Adult Dehydration

Etiology

Body water is lost through the skin, lungs, kidneys, and gastrointestinal tract. Dehydration occurs when water loss exceeds replacement and may result from the loss of water without sodium. This condition often arises from the failure to replace obligatory water loss. Multiple factors contribute to dehydration (see Table 1).[1]

Table 1. Causes of Dehydration

Epidemiology

Dehydration is a common condition in adults, particularly among vulnerable populations such as older adults and those with chronic diseases. The incidence of dehydration varies depending on the definition, diagnostic criteria, and population studied. However, epidemiological data indicate that dehydration is a significant contributor to global hospital admissions and poor health outcomes.[5] Older individuals are 20% to 30% more prone to developing dehydration due to factors such as immobility, impaired thirst mechanism, diabetes, renal disease, and polypharmacy.[6][7]Prevalence and Risk Factors

Dehydration can affect individuals of all ages, but older adults are disproportionately impacted due to physiological changes, reduced thirst sensation, and a higher prevalence of comorbid conditions. Older individuals in institutionalized settings face even greater risks, with factors such as diminished cognition and dependence on caregivers for fluid intake, compounded by environmental issues like inadequate access to fluids.[8]Poor fluid intake is one of the most common causes of dehydration in adults, often influenced by factors such as mobility limitations, cognitive impairment, and social determinants of health. Chronic medical conditions, including diabetes mellitus, renal disease, and gastrointestinal disorders, contribute to dehydration by increasing fluid loss or impairing fluid retention mechanisms. Medication use, particularly diuretics, laxatives, and certain classes of antihypertensive drugs, is also a significant risk factor for dehydration in adults.[9]

Hospitalization and Mortality Rates

Dehydration is one of the leading causes of hospitalization, accounting for approximately 1% to 3% of all hospital admissions in the United States. However, this condition is higher during extreme weather events such as heat waves.[10] Research shows that dehydration is associated with longer hospital stays, higher healthcare costs, and increased morbidity and mortality rates. Severe dehydration can lead to life-threatening complications, including acute kidney injury (AKI), electrolyte imbalances, and cognitive impairment, particularly in older adults and those with underlying chronic conditions.[11]In community-dwelling adults, dehydration increases the risk of falls, urinary tract infections (UTIs), and cognitive decline.[2] Mortality rates in hospitalized patients range around 15%, depending on the severity of dehydration and the presence of comorbid conditions.[12][13] Dehydration is also a leading cause of readmissions among older adults, highlighting the need for more effective prevention and post-discharge monitoring strategies.[14]Geographic and Seasonal Variability

The incidence of dehydration varies geographically, with higher rates reported in regions with extreme temperatures, limited access to clean water, and high rates of infectious diseases contributing to fluid loss. Seasonal variations also impact dehydration rates, with increased hospitalizations observed during the summer months due to elevated perspiration and inadequate fluid replacement.[15][16]] Individuals in professions with prolonged exposure to high temperatures, such as construction workers and outdoor laborers, are also at increased risk of dehydration.

Pathophysiology

Water is essential for maintaining various physiological functions in the body. The human body is composed of 55% to 65% water, with two-thirds found intracellularly and one-third in the extracellular space. Of the extracellular water, one-fifth is found in the intravascular space.[17][18] The body depends on a complex system to maintain euvolemia, which refers to the stable and normal volume of blood and extracellular fluid.

Dehydration occurs when fluid loss exceeds intake, leading to a reduction in total body water, which results in clinical abnormalities in thermoregulation, skin elasticity, and circulatory stability. The most common underlying causes of dehydration include impaired thirst mechanisms, reduced renal concentrating ability, and an increased risk of fluid loss due to illness or environmental factors.

Physiological Mechanisms of Dehydration

The body has several homeostatic mechanisms to counteract dehydration and maintain euvolemia:

• Thirst mechanism and hypothalamic regulation: Osmoreceptors in the hypothalamus trigger the thirst response and promote water intake when plasma osmolality increases. However, this mechanism is less sensitive in older adults, making them more prone to dehydration.[19]

• Antidiuretic hormone and renal water retention: When plasma osmolality increases, the posterior pituitary gland secretes ADH, also known as vasopressin, which increases water reabsorption in the renal collecting ducts. This process reduces urine output and helps conserve water, which is essential for maintaining blood pressure and preventing hypovolemia. Please see StatPearls' companion resource, "Physiology, Vasopressin," for more information. 

