Hyperosmolar Hyperglycaemic State (HHS)
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  • Hyperosmolar hyperglycaemic state (HHS) was formerly known as HyperOsmolar Non-Ketotic coma (HONK).
  • HHS is a condition that occurs in patients who suffer from type 2 diabetes mellitus and have very high blood sugars (over 33.3mmol/L).
  • The condition can have an insidious onset, worsening over several days or weeks before the patient presents to a health care provider.
  • HHS is often caused by a combination of illness (i.e. infection) and dehydration.
  • HHS is an emergency with a high associated-mortality and therefore requires specialist treatment, usually in a high-dependency setting.


  • In type 1 diabetes, an absolute lack of insulin can cause high blood sugars and lead to the production of ketones which results in Diabetic Ketoacidosis (DKA)- see related article here.
  • In type 2 diabetes, however, patients usually retain some usable insulin and the body will not need to resort to ketone production. Therefore someone with type 2 diabetes can have extraordinarily high blood sugar levels without a clinically significant rise in ketones.
    • In HHS, the pancreas is still able to produce small amounts of insulin and this is enough to suppress lipolysis and therefore prevent ketogenesis which would lead to DKA but not enough to lower blood glucose levels to a safe level.
  • Importantly, patients with type 2 diabetes who are insulin dependent may develop DKA rather than HHS (as they do not have any usable insulin).
  • HHS can be the first presentation of type 2 diabetes.[1]


  • There are fewer hospital admissions for HHS than there are for DKA.
  • Sources report HHS accounts for less than 1% of all primary diabetic admissions.
  • However, the mortality rate for HHS is 10-20% which is about 10x higher than that of DKA[2].
  • Poor outcomes with HHS occur in:
    • Patients at the extremes of age (very young or very old)
    • Those who present with coma and
    • Those with profound hypotension.


  • While DKA and HHS are separate emergencies, they represent 2 points along the same spectrum of metabolic derangement caused by a lack of insulin.
  • Roughly 1 in 3 patients who present with a hyperglycaemic crisis will actually have a mixed picture of DKA and HHS[3].
  • As patient’s blood glucose levels gradually rise they will have increasing polyuria due to the osmotic diuresis effect of glucose in urine and this will cause polydipsia.
  • As the patient loses more and more fluid through their urine they will develop profound dehydration and electrolyte imbalances.
  • The urine will become hyperosmolar.
  • Osmolality is calculated from the formula:
    • Osmolality = 2 Na +urea +glucose.
      • NB The equation doubles the value for sodium as it presumes that the body will maintain a balance of anions and cationsOsmolality Hyperosmolality

Clinical presentation

  • Patients with HHS often present with symptoms of:
    • Increased thirst
    • Recent weight loss
    • Urinary frequency
    • Nausea
    • Vomiting
    • Disorientation, drowsiness, reduced GCS, coma
  • It is also important to consider the cause for their deterioration i.e. a chest infection or a urinary infection and a patient may present with symptoms associated with the underlying cause.

Clinical features

  • On examination of a patient with HHS you will notice signs of volume depletion:
    • Dry mucus membranes (dry mouth)
    • Reduced skin turgor
    • Reduced urine output
    • Cold, clammy peripheries
    • Mottled skin (sign of circulatory collapse secondary to hypovolaemia).
    • Physiological responses to hypovolaemia: tachycardia, hypotension

Diagnosing HHS

  • An important step in the management of HHS is recognising it as a potential differential!
  • HHS should be a differential for anyone presenting with altered mental status, especially if they have a history of type 2 diabetes (although, as mentioned above this could be their first presentation of diabetes).

Differentials for diabetic emergencies

  • HHS is characterised by:
    • Profound hyperglycaemia (glucose >33.3mmol/L)
    • Hyperosmolality (serum osmolality >320mmol/kg)
    • Volume depletion in the absence of ketoacidosis (pH>7.3 and HCO3>15mmol/L)


Acute management of HHS

Treatment of HHS requires consideration of 5 different goals:

  1. Replace fluid and electrolyte losses.
    • These patients are profoundly dehydrated and require careful and considered fluid resuscitation.
    • A Cochrane review has recommended the use of crystalloid rather than colloid fluids[2].
    • Replacing fluids too quickly might lead to cerebral oedema or cerebral pontine myelinosis as it causes fluid shifts and further electrolyte imbalances.
    • Replacing fluids too slowly would be futile and the patient would likely remain hypotensive and hypoperfused.
  2. Normalise blood glucose levels
    • Fluid replacement will start to bring down blood glucose levels. Once fluid replacement alone stops bringing the plasma glucose down an insulin infusion can be started.
    • A fixed rate intravenous insulin infusion should be started at a very low dose to prevent bringing the glucose down too quickly.
    • A rapid decrease in glucose might cause the patient to become hypoglycaemic.
  3. Normalise osmolality.
    • Rapid changes in osmolality can also be harmful.
    • Fluid replacement alone (without insulin) will lower blood glucose which will reduce osmolality causing a shift of water into the intracellular space. This will cause a rise in serum sodium (a fall in blood glucose of 5.5 mmol/L will result in a 2.4 mmol/L rise in sodium).
    • Rising sodium is only worrying if the osmolality is not declining at the same time.
    • To prevent cerebral pontine myelinosis sodium can only be safely reduced at a rate of 4-6 mmol/hr.
    • Patients with HHS are potassium deplete and require potassium replacement.
  4. Treat pre-disposing cause
    • Consider the predisposing cause (i.e. infection, MI, stroke) and treat accordingly.
  5. Prevention of complications including:
    1. Arterial or venous thrombosis
      • Hypernatraemia and increasing ADH levels, which both occur in HHS, can lead to a hypercoagulable state.
      • All patients will require low-molecular weight heparin to reduce their risk of developing an arterial or venous thromboembolism.

Cerebral oedema.

    • See above for careful management of fluids, glucose and electrolytes.

Foot ulcers

Patients with HHS will need to be treated in a high dependency setting.

Further management

  • Correcting blood glucose, electrolyte imbalances and increased osmolality will be done carefully as rapid correction is harmful.
  • These patients do best when they are cared for with an MDT approach:
    • Mobility: Early mobilisation is essential for recovery.
    • Nutrition: dietician involvement to assess nutritional status and give advice regarding re-feeding once well enough to avoid re-feeding syndrome.
  • Diabetes management:
    • IV insulin can be discontinued once the patient is eating and drinking and SC insulin therapy can recommence.
    • All people with HHS should be referred to the specialist diabetes team.
    • Education! All patients will receive education to reduce the chance of reoccurrence and long-term complications.


  1. Kitabchi AE, Umpierrez GE, Murphy MB, et al. Management of hyperglycemic crises in patients with diabetes. Diabetes Care. 2001;24:131-153
  2. Diabetic ketoacidosis and hyperosmolar hyperglycaemic state – UpToDate
  3. Wachtel TJ, Tetu-Mouradjian LM, Goldman DL, et al. Hyperosmolarity and acidosis in diabetes mellitus: a three-year experience in Rhode Island. J Gen Intern Med. 1991;6:495-502
  4. Diabetes UK (2012). The management of the hyperosmolar hyperglycaemic state (HHS) in adults with diabetes
  5. Perel, P. and Roberts, J. (2011). Colloids vs crystalloids for fluid resuscitation in critically ill patients. Cochrane Database of Systemic Reviews. Issue 3.

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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