hiperosmolar

Hyperosmolar, or hiperosmolar, describes a state in which extracellular fluids have an elevated osmolality due to increased solute concentration. Plasma osmolality normally ranges from about 275 to 295 mOsm/kg. A hyperosmolar state is typically defined as plasma osmolality above 295–300 mOsm/kg, with more pronounced cases common in hyperosmolar hyperglycemic states where osmolality often exceeds 320 mOsm/kg.

Causes include marked hyperglycemia, hypernatremia, and elevated blood urea nitrogen, often in the setting of dehydration or renal impairment. Other contributors include ingestion of osmotically active substances and conditions causing osmotic diuresis. The dominant driver is the rise in non-volatile solutes that draws water from cells, particularly brain cells, leading to cellular dehydration.

Clinical features range from thirst, dry mucous membranes, tachycardia, and hypotension to altered mental status from confusion to coma. In adults with type 2 diabetes or elderly patients, hyperosmolar states often present with dehydration and progressive confusion rather than ketotic features seen in diabetic ketoacidosis.

Diagnosis relies on plasma osmolality measurements or calculations. One common calculation uses sodium, glucose, and BUN: osm_calc = 2 × Na + glucose/18 + BUN/2.8 (with glucose in mg/dL and BUN in mg/dL). An osmolar gap may indicate unmeasured solutes such as alcohols.

Management focuses on gradual volume repletion with isotonic saline, correction of hyperglycemia and electrolyte disturbances, and treatment of the underlying cause. Potassium balance should be monitored, and insulin is used carefully after fluid resuscitation to avoid rapid shifts in osmolality. Prognosis varies with the underlying condition and prompt treatment; mortality is higher when diagnosis is delayed or comorbidities are present.