Hyperglycemic Hyperosmolar Syndrome (HHS) is an uncommon form of a diabetic crisis that can occur in dogs and cats that has the following characteristics:

  • Severe hyperglycemia (>600 mg/dl)
  • Minimal to absent ketones
  • Increased serum osmolarity (> 350 mosm/kg – normal ~ 300)

Like diabetic ketoacidosis (DKA), HHS is caused by a lack of insulin with increased counter-regulatory hormones (glucagon, epinephrine, cortisol, growth hormone).  Unlike DKA though it is believed that there is not lipolysis so there isn’t ketosis.  Animals with HHS are significantly more dehydrated and hypovolemic than animals with DKA and rehydration plays an even more crucial role than it does in DKA.

Therapy for Hyperglycemic Hyperosmolar Syndrome in Dogs and Cats

When an animal’s glucose becomes as high as we see in HHS and their osmolarity increases, the brain forms substances called idiogenic osmoles.  This is because a body is always trying to stay in homeostasis between the blood and tissues.  Forming idiogenic osmoles allows the osmolarity of the brain to increase to that of the blood.  If you suddenly drop the glucose in the blood in these animals, the osmolarity of the blood will be severely less than that of the brain (idiogenic osmoles do not go away right away).  The physiologic response to unequal osmolarity is for water to move from the area of lower osmolarity to that with higher osmolarity.  In the case of an animal where the glucose drops too quickly, this would mean water would move from the blood (which now has lower osmolarity) to the brain (which still has those idiogenic osmoles).  Fluid moving into the brain means there is formation of cerebral edema.

For this reason, we never start these animals on insulin right away.  The main goal is to rehydrate, improve kidney perfusion and therefore slowly bring down the glucose and osmolarity.  Also because these animals do not have many ketones, the addition of insulin is less crucial than just