Sodium

Hyponatremia

• Serum [Na+] <136 mmol/l Blood biochemistry: sodium Hyponatremia.
• Plasma osmolality may be normal, high or low (n = 290-310 mOsm/kg)
• Retention of water, eg in response to decreased blood volume or blood pressure.
• Causes include:
  • Gastrointestinal loss.
  • Congestive cardiac failure.
  • Diuretic therapy.
  • Hypoadrenocorticism.
• Clinical signs:
  • Lethargy.
  • Weakness.
  • Vomiting.
  • Muscle cramping.
  • Seizures Seizures - due to changes in brain volume.
  • Wide QRS and ST segment elevation.
  • Water retention will increase bodyweight.
• Severe hyponatremia (<110 mmol/l) give 3% saline over 24 h: mmol Na+ required = 0.2 x bodyweight (kg) x (normal [Na+] - patient's [Na+]).
  Correct slowly as oversupplement, too fast can cause central pontine myelinolysis.
• Less severe (<120 mmol/l)  correct underlying cause and give 0.9% saline.
  For composition of solutions see the Parenteral fluids comparison table Parenteral fluids comparison table.

Hypernatremia

• Serum [Na+] = >156 mmol/l Hypernatremia.
• Free water loss, eg heat exhaustion Fluid therapy: for heat exhaustion.
• Diabetes insipidus.
• Can be caused by excess administration, eg giving sodium bicarbonate.
• Shift of water from ICS → ECS → cell dehydration.
• Clinical signs - related to the CNS:
  • Lethargy.
  • Confusion.
  • Muscle weakness.
  • Seizures Seizures.
  • Coma.
• Give hypotonic fluid, eg 5% dextrose in water or 0.45% NaCl.
  For composition of solutions see the Parenteral fluids comparison table.
• In patients with long-standing hypernatremia, correct slowly to prevent cerebral edema.
• Equation for replacement of H2O:
  • Free water deficit = 0.4x lean bodyweight (kg) x ((plasma[Na+]/140) -1).
    Do not lower plasma [Na+] more than 15 mEq/L in first 8 h.

Potassium

Calcium

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Brady C A, Vite C H, Drobatz K J (1999) Severe neurologic sequelae in a dog after treatment of hypoadrenal crisis. JAVMA 215 (2), 210, 222-225 PubMed.
• Churcher R K, Watson A D, Eaton A (1999) Suspected myelinolysis following rapid correction of hyponatremia in a dog. J Am Anim Hosp Assoc 35 (6), 493-497 PubMed.

Other sources of information

• Wingfield W E (1997) Veterinary Emergency Medicine Secrets. Eds Hanley & Belfus ISBN 1560534214.