• Renin-angiotensin-aldosterone system activation: When intravascular volume is low, the kidneys release renin, which converts angiotensinogen into angiotensin I. The angiotensin-converting enzyme (ACE) then converts angiotensin I to angiotensin II. Angiotensin II stimulates aldosterone release from the adrenal glands, promoting sodium and water retention. Angiotensin II also causes vasoconstriction, which helps maintain blood pressure during dehydration. Please see StatPearls' companion resource, "Physiology, Renin Angiotensin System," for more information.

Types of Dehydration and their Pathophysiological Effects

Dehydration is categorized based on the relative loss of water and sodium, each with distinct pathophysiological effects.

• Isotonic dehydration: This occurs when water and sodium are lost equally, as seen in conditions like vomiting, diarrhea, and hemorrhage. This leads to hypovolemia or reduced plasma volume, manifesting as tachycardia, hypotension, and diminished organ perfusion.[17]

• Hypertonic dehydration: This occurs when water loss exceeds sodium loss, resulting in hypernatremia. Common causes include inadequate fluid intake, excessive sweating, and diabetes insipidus. The resulting cellular dehydration can lead to neurological symptoms such as confusion, seizures, and coma.[20]

• Hypotonic dehydration: This occurs when sodium loss exceeds water loss, resulting in hyponatremia. It is commonly seen in individuals using diuretics or those with chronic kidney disease (CKD) or adrenal insufficiency. The resulting fluid shift into cells can lead to cerebral edema, muscle weakness, and lethargy.[17] 

Systemic Effects of Dehydration

Dehydration involves multiple organ systems, leading to significant physiological consequences, as mentioned below.[14]

• Cardiovascular effects: Hypovolemia decreases cardiac output, which stimulates tachycardia and hypotension. In severe cases, shock and multiple organ failure may occur. 

• Neurological effects: Hypertonic dehydration induces an osmotic shift, leading to the shrinkage of brain cells, which can cause delirium, confusion, and seizures. In contrast, hypotonic dehydration results in cerebral edema, raising intracranial pressure and increasing the risk of brain herniation.

• Renal effects: Reduced renal perfusion can lead to AKI, presenting with oliguria or anuria. Prolonged dehydration increases the risk of nephrolithiasis (kidney stones) and may contribute to the development of CKD.

• Gastrointestinal effects: Hypoperfusion of the gut mucosa can lead to ischemic injury, which can cause nausea and impaired nutrient absorption.

• Musculoskeletal effects: Fluid and electrolyte imbalances can cause muscle cramps, weakness, and an increased risk of falls, especially in older adults.

History and Physical

A comprehensive history is essential when assessing dehydration, as symptoms and risk factors vary depending on severity and etiology. Early symptoms may include increased thirst, dry mouth, weakness, and decreased urine output. As dehydration worsens, additional symptoms such as dizziness, muscle weakness, palpitations, confusion, and irritability may emerge. In severe cases, lethargy, seizures, and hypovolemic shock can occur. Important historical factors to evaluate include recent fluid intake, excessive fluid losses from vomiting, diarrhea, perspiration, or diuretic use, as well as the presence of underlying conditions such as diabetes, kidney disease, and heart failure.[21]The physical examination may reveal tachycardia, hypotension upon standing, and delayed capillary refill, indicating reduced intravascular volume (see Table 2). In cases of moderate-to-severe dehydration, decreased skin turgor and dry mucous membranes are common. Severe cases may present with confusion, lethargy, or even coma, especially with hypernatremia. Dark-colored urine and oliguria are frequently observed, and in extreme cases, dehydration can lead to shock, characterized by profound hypotension, cool, moist, and clammy skin, and poor circulation to vital organs.[22]

Table 2. Signs and Symptoms of Dehydration

Evaluation

Laboratory testing is crucial in diagnosing dehydration and assessing electrolyte imbalances. Common findings include an elevated blood urea nitrogen (BUN) to creatinine ratio greater than 20:1, suggesting prerenal azotemia due to reduced renal perfusion.

