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 free water with or without sodium. This condition often arises when obligatory water losses are not adequately replaced. Multiple factors contribute to dehydration (see Table 1).[6]

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.[7] 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.[8][9]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.[10] There is an estimation that about 24% of non-hospitalized older adults are dehydrated, with a higher prevalence among long-term care residents (34%) than community-dwelling older adults (19%).[11]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.[12]

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.[13] Research results show 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, electrolyte imbalances, and cognitive impairment, particularly in older adults and those with underlying chronic conditions.[14]In community-dwelling adults, dehydration increases the risk of falls, urinary tract infections (UTIs), and cognitive decline.[3] Mortality rates in hospitalized individuals range around 15%, depending on the severity of dehydration and the presence of comorbid conditions.[15][16] Dehydration is also a leading cause of readmissions among older adults, highlighting the need for more effective prevention and post-discharge monitoring strategies.[17]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.[18][19] 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 (total body water), with two-thirds intracellular and one-third extracellular. Of the extracellular water, one-fifth is found in the intravascular space.[1][20] The body depends on a complex system to maintain euvolemia, the stable, normal volume of blood and extracellular fluid.

Dehydration occurs when fluid loss exceeds intake, reducing total body water and leading to clinical abnormalities in thermoregulation, skin elasticity, and circulatory stability. Dehydration is often used interchangeably with hypovolemia or volume depletion, which is a reduction in intravascular volume.[1] Both of these can coexist in some conditions like inadequate fluid intake, gastrointestinal losses through diarrhea or vomiting, osmotic diuresis, and excessive sweating.[17] 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 maintains water homeostasis through coordinated actions of the thirst mechanism, antidiuretic hormone (ADH), and the renin-angiotensin-aldosterone system (RAAS). 

• Thirst mechanism and hypothalamic regulation: Inadequate water intake or fluid loss can elevate plasma osmolality. Specialized neurons in the hypothalamus (osmoreceptors) can detect increased plasma osmolality and trigger a thirst response, promoting increased water intake.[17] However, this mechanism is less sensitive in older adults, making them more prone to dehydration.[21]
• ADH and renal water retention: When plasma osmolality increases, the posterior pituitary gland secretes ADH, also known as arginine vasopressin (AVP). AVP acts on V2 receptors in the renal collecting duct to insert aquaporin-2 (AQP2) water channels into the apical membrane, increasing water reabsorption and concentrating the urine.[22] 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. 
• RAAS 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, which increases sodium reabsorption through epithelial sodium channels in the distal nephron. Water reabsorption occurs secondarily by following the osmotic gradient created by sodium transport.[23] 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 in equal proportions, as seen in conditions such as vomiting, diarrhea, and hemorrhage. This leads to hypovolemia or reduced plasma volume, manifesting as tachycardia, hypotension, and diminished organ perfusion.[1] As there is extracellular fluid contraction without significant change in osmolality, it is harder to detect by osmolality alone.[24]
• Hypertonic dehydration: This occurs when free water loss exceeds sodium loss, resulting in hypernatremia and increased plasma osmolality (>300 mOsm/kg).[4] An increased osmotic gradient draws water out of cells, leading to intracellular volume contraction. This is the most common type of dehydration in older adults. 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.[24]
• 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. Hyponatremia results in decreased osmotic gradient, which drives water into the cells, leading to intracellular swelling and concurrent extracellular volume depletion.[25] The resulting fluid shift into cells can lead to cerebral edema, muscle weakness, and lethargy.[1] 

Systemic Effects of Dehydration

Dehydration affects multiple organ systems and leads to significant physiological consequences, as outlined below.[17]

• 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, causing brain cells to shrink and leading to 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 an acute kidney injury, 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, resulting in 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.

