Volume Depletion and Dehydration

Volume status is a balance between water and solutes, the majority of which is Na. Volume depletion (also known as hypovolemia) refers to a loss of both water and Na, whereas dehydration refers only to a loss of water. Dehydration is primarily caused by decreased water intake and presents with increased thirst and can progress to altered mental status and low blood pressure if severe. Volume depletion can be caused by GI losses, renal losses, bleeding, poor oral Na intake, or third spacing of fluids. The clinical presentation has relatively nonspecific symptoms but will ultimately cause low blood pressure if severe. The diagnosis of these imbalances is based on lab findings in addition to clinical symptoms and signs, which can be subtle and unreliable. Management requires differentiation between these 2 conditions. The treatment is to administer fluids with tonicity similar to those lost; isotonic fluids are used for volume depletion, and hypotonic fluids are used for dehydration.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Definitions and Etiology

Definitions

Dehydration refers only to a loss of water, while volume depletion refers to a loss of both water and Na+

Etiology

  • Dehydration due to decreased oral water intake:
    • Acute or critical illness 
    • Decreased access to water
    • Altered thirst mechanisms in childhood or old age
    • Dementia
  • Volume depletion (hypovolemia) due to decreased oral Na intake: 
    • Acute or critical illness
    • Eating disorders
    • Dementia
  • Volume depletion due to increased volume losses: 
    • Bleeding
    • GI losses: 
      • Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
      • Vomiting
      • Drains (e.g., nasogastric tube)
    • Renal:
      • Osmotic diuresis ( diabetic ketoacidosis Diabetic ketoacidosis Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) are serious, acute complications of diabetes mellitus. Diabetic ketoacidosis is characterized by hyperglycemia and ketoacidosis due to an absolute insulin deficiency. Hyperglycemic Crises)
      • Diuretic therapy
      • Diabetes insipidus Diabetes Insipidus Diabetes insipidus (DI) is a condition in which the kidneys are unable to concentrate urine. There are 2 subforms of DI: central DI (CDI) and nephrogenic DI (NDI). Both conditions result in the kidneys being unable to concentrate urine, leading to polyuria, nocturia, and polydipsia. Diabetes Insipidus
      • Postobstructive/postacute tubular necrosis diuresis
    • Third-space losses:
      • Burns Burns A burn is a type of injury to the skin and deeper tissues caused by exposure to heat, electricity, chemicals, friction, or radiation. Burns are classified according to their depth as superficial (1st-degree), partial-thickness (2nd-degree), full-thickness (3rd-degree), and 4th-degree burns. Burns
      • Severe pancreatitis
    • Insensible losses:
      • Skin/mucous membranes (e.g., fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever)
      • Respiratory tract

Pathophysiology

The relative differences between losses of water and Na determine how water shifts between the fluid compartments of the body. With volume depletion and dehydration, there are fluid shifts between the compartments.

Fluid compartments of the body

  • Total body water (TBW):
    • 50% of body weight for adult women and 60% of body weight for adult men
    • Varies with muscle mass (more water) and fat (less water)
    • Decreases in the elderly, as muscle mass is replaced with fat 
    • Decreases in obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity
  • Intracellular fluid (ICF): fluid enclosed within cells = ⅔ of TBW
  • Extracellular fluid (ECF): fluid outside the cells = ⅓ of TBW
    • Divided into 2 subcompartments 
    • Intravascular fluid = plasma (in blood)
      • ¼ of the ECF
      • Approximately 8% of TBW (⅓ x ¼)
    • Interstitial fluid (IF)
      • Fluid between cells; not in the blood
      • ¾ of the ECF
      • Approximately 25% of TBW (⅓ x ¾)
Water distribution

Distribution of total body water within the body

Image by Lecturio.

