According to the lay press, 75% of Americans are chronically dehydrated. While this is not supported by medical literature, dehydration is common in elderly patients. It has been reported to occur in 17% to 28% of older adults in the United States. Dehydration is a frequent cause of hospital admission. It can cause morbidity and mortality on its own and complicates many medical conditions. Dehydration may also be over-diagnosed. This can lead to misdiagnosis of the real cause of the patient's illness and lead to over-treatment with fluids. Dehydration is easily treatable and preventable. A thorough understanding of the causes and diagnosis of dehydration can improve patient care.
Body water is lost through the skin, lungs, kidneys, and GI tract. The loss of body water without sodium causes dehydration. Water is lost from the skin, lungs, gastrointestinal tract, and kidneys. Dehydration results when water losses from the body exceed water replacement. It may be caused by failure to replace obligate water losses. There are several forms of dehydration. Isotonic water loss occurs when water and sodium are lost together. Causes of isotonic water loss are vomiting, diarrhea, sweating, burns, intrinsic kidney disease, hyperglycemia, and hypoaldosteronism. Hypertonic dehydration occurs when water losses exceed sodium losses. Serum sodium and osmolality will always be elevated in hypertonic dehydration. Excess pure water loss occurs through the skin, lungs, and kidneys. Etiologies are fever, increased respiration, and diabetes insipidus. Hypotonic dehydration is mostly caused by diuretics, which cause more sodium loss than water loss. Hypotonic dehydration is characterized by low sodium and osmolality.
The source of water loss may also understand the etiologies of dehydration:
There is no recent data on rates of dehydration in the general population, but we do know much of the epidemiology of dehydration in adults. Healthy adults with access to water rarely become dehydrated. Any adult may develop dehydration as a complication of an illness such as hyperglycemia. Dehydration may cause illness or be caused by an illness, so searches of databases may not capture all cases of dehydration. The data that we do have shows that older adults are more likely to develop dehydration. The elderly population is also 20% to 30% more prone to developing dehydration due to immobility, impaired thirst mechanism, diabetes, renal disease, and falls.
Water plays a key role in maintaining multiple physiological functions within the body. The human body is 55% to 65% of water. Two-thirds of that water is intracellular, and one-third is extracellular. One-fifth of extracellular water is intravascular. The body has a complex system designed to maintain euvolemia. Water is absorbed through the gastrointestinal tract. The primary control of water homeostasis is through osmoreceptors in the brain. Dehydration, as perceived by these osmoreceptors, stimulates the thirst center in the hypothalamus, which leads to water consumption. These osmoreceptors can also cause conservation of water by the kidney. When the hypothalamus detects lower water concentration, it causes the posterior pituitary to release antidiuretic hormone (ADH), which stimulates the kidneys to reabsorb more water. Decreased blood pressure, which often accompanies dehydration triggers renin secretion from the kidney. Renin converts angiotensin I to angiotensin II, which increases aldosterone release fro the adrenals. Aldosterone increases the absorption of sodium and water from the kidney. Using these mechanisms, the body regulates body volume and sodium and water concentration.
Hypovolemic patients can present with a wide assortment of symptoms and physical exam findings. Some of the most common presenting symptoms of dehydration include but are not limited to fatigue, thirst, dry skin and lips, dark urine or decreased urine output, headaches, muscle cramps, lightheadedness, dizziness, syncope, orthostatic hypotension, and palpitations. The patient's history may elicit factors that could cause dehydration, such as exercise, heat exposure, medications, illness, impaired access to water, fever, or fluid loss.
Vital signs may show hypotension, tachycardia, fever, and tachypnea. Hypotension will not appear until significant dehydration is present. Tachycardia may be absent due to medications such as beta-blockers. A patient may appear lethargic or obtunded upon observation in severe cases of dehydration. The physical examination could show dry mucosa, skin tenting, delayed capillary refill, or cracked lips. A 2015 Cochrane review evaluated predictors of dehydration in the elderly. Historical and physical findings tested were dry axilla, mucous membranes, tongue, increased capillary refill time, poor skin turgor, sunken eyes, orthostatic blood pressure drop, dizziness, thirst, urine color, weakness, blue lips, altered mentation, tiredness, and appetite. Of all these factors only fatigue and missed drinks between meals predicted the diagnosis of dehydration.
There is no gold standard test for dehydration. Serum and plasma osmolality tests are often used to diagnose but may be affected by the type of fluid lost or the acuity of the fluid loss. A reasonable definition of dehydration due to water loss is serum osmolality greater than or equal to 295 mOsm/kg. The 2015 Cochrane review used serum osmolality of greater than 294 mOsm/kg to define dehydration. Weight loss equal to or greater than 3% over 7 days may also indicate dehydration if this data is available In the 2015 Cochrane review of diagnostic tests for dehydration in elderly patients, bioelectrical impedance analysis, urine specific gravity, the osmolality of urine, saliva or tears, tear volume, number of urine voids, and urine volume were not useful as stand-alone tests for dehydration in the elderly.
