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 (1015% 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 =>
metabolic acidosis and shock
Na,
K,
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
Urine output
U-Na
U-osmol
U-spec grav.
Increased
Increased
Decreased
Decreased
Skin/GI loss,
3rd spacing
Decreased
Decreased
Increased
Increased
SIADH
Decreased
Decreased
Increased
(>S-osmol)
Increased
Excess i.v. fluid
Increased
Decreased
Decreased
Heart failure /
fluid retention
Decreased
Rénal loss
(diuretics, adrenal
insufficiency)
Increased
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.