Age-Related Pathophysiology

Many physiological changes in older adults make them more vulnerable to dehydration:

• Blunted thirst mechanism: This seems to be related to a deficit in central nervous system pathways with age, rather than osmoreceptors.[21]
• Decrease in kidney function: The kidneys' ability to concentrate urine decreases with age, which seems to be related to resistance to vasopressin.[26]
• Reduced Total Body Water: There is a significant decline in total body water with age due to decreased lean muscle mass, as muscle holds more water than fat.[27]
• Polypharmacy: Medications like diuretics, laxatives, ACE inhibitors, angiotensin receptor blockers (ARBs), anticholinergics, and psychotropic medications increase dehydration risk.[28]

History and Physical

A comprehensive history is essential when assessing dehydration, as symptoms and risk factors vary depending on severity and etiology. A thorough history includes:

• Fluid intake assessment: Reduced fluid intake and skipping drinks between meals are among the most common causes of dehydration in older adults. Also assess for barriers to drinking like cognitive impairment, functional dependence, restricted access to fluids, and voluntary fluid restriction.
• Fluid loss: Due to vomiting, diarrhea, polyuria with diabetes or diuretic use, fever, excessive sweating, third spacing (ascites, pleural effusion).[28]
• Medication history: Look for medications like diuretics, ACE inhibitors, ARBs, SGLT2 inhibitors, laxatives, lithium, psychotropics, and anticholinergics.[28]
• Comorbidities like cognitive impairment, diabetes mellitus, CKD, heart failure, and immobility increase the risk of dehydration.

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. 

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.[29]

Table 2. Signs and Symptoms of Dehydration

Evaluation

Evaluation of dehydration requires a systematic approach that combines laboratory and point-of-care testing. Clinical assessment remains the cornerstone of diagnosis, with test results used to confirm the diagnosis, assess severity, identify underlying causes, and guide fluid and electrolyte replacement.

Laboratory Evaluation: 

Although no single test is considered the gold standard for diagnosing dehydration, direct measurement of serum osmolality is a valuable diagnostic marker for assessing hypertonic dehydration, with values greater than 295 mOsm/kg suggesting impending dehydration, and greater than 300 mOsm/kg indicating current dehydration.[1] However, it cannot detect isotonic dehydration, and the rate of fluid loss can influence its accuracy.

Specific electrolyte abnormalities vary based on the type of dehydration. Hypernatremia (sodium >145 mEq/L) suggests water loss or hypertonic dehydration, whereas hyponatremia (sodium <135 mEq/L) indicates sodium loss or hypotonic dehydration.[1] A blood urea nitrogen-to-creatinine ratio (BUN:Cr) greater than 20:1 suggests prerenal azotemia, consistent with volume depletion, due to increased proximal tubular urea reabsorption and water retention with vasopressin release.[30] Hypokalemia is commonly associated with dehydration due to diarrhea or diuretic use, while hyperkalemia in a dehydrated patient may suggest adrenal insufficiency. 

Elevated hemoglobin or hematocrit (hemoconcentration) suggests volume contraction, although it is nonspecific and requires baseline comparison. Elevated lactate (>2 mmol/L) suggests tissue hypoperfusion and may indicate hypovolemic shock. Serum electrolytes and blood gas analysis can detect acid-base disturbances in severe dehydration, such as hypokalemic metabolic alkalosis from vomiting-induced dehydration, hyperchloremic metabolic acidosis from diarrhea, or lactic acidosis from shock.

Urine studies provide important information but have some limitations. Urine specific gravity greater than 1.020 and urine osmolality exceeding 450 mOsm/kg indicate concentrated urine, reflecting renal compensation for fluid loss. However, urine osmolality can be affected by glucose and protein levels, and both can be misleading during rehydration. Urine sodium levels below 20 mEq/L and Fractional Excretion of Sodium (FENa) less than 1% suggest hypovolemia, but these can be unreliable with diuretic use and in CKD.