Fluid shifts with illness/disease

  • Occur due to diffusion across a semipermeable membrane 
  • Regulated by a difference in plasma osmolality between ECF and ICF
  • Plasma osmolality = total body sodium (TBNa+)/TBW
  • Dehydration: 
    • Water is lost, but Na is not.
    • ICF contracts more than ECF.  
      • Water is lost from ECF → ECF osmolality increases → water diffuses from ICF to ECF
      • ⅔ of total lost water is from ICF, ⅓ is from ECF.
      • Net effect: ECF hypertonicity and hypernatremia Hypernatremia Hypernatremia is an elevated serum sodium concentration > 145 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled by the hypothalamus via the thirst mechanism and antidiuretic hormone (ADH) release. Hypernatremia occurs either from a lack of access to water or an excessive intake of sodium. Hypernatremia 
    • Example: ↓ water intake or inadequate water replacement in critical illness
  • Hypotonic loss of fluid:
    • Water loss exceeds Na loss.
    • ECF and ICF both contract:
      • Hypotonic fluid is lost from ECF → ECF osmolality increases → water diffuses from ICF to ECF
      • Less water shifts from ICF to ECF compared to the loss of only water (with dehydration).
      • Net effect is ECF hypertonicity and hypernatremia Hypernatremia Hypernatremia is an elevated serum sodium concentration > 145 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled by the hypothalamus via the thirst mechanism and antidiuretic hormone (ADH) release. Hypernatremia occurs either from a lack of access to water or an excessive intake of sodium. Hypernatremia.
    • Examples:
      • Increased insensible losses ( fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, tachypnea, excessive sweating)
      • Polyuria (diabetes insipidus, postobstructive diuresis)
      • Osmotic diuresis ( diabetic ketoacidosis Diabetic ketoacidosis Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) are serious, acute complications of diabetes mellitus. Diabetic ketoacidosis is characterized by hyperglycemia and ketoacidosis due to an absolute insulin deficiency. Hyperglycemic Crises)
  • Hypertonic loss of fluid:
    • Na loss exceeds water loss.
    • Can result in either hyponatremia Hyponatremia Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. Hyponatremia or hypernatremia Hypernatremia Hypernatremia is an elevated serum sodium concentration > 145 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled by the hypothalamus via the thirst mechanism and antidiuretic hormone (ADH) release. Hypernatremia occurs either from a lack of access to water or an excessive intake of sodium. Hypernatremia
    • ECF contracts and ICF expands:
      • Fluid is lost from ECF → ECF contracts and ECF osmolality decreases
      • ↓ ECF osmolality causes water to shift from ECF to ICF via diffusion.
      • Normal ⅔-to-⅓ relationship between ICF and ECF is lost
    • Examples:
      • Loop diuretics Loop diuretics Loop diuretics are a group of diuretic medications primarily used to treat fluid overload in edematous conditions such as heart failure and cirrhosis. Loop diuretics also treat hypertension, but not as a 1st-line agent. Loop Diuretics (furosemide, bumetanide, torsemide)
      • Salt-wasting nephropathy ( Bartter syndrome Bartter syndrome Bartter syndrome is a rare autosomal recessive disorder that affects the kidneys and presents either antenatally with severe or life-threatening manifestations or in childhood or adulthood with a milder course, depending on the genetic defect. Clinical disease results from defective renal reabsorption of sodium chloride in the thick ascending limb of the loop of Henle. Bartter Syndrome, Gitelman syndrome Gitelman syndrome Gitelman syndrome is a rare genetic autosomal recessive disorder that affects the sodium-chloride cotransporter in the distal convoluted tubule of the nephron and causes electrolyte abnormalities. The syndrome presents clinically with symptoms of hypokalemia and hypomagnesemia. Gitelman Syndrome)
      • Primary adrenal insufficiency Adrenal Insufficiency Adrenal insufficiency (AI) is the inadequate production of adrenocortical hormones: glucocorticoids, mineralocorticoids, and adrenal androgens. Primary AI, also called Addison’s disease, is caused by autoimmune disease, infections, and malignancy, among others. Adrenal insufficiency can also occur because of decreased production of adrenocorticotropic hormone (ACTH) from disease in the pituitary gland (secondary) or hypothalamic disorders and prolonged glucocorticoid therapy (tertiary). Adrenal Insufficiency and Addison’s Disease (Addison disease)
  • Isotonic loss of fluid:
    • Na and water lost at the same rate
    • ECF contracts, ICF does not change.
    • Isotonic fluid is lost from ECF → ECF osmolality does not change → no gradient for diffusion with ICF
    • Plasma osmolality and serum Na do not change.
    • Examples: 
      • Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
      • Loss of whole blood
      • Third-space losses

