Hypertonic Dehydration

Definition, Etiology, PathogenesisTop

Hypertonic dehydration is loss of water associated with increased effective osmolality of body fluids.

Causes include inadequate water intake (most frequently in unconscious patients); loss of water via the lungs (hyperventilation); or loss of hypotonic fluids via the skin, gastrointestinal tract, or kidneys (vasopressin disorders [previously known as diabetes insipidus], osmotic diuresis caused by glycosuria). An increased osmotic pressure of the extracellular fluid (ECF) results in a shift of water from the intracellular fluid (ICF) to the ECF, which reduces the volume of the intracellular compartment (cellular dehydration).

Clinical FeaturesTop

Manifestations depend on the severity of dehydration of central nervous system (CNS) cells and the severity of hypovolemia. The key factor is the time over which dehydration developed; CNS manifestations are less severe when hypertonic dehydration develops slowly. The patient has symptoms of dehydration (dry mucous membranes and skin, hypotension, tachycardia, oliguria), features of hypertonicity (extreme thirst), and CNS symptoms (confusion, hallucinations, hyperthermia).

DiagnosisTop

Diagnosis is based on a positive history of current or prior loss of body fluids as well as the presence of clinical manifestations of dehydration, hypovolemia, hypernatremia, and increased serum osmolality.

TreatmentTop

Administer hypotonic fluids:

1) Oral administration of glucose-free fluids, such as unsweetened tea or water.

2) Slow IV administration of hypotonic fluids (except for patients with hypotension, in whom isotonic fluids should be administered until hypotension is corrected) to achieve a simultaneous decrease in the hyperosmolality of the ECF and the ICF (excessively rapid correction of ECF hyperosmolality is associated with a risk of cerebral edema).

Also see Hypernatremia.