Addisonian crisis: lactated Ringer's or saline?
5-year-old crossbreed dog in Addisonian crisis with several weeks of clinical signs. Sodium 116 mmol/L (140–155) and potassium 7.6 mmol/L (3.5–5.5).
Which statement about fluid therapy is correct?
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A. A balanced crystalloid can be used: its potassium does not worsen hyperkalaemia and, with sodium this low, it helps avoid raising it too quickly
Correct. Lactated Ringer's contains less potassium than this dog's plasma, and volume expansion lowers potassium. 0.9% saline is also acceptable, but with severe chronic hyponatraemia it may raise sodium too quickly.
B. Lactated Ringer's is contraindicated because it contains potassium
This is a common misconception. Its potassium concentration (about 4 mmol/L) is lower than the patient's, so it does not raise it; volume expansion is what lowers potassium.
C. 5% dextrose, because it contains no potassium and prevents hypoglycaemia
5% dextrose is equivalent to free water: it does not expand intravascular volume and would worsen hyponatraemia.
D. 7.5% hypertonic saline to normalise sodium within a few hours
With chronic hyponatraemia, raising sodium quickly can cause myelinolysis (osmotic demyelination), with neurological signs days later.
lightbulb Key takeaway
Sodium should not rise more than 10–12 mmol/L in 24 hours: measure it every 4–6 hours. Remember that sodium also rises when glucocorticoids are given and volume is restored, because the kidney excretes free water again.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.