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Fluid therapy: for electrolyte abnormality

ISSN 2398-2950

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  • Serum [Na2+]   Blood biochemistry: sodium  <136 mmol/l   Hyponatremia  .
  • Retention of water, eg in response to decreased blood volume or blood pressure.
  • Clinical signs   →   lethargy, weakness, vomiting, muscle cramping, seizures, wide QRS and ST segment elevation.
  • Severe hyponatremia (<110 mmol/l)   →   give 3% saline over 24 hours.
  • mmol Na+ required = 0.2 x body weight (kg) x (normal [Na+] - patients [Na+]).
  • Less severe (<120 mmol/l)   →   correct underlying cause and give 0.9% saline.


  • Serum [Na+] = >160 mmol/l   Hypernatremia  .
  • Free water loss, eg heat exhaustion.
  • Shift of water from ICS to ECS   →   cell dehydration, brain cells especially vulnerable.
  • Clinical signs   →   lethargy, confusion, muscle weakness, seizures and coma.
  • Give hypotonic fluid, eg 5% dextrose in water or 0.45% NaCl.
  • In cats with longstanding hypernatremia, correct slowly to prevent cerebral edema.


  • Imbalances are common.
  • Small changes in ECF [K+] can have serious effects on cell membrane depolarization, especially cardiac muscle.


  • Serum [K+] <3.5 mmol/l   Blood biochemistry: potassium      Hypokalemia  .
  • An important iatrogenic cause of hypokalemia is using replacement crystalloid solutions such as Hartmann's for maintenance. The [K+] in these solutions is inadequate to match normal daily losses.
  • Many fluid losses contain K+ in excess of normal ECF [K+]. This coupled with anorexia of many ill cats makes hypokalemia common.
  • Clinical signs   →   muscle weakness, lethargy, confusion, vomiting, cardiac arrhythmias.
  • Potassium should be supplemented by adding KCl to intravenous fluids. The desired [K+] of the fluids depends on the severity of the hypokalemia, eg give fluids with 30 mmol/l [K+] for mild hypokalemia of 2.5-3.4 mmol/l.
  • Never exceed an infusion rate of 0.5 mmol/kg/hr.
  • Monitor ECG   ECG: overview  when giving rapid infusions of potassium.


  • Serum [K+] >5.5 mmol/l   Hyperkalemia  .
  • Clinical signs   →   weakness, lethargy and life-threatening cardiac arrhythmias.
  • Potassium free fluids such as 5% dextrose in water should be infused to dilute the potassium and increase renal excretion.
  • For patients with severe hyperkalemia and ECG abnormalities, additional therapies such as bicarbonate or insulin/dextrose may be needed. Bicarbonate   Sodium bicarbonate  and insulin/dextrose cause K+ to shift from the ECF to ICF.
  • Regular insulin   Insulin  0.1-0.25 units/kg IV bolus + 0.5-1.5 g/kg glucose   Glucose  IV over 2 hours is one treatment for severe hyperkalemia.
  • 10% calcium chloride   Calcium chloride  (0.2 ml/kg) may be given to cats with critical hyperkalemia and life-threatening cardiac arrhythmias. This antagonizes the effect of K+ on polarization of cardiac cells.



  • Serum [Ca2+] <1.75 mmol/l.
  • Clinical signs   →   restlessness, muscle fasciculations, tetany, prolonged QT and ST segments.
  • Administer 10% calcium chloride   Calcium chloride  at 5-15 mg/kg over 1 hour. Alternatively, a dose for supplementation using calcium gluconate   Calcium gluconate  should be included.
  • Monitor ECG during infusion.

Further Reading


Refereed papers

Other sources of information

  • Haskins S C & Aldrich J (1994) Perioperative supportive care. In: Anaesthesia of the Cat. Eds L W Hall and P M Taylor. Balliere Tindall. pp 289-290. ISBN 0 7020 1665 9.