Vet’s 2025 Guide to Canine Hyponatremia Low Sodium in Dogs🩺

By Dr. Duncan Houston BVSc

💡 What Is Hyponatremia?

Hyponatremia is defined as a serum sodium concentration below ~140 mEq/L in dogs. This electrolyte imbalance usually reflects too much water relative to sodium, leading to low blood osmolality and potential cell swelling—most critically in the brain.

🚩 Who Gets It & Why?

• 💧Water intoxication – dogs that drink or ingest excessive water, e.g., from hoses or pools.
• ⚖️Hypovolemic loss – vomiting, diarrhea, diuretics causing sodium and water loss.
• 🌊Hypervolemic dilution – CHF, liver disease, nephrotic syndrome, causing fluid overload.
• 🧠SIADH / ADH excess – inappropriate antidiuretic hormone, adrenal or thyroid disease.
• 🧬Other: excessive hypotonic fluid infusion, primary polydipsia, pseudohyponatremia from lab error.

👀 Clinical Signs

• 😔 Mild: lethargy, weakness, poor appetite.
• 🤢 GI signs: vomiting, diarrhea, appetite loss.
• 🧠 Neurologic: disorientation, tremors, seizures, coma in acute or severe cases.
• 🫀 Depending on cause: dehydration signs or fluid overload (edema, ascites).

🧪 Diagnosis & Lab Work

• Confirm low Na+: <140 mEq/L via ion-selective electrode is accurate.
• Assess osmolality: plasma osmolality <290 mOsm/kg confirms true hyponatremia; correct for glucose if hyperglycemic.
• Urine studies:
  • Urine osmolality: <100 mOsm/kg = primary polydipsia; >100 = SIADH or volume loss.
  • Urine sodium: <20 mEq/L indicates hypovolemia; >20 suggests SIADH, Addison’s, diuretics.
• Blood tests: CBC, chemistry, BUN, T4/TSH, cortisol (ACTH stim).
• Imaging if needed: ultrasound for CHF, liver/kidney disease.
• ECG/echo: if heart failure is suspected.

🛠 Treatment Strategies

1. Treat the Underlying Cause

• 🚱 Water intoxication: restrict water access, educate owners.
• 🚽 Replace fluids and sodium in hypovolemia using isotonic saline.
• 💧 Reduce fluid and use diuretics in CHF/liver/cirrhosis
• 🧪 Treat Addison’s, hypothyroidism, SIADH, or reduce ADH stimulators.

2. Correct Sodium Carefully

• ⏱ Chronic cases (<48h onset): correct slowly—≤0.5 mEq/L/h or ≤10–12 mEq/day to avoid osmotic demyelination.
• ⚠️ Acute/severe (seizures): hypertonic saline (3%) small bolus (1 mL/kg) to raise Na+ by ~2 mEq/L.
• 💧 For volume:
  • Hypovolemic: isotonic saline until stable, monitor serum Na+ every 4–6h.
  • Euvolemic/hypervolemic: restrict free water, use diuretics & possibly vaptans if available.

3. Monitor & Prevent Complications

• 📉 Monitor Na+ frequently to guide fluids and prevent over-correction.
• 🧠 Watch for neurologic changes; if osmotic demyelination suspected, slow infusion and give desmopressin.

📈 Prognosis

• ⚠️ Hyponatremia is associated with higher mortality, even if mild.
• 🧩 Prognosis depends on the speed of correction and treating the root cause.
• 🏥 Acute severe cases: ICU care can save dogs, but seizures worsen outcomes.
• ⏳ Chronic mild cases: often managed outpatient with careful monitoring.

🏡 Ask A Vet App Home‑Support Tools 📲🐶

• 📆 Reminders for fluid restrictions, medication, and rechecks.
• 📊 Log Na+ levels, urine output, water intake, symptoms.
• 📸 Upload photos/video of neurologic signs (e.g., weakness).
• 🔔 Alerts for extreme thirst, vomiting, seizures signaling vet evaluation.
• 📚 In-app guides on fluid calculation, slow correction, and identifying emergency signs.

🔑 Key Takeaways 🧠✅

• Low sodium in dogs stems from excess water or loss of sodium, diagnosed by labs and osmolality urine studies.
• Identify cause: dehydration, CHF, SIADH, endocrine disorders, polydipsia.
• Treatment focuses on gentle correction—acute cases with hypertonic saline; chronic cases with slow isotonic correction.
• Frequent monitoring prevents serious neurologic complications.
• Using the Ask A Vet app ensures precise tracking, timely alerts, and remote vet teamwork.

🩺 Final Thoughts ❤️

In 2025, we understand canine hyponatremia as a complex but treatable condition. when we diagnose underlying causes, manage fluid and sodium carefully, and monitor closely, dogs can recover successfully. Owners play a key role in safe water management and real-time tracking—and with Ask A Vet, they are empowered to spot changes early, optimize care, and collaborate with veterinarians to steer dogs toward healthy outcomes. 🐾✨

Visit AskAVet.com and download the Ask A Vet app to log fluid intake, meds, Na+ readings, upload symptoms & stay connected to your vet. 📲🐶