Clinical Presentation

The clinical presentation of dehydration and volume depletion varies greatly depending on the severity, from asymptomatic to potentially fatal hypovolemic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock.

Clinical history

  • Can be asymptomatic
  • Symptoms with mild and moderate hypovolemia are often nonspecific: 
    • Fatigue
    • Dizziness
    • Thirst
    • Muscle cramps
  • Symptoms with severe hypovolemia are mostly related to hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension:
    • Chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain (coronary artery ischemia)
    • Abdominal pain ( mesenteric ischemia Mesenteric Ischemia Mesenteric ischemia is a rare, life-threatening condition caused by inadequate blood flow through the mesenteric vessels, which results in ischemia and necrosis of the intestinal wall. Mesenteric ischemia can be either acute or chronic. Mesenteric Ischemia)
    • Altered mental status/severe dizziness (cerebral ischemia)

Physical exam

  • Signs of dehydration and hypovolemia:
    • Dry mucous membranes
    • Dry skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin
    • Decreased skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin turgor ( skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin tenting when pinched)
    • Mildly decreased supine blood pressure
    • Orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
    • Weight loss
  • Signs of shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock:
  • Hypotension (systolic blood pressure < 100 mm Hg)
  • Tachycardia (> 90–100 beats/min)
  • Tachypnea (respiratory rate > 20)
  • Cool extremities
  • Altered mental status
  • Decreased capillary refill time > 2 seconds
  • Decreased urine output
  • Decreased jugular venous pressure
  • Findings are less reliable in the elderly:
    • Orthostatic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension may be due to autonomic dysfunction.
    • Skin turgor is typically lost with age. 
  • Urine output may be paradoxically high with specific etiologies:
    • Diabetes insipidus Diabetes Insipidus Diabetes insipidus (DI) is a condition in which the kidneys are unable to concentrate urine. There are 2 subforms of DI: central DI (CDI) and nephrogenic DI (NDI). Both conditions result in the kidneys being unable to concentrate urine, leading to polyuria, nocturia, and polydipsia. Diabetes Insipidus
    • Osmotic diuresis 
    • Salt-wasting nephropathy ( Bartter syndrome Bartter syndrome Bartter syndrome is a rare autosomal recessive disorder that affects the kidneys and presents either antenatally with severe or life-threatening manifestations or in childhood or adulthood with a milder course, depending on the genetic defect. Clinical disease results from defective renal reabsorption of sodium chloride in the thick ascending limb of the loop of Henle. Bartter Syndrome, Gitelman syndrome Gitelman syndrome Gitelman syndrome is a rare genetic autosomal recessive disorder that affects the sodium-chloride cotransporter in the distal convoluted tubule of the nephron and causes electrolyte abnormalities. The syndrome presents clinically with symptoms of hypokalemia and hypomagnesemia. Gitelman Syndrome)
  • Evaluation of TBNa+:
    • Normal TBNa+ → normal blood pressure and skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin turgor (normal physical exam)
    • Decreased TBNa+ → signs of volume depletion
Skin turgor

Decreased skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin turgor (i.e., skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin tenting when pinched):
A sign of decreased total body Na+.

Image by Lecturio.

