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What is hyperosmolar hyperglycemic syndrome?

Hyperosmolar hyperglycemic syndrome (HHS) occurs when your blood sugar levels remain abnormally high for an extended time, causing osmotic diuresis that ultimately is uncompensated and leads to a hypernatremic hypovolemic state.

Simply put, an external stressor, such as infection or medication, causes an imbalance in blood glucose levels, which causes increased urination. If an individual does not drink enough water to compensate, it can develop into HHS.

A high blood glucose level results in the reabsorptive capacity of the kidneys being exceeded; thus, the excess glucose exits the body through the urine. However, this results in the body losing water. You will get severely dehydrated if you do not drink enough water to compensate for such osmotic losses.

In uncontrolled diabetes, the glucose level in your blood might rise to dangerously high levels, sometimes exceedingly tenfold the usual level. Additionally, associated water loss causes the blood to become more concentrated than usual. The process is referred to as hyperosmolarity. It is a condition in which the blood contains an abnormally high number of salts such as sodium, glucose, and other chemicals. This extracts water from the rest of the body's organs to balance the low water content in your blood.

The condition was formerly known by the various names¹ below:

  • Hyperosmolar hyperglycemic nonketotic syndrome

  • Hyperosmolar coma

  • Diabetic hyperosmolar syndrome

  • Hyperosmolar nonketotic coma (HONK)

  • Nonketotic hyperglycemic coma (NKHS)

How common is hyperosmolar hyperglycemic syndrome?

HHS is a less prevalent complication of diabetes than any other complication. It is responsible for less than 1%² of diabetes-related hospitalizations. In addition, if type 2 diabetes is managed well, the chances of developing the condition are minimal.

How is it diagnosed?

Your doctor will examine you, inquire how you feel, and order a blood test to determine the amount of glucose in your blood. For example, an extremely high blood sugar level of more than 600mg/dL¹ combined with low ketone levels, such as acids in the blood and urine, can assist the physician in diagnosing HHS.

The doctor may diagnose you through the following processes:

Serum osmolarity test

A serum osmolarity test determines electrolyte imbalances seen in HHS.

Anion gap

HHS can be diagnosed through an anion gap blood test where a wide anion gap, usually greater than 12, could indicate HHS.

Serum creatinine levels

An increase in serum creatinine levels could indicate the presence of HHS.

Blood urea nitrogen levels

People with HHS may present markedly high blood urea nitrogen levels.

Hemoglobin A1C

The A1C test demonstrates the average blood glucose levels over the last three months and helps establish a diagnosis of diabetes.

Urine analysis

A urine analysis helps doctors determine the specific urine gravity, where a high urine specific gravity shows HHS presence.

Sodium level

Sodium may be low or high depending on volume deficits. Hyperglycemia may cause dilutional hyponatremia.


Ketone levels are none to minimal when you have HHS.

Complete blood count

White blood cell count is usually high in hyperglycemia. A count above 25k may indicate infection.

Potassium levels

Serum potassium levels may be abnormally high due to extracellular potassium shift resulting from insufficient insulin, hypertonicity, and acidemia. People with HHS may experience low potassium levels³ due to severe potassium shortage, especially in severe cases.

Your doctor will also follow a systematic approach for physical diagnosis.⁴ This includes:

  • General appearance, i.e., generally tired and out of breath

  • Cardiovascular, i.e., weak and thready pulse

  • Skin, i.e., poor skin turgor

  • Genitourinary, i.e., increased urine output due to dehydration

You should seek medical assistance if you have diabetes and have the following symptoms:

  • Extreme thirst

  • Dry skin due to dehydration

  • Changes in sight or vision

  • Shock or confused

  • Frequent urination

What is the prognosis for hyperosmolar hyperglycemic syndrome patients?

While the mortality rate attributed to HHS ranges from 5% to 15%,⁴ the long period prognosis is highly dependent on your age, general health, and the severity of the condition. If you have been diagnosed with HHS, you will need to work closely with your doctor after leaving the hospital.

You may lower your chance of getting the condition again by managing your diabetes and making healthy lifestyle changes.

What are the risk factors for developing hyperosmolar hyperglycemic syndrome?

HHS is riskier if you have diabetes and your blood sugar level remains abnormally high over an extended period. The excess sugar is excreted in the urine, causing you to urinate frequently. Consequently, you may have a significant uncompensated fluid loss, particularly in the elderly, where thirst is blunted such that fluid loss does not result in thirst.

