Hyperosmolar hyperglycemic state (HHS) is 1 of 2 serious metabolic derangements that occurs in patients with diabetes mellitus (DM) and can be a life-threatening emergency.  It is less common than the other acute complication of diabetes, diabetic ketoacidosis (DKA). HHS was previously termed hyperosmolar hyperglycemic nonketotic coma (HHNC); however, the terminology was changed because coma is found in fewer than 20% of patients with HHS. 
HHS most commonly occurs in patients with type 2 DM who have some concomitant illness that leads to reduced fluid intake. Infection is the most common preceding illness, but many other conditions can cause altered mentation, dehydration, or both. Once HHS has developed, it may be difficult to differentiate it from the antecedent illness. The concomitant illness may not be identifiable. (See Etiology.) HHS has also been reported in patients with type 1 DM, in whom DKA is more common.
HHS usually presents in older patients with type 2 DM and carries a higher mortality than DKA, estimated at approximately 10-20%. (See Epidemiology.)
HHS is characterized by hyperglycemia, hyperosmolarity, and dehydration without significant ketoacidosis. Most patients present with severe dehydration and focal or global neurologic deficits. [3, 2, 4] In as many as one third of cases, the clinical features of HHS and DKA overlap and are observed simultaneously (overlap cases); this suggests that these 2 states of uncontrolled DM differ only with respect to the magnitude of dehydration and the severity of acidosis. (See Presentation.)
Plasma glucose level of 600 mg/dL or greater
Effective serum osmolality of 320 mOsm/kg or greater
Profound dehydration, up to an average of 9L
Serum pH greater than 7.30
Bicarbonate concentration greater than 15 mEq/L
Small ketonuria and absent-to-low ketonemia
Some alteration in consciousness
Detection and treatment of an underlying illness are critical. Standard care for dehydration and altered mental status is appropriate, including airway management, intravenous (IV) access, crystalloid administration, and any medications routinely given to coma patients. Although many patients with HHS respond to fluids alone, IV insulin in dosages similar to those used in DKA can facilitate correction of hyperglycemia. Insulin used without concomitant vigorous fluid replacement increases the risk of shock. (See Treatment.)
Insulin-sensitive tissues normally take up glucose during meals, when the glycemic rise of ingested carbohydrates stimulates insulin secretion. The increased insulin levels inhibit glucagon release from the pancreatic islets, and the ratio of plasma insulin to glucagon becomes relatively high.
A high insulin-to-glucagon ratio favors storage of glucose as glycogen in liver and muscle and lipogenesis in adipocytes. Insulin-dependent transport of glucose across the cell membranes of insulin-sensitive tissues drives potassium into these cells. A high insulin-to-glucagon ratio during meals also favors amino acid uptake by muscle.
Between meals, insulin secretion is not stimulated, and the insulin-mediated glucagon inhibition in the pancreatic islets stops. The glucagon levels rise in the plasma, leading to a decrease in the plasma insulin-to-glucagon ratio. The consequence of this decrease is the breakdown of glycogen in the liver and muscle and gluconeogenesis by the liver, both of which maintain the plasma glucose concentration in the normal range. A fall in the insulin-to-glucagon ratio also favors lipolysis and the formation of ketone bodies by the liver.
Several tissues in the body use glucose regardless of the insulin-to-glucagon ratio. These insulin-independent tissues include the brain and the kidneys.
In patients with a preexisting lack of or resistance to insulin, a physiologic stress such as an acute illness can cause further net reduction in circulating insulin. The basic underlying mechanism of HHS is a relative or absolute reduction in effective circulating insulin with a concomitant elevation of counterregulatory hormones. [2, 3]
Decreased renal clearance and decreased peripheral utilization of glucose lead to hyperglycemia. Hyperglycemia and hyperosmolarity result in an osmotic diuresis and an osmotic shift of fluid to the intravascular space, resulting in further intracellular dehydration. This diuresis also leads to loss of electrolytes, such as sodium and potassium. [2, 3, 4]
Unlike patients with DKA, patients with HHS do not develop significant ketoacidosis, but the reason for this is not known. Contributing factors likely include the availability of insulin in amounts sufficient to inhibit ketogenesis but insufficient to prevent hyperglycemia. Additionally, hyperosmolarity itself may decrease lipolysis, limiting the amount of free fatty acids available for ketogenesis. In addition, levels of counterregulatory hormones are found to be lower in patients with HHS than in those with DKA. [2, 3, 4]
Obesity is the most prevalent cause of insulin resistance. Pregnancy is a state of insulin resistance largely due to the action of placental hormones on maternal circulation. High circulating levels of epinephrine, glucagon, growth hormone, and cortisol (the 4 major counterregulatory hormones) cause insulin resistance. Their levels increase during acute illnesses (eg, major infections, myocardial infarction [MI], or pancreatitis) or stress (eg, surgery, major psychiatric illness, or multiple injuries).