Specific electrolyte abnormalities vary based on the type of dehydration. Hypernatremia (sodium >145 mEq/L) suggests water-loss dehydration, whereas hyponatremia (sodium <135 mEq/L) indicates sodium-loss dehydration.[17] Hypokalemia is commonly associated with dehydration due to diarrhea or diuretic use, while hyperkalemia in a dehydrated patient may suggest adrenal insufficiency. Elevated hematocrit levels reflect hemoconcentration and reduced plasma volume.

Although no single test is considered the gold standard for diagnosing dehydration, serum osmolality is commonly used, with a value greater than 295 mOsm/kg serving as a reasonable threshold for dehydration due to water loss. However, the accuracy of these tests can be influenced by the rate of fluid loss. When available, a weight loss of 2% or more can indicate dehydration or impending dehydration.[14] A 2015 Cochrane review found that bioelectrical impedance analysis, urine specific gravity, urine osmolality, saliva or tear osmolality, tear volume, urine voiding frequency, and urine volume were unreliable diagnostic tools when used alone in older patients.[21]Urine studies help differentiate the underlying causes of dehydration. A urine specific gravity greater than 1.020 and urine osmolality exceeding 450 mOsm/kg indicate concentrated urine, reflecting renal compensation for fluid loss. Urine sodium levels below 20 mEq/L suggest hypovolemia with an appropriate renal response, while levels greater than 40 mEq/L may indicate renal salt-wasting or adrenal insufficiency. Blood gas analysis can detect acid-base disturbances in severe dehydration, such as metabolic alkalosis in vomiting-induced dehydration or metabolic acidosis, including lactic acidosis.

More severe forms of dehydration may present with shock. Additional tests, such as ultrasound of the inferior vena cava (IVC), can help assess intravascular volume status. An increase in IVC diameter of more than 50% with respiration indicates severe fluid depletion, while IVC collapse with inspiration may correlate with right atrial pressure and intravascular volume.[23] Although IVC ultrasound is useful, its accuracy can be affected by conditions such as cirrhosis, chronic heart disease, and mechanical ventilation.[24] Additionally, IVC sonography has limited value in assessing fluid responsiveness. Noninvasive cardiac output monitoring (NICOM) offers a more comprehensive evaluation of fluid status and can guide individualized fluid management in hypotensive patients.[25]

Treatment / Management

Dehydration treatment focuses on rapid fluid replacement and identifying the underlying cause of fluid loss. The choice of route, type, and volume of fluid therapy depends on the severity of dehydration, electrolyte imbalances, and comorbid conditions. A more cautious approach is necessary for older adults and patients with heart or kidney failure. Please see StatPearls' companion resource, "Fluid Management," for more information.

Mild-to-Moderate Dehydration

Oral rehydration therapy (ORT) is the preferred treatment for mild-to-moderate dehydration. ORT is effective, safe, and less invasive than IV fluid therapy.[26] Recommended oral fluid options include:

• Oral rehydration solutions: The World Health Organization (WHO) recommends solutions containing glucose and electrolytes, including sodium, potassium, chloride, and bicarbonate, to enhance water absorption.

• Homemade oral rehydration solution: 1 teaspoon salt + 6 teaspoons sugar + 1 liter of water.

• Clear liquids: Water, diluted fruit juices, and sports drinks are suitable for mild cases, but excessive sugar intake should be avoided. 

• Beverages to avoid: Certain drinks containing caffeine, alcohol, or carbonation should be avoided, as they can worsen dehydration.

• ORT administration: Adults should consume 1 to 2 liters of oral rehydration solutions over the first 4 hours, continuing as needed to maintain hydration.