Point-of-Care Assessments:

Point-of-care ultrasound (POCUS) evaluation of the inferior vena cava (IVC) provides a rapid estimate of right atrial pressure or intravascular volume in spontaneously breathing patients. IVC diameter less than 2.1 cm with more than 50% inspiratory collapse suggests low right atrial pressure and possible intravascular volume depletion. In contrast, a dilated IVC is consistent with elevated right atrial pressure or volume overload.[31] However, IVC assessment reflects fluid tolerance rather than absolute volume status and is unreliable in the presence of mechanical ventilation, elevated intra-abdominal pressure, ascites, right heart failure, or obesity.

Noninvasive cardiac output monitoring (NICOM) offers a more comprehensive evaluation of fluid status and can guide individualized fluid management in hypotensive individuals.[32] However, its primary role is hemodynamic monitoring rather than diagnosing dehydration. Another emerging point-of-care test is salivary osmolality, with values more than 93 mOsm showing good sensitivity and specificity for detecting both hypertonic and isotonic dehydration.[24][33] However, further studies are needed before widespread clinical adoption.

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, comorbid conditions, and the patient's ability to tolerate oral intake. 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 if the patient can tolerate oral intake. ORT is effective, safe, and less invasive than IV fluid therapy.[34] The physiological basis of ORT is that coupled sodium-glucose cotransport across the intestinal brush border remains intact even during diarrhea, enabling enhanced water absorption.[35] ORT may require less volume than intravenous fluid therapy to achieve a similar pressor effect because oral fluid has an independent pressor effect mediated by the portal-hepatic osmoreceptor reflex.[36](A1)

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. Reduced-osmolarity oral rehydration solutions (<250 mOsm/L) are preferred over the older standard WHO-ORS (311 mOsm/L), as they reduce the risk of hypernatremia.[35] 
(A1)

Commercially available ORS formulations, such as Pedialyte or CeraLyte, are appropriate, but avoid sports and carbonated soft drinks.

• Homemade oral rehydration solution: Half 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: Drinks containing caffeine, alcohol, or carbonation can worsen dehydration.
• ORT administration: Adults should consume 1 to 2 liters of oral rehydration over the first 4 hours, continuing as needed to maintain hydration.

Severe Dehydration

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

• Isotonic crystalloids: Lactated Ringer solution, Plasma-Lyte A, or 0.9% normal saline are preferred first-line management options. Balanced crystalloids, such as Lactated Ringer solution or Plasma-Lyte, may reduce the risk of hyperchloremic metabolic acidosis and major adverse kidney events compared with 0.9% normal saline in hospitalized and critically ill adults.[37] However, the benefit of balanced crystalloids is small and context-dependent, and normal saline remains the appropriate first-line treatment for most cases of dehydration.
• Hypotonic fluids (for hypernatremic dehydration): 0.45% Saline (half-normal saline) is used to correct hypernatremia while gradually reducing the risk of cerebral edema.
• Dextrose-containing fluids (for hypoglycemia or ongoing fluid loss): 5% dextrose in 0.9% normal saline (D5-0.9% normal saline) is administered with saline to prevent dilutional hyponatremia, which can occur with 5% dextrose in water (D5W) infusion alone.
(B3)

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.[38][39](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): Previous recommendations have been to reduce serum sodium by no more than 10 mEq/L per 24 hours (or 0.5 mmol/L per hour) for chronic or unknown-duration hypernatremia to avoid cerebral edema.[40] However, emerging evidence suggests 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.[41][42] In acute hypernatremia (developed over hours), rapid correction at 1 mmol/L per hour is appropriate and improves prognosis without increasing the risk of cerebral edema.
  • Hyponatremia (<135 mEq/L): Hypovolemic hyponatremia should be treated with isotonic crystalloid solutions to restore intravascular volume. 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.[43]
• Potassium abnormalities: 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 to protect the heart. 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 to restore acid-base balance.
(B3)

