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Hyponatremia in dogs | VETgirl Veterinary Continuing Education Videos

May 2018

In this VETgirl online veterinary continuing education video, we discuss hyponatremia in the veterinary patient. While uncommon, hyponatremia can be seen in the small animal patient due to either an excessive retention of free water or an excessive loss of sodium. For that reason, hyponatremia is often referred to as “water toxicity.” In dogs, water toxicity can be seen when a dog ingests an excessive amount of water, resulting in subsequent hyponatremia. Signs of “water toxicity” are typically localized to the central nervous system (secondary to cerebral edema), and typically occur with sodium levels of < 125 mEq/L.

In this VETgirl video, a 5-year-old, male neutered Border Collie Mix, presented to the emergency clinic with ataxia, which rapidly progressed to lateral recumbency. This occurred after the patient was swimming and playing in the freshwater river for several hours prior to presentation. Initial clinicopathologic testing revealed a severe hyponatremia (Na 123 mEq/L), hypochloremia (Cl 90), and hyperlactatemia (5.1). As the hyponatremia developed quickly in this patient, the general guideline is that it can be corrected relatively quickly. (VETgirl’s mantra – What happens slowly, treat slowly and what happens quickly, you can treat quickly). This patient was bolused 30 mL/kg of 0.9% NaCl, at which point the lactate normalized. The patient was continued on 0.9% NaCl with potassium chloride supplementation, and a nasogastric tube was placed to suction excessive river water from the stomach. Electrolytes were closely monitored every 3-4 hours, and the patient’s symptoms resolved and electrolytes normalized with 24 hours of treatment. A baseline cortisol was also normal (ruling out hypoadrenocorticism) also.

Hyponatremia causes an osmotic gradient, resulting in fluid shifts into the brain cells; this results in increase in brain volume and edema. Dogs with acute hyponatremia (hours) are more likely to be symptomatic than chronic hyponatremia (which occurs over days to weeks); that’s because with chronicity, the creation of idiogenic osmoles within the CNS are formed to help equilibrate the osmotic gradient. Most cases of hyponatremia are hyposmolar (that’s why the formula for osmolality is often “dumbed” down to 2 X Na).

To prevent osmotic demyelination syndrome (myelinolysis), chronic hyponatremia should be corrected slowly, no faster than 0.5 mEq/L/hr. This is one of the reasons why VETgirl has personally moved away from using saline to volume resuscitate hypoadrenocorticism patients, as they are typically chronic. Again, symptomatic patients with acute hyponatremia typically can have their sodium corrected more rapidly (e.g., at a faster rate of 1 to 2 mEq/L/hr). Thankfully, with appropriate treatment, many patients can do well. Be sure to check out our other VETgirl videos for great advice and case examples.

  1. Hi Justin,
    Thank you for the hyponatremia podcast.
    Just a quick question regarding the calculation of correction Infusate rate in these patient using 0.9% Nacl. I always use the online human calculation from Medscape website and was wondering if that is something you agree with?

    Best regards,

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