Severe Dehydration

When a patient presents with severe dehydration or cannot tolerate ORT, IV fluid therapy is necessary to rapidly restore fluid balance and correct electrolyte disturbances. Common IV fluids used include:

• Isotonic crystalloids (first-line treatment): Normal saline (0.9%) is preferred for treating hypovolemia and most dehydration cases. While effective, administering large volumes may lead to hyperchloremic acidosis.[27] 
  • Lactated ringers contain bicarbonate precursors, which are beneficial in acidotic states, such as in patients with diarrhea or sepsis.

• Hypotonic fluids (for hypernatremic dehydration): Saline (half normal saline, 0.45%) is used to gradually correct hypernatremia while reducing the risk of cerebral edema.

• Dextrose-containing fluids (for hypoglycemia or ongoing fluid loss): 5% Dextrose with 0.9% normal saline (D5-0.9% normal saline) is administered with saline to prevent dilutional hyponatremia, which could occur with 5% dextrose in water (D5W) infusion alone.

In most cases of dehydration, isotonic crystalloid fluids are the preferred choice. However, colloids, such as albumin, may be appropriate in specific circumstances, such as in patients with liver cirrhosis or hypoalbuminemia who do not respond to standard treatments.[28][29](A1)

Electrolyte and Acid-Base Correction

Dehydration often leads to electrolyte imbalances that require prompt correction. Untreated disturbances can lead to severe complications, including cardiac, neurological, and metabolic dysfunction.

• Sodium abnormalities: Sodium abnormalities, including hypernatremia and hyponatremia, are common electrolyte disturbances that require careful management to prevent severe complications.
  • Hypernatremia (>145 mEq/L): This should be corrected slowly with hypotonic fluids, such as 0.45% saline or D5W, at a rate not exceeding 6 to 12 mEq/L per 24 hours to prevent cerebral edema. However, studies suggest that there is no increased risk of mortality, seizures, alteration of consciousness, or cerebral edema, even when the correction rate exceeds 12 mEq/L per 24 hours.[30] 
  • Hyponatremia (<135 mEq/L): If symptomatic (eg, seizures and confusion), hypertonic saline (3% NaCl) should be administered cautiously under close monitoring, with a correction rate not exceeding 4 to 8 mEq/L per 24 hours to avoid osmotic demyelination syndrome.[31]
(B3)

• Potassium abnormalities: Potassium abnormalities, including hypokalemia and hyperkalemia, require prompt intervention to prevent life-threatening complications.
  • Hypokalemia (<3.5 mEq/L) can be managed based on severity. For mild cases, oral potassium chloride (KCl; 20–40 mEq/d) is recommended. In severe cases, IV potassium (10–20 mEq/h) should be administered, with continuous electrocardiogram (ECG) monitoring to prevent cardiac arrhythmias.
  • Hyperkalemia (>5.5 mEq/L) should be treated with calcium gluconate for cardiac protection. This is followed by an insulin-glucose infusion to shift potassium intracellularly. Loop diuretics may also be used to enhance renal potassium excretion.

• Acid-base balance:
  • Metabolic acidosis (eg, severe diarrhea and diabetic ketoacidosis [DKA]): Bicarbonate therapy should be considered if the blood pH falls below 7.1.
  • Metabolic alkalosis (eg, caused by vomiting or diuretic use): This condition can be corrected by replenishing potassium and chloride deficits with potassium chloride supplementation to restore the acid-base balance.

Treat Underlying Causes

Effective management of dehydration involves replacing fluid and electrolytes and addressing the underlying causes. Treating the root cause helps prevent recurrence and promotes a more complete and lasting recovery.

• Diarrhea or vomiting: Antiemetics, such as ondansetron or metoclopramide, and antidiarrheals, such as loperamide for noninfectious diarrhea, are recommended.
• Diabetes-related dehydration: In DKA, hyperglycemia should be managed with insulin, and fluid replacement should be provided in cases of hyperosmolar hyperglycemic state (HHS).
• Sepsis-induced dehydration: Early IV fluid resuscitation should be initiated, along with prompt antibiotic therapy.
• Diuretic-induced dehydration: Medication should be adjusted, and lost electrolytes should be replenished to restore fluid and electrolyte balance.