Diagnosis

Determining the volume status is often challenging, and the history, physical exam, and lab results must be integrated. Outside of extremes, signs and symptoms of dehydration are subtle and unreliable and should not be used alone for detecting dehydration and volume depletion.

Laboratory evaluation

  • Blood tests:
    • BUN/creatinine ratio: 
      • Normal: approximately 10:1
      • Elevated ratio (> 20:1) suggests hypovolemia.
      • Inaccurate if glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids or GI bleeding (unrelated causes of elevated BUN)
    • Serum Na+:
      • Can be high or low, depending on the tonicity of fluid lost
      • Hypovolemia stimulates antidiuretic hormone (ADH) secretion (contributes to hyponatremia Hyponatremia Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. Hyponatremia).
    • Serum K+:
      • Can be high or low, but is usually low
      • Elevated: if there is decreased secretion from renal dysfunction or decreased distal Na+ delivery
      • Low: if K+ is lost in GI fluids or if there is increased secretion from high aldosterone state 
    • Acid–base disorders:
      • Metabolic alkalosis Metabolic alkalosis The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. Metabolic alkalosis also occurs when there is an increased loss of acid, either renally or through the upper GI tract (e.g., vomiting), increased intake of HCO3-, or a reduced ability to secrete HCO3- when needed. Metabolic Alkalosis: if hypovolemia is due to diuretics or upper GI losses
      • Metabolic acidosis Metabolic acidosis The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. Metabolic acidosis occurs when there is an increase in the levels of new non-volatile acids (e.g., lactic acid), renal loss of HCO3-, or ingestion of toxic alcohols. Metabolic Acidosis: with bicarbonate loss due to diarrhea, lactic acidosis with shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock, or ketoacidosis with diabetic ketoacidosis Diabetic ketoacidosis Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) are serious, acute complications of diabetes mellitus. Diabetic ketoacidosis is characterized by hyperglycemia and ketoacidosis due to an absolute insulin deficiency. Hyperglycemic Crises ( DKA DKA Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) are serious, acute complications of diabetes mellitus. Diabetic ketoacidosis is characterized by hyperglycemia and ketoacidosis due to an absolute insulin deficiency. Hyperglycemic Crises)
    • Albumin and hematocrit:
      • Concentration increases with hypovolemia
      • Must consider baseline values 
  • Urine studies:
    • Urine sodium (UNa+): < 20 mEq/L suggests hypovolemia
    • UNa+ is inaccurate with:
      • Metabolic alkalosis Metabolic alkalosis The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. Metabolic alkalosis also occurs when there is an increased loss of acid, either renally or through the upper GI tract (e.g., vomiting), increased intake of HCO3-, or a reduced ability to secrete HCO3- when needed. Metabolic Alkalosis: UNa+ > 20 mEq/L due to Na+ being paired with filtered HCO3
      • Edematous states (low effective arterial blood volume): CHF CHF Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure, cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis, nephrotic syndrome Nephrotic syndrome Nephrotic syndrome is characterized by severe proteinuria, hypoalbuminemia, and peripheral edema. In contrast, the nephritic syndromes present with hematuria, variable loss of renal function, and hypertension, although there is sometimes overlap of > 1 glomerular disease in the same individual. Nephrotic Syndrome
      • AKI AKI Acute kidney injury refers to sudden and often reversible loss of renal function, which develops over days or weeks. Azotemia refers to elevated levels of nitrogen-containing substances in the blood that accompany AKI, which include BUN and creatinine. Acute Kidney Injury/ CKD CKD Chronic kidney disease (CKD) is kidney impairment that lasts for ≥ 3 months, implying that it is irreversible. Hypertension and diabetes are the most common causes; however, there are a multitude of other etiologies. In the early to moderate stages, CKD is usually asymptomatic and is primarily diagnosed by laboratory abnormalities. Chronic Kidney Disease (unable to conserve Na+)
      • Diuretic use
      • Bilateral renal artery stenosis Renal artery stenosis Renal artery stenosis (RAS) is the narrowing of one or both renal arteries, usually caused by atherosclerotic disease or by fibromuscular dysplasia. If the stenosis is severe enough, the stenosis causes decreased renal blood flow, which activates the renin-angiotensin-aldosterone system (RAAS) and leads to renovascular hypertension (RVH). Renal Artery Stenosis
      • Very-low-sodium diet
      • Salt-wasting nephropathy ( Bartter syndrome Bartter syndrome Bartter syndrome is a rare autosomal recessive disorder that affects the kidneys and presents either antenatally with severe or life-threatening manifestations or in childhood or adulthood with a milder course, depending on the genetic defect. Clinical disease results from defective renal reabsorption of sodium chloride in the thick ascending limb of the loop of Henle. Bartter Syndrome, Gitelman syndrome Gitelman syndrome Gitelman syndrome is a rare genetic autosomal recessive disorder that affects the sodium-chloride cotransporter in the distal convoluted tubule of the nephron and causes electrolyte abnormalities. The syndrome presents clinically with symptoms of hypokalemia and hypomagnesemia. Gitelman Syndrome)
    • Fractional excretion of Na+ (FENa+):
      • Useful only if AKI AKI Acute kidney injury refers to sudden and often reversible loss of renal function, which develops over days or weeks. Azotemia refers to elevated levels of nitrogen-containing substances in the blood that accompany AKI, which include BUN and creatinine. Acute Kidney Injury is also present
      • FENa+ < 1 suggests hypovolemia
    • Urine osmolality: > 450 mOsm/kg suggests hypovolemia
    • Urine osmolality is inaccurate with:
      • AKI AKI Acute kidney injury refers to sudden and often reversible loss of renal function, which develops over days or weeks. Azotemia refers to elevated levels of nitrogen-containing substances in the blood that accompany AKI, which include BUN and creatinine. Acute Kidney Injury/ CKD CKD Chronic kidney disease (CKD) is kidney impairment that lasts for ≥ 3 months, implying that it is irreversible. Hypertension and diabetes are the most common causes; however, there are a multitude of other etiologies. In the early to moderate stages, CKD is usually asymptomatic and is primarily diagnosed by laboratory abnormalities. Chronic Kidney Disease (unable to concentrate urine)
      • Diuretics
      • Diabetes insipidus Diabetes Insipidus Diabetes insipidus (DI) is a condition in which the kidneys are unable to concentrate urine. There are 2 subforms of DI: central DI (CDI) and nephrogenic DI (NDI). Both conditions result in the kidneys being unable to concentrate urine, leading to polyuria, nocturia, and polydipsia. Diabetes Insipidus
    • Urine specific gravity:
      •  > 1.015 suggests hypovolemia
      • Inaccurate if recent IV contrast or severe proteinuria