Additionally, diseases characterized by excessive production of these counterregulatory hormones (eg, pheochromocytoma, glucagonoma, acromegaly, and Cushing syndrome) may induce insulin resistance. Finally, parenteral nutrition and administration of some medications (notably, glucocorticoids, tretinoin, antiretrovirals, antipsychotics, [6, 7] and cyclosporine and other immunosuppressive agents) cause insulin resistance.
Insulin deficiency is due to autoimmune destruction of the beta cells in type 1 DM. In type 2 DM, a defect in the first-phase release of insulin occurs, which leads to relative insulinopenia. The defective insulin secretion in persons with type 2 DM is due to the direct toxic effect of glucose on beta cells. Many patients with diabetes treated with insulin become relatively insulinopenic when they fail to adjust the dose of insulin upwards during illnesses or periods of stress.
In the absence of adequate insulin activity, hyperglycemia develops. Decreased glucose use occurs in peripheral tissues, including adipocytes and muscles; glucose cannot be stored as glycogen in muscle and liver tissue; and hepatocytes, under the influence of glucagon, stimulate gluconeogenesis.
The resulting elevation in plasma glucose concentration leads to further impairment of insulin release by pancreatic beta cells. In this setting of inadequate insulin action, the magnitude of the rise in plasma glucose concentration also depends, in part, on the level of hydration and oral carbohydrate (or glucose) loading.
Under normal circumstances, all of the glucose filtered by the kidneys is reabsorbed. When glycemia reaches approximately 180 mg/dL, proximal tubular transport of glucose from the tubular lumen into the renal interstitium becomes saturated, and further glucose reabsorption is no longer possible. The glucose that remains in the renal tubules continues to travel into the distal nephron and, eventually, the urine, carrying water and electrolytes with it.
Osmotic diuresis then results. The direct consequence of this osmotic diuresis is a decrease in total body water. Within the vascular space, in which gluconeogenesis and dietary intake continue to add glucose, the loss of water results in further hyperglycemia and loss of circulating volume.
Hyperglycemia and the rise in the plasma protein concentration after intravascular water loss cause a hyperosmolar state. The hyperosmolarity of the plasma triggers release of antidiuretic hormone, which ameliorates renal water loss. Hyperosmolarity also stimulates thirst, a defense mechanism that is impaired in people dependent on others for care.
In the presence of HHS, if the renal water loss is not compensated for by oral water intake, dehydration leads to hypovolemia. Hypovolemia, in turn, leads to hypotension, and hypotension results in impaired tissue perfusion. Coma is the end stage of this hyperglycemic process, when severe electrolyte disturbances occur in association with hypotension.
Any process that accelerates water loss, such as diarrhea or severe burns, accelerates the development of hyperosmolarity and hypotension. In this severely dehydrated and hyperosmolar state, hypotension causes a massive stimulation of the renin-angiotensin-aldosterone system and, eventually, renal shutdown. Oliguria precludes further excretion of glucose from the kidneys, which conserves circulating volume but exacerbates hyperglycemia.
HHS most commonly occurs in patients with type 2 DM who have some concomitant illness that leads to reduced fluid intake. In general, any illness that predisposes to dehydration or to reduced insulin activity may lead to HHS. [2, 4] A wide variety of major illnesses may trigger HHS by limiting patient mobility and free access to water.
When considering treatment of a patient with HHS, assess for and address any acute illness and contributions from medications.
Acute febrile illnesses, including infections, account for the largest proportion of HHS cases. A preceding or intercurrent infection (in particular, pneumonia or urinary tract infection [UTI]  ) is the single most common cause, but in a number of patients, the concomitant illness is not identifiable.
