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Managing hyperosmolar syndrome

Hyperosmolar syndrome is an uncommon complication of untreated feline diabetes mellitus. In animals in which target tissue resistance to insulin plays a role in the disease, insulin levels can be elevated. In these cases, ketosis is suppressed and plasma glucose concentrations can become very high.


Physical examination often reveals profound dehydration, and the cat is typically lethargic, extremely depressed, or comatose. The severity of the hyperosmolality correlates directly with the severity of these signs.

Hyperosmolar syndrome represents an emergency situation. Affected cats will become progressively weaker, anorexic, lethargic, and drink less. Ultimately, blood glucose levels become so high that osmosis shifts water from brain cells and coma results.

Management guidelines

Goals of management include correcting fluid deficits and electrolyte balance associated with severe dehydration, reducing blood glucose via insulin therapy, correcting the hyperglycemic, hyperosmolar state, and managing concurrent diseases.

Fluid therapy is critical to alleviate this syndrome, especially in the first 4 to 6 hours of management. The goal is to reduce blood glucose at the rate of 50 mg/dL/hr. When the blood glucose approaches 300 mg/dL, the IV fluid selection should be changed to 5% dextrose solution.

Intravenous isotonic fluid and insulin therapy usually resolve hyperosmolality, but must be done slowly to minimize the shift of water from the extracellular to the intracellular compartment.

Delay insulin therapy (typically 4–6 hours) until fluid therapy has improved the cat’s condition, corrected dehydration and improved urine production, hyperglycemia, hyperosmolality, and electrolyte levels.

Evaluation of management

When evaluating the effectiveness of fluid therapy, also monitor:

  • Urine
  • Blood pressure
  • Blood glucose
  • Serum electrolytes
  • BUN and urine glucose