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: Intravenous fluids and Insulin are used to manage DKA and the hyperosmolar hyperglycemic state (HHS).
• Sepsis-induced dehydration: Early intravenous 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 for assessing treatment response to dehydration and ensuring 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.
  • POCUS assessment of IVC to guide fluid tolerance or overload
• 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 is recommended, with adjustments based on activity level, climate, and illness.
• Older adults: Offer drinks between meals and provide a wider selection of beverages to increase fluid intake. 
• Hydration in illness: Increased fluid intake is recommended during febrile illness, diarrhea, and vomiting.
• Medications: 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
• Diabetes insipidus
• Hyperosmolar hyperglycemic state
• Sepsis
• Adrenal insufficiency
• Heat stroke or heat exhaustion
• Diuretic overuse
• Gastrointestinal bleeding
• Hypovolemic shock
• Syndrome of inappropriate ADH secretion
• Fever
• Hypercalcemia
• Hyperthyroidism
• Pheochromocytoma
• Primary polydipsia
• Salt wasting nephropathy

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 intravenous fluid replacement, and patients typically recover within 24 to 48 hours without complications.
• Severe dehydration: The prognosis worsens if hypovolemia, electrolyte imbalances, or organ dysfunction develop. If left untreated, severe dehydration can lead to hypovolemic shock, acute kidney injury, 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.[44][45] 
  • Serum osmolality more than 300 mOsm/kg.[1]
  • Complications such as acute kidney injury or metabolic acidosis.
  • Older patients with age greater than 65 years: Due to impaired thirst sensation, cognitive impairment, or mobility limitations that hinder access to fluids.[16] 
  • Presence of infections, sepsis, or uncontrolled diabetes (eg, DKA and HHS), which contributes to dehydration.[46][47]
  • Hospital-acquired dehydration has higher mortality than community-acquired.[48]

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, acute kidney injury, and cardiac dysfunction.
• Patients with diabetes: Poor glycemic control increases the risk of dehydration through osmotic diuresis, leading to higher rates of hospitalization and mortality.[46]

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 due to dehydration leads to prerenal azotemia, which, if not managed promptly, can progress to acute tubular necrosis.[49]
• Electrolyte imbalances: Dehydration can lead to hypernatremia, hyponatremia, hypokalemia, and hyperkalemia, which can cause 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.[50]
• CKD: Recurrent episodes of dehydration can contribute to progressive renal damage, particularly in individuals with diabetes or hypertension.[51]

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.[52] 
• Venous thromboembolism: Decreased intravascular volume, which increases blood viscosity, can increase the risk of VTE.[53]

Neurological Complications

• Cognitive impairment and delirium: Dehydration can reduce cerebral perfusion, causing confusion, disorientation, and delirium, particularly in older patients.[54]
• 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.[25]
• Cerebral hemorrhage: Severe hypernatremia can cause brain shrinkage, leading to vascular rupture and intracranial hemorrhage.[40]

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.[55]
• 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 acute kidney injury. 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.[52]

Metabolic and Endocrine Complications

• Hyperglycemia and diabetic ketoacidosis: In individuals with diabetes, dehydration exacerbates hyperglycemia, increasing the risk of DKA or HHS.[47]
• Metabolic acidosis: Severe dehydration and sepsis may lead to hypoperfusion and tissue hypoxia, resulting in lactic acidosis.
• Metabolic alkalosis: Dehydration from vomiting leads to loss of hydrochloric acid, resulting in hypochloremic metabolic alkalosis.

Pharmacological Complications

• Increased drug concentration: Concentration of hydrophilic drugs (like aminoglycosides, lithium, digoxin) increases due to volume contraction, leading to adverse effects.
• Increased metabolism: Dehydration upregulates CYP2E1 expression, thereby altering the metabolism of drugs that are substrates of this enzyme (such as acetaminophen).[56]

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).[57]
• 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 individuals.
• Severe hypernatremia: If left untreated, hypernatremia can have a mortality rate as high as 50% when sodium levels exceed 160 mEq/L.[58]
• Hospitalized patients: Severe dehydration requiring hospital admission has a mortality rate of 5% to 15%, especially in older adults, critically ill individuals, and those with sepsis or multiple organ dysfunction.[45]