The stress response to any acute illness tends to increase hormones that favor elevated glucose levels. Cortisol, catecholamines, glucagon, and many other hormones have effects that tend to counter those of insulin. Examples of such acute conditions are as follows:
Silent MI – Consider MI in all patients with HHS until it is excluded
Pulmonary embolism (PE)
Patients with underlying renal dysfunction, congestive heart failure (CHF), or both are at increased risk.
Drugs that raise serum glucose levels, inhibit insulin, or cause dehydration may cause HHS. Examples include the following:
Atypical antipsychotics (clozapine, olanzapine)
Alcohol and cocaine
Antiarrhythmics (eg, encainide and propranolol)
Antiepileptics (eg, phenytoin)
Antihypertensives (eg, calcium channel blockers and diazoxide)
Diuretics (eg, chlorthalidone, ethacrynic acid, and thiazides)
Histamine-receptor blockers (eg, cimetidine)
Total parenteral nutrition (TPN) solutions and fluids that contain dextrose
Noncompliance with oral hypoglycemics or insulin therapy can result in HHS.
Other conditions and illnesses associated with HHS include the following:
Cushing syndrome (eg, endogenous, exogenous, ectopic)
Hemodialysis and peritoneal dialysis
Gastrointestinal (GI) hemorrhage
Neuroleptic malignant syndrome
Surgery (especially cardiac surgery)
Elder abuse and neglect also may contribute to underhydration.
A Taiwanese study, by Lu et al, suggested that an inverse relationship exists between ambient temperature and hospital admissions for HHS and DKA. The study found that admission rates for the two conditions were significantly greater in winter than in summer, although the investigators also noted that admission rates for HHS were significantly lower in the fall. 
United States statistics
No population-based studies of HHS have been conducted. According to the US National Hospital Discharge Survey funded by the National Center for Health Statistics, there were 10,800 annual discharges for HNS in the United States from 1989 to 1991. HHS affects approximately 1 of 500 patients with DM. The overall incidence of HHS is less than 1 case per 1000 person-years, making it significantly less common than DKA. As the prevalence of type 2 DM increases, the incidence of HHS will likely increase as well. 
HHS has a mean age of onset early in the seventh decade of life. The average age of patients with HHS is 60 years. Most published series report an average age of 57-69 years at diagnosis. [2, 4, 9] In contrast, the mean age of onset for DKA is early in the fourth decade of life. HHS may also occur in younger people. In particular, as rates of obesity increase in children, the prevalence of type 2 DM is also rising in this age group and may lead to an increased incidence of HHS in this population. [10, 11, 12]
Nursing home populations are at risk for HHS. Underlying comorbidities that prevent adequate hydration, including immobility, advanced age, debility, dementia, agitation, and restraint use, place these patients at risk. Impaired senses, such as deafness and blindness, may lead to social isolation and also increase the risk of HHS.
No sex predilection is noted in most published series of HHS. However, some data suggest that the prevalence is slightly higher in females than in males. In the US National Hospital Discharge Survey (see above), 3700 persons were male and 7100 were female.
African Americans, Hispanics, and Native Americans are disproportionately affected by HHS as a consequence of an increased prevalence of type 2 DM.  In the US National Hospital Discharge Survey of 10,800 hospital discharges listing HHS in the United States between 1989 and 1991, there were 6300 white patients and 2900 African American patients; the remainder of the discharges were people of other races or of unknown race.
Overall mortality for HHS is typically 10-20%, though figures as high as 58% have been reported. Older age, the presence of concurrent illnesses, and severity of the metabolic derangements (especially dehydration) contribute to this high mortality, as do delay in establishing the diagnosis and failure to treat HHS aggressively from the outset also may contribute to this high mortality rate. In children, mortality from HHS also appears to be higher than mortality from DKA, but too few cases have been reported to allow accurate calculation of pediatric mortality.
A study by Kao et al indicated that in nonelderly patients with diabetes, those with hyperglycemic crisis episodes (HHS or DKA) had a mortality hazard ratio that was four-fold higher than for patients without such episodes. 
Diabetic teaching, provided both in the hospital and after discharge by the primary care physician, a visiting home nurse, or both, is essential for modifying behavior and enhancing compliance. A certified diabetes educator should instruct all patients on management of sick days and provide a thorough review of self-care. A home evaluation by a visiting nurse may help identify factors limiting adequate access to water.
Having had HHS places patients at risk for further episodes. Diabetic teaching is vital for preventing a recurrence of HHS. Warn patients to avoid poor glycemic control and dehydration.
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