Blood urea nitrogen to creatinine ratio should be higher than 10:1 in dehydration, but this may be mimicked by high urea production, low creatinine due to low muscle lass and urea reabsorption due to upper gastrointestinal bleed. Urine tests may suggest volume depletion. Urine sodium concentration should be low, fractional excretion of sodium should be under 1%, and urine osmolality should be greater than 450 mOsm/kg. These tests of renal perception of low blood flow may also be abnormal in heart failure, cirrhosis, nephrotic syndrome, and other causes of kidney disease.
Ultrasound can be used to assess a patient’s fluid volume by measuring the collapsibility of the inferior vena cava (IVC) with respiration. A variation in the diameter of the IVC greater than 50% with respiration indicates a collapsible IVC. IVC collapse with inspiration may correlate with right atrial pressure and intravascular volume. Ultrasound evaluation of the IVC may be influenced by cirrhosis, chronic heart conditions, and ventilation (spontaneous or mechanical). IVC ultrasound has limited ability to predict fluid responsiveness. It may be used as part of the entire clinical picture.
Treatment of dehydration is aimed at rapid fluid replacement as well as identification of the cause of fluid loss. Patients with fluid deficits should be given isotonic fluid boluses tailored to the individual circumstance. Patients with more severe dehydration get larger boluses of isotonic fluid. A more careful approach is needed in elderly patients and patients with heart failure and kidney failure. In these patients, small boluses should be given, followed by frequent reassessment and additional bolus as needed.
Blood pressure, heart rate, serum lactate, hematocrit (if bleeding there is no blood loss), and urine output may be used to assess the volume deficit and to assess response to fluids.
Isotonic crystalloid fluid should be used in most cases of dehydration. Colloids such as albumin may be used in specific situations but do not improve outcomes.
The choice of crystalloid should be customized to the patient. Normal saline, lactated Ringer's solution, and a balanced crystalloid solution may all be used. Normal saline may cause hyperchloremic metabolic acidosis in large volumes. Buffered crystalloids may cause hyponatremia. Lactated Ringer's solution also contains potassium, so it should not be used in renal failure or hyperkalemia. No fluid has proved superior in all patients.
In patients with dehydration and severe hyponatremia, rapid volume repletion may cause a rapid rise in the sodium. This can cause central pontine myelinolysis (CPM). The clinician must weigh the risks of continued dehydration against the risks of CPM. The patient's volume status and serum sodium must be followed closely.
As the patient is being resuscitated, clinical and laboratory examination must focus on the discovery and correction of the cause of dehydration.
The principle differential of dehydration in adults is the loss of body water versus the loss of blood. This is important because blood loss should be replaced with blood, while water loss should be replaced with fluid. The next point to consider is the differential diagnosis of the cause of dehydration, as discussed under etiology.
When the underlying cause of dehydration is treated, and the patient's volume has been restored, the majority of patients recover fully. Failure to treat dehydration in older adults may lead to significant mortality.
Complications of dehydration occur due to inadequate fluid replacement and over-aggressive fluid replacement. Complications of under-resuscitation are due to hypoperfusion of vital organs and complications due to renal efforts to retain fluid. Altered mental status, renal failure, shock liver, lactic acidosis, hypotension, and death are related to organ-hypoperfusion. Fluid and electrolyte abnormalities such as uremia, hyponatremia, hypernatremia, hypokalemia, hyperkalemia, metabolic acidosis, and metabolic alkalosis may occur. Excess fluid administration to correct dehydration may cause peripheral edema and pulmonary edema. In patients with severe hyponatremia, volume correction may cayuse a rapid rise in sodium, which can cause central pontine myelinolysis.
Renal cosultation will be needed at times, especially with severe hyponatremia, but in most cases the treating clinician can evaluate and correct dehydration.
Although the CDC does not have defined guidelines on water intake recommendations, adults are encouraged to maintain between 2-3 L per day.  Patients should be encouraged to replace their losses to keep up with activity, for example, marathon runners water should drink more than a nonmobile person. In elderly patients, excessive free water drinking can cause hyponatremia so balanced hydration solutions are recommended.
1. Dehydration is common in elderly patients and with certain diseases.
2. Dehydration is uncommon in adults with no medical problems and free access to water.
3. Because adequate volume is essential to the peak function of the human body, there are multiple mechanisms to achieve and maintain euvolemia.
4. The diagnosis of volume depletion depends on the careful assessment of physical exam, history, and laboratory tests. There is no one test to diagnose dehydration.
5. The first goal of treatment of dehydration is to restore circulating volume. The second goal is to find the cause of the dehydration so that it will not recur.
6. In patients with normal heart and renal function, liberal fluid may be given to restore volume quickly. In patients with heart failure and renal disease, volume still needs to be replaced, but a more a=careful approach is indicated. This is best accomplished with small volumes given quickly, followed by immediate reassessment and redosing as needed.
7. In severe hyponatremia, rapid correction of volume deficits may cause a sharp rise in the serum sodium that can cause central pontine myelinolysis (CPM). The clinician must assess the risks and benefits of rapid volume repletion versus the risk of CPM. In all cases, the volume status and sodium levels must be monitored closely.
Often because water intake is not the most pressing topic for the average clinical visit, it very frequently is overlooked in regards to patient care. If we can start to encourage more healthy lifestyle choices as well as daily hydration, it can lead to decreased morbidity, mortality, and complications associated with dehydration. Healthcare providers should look toward implementing more incentives and initiatives toward increasing hydration amongst staff and patient populations.
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