Monitoring and Prevention

Regular monitoring and prevention of dehydration are essential to avoid complications and promote optimal health in patients. Consistently assessing fluid status and implementing preventive measures can help reduce the risk of dehydration, particularly in vulnerable populations.

• Monitoring response to treatment: Effective monitoring of clinical signs and laboratory parameters is essential to assess the response to dehydration treatment and ensure optimal hydration status.
  • Clinical signs: Heart rate, blood pressure, urine output, skin turgor, and mental status.
  • Laboratory parameters: Serial measurements of electrolytes, BUN/creatinine, and serum osmolality.
  • Urine output goal: More than or equal to 0.5 mL/kg/h, indicating normal hydration status).

• Prevention strategies: These strategies focus on maintaining proper hydration and minimizing risk factors to reduce the likelihood of dehydration.
  • Adequate fluid intake: At least 2 to 3 L/d of fluid intake is recommended, with adjustments based on activity level, climate, and illness.
  • Hydration in illness: Increased fluid intake is recommended during febrile illness, diarrhea, and vomiting.
  • Diuretics or laxatives: Excessive use of diuretics or laxatives should be avoided, and medications should be adjusted in older patients and those at high risk.

Differential Diagnosis

Dehydration should be differentiated from conditions with similar signs and symptoms, including:

• Gastroenteritis
• Diabetic ketoacidosis
• Hyperosmolar hyperglycemic state
• Sepsis
• Adrenal insufficiency
• Heat stroke or heat exhaustion
• Diuretic overuse
• Gastrointestinal bleeding
• Hypovolemic shock
• Syndrome of inappropriate ADH secretion

Prognosis

The prognosis of dehydration in adults depends on the severity of the condition, underlying causes, comorbidities, and the timeliness of treatment. Mild-to-moderate dehydration typically has an excellent prognosis with prompt oral or IV rehydration. However, severe dehydration carries a higher risk of life-threatening complications if not quickly recognized and appropriately managed.

Prognosis Based on Severity

• Mild-to-moderate dehydration: Most cases resolve quickly with oral or IV fluid replacement, and patients typically recover within 24 to 48 hours if no complications arise.
• Severe dehydration: The prognosis worsens if hypovolemia, electrolyte imbalances, or organ dysfunction develop. If left untreated, severe dehydration can lead to hypovolemic shock, AKI, and multiple organ failure.
• Recurrent or chronic dehydration: Individuals with underlying conditions such as diabetes, kidney disease, heart failure, or neurological disorders are more prone to experience recurrent dehydration, which can lead to long-term complications and worsen underlying health conditions.

Prognostic Factors Affecting Outcome

Various factors affect the clinical outcome of dehydration, as mentioned below.

• Good prognostic factors
  • Early recognition and appropriate oral or IV rehydration.
  • Mild electrolyte disturbances that are quickly corrected.
  • Absence of preexisting renal or cardiovascular disease.

• Poor prognostic factors
  • Severe electrolyte imbalances, such as severe hypernatremia (>160 mEq/L) or hyponatremia (<120 mEq/L), especially when accompanied by neurological symptoms.[32][33] 
  • Complications such as AKI or metabolic acidosis.
  • Older patients with impaired thirst sensation, cognitive impairment, or mobility limitations that hinder access to fluids.[13] 
  • Presence of infections, sepsis, or uncontrolled diabetes (eg, DKA and HHS), which contributes to dehydration.[34][35]

Prognosis in Special Populations

• Older adults: They have a poorer prognosis due to decreased physiological reserve, a blunted thirst response, and the effects of polypharmacy.
• Patients with critical illness: Dehydration increases mortality risk in conditions such as sepsis, AKI, and cardiac dysfunction.
• Diabetic patients: Poor glycemic control increases the risk of dehydration through osmotic diuresis, leading to higher rates of hospitalization and mortality.[34]

Complications

Untreated or severe dehydration can result in serious complications affecting multiple organ systems, including the renal, circulatory, neurological, and metabolic systems. The severity of these complications depends on the degree of dehydration, underlying medical conditions, and the delay in initiating rehydration.