Other diagnostic tools

  • If it is unclear that hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension is due to hypovolemia:
    • Test volume responsiveness:
      • IV fluid test bolus 250–500 mL over 5–10 minutes
      • Passive leg Leg The lower leg, or just "leg" in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, and the muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia. Leg raising may be used as a maneuver to assess whether a individual is fluid-responsive.
      • Volume responsiveness implies an improvement in cardiac output and tissue perfusion.
    • Hemodynamic monitoring devices may be used to assist in volume management by measuring:
      • Cardiac output
      • Pulse pressure variation
      • Stroke volume variation
  • Chest x-ray: 
    • Expected to be clear of signs of pulmonary edema Pulmonary edema Pulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure. Pulmonary Edema in hypovolemia
    • Inaccurate if chronic or unrelated lung disease
  • Point-of-care bedside ultrasonography/echocardiography:
    • For individuals with undifferentiated hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension in the ED
    • Occasionally used for difficult-to-determine volume status
    • Vena cava assessment:
      • Euvolemia/hypovolemia: IVC diameter decreases during inspiration.
      • Hypervolemia: IVC diameter decreases less or not at all during inspiration.
    • Elevated systolic EF:
      • Hypovolemia → less blood in the ventricle → higher fraction is ejected to maintain the stroke volume
      • Can be inaccurate if the baseline EF is unknown

Management

The primary management of hypovolemia is to replace the fluids lost with similar tonicity of fluids; electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes must also be monitored.

