Vet Guide to Hyperosmolar Coma in Diabetic Dogs 2025 🐶🩺 

By Dr. Duncan Houston BVSc

Hyperosmolar coma (also called hyperosmolar hyperglycemic state, HHS) is a rare but life-threatening complication of canine diabetes mellitus. It develops when extremely high blood glucose (>600 mg/dL) causes severe dehydration and elevated serum osmolality (>320 mOsm/kg), leading to CNS disturbances: confusion, seizures, stupor, or coma.

📍 Causes & Risk Factors

• Occurs in long-standing or poorly controlled diabetic dogs, especially when dehydration is prolonged. Triggers include infection, stress, and concurrent illnesses such as pancreatitis or UTI.
• Unlike DKA, ketone production is minimal or absent; hyperglycemia is severe (>600 mg/dL) and hyperosmolality >320–350 mOsm/kg.

👀 Clinical Signs

• Severe polydipsia and polyuria fail to prevent dehydration and weakness; CNS signs include depression, confusion, seizures, and coma.
• Physical exam reveals extreme dehydration and altered mentation or unresponsiveness.

🔬 Diagnosis

• Bloodwork: Serum glucose >600 mg/dL, osmolality >320 mOsm/kg, minimal ketonemia.
• Urinalysis: Glucosuria present, ketones absent or very low—a key distinction from DKA.
• CNS assessment: Neurologic signs, seizures, or coma necessitate hospitalization.

💊 Treatment & Management

• Slow IV fluid therapy: Begin isotonic saline to correct dehydration gradually—especially during first 4–6 h—to minimize cerebral swelling.
• Low-dose insulin: Initiated after rehydration starts to gently lower glucose without dramatic shifts.
• Electrolyte support: Monitor and replace potassium, sodium, and other electrolytes as fluids shift.
• Treat underlying causes: Identify and treat co‑morbidities (infections, pancreatitis) to prevent recurrence.
• Neurologic care: Manage seizures, mentation changes, and monitor for CNS complications.

📈 Prognosis & Monitoring

• Guarded prognosis; mortality can reach ~50% in humans. Early, careful fluid and glycemic control improve survival.
• Frequent re-evaluation of hydration, glucose, electrolytes, and neurologic function is essential.
• Post-crisis, tight diabetic control and diligent monitoring are critical to avoid recurrence.

✅ Dr Houston’s Clinical Tips

• 🔍 Watch for PU/PD in diabetics—don’t ignore excessive thirst or weakness.
• 📊 Check serum osmolality if dogs present with confusion or severe dehydration.
• 🚰 Begin fluids before insulin to avoid rapid osmotic shifts.
• 📅 Monitor electrolytes diligently during fluid therapy.
• 🛑 Control triggering infections or diseases to prevent hyperosmolar episodes.
  

If your diabetic dog becomes lethargic, disoriented, has seizures, or isn’t drinking despite PU/PD, seek emergency care immediately. With timely treatment, we can guide recovery and refine long-term diabetes plans to protect your pet’s health and happiness. 🐾❤️