Renal Complications

• Acute kidney injury: Reduced renal perfusion leads to prerenal azotemia, which, if not managed promptly, can progress to acute tubular necrosis.

• Electrolyte imbalances: Dehydration can result in hypernatremia, hyponatremia, hypokalemia, and hyperkalemia, potentially leading to neuromuscular and cardiac dysfunction.

• Kidney stones: Chronic dehydration reduces urine volume and increases solute supersaturation, which promotes the formation of calcium oxalate and uric acid stones.[36]

• Chronic kidney disease: Recurrent episodes of dehydration can contribute to progressive renal damage, particularly in individuals with diabetes or hypertension.[37]

Cardiovascular Complications

• Hypovolemic shock: Severe dehydration can lead to intravascular volume depletion, causing hypotension, tachycardia, and impaired organ perfusion.

• Cardiac arrhythmias: Electrolyte imbalances (such as hypokalemia, hyperkalemia, and hypomagnesemia) may precipitate life-threatening arrhythmias.

• Orthostatic hypotension and falls: Reduced circulating volume can cause dizziness and syncope upon standing, increasing the risk of falls and fractures, particularly in older adults.[38] 

Neurological Complications

• Cognitive impairment and delirium: Dehydration can reduce cerebral perfusion, causing confusion, disorientation, and delirium, particularly in older patients.[39]

• Seizures: Electrolyte imbalances such as hypernatremia or hyponatremia can disrupt neuronal function, leading to seizures and altered mental status.

• Cerebral edema: Rapid correction of hypernatremia can cause osmotic shifts, resulting in brain swelling and increased intracranial pressure.

Gastrointestinal and Hepatic Complications

• Constipation and bowel obstruction: Inadequate fluid intake reduces water content in the stool, potentially leading to severe constipation and fecal impaction.[40]

• Gastrointestinal ischemia (mesenteric ischemia): Decreased blood flow to the intestines may cause ischemic colitis, presenting with abdominal pain, bloody stools, and bowel necrosis.

• Liver dysfunction: Hypovolemia-induced liver hypoperfusion may exacerbate hepatic dysfunction, particularly in patients with cirrhosis.

Musculoskeletal Complications

• Muscle spasms and weakness: Electrolyte imbalances, including sodium, potassium, and magnesium deficiencies, can lead to muscle spasms and weakness.

• Risk of rhabdomyolysis: Severe dehydration, particularly in athletes, military personnel, or patients with critical illness, can trigger muscle breakdown, presenting with myoglobinuria and AKI. Please see StatPearls' companion resource, "Rhabdomyolysis," for more information.

• Falls and fractures: Orthostatic hypotension and muscle weakness increase the risk of injury, especially in older patients.[38]

Metabolic and Endocrine Complications

• Hyperglycemia and diabetic ketoacidosis: In individuals with diabetes, dehydration exacerbates hyperglycemia, increasing the risk of DKA or HHS.[35]

• Metabolic acidosis: Severe dehydration and speis may lead to hypoperfusion and tissue hypoxia, resulting in lactic acidosis.

• Metabolic alkalosis: Dehydration caused by vomiting leads to the loss of hydrochloric acid, resulting in hypochloremic metabolic alkalosis.

Complications in Special Populations

• Older adults: Increased risk of falls, cognitive decline, UTIs, and hospitalizations due to reduced thirst perception and diminished renal function.

• Pregnant women: Dehydration increases the risk of preterm labor, fetal distress, and low amniotic fluid levels (oligohydramnios).[41]

• Critically ill and hospitalized patients: Dehydration can contribute to sepsis, pressure ulcers, impaired wound healing, and multiple organ dysfunction.

Death and Mortality Risk

• Untreated severe dehydration: This carries a high risk of mortality, especially in older adults and critically ill patients.

• Severe hypernatremia: If left untreated, hypernatremia can have a mortality rate as high as 50% when sodium levels exceed 160 mEq/L.[42]

• Hospitalized patients: Severe dehydration requiring hospital admission has a mortality rate of 5% to 15%, especially in older adults, critically ill patients, and individuals with sepsis or multiple organ dysfunction.[33]