Dehydration commonly affects patients of all ages and may complicate other medical problems, and cause significant illness. Dehydration can be easily treated and prevented. A detailed understanding of the etiology and diagnosis of dehydration can improve patient care.

Dehydration is caused when water losses from the body exceed water replacement. Healthy adults with adequate access to water seldom become dehydrated. Any adult may suffer from dehydration as a complication of an illness such as hyperglycemia. Evidence shows that older adults are more likely to develop dehydration. This population has 20% to 30% higher chances of developing dehydration due to immobility, impaired thirst mechanism, diabetes, renal disease, and falls.

Hypovolemic patients show a wide spectrum of symptoms and physical exam findings, with the most common being fatigue, thirst, dry skin and lips, dark urine or reduced urine output, headaches, muscle cramps, lightheadedness, dizziness, syncope, orthostatic hypotension, palpitations. The patient′s history is crucial to identify dehydration triggers, like exercise, heat exposure, medications, illness, impaired access to water, fever, or fluid loss.

A dehydrated patient may have hypotension, tachycardia, fever, and tachypnea. Hypotension is only present in cases of significant dehydration. Tachycardia may not appear due to medications such as beta-blockers. Severe cases of dehydration may show the patient to be lethargic or obtunded. 

There remains no gold standard test for dehydration; however, serum and plasma osmolality tests may help to diagnose but may be affected by fluid loss or fluid loss acuity. A reasonable definition of dehydration due to water loss is serum osmolality >/=295 mOsm/kg. Weight loss >/= 3% over seven days may also indicate dehydration. 

Treatment of dehydration aims at rapid fluid replacement and identifying the cause of fluid loss. Patients with fluid deficits must receive isotonic fluid boluses tailored to the individual circumstance. Patients with more severe dehydration should receive larger boluses of isotonic fluid. Elderly patients and those with heart failure and kidney failure demand a more careful approach with small boluses, followed by frequent reassessment and additional bolus as needed.

Isotonic crystalloid fluids are suitable in most cases of dehydration. Colloids such as albumin are reserved for specific situations but do not improve outcomes. Crystalloids should be customized according to the patient. It is reasonable to use normal saline lactated Ringer′s solution and a balanced crystalloid solution. If given in large volumes, normal saline may cause hyperchloremic metabolic acidosis. Buffered crystalloids may induce hyponatremia. Since Lactated Ringer′s solution also contains potassium, it must not be given during renal failure or hyperkalemia. No single fluid has proved suitable for all patients.

In patients with dehydration and severe hyponatremia, rapid volume repletion may lead to a rapid rise in sodium, causing central pontine myelinolysis (CPM). The clinician must thus weigh the risks of continued dehydration against the dangers of CPM. 

Most patients recover fully after treating the underlying cause of dehydration and restoring the patient′s volume. Failure to treat dehydration in older adults may cause significant mortality.

Taylor K, Jones EB. Adult Dehydration. [Updated 2022 Oct 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555956/