Hyperosmolar hyperglycemic state (HHS) is a life-threatening diabetes emergency that requires hospital treatment with intravenous fluids, insulin, and electrolyte replacement. Blood glucose levels climb above 600 mg/dL, and the blood becomes dangerously concentrated, which can lead to seizures, coma, and organ failure if not corrected. Treatment focuses on gradually rehydrating the body, lowering blood sugar at a controlled pace, and identifying whatever triggered the crisis in the first place.
What Happens in HHS
HHS develops when blood sugar rises so high that the body tries to flush the excess glucose through the kidneys, pulling massive amounts of water with it. This creates severe dehydration and makes the blood abnormally thick and concentrated. The American Diabetes Association defines HHS as a blood glucose above 600 mg/dL, an effective blood osmolality above 320 mOsm/L (a measure of how concentrated the blood is), and an arterial pH above 7.30, meaning the blood hasn’t turned significantly acidic the way it does in diabetic ketoacidosis (DKA).
Most people with HHS have type 2 diabetes, and many are older adults. The condition usually builds over days to weeks, not hours. By the time someone reaches the emergency room, they may have lost several liters of fluid and can be confused, lethargic, or unresponsive.
What Triggers It
Infection is the single most common trigger, responsible for roughly half of all HHS cases. Pneumonia accounts for over 50% of those infections, followed by urinary tract infections at about 21%. Other triggers include corticosteroid use (around 21% of cases), antipsychotic medications, stroke, heart attack, and simply not taking diabetes medications as prescribed. Tube feeding and IV nutrition in hospitalized patients can also push blood sugar high enough to set off HHS.
Identifying and treating the underlying trigger is just as important as correcting the blood sugar itself. If a pneumonia or UTI is driving the crisis, antibiotics need to start alongside the rest of the treatment plan. Without addressing the root cause, blood sugar is much harder to bring under control.
Fluid Replacement Comes First
The most critical step in treating HHS is replacing the enormous volume of fluid the body has lost. People with HHS are typically 8 to 12 liters dehydrated. Treatment starts with normal saline (0.9% sodium chloride) given intravenously, with potassium added as needed.
The goal is to replace about half of the estimated fluid loss within the first 12 hours and the rest over the following 12 hours. The medical team checks blood osmolality every hour at the start and adjusts the fluid rate to ensure it’s steadily declining. If osmolality isn’t dropping despite adequate fluid replacement, a more dilute saline solution (0.45% sodium chloride) may be substituted. Guidelines from the Joint British Diabetes Societies note there’s no evidence supporting the use of anything more dilute than that.
Rehydration alone can lower blood sugar significantly, even before insulin is started. That’s because restoring fluid volume helps the kidneys clear excess glucose and improves blood flow to tissues that were essentially starved of circulation.
Insulin: Low and Slow
Insulin is given intravenously, but at carefully controlled rates. In adults, the typical approach is an initial dose of 0.1 units per kilogram of body weight, followed by a continuous drip of 0.1 units per kilogram per hour. An alternative protocol skips the initial dose and uses a slightly higher continuous rate of 0.14 units per kilogram per hour. In children, no initial bolus is given because it increases the risk of brain swelling. Instead, a continuous infusion of 0.1 units per kilogram per hour is started right away.
The insulin drip continues until blood glucose drops to the 250 to 300 mg/dL range. At that point, the rate is adjusted and sugar-containing fluids may be added to prevent blood sugar from falling too fast. The transition from IV insulin to injectable insulin under the skin happens once the patient is eating, drinking, and clinically stable.
Why the Pace of Correction Matters
One of the biggest dangers during HHS treatment is correcting blood sugar and blood concentration too quickly. If glucose drops faster than about 90 to 120 mg/dL per hour, or if osmolality falls more than 3 to 8 mOsm/kg per hour, the rapid shift in fluid balance can cause cerebral edema, a potentially fatal swelling of the brain. Sodium levels also need to come down gradually, no more than 10 mmol/L over a full 24-hour period.
This is why HHS treatment is not simply about pumping in fluids and insulin as fast as possible. The medical team is constantly balancing the need to rehydrate against the risk of overcorrecting. Blood glucose is checked every hour, and electrolytes and blood gases are monitored every two to three hours throughout the acute phase of treatment.
Electrolyte Replacement
Potassium is the electrolyte that requires the most attention during HHS treatment. Even though potassium levels in the blood may look normal or even high when someone first arrives at the hospital, total body potassium is almost always severely depleted. As insulin pushes glucose back into cells, potassium follows, and blood levels can plummet dangerously. This can cause heart rhythm problems, so potassium is replaced intravenously and monitored closely.
Sodium and chloride losses are also significant, which is why normal saline is the starting fluid. The medical team adjusts sodium replacement based on serial blood draws, always watching the rate of change to avoid overcorrection.
What Recovery Looks Like
HHS typically requires treatment in an intensive care unit, at least for the first 24 to 48 hours. The acute phase of fluid and insulin correction can take one to three days depending on how severe the dehydration and blood sugar elevation were at presentation. Resolution is defined by blood glucose returning below 300 mg/dL, osmolality normalizing, and the patient becoming alert and able to eat and drink.
Even after the crisis resolves, recovery isn’t instant. Many patients, especially older adults, experience lingering confusion or weakness that can take days to clear. Some may have developed complications during the crisis itself, including blood clots, kidney injury, or rhabdomyolysis (muscle breakdown from severe dehydration). Hospital stays of a week or more are not unusual.
After discharge, the focus shifts to preventing another episode. That means working out a reliable diabetes management plan, reviewing all medications (especially corticosteroids or antipsychotics that raise blood sugar), and making sure infections are caught and treated early. For people who weren’t previously diagnosed with diabetes, HHS is sometimes the event that reveals the disease for the first time, making follow-up care especially important.