Hypovolemic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock management

  • Aggressive administration of isotonic IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids:
    • Usually 0.9% normal saline
    • Blood transfusion if there is bleeding
  • Monitor blood pressure closely:
    • Decrease IV fluid rate when blood pressure improves.
    • Consider vasopressors if blood pressure does not improve with large volumes of IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids.
  • Address electrolytes Electrolytes Electrolytes are mineral salts that dissolve in water and dissociate into charged particles called ions, which can be either be positively (cations) or negatively (anions) charged. Electrolytes are distributed in the extracellular and intracellular compartments in different concentrations. Electrolytes are essential for various basic life-sustaining functions. Electrolytes when blood pressure improves.

Moderate-to-severe hypovolemia management

  • Initial rehydration:
    • Bolus of 1–2 L isotonic IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids to start (usually normal saline)
    • Treat aggressively to prevent possible progression to shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock.
  • Na management:
    • Normal serum Na+ (sNa+):
      • Continue isotonic IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids until signs/symptoms improve.
      • May need continuous maintenance IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids if there are ongoing losses (e.g.,  diarrhea) 
    • Hypernatremia:
      • Switch to hypotonic fluids (0.45% NaCl or 5% dextrose in water) once hypovolemia symptomatically improves.
      • Exception: may need to use 5% dextrose in water earlier if there is severe hypernatremia Hypernatremia Hypernatremia is an elevated serum sodium concentration > 145 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled by the hypothalamus via the thirst mechanism and antidiuretic hormone (ADH) release. Hypernatremia occurs either from a lack of access to water or an excessive intake of sodium. Hypernatremia
      • Monitor closely to avoid overcorrection.
    • Hyponatremia:
      • Acutely symptomatic hyponatremia Hyponatremia Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. Hyponatremia → give 3% NaCl (hypertonic saline) until symptoms improve
      • Moderate-to-severe hyponatremia Hyponatremia Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. Hyponatremia, but not acutely symptomatic → give isotonic fluids (normal saline) at a more conservative rate than if sNa+ is normal
      • Mild hyponatremia Hyponatremia Hyponatremia is defined as a decreased serum sodium (sNa+) concentration less than 135 mmol/L. Serum sodium is the greatest contributor to plasma osmolality, which is very tightly controlled via antidiuretic hormone (ADH) release from the hypothalamus and by the thirst mechanism. Hyponatremia → give isotonic fluids at a similar rate as with normal sNa+

Mild hypovolemia management

  • If sNa+ is high or low: address before replacing fluid specifically for hypovolemia.
  • If sNa+ is normal:
    • Give gentle isotonic IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids (usually normal saline; less likely to need transfusion).
    • Increased oral intake of fluids alone may be sufficient if very mild.

Follow-up and monitoring

  • Identify and treat other electrolyte abnormalities.
  • Identify and treat underlying diseases contributing to hypovolemia.
  • Monitor closely to determine when IV fluid rate adjustment is needed:
    • Clinical signs:
      • Blood pressure
      • Heart rate
      • Urine output
    • Labs: 
      • BUN
      • Creatinine
      • BNP
      • Lactic acid

