mEq/L
      • Asymptomatic
        • Slow correction over 24-48 hours
        • Slow correction:
          • Calculate the Total fluid requirement of child using Holliday Segar Method
          • You should also know the Na level in common pediatric IV fluid (DNS, EP, NS)
            • Calcualte Sodium deficit: Na deficit= Body Weight x 0.6 x (Desired Na i.e 125 – Observed Na)
        • Replacement rate:
          • 1/2 of Total sodium deficit replaced in 8 hours and next 1/2
            is repalced in next 16 hours.

Note: 60% of child body weight is water so we multiply by 0.6. Use 125mEq/L as upper limit i.e desired Na as patient remain asymptomatic above that and treating
underlying causes can correct hyponatremia itself.

        • Example:
          • BW: 10kg, Serum Na: 110mmol/l
          • Total fluid requirement: 1000ml
          • Sodium requirement= Body Weight x 0.6 x (Desired Na i.e 125 – Observed Na)
            • 10 x 0.6 x ( 125- 110)
            • 90mEq
          • 90 mEq Na needs to supplemented in 1000ml fluid
            • 45 mEq in 500ml in 1st 8 hours
              • Which fluids to use? Use the fluids which have approx 45 mEq in 500ml.
            • In this case, 250ml DNS =38mEq and 250ml Isolyte-P = 6mEq will replace the sodium requirement.
          • Next, 45 mEq in 500ml need to be replaced over 16 hours.
      • Treat the underlying causes

Note: Rate of sodium correction should not be >12 mEq/24hours i.e 0.5 mEq/hr