Electrolyte Requirements

 

Reviewed by Carl Kuschel and David Knight
January 2007
Clinical Guidelines Back Newborn Services Home Page
Summary Requirements Sodium Requirements Hyponatraemia Hypernatraemia
Potassium Requirements Hypokalaemia Hyperkalaemia References

Summary Requirements

Day 1
  • No routine electrolytes
Day 2 onwards
  • Add electrolytes:
Na+ 3 mmol/kg/day (very preterm infants may need more)
K+ 2 mmol/kg/day
Ca2+ 1 mmol/kg/day
  • Do not add Ca2+ routinely in relatively well infants only likely to be on short term IV fluids.
    • This is most babies as the sicker, longer term babies will be on IVN)
Additive Concentration Requirement Formula
Na+ 4 Molar
(4mmol/ml)
3 mmol/kg/day
(0.75ml/kg/day)
      500 x weight (kg) x 0.75     
24 hour total fluids (ml)
K+ 1 Molar
(1mmol/ml)
2 mmol/kg/day
(2ml/kg/day)
      500 x weight (kg) x 2      
24 hour total fluids (ml)
Ca2+ 10% Ca gluconate
(0.22mmol/ml)
1 mmol/kg/day
(4.5ml/kg/day)
      500 x weight (kg) x 4.5     
24 hour total fluids (ml)
Note:
  • Assumes that additives are added to a 500ml bag of fluid.
  • Add Heparin 250units/500ml to central venous line (including long line) fluids.
  • If daily requirements are increased or decreased, these formulations need to be recalculated.
  • This system does not take into account the amount of sodium in arterial fluids or other infusions and calculations need to be adjusted accordingly.

Sodium Requirements

Hyponatraemia

Definition
  • Serum Na+ <130
Commonest Causes
  • Prematurity.
  • Inadequate Na+ intake.
  • Excessive water intake.
    • Excessive maternal fluid intake during labour/delivery can lead to neonatal hyponatraemia.
  • Diuretic therapy, especially loop diuretics (e.g. furosemide).
  • Acute tubular necrosis  (tubular Na+ loss) and other causes of renal failure.
  • Indomethacin.
    • Reduces free water clearance and fractional excretion of sodium, with the lower free water clearance leading to hyponatraemia.
  • SIADH.
    • ADH has a limited ability to concentrate the urine in the newborn, and acts primarily as a vasopressor.
  • Excess Na+ loss.
    • Diarrhoea, Gastric, pleural, CSF, 17OH progesterone deficiency.
Investigation
  • An isolated low Na+ should not be treated.
    • Repeat the sample.
    • There is an error of measurement within the analyser of ±4mmol/L.
  • Urinary Na+ if high Na+ requirements.  This may allow for an estimate of sodium replacement.
Management
  • Treatment will depend on the underlying cause and the severity of the hyponatraemia.
    • It can sometimes be difficult to determine whether the main cause of hyponatraemia is excessive water, inadequate body sodium, or a combination of the two.
  • Excessive water:
    • Reduce the water (fluid) intake.
  • Reduced body sodium (from inadequate intake or increased excretion):
    Oral sodium supplements
    • 2 Molar NaCl supplements (1ml = 2mmol NaCl).
    • Usually start at 3mmol/kg/day additional NaCl.
    • Occasional infants will require ≥12mmol/kg/day NaCl.
    Intravenous sodium infusion

Hypernatraemia

Definition
  • Serum Na+ >150mmol/L.
    • In NICU, management is usually altered for serum Na+>145mmol/L.
Commonest Causes
  • Excessive water loss.
    • Very preterm insensible water loss.
    • Diarrhoea.
    • Polyuria.
  • Excess Na+ intake.
    • Relatively common with sodium bicarbonate infusions.
    • Other medications and infusions may contain large quantities of sodium.  For example, an arterial line containing 0.9% NaCl and running at 1ml/hour will give 3.6mmol/day of NaCl.
Investigation
  • Interpret high Na+ values in clinical context.  Is the baby dehydrated?  Are there ongoing fluid losses?  Is the baby receiving medications or infusions that contain large amounts of Na+?
Management

Potassium Requirements

Hypokalaemia

Definition
  • Serum K+ <3.5mmol/L
    • Capillary K+ values are generally higher than arterial K+ values so a low K+ on a capillary sample indicates significantly lower arterial K+ values.
Commonest Causes
  • Inadequate intake
  • Alkalosis (particularly infants receiving sodium bicarbonate infusions).
    • Alkalosis may be secondary to bicarbonate treatment, over-ventilation, or loss of acid from gastric secretions.
  • Renal causes
  • Diarrhoea
  • Medications (including diuretic therapy, sodium bicarbonate infusions, salbutamol, and insulin)
Investigation
  • Evaluate baby for potential causes of hypokalaemia (as above).
Management
  • Treatment will depend on the underlying cause and the severity of the hypokalaemia.

    CAUTION:  Consider delayed treatment or monitor carefully if urine output is low or renal function is abnormal.

    Oral potassium supplements
    • 2 Molar KCl supplements (1ml = 2mmol KCl).
    • Usually start at 2mmol/kg/day additional KCl.
    • Monitor the serum K+ carefully and adjust dose accordingly.
    Intravenous potassium infusion

Hyperkalaemia

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