Overview/pathophysiology

Hyperglycemic hyperosmolar syndrome (HHS), also known as hyperosmolar hyperglycemic nonketotic syndrome (HHNK), hyperosmolar coma, nonketotic hyperosmolar coma, hyperosmolar nonketotic syndrome, hyperosmolar hyperglycemic nonketotic coma, and nonketotic hyperglycemic hyperosmolar coma, is a life-threatening emergency resulting from a lack of effective insulin, or severe insulin resistance, causing extreme hyperglycemia. Often HHS is precipitated by a stressor such as trauma, injury, or infection that increases insulin demand. It is believed that enough insulin to prevent acidosis resulting from lipolysis and formation of ketone bodies is effective at the cellular level. Without adequate insulin to facilitate transport into cells, or with severe insulin resistance, glucose molecules accumulate in the bloodstream, causing serum hyperosmolality with resultant osmotic diuresis and simultaneous loss of electrolytes, most notably potassium, sodium, and phosphate. Patients may lose up to 25% of their total body water. Fluids are pulled from individual body cells by increasing serum hyperosmolality and extracellular fluid loss, causing intracellular dehydration and body cell shrinkage. Neurologic deficits (i.e., slowed mentation, confusion, seizures, stroke-like symptoms, coma) can occur as a result. Loss of extracellular fluid stimulates aldosterone release, which facilitates sodium retention and prevents further loss of potassium. However, aldosterone cannot halt severe dehydration. As extracellular volume decreases, blood viscosity increases, causing slowing of blood flow. Thromboemboli are common because of increased blood viscosity, enhanced platelet aggregation and adhesiveness, and possibly patient immobility. Cardiac workload is increased and may lead to myocardial infarction. Renal blood flow is decreased, potentially resulting in renal impairment or failure. Stroke may result from thromboemboli or decreased cerebral perfusion. Mortality rate of HHS ranges from 10%-50%, which is higher than that of diabetic ketoacidosis (DKA) (1.2%-9%). Mortality data are difficult to interpret because of the high incidence of coexisting diseases or comorbidities.

Historically, HHS and DKA were described as distinct syndromes; but one third of patients exhibit findings of both conditions. HHS and DKA may be at opposite ends of a range of decompensated diabetes, differing in time of onset, degree of dehydration, and severity of ketosis. HHS occurs most commonly in older people with type 2 diabetes mellitus (DM), but with the recent obesity epidemic, occasionally obese children and teenagers with both diagnosed and undiagnosed type 2 DM manifest HHS. The cascade of events in HHS begins with osmotic diuresis. Glycosuria impairs the ability of the kidney to concentrate urine, which exacerbates the water loss. Normally, the kidneys eliminate glucose above a certain threshold and prevent a subsequent rise in blood glucose level. In HHS, the decreased intravascular volume or possible underlying renal disease decreases the glomerular filtration rate (GFR), causing the glucose level to increase. More water is lost than sodium, resulting in hyperosmolarity. Insulin is present, but not in adequate amounts to decrease blood glucose levels, and with type 2 DM, significant insulin resistance is present.

Unlike DKA, in which acidosis produces severe symptoms requiring fairly prompt hospitalization, symptoms of HHS develop more slowly and often are nonspecific. The cardinal symptoms of polyuria and polydipsia are noted first but may be ignored by older persons or their families. Neurologic deficits may be mistaken for senility. The similarity of these symptoms to those of other disease processes common to this age group may delay differential diagnosis and treatment, allowing progression of pathophysiologic processes with resultant hypovolemic shock and multiple organ failure.

Health care setting

Acute care (usually intensive care) unless the condition is not severe

Assessment

See Table in “Diabetic Ketoacidosis,” p. 358. Note: Patients with HHS may be older than 50 yr and have preexisting cardiac or pulmonary disorders. The incidence of type 2 DM is increasing in children, teenagers, and young adults, so younger people are now presenting with HHS. Assessment results often cannot be evaluated based on accepted normal values. Evaluate results based on what is normal or optimal for the individual patient. Central venous pressure (CVP), heart rate (HR), and blood pressure (BP) should be evaluated in terms of deviations from patient’s baseline and concurrent clinical status.