Hyponatremia in neonatology
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Hyponatremia in neonatology. Kirsten L Brunsvig 03.05.10. Sodium. Dominating cation in the ECF Princible determinant for extracellular osmolality Necessary for the maintenance of intravascular volume.

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Hyponatremia in neonatology l.jpg

Hyponatremia in neonatology

Kirsten L Brunsvig

03.05.10


Sodium l.jpg
Sodium

  • Dominating cation in the ECF

  • Princible determinant for extracellular osmolality

    • Necessary for the maintenance of intravascular volume.

  • Unique among electrolytes because water balance, not sodium balance, usually determines its concentration.


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Total body water

  • Distribution of body water

    • Extracellular fluid

      • Intravascular

      • Interstitial

    • Intracellular fluid

  • 40 SA

    • Total body water = 75% of body weight

    • ECF = 45 % of total body water

  • 27 SA

    • Totale body water = 80% of body weight

    • ECF = 70% of total body water


Water loss l.jpg
Water loss

  • Preterm infants have greater weight loss (10-15% vs 5%), associated with increased diuresis, comparet to term infants.

  • Water loss:

    • Kidneys

    • Skin

      • Large insensible water loss, especially in the ELBW infants with very thin skin

    • Lungs

      • Decreases with increasing GA, but less important than skin water loss.

    • Other (stoll, gastric drainage, thoracostomy)


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[Na] regulation

  • [Na] thirst and ADH water intake/retention and normalization of [Na]

  • [Na] decreased ADH water loss and normalization of [Na]

  • However, volume depletion takes presendence over osmolality and causes increase in ADH even if the patient has hyponatremia.

  • Also, excretion of Na in the kidneys is not regulated by osmolality, but plasma volume and a variety of regulatory systems.


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Mechanism of hyponatremia

  • Dilutional (most common in the neonate)

  • Excessive Na+ loss

  • Na+ deficiency


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Differential diagnoses

  • Volume overload

    • Too much volume given

    • Congestive heart failure

    • Renal/liver failure

    • Paralysis with fluid retention

    • Diluted formulas


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Differential diagnosis

  • Increased Na+ loss

    • VLBW: renal tubular Na+ losses high

    • Salt-losing nephropathies

    • GI-losses

    • Skin losses

    • 3rd space (e.g. NEC)

    • Adrenal insufficiency

      • Mineralocorticoid deficiency => Na, K, metabolic acidosis and shock


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Differential diagnosis

  • Inadequate Na+ intake

    • Normal: 2-4mmol/kg/j

  • Drug induced

    • Diuretics

    • Indomethacine can lead to H2O retention

    • Opiates, carbamazepine, barbiturates can cause SIADH

    • Mannitol/hypertonic glucose can cause hyperosmolarity with salt wasting.


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Differential diagnosis

  • SIADH

    = syndrome of inappropriate ADH secretion

    • CNS disorders (IVH, hydrocephalus, asphyxia, meningitis)

    • Lung diseases

    • Critically ill preterm and term neonates


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Patient with hyponatremia

  • Important questions

    • Seizures? (<120mmol/l) –urgency!

    • How much Na and free water is the patient receiving?

    • Weight gain or weight loss?

    • Urine output?

    • Renal salt-wasting medication?


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Clinical examination

  • Complete examination

  • Seizures?

  • Oedema?

  • Decreased skin turgor/ dry mucous membranes as signs of dehydration?

  • Weight gain/loss

  • Fluid intake/output over 24hours


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Further tests

  • S-Na, S-Osmolality

  • U-Na, U-osmolality, U-specific gravity

  • S-electrolytes, S-creatinin, S-total protein to evalue renal function



Treatment l.jpg
Treatment

  • Seizures: emergency

    • NaCl 3%

    • Total body Na-deficit/2 over 12-24 hours

      Rapid corrections may result in brain damage.

      [Na] deficit x weight (kg) x 0.6

      Total body water = 60-75% of weight

      Usually use 60% to minimize the likelihood of overly rapid correction

      [Na] deficit = [Na] desired – [Na] patient


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Treatment

  • Volume overload

    • Fluid restriction

      • usually by 20ml/kg/d

    • S-NA every 6-8h

    • Treat underlying cause

  • Inadequate intake of Na

    • 2-4 mmol/kg/d, increased in premature

  • Increased Na-losses

    • Treat underlying cause

    • Increase Na-intake


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Treatment

  • Drug induced (e.g. Furosemid)

    • Increase intake may be required

    • Indomethacin

      • Treated with fluid restriction

  • SIADH

    • Restrict fluids,

    • Furosemide can be tried.


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Long term prognosis

  • Hyponatremia has been associated with adverse neurological developmental outcomes.

    • Increased risk of cerebral palsy

    • Increased risk of hearing loss

  • Large variations in Na have also been found associated with impaired functional outcomes at 2 years.