Hyponatremia in neonatology

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

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 • 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)

[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.

Mechanism of hyponatremia • Dilutional (most common in the neonate) • Excessive Na+ loss • Na+ deficiency

Differential diagnoses • Volume overload • Too much volume given • Congestive heart failure • Renal/liver failure • Paralysis with fluid retention • Diluted formulas

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

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.

Differential diagnosis • SIADH = syndrome of inappropriate ADH secretion • CNS disorders (IVH, hydrocephalus, asphyxia, meningitis) • Lung diseases • Critically ill preterm and term neonates

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?

Clinical examination • Complete examination • Seizures? • Oedema? • Decreased skin turgor/ dry mucous membranes as signs of dehydration? • Weight gain/loss • Fluid intake/output over 24hours

Further tests • S-Na, S-Osmolality • U-Na, U-osmolality, U-specific gravity • S-electrolytes, S-creatinin, S-total protein to evalue renal function

Laboratory findings

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

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

Treatment • Drug induced (e.g. Furosemid) • Increase intake may be required • Indomethacin • Treated with fluid restriction • SIADH • Restrict fluids, • Furosemide can be tried.

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.

Hyponatremia in neonatology