Other risk factors¹ include:

  • Age, especially older people, usually in their 60s⁴ or 70s⁴

  • Poor kidney function

  • Impaired thirst

  • Disease or infection,⁴ such as pneumonia or a urinary tract infection

  • Discontinued medication to treat diabetes

  • Developing a heart attack or a stroke

  • Medications that may trigger the condition, such as steroids or diuretics

What are the signs and symptoms of hyperosmolar hyperglycemic syndrome?

HHS symptoms often manifest gradually and might take days or weeks to manifest. The symptoms⁵ include:

  • Excessive urination

  • Excessive thirst 

  • Weakness

  • Rapid heartbeat

  • Poor skin turgor

  • Dry mucous membranes 

  • Low blood pressure

  • Seizures (in up to 25% of people with HHS )

  • Confusion, hallucinations, sleepiness, or inability to stand or walk

  • Headaches

  • Chest pain and chest tightness

  • Blurred vision or loss of vision

What are the complications related to developing hyperosmolar hyperglycemic syndrome?

If not treated, HHS may result in complications⁴ such as:

  • Brain swelling

  • Organ failure

  • Coma

  • Seizures

What should I do to relieve symptoms of hyperosmolar hyperglycemic syndrome?

If you have HHS symptoms, you should drink lots of water and immediately contact emergency health services or go to the hospital. Doctors will give you IV fluids as well as insulin and potassium as appropriate to alleviate your symptoms.

Treatment of hyperosmolar hyperglycemic syndrome

The conventional treatment in the management of HHS is aggressive hydration with isotonic or hypotonic fluid and appropriate electrolyte replacement depending on your sodium and potassium levels. If you are an adult, you should receive an initial fluid bolus of 15 to 20ml/kg, followed by a 200 to 250ml/hour infusion rate.

You’ll most likely be hospitalized in the ICU. You should consult an endocrinologist or an intensive care expert. Doctors should begin with appropriate resuscitation, paying particular attention to the airway, breathing, and circulation (ABC).

You may have an altered mental state if you have HHS due to severe fluid loss and impaired cerebral perfusion. As a general rule, if your Glasgow coma score is less than 8, the doctor will protect your airway, i.e., intubate you.

The infusion rate for young people with HHS should be double the maintenance rate. Hydration with isotonic fluid¹ has been demonstrated to help minimize the production of counterregulatory hormones during HHS.

When physicians use isotonic fluid alone, it may lower your serum glucose by around 75mg/hour to 100mg/hour. Although your blood potassium levels are often elevated in HHS, your total body potassium levels are low due to the extracellular shift that insufficient insulin causes to your body.

So typically, you’d be treated with potassium replacement therapy¹ until 5mEq/L.Potassium replacement is initiated immediately if the serum potassium is <5.3mEq/L as long as there is adequate urine output (approximately >50mL/hour).

Insulin therapy should not be initiated if serum potassium is below 3.3mEq/L, as insulin will further lower the potassium level in the bloodstream by driving potassium into the cells.

Additionally, your physician will address any underlying disorders or infections that may have contributed to the HHS. Typically, you will remain in the hospital so that your healthcare team can carefully monitor you for problems.

Are there any complications of HHS therapy?

Hypoglycemia and hypokalemia are the most common complications of the treatment of DKA and HHS. These complications have become much less common since low-dose intravenous (IV) insulin treatment and careful monitoring of serum potassium have been implemented.

What can I do to avoid getting hyperosmolar hyperglycemic syndrome?

The most effective strategy to avoid HHS is to have a healthy lifestyle and manage your diabetes. You should consider doing the following:

  • Follow a healthy diet with regular exercise

  • Recognize the signs of HHS and get care immediately if you experience any symptoms

  • Avoid excessive drinking

  • Get extra rest and monitor your blood sugar more often when unwell

  • Maintain regular blood sugar checks to ensure you're staying within your desired range, especially if you have diabetes

  • Take insulin and other diabetic medicines exactly as prescribed by your physician

The lowdown

HHS develops when your blood sugar levels stay excessively high over a lengthy period, leaving you dehydrated and confused. It is common among older people with other conditions such as pneumonia and heart diseases.

HHS's significant symptoms are severe dehydration and excessive urination. Intravenous medication can help treat the condition.

Sustaining a healthy lifestyle and taking diabetes medications as prescribed will help avoid HHS.

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