Hyperosmolar Hyperglycaemic State

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Overview

Also known as hyperosmolar hyperglycaemic non-ketotic coma (HONK), hyperosmolar hyperglycaemic state (HHS) is a potentially life-threatening endocrine emergency usually seen in patients with type 2 diabetes mellitus (T2DM).

HHS must be differentiated from diabetic ketoacidosis (DKA), as their management steps vary significantly, and giving a patient with HHS insulin can lead to adverse outcomes.

To help make sense of this chapter, it may be helpful to refer to Endocrine and Metabolic Physiology.

Pathophysiology

HHS is usually precipitated by an acute illness (e.g. infection, myocardial infarction etc.). The stress leads to the release of hormones such as cortisol and glucagon, leading to increased blood glucose concentrations. Since there is a relative insulin deficiency (as patients with T2DM have insulin resistance), blood glucose concentrations cannot be effectively controlled, leading to incredibly high glucose concentrations (often over 40 mmol/L).

The increased blood glucose concentration leads to an osmotic shift of water into the blood vessels, away from cells, leading to intracellular dehydration. Ketosis does not occur as insulin is still released in T2DM, preventing adipose breakdown which leads to the production of ketones.

Epidemiology

  • More commonly seen in the elderly, however, younger adults are being increasingly diagnosed with T2DM
  • HHS may be the first presentation of T2DM in some patients

Risk Factors

  • Acute illness (e.g. infection, stroke, myocardial infarction)
  • Hyper-/hypothermia
  • Burns
  • Cushing’s syndrome
  • Substance misuse (e.g. alcohol, cocaine etc.)
  • Dehydration 

Presentation

HHS often presents as acute cognitive impairment in a patient with a history of type 2 diabetes mellitus. Features are:

  • Acute cognitive changes (e.g. drowsiness, confusion etc.)
  • Polyuria – onset is usually over days-weeks
  • Polydipsia – onset is usually over days-weeks
  • Fatigue
  • Lethargy
  • Weakness
  • Headaches
  • Nausea and vomiting
  • Tachycardia – due to hypovolaemia
  • Hypotension – due to hypovolaemia
  • Focal neurological deficits
  • Seizures

Differential Diagnoses

Diabetic ketoacidosis

  • Patients are often younger
  • There may be a known history of type 1 diabetes mellitus
  • Abdominal pain is more commonly seen in DKA
  • pH is <7.30
  • bicarbonate is <15 mmol/L
  • Ketones are elevated

Alcoholic ketoacidosis

  • Consider alcoholic ketoacidosis in a patient with a similar presentation to a DKA or HHS but capillary blood glucose is normal or low
  • There may be a history of alcohol abuse
  • Examination may reveal signs associated with alcohol abuse (e.g. signs of liver disease, smelling like alcohol etc.)
  • Ketones are elevated

Investigations

  • Blood glucose:
    • High, usually ≥30 mmol/L
    • Blood ketones – used to distinguish HHS from DKA
    • Negative or low, unlike in DKA
  • Venous or arterial blood gas:
    • Acidosis is not present, but may show mild acidosis (pH >7.30 and bicarbonate >15 mmol/L)
    • May show lactic acidosis (e.g. if due to sepsis)
  • Serum osmolality:
    • Elevated (≥320 mOsm/kg) due to hypovolaemia
  • FBC:
    • May show leukocytosis, which is common in HHS
    • Higher levels (usually >25 x 109/L) suggest an infection
  • U&Es:
  • ECG:
    • To look for triggers of HHS (e.g. myocardial infarction), or complications of HHS (e.g. hypo/hyperkalaemia)

Diagnosis

Overview

There are no specific diagnostic criteria for HHS, but it is important to differentiate HHS from DKA, as their management plans differ. HHS tends to have hyperglycaemia in the absence of ketosis and significant acidosis, and the serum osmolality is usually high.

Management

The three main elements of managing HHS are:

  • IV fluids to correct osmolality – monitor the serum osmolality:
    • Serum osmolality can be estimated via the formula: (2 x Na+) + glucose + urea
    • Rapid changes in serum osmolality can lead to central pontine myelinolysis (CPM) and cardiovascular collapse (e.g. fluid overload)
  • Replace fluid and manage electrolyte imbalances
  • Gradually normalise blood glucose concentration:
    • Fluid replacement alone with normal saline can gradually reduce blood glucose and osmolality
    • Using insulin before adequate fluid replacement can lead to a rapid decline in glucose and hence, serum osmolality which can precipitate CPM and cardiovascular collapse.
    • Insulin should be considered if fluid replacement alone is ineffective. If significant ketonaemia is present, this can suggest a mixed DKA/HHS picture and insulin may be given at a rate of 0.05 units/kg/hr. If there is no ketonaemia present, do not start insulin.

Complications

  • Cerebral oedema
  • Central pontine myelinolysis (CPM)
  • Fluid overload and cardiac oedema
  • Venous thromboembolism
  • Ischaemia or infarction affecting any organ

Prognosis

  • The mortality rates of HHS can be up to 10 times higher than in patients with DKA

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