Clinical Relevance

  • Edematous states: conditions such as congestive heart failure Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure, cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis, and nephrotic syndrome Nephrotic syndrome Nephrotic syndrome is characterized by severe proteinuria, hypoalbuminemia, and peripheral edema. In contrast, the nephritic syndromes present with hematuria, variable loss of renal function, and hypertension, although there is sometimes overlap of > 1 glomerular disease in the same individual. Nephrotic Syndrome with total body fluid overload (↑ ECF) but decreased effective arterial blood volume. Still, the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys paradoxically react as if the body is volume depleted and continue to maximize the reabsorption of Na+ and water, leading to a vicious cycle of fluid retention. Loop diuretics Loop diuretics Loop diuretics are a group of diuretic medications primarily used to treat fluid overload in edematous conditions such as heart failure and cirrhosis. Loop diuretics also treat hypertension, but not as a 1st-line agent. Loop Diuretics are required for clinical volume overload, which manifests with pitting edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema, ascites Ascites Ascites is the pathologic accumulation of fluid within the peritoneal cavity that occurs due to an osmotic and/or hydrostatic pressure imbalance secondary to portal hypertension (cirrhosis, heart failure) or non-portal hypertension (hypoalbuminemia, malignancy, infection). Ascites, and weight gain.
  • Hypovolemic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock: Loss of intravascular volume is so severe that tissue perfusion is compromised. Clinical signs include low blood pressure, tachycardia, cool extremities, altered mental status, and decreased urine output. Lactic acidosis can be a helpful indicator of compromised tissue perfusion. Treatment is aggressive isotonic IV fluid resuscitation. If this treatment does not restore the hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension and tissue perfusion, then vasopressors are indicated.  
  • Acute blood loss: Bleeding is an isotonic loss of fluid. The decrease in hemoglobin and hematocrit that accompany hemorrhage is due to the kidney’s response to the hypovolemia. This response is to reabsorb more water, which then dilutes the ECF and causes the concentration of hemoglobin and hematocrit to fall. This renal compensation also explains the time lag from when the bleeding stops to when the hemoglobin and hematocrit stabilize.
  • Insensible losses: small amounts of fluid normally lost throughout the day via respiration and sweating. These volumes are usually very small and clinically inconsequential. However, if the individual has tachypnea or fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, the volume losses can become clinically significant and lead to hypovolemia. Hypovolemia may occur even in critically ill individuals who are intubated and mechanically ventilated. Treatment is to replace these ongoing losses with maintenance hypotonic IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids.
  • Third spacing: fluid moving from the intravascular space into the interstitial, or “third,” space. This movement can involve large volumes of fluids in individuals with large burns or severe pancreatitis. The movement is important because this fluid does not quickly mobilize back into the circulation and is essentially considered “lost.” Treatment is to aggressively replace the lost fluid volume with isotonic IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids, as third spacing can be extensive enough to cause severe hypovolemia.
  • Postobstructive polyuria: brisk diuresis that can occur after the resolution of AKI AKI Acute kidney injury refers to sudden and often reversible loss of renal function, which develops over days or weeks. Azotemia refers to elevated levels of nitrogen-containing substances in the blood that accompany AKI, which include BUN and creatinine. Acute Kidney Injury caused by severe urinary tract obstruction Urinary tract obstruction Urinary tract obstruction (UTO) refers to the blockage of the urinary tract, which can occur anywhere in the urinary tract. Urinary tract obstruction can be acute or chronic, partial or complete, and unilateral or bilateral. Urinary tract obstruction can cause acute or chronic kidney disease. Urinary Tract Obstruction. Polyuria can also be caused by impaired urinary concentrating ability from acute tubular necrosis (ATN) with osmotic diuresis from the high levels of solutes (e.g., Na and urea) that accumulate during AKI AKI Acute kidney injury refers to sudden and often reversible loss of renal function, which develops over days or weeks. Azotemia refers to elevated levels of nitrogen-containing substances in the blood that accompany AKI, which include BUN and creatinine. Acute Kidney Injury. Management is with hypotonic IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids given at half the volume of the urine output, with caution not to cause increased urine output from overaggressive hydration.
  • Diabetes insipidus Diabetes Insipidus Diabetes insipidus (DI) is a condition in which the kidneys are unable to concentrate urine. There are 2 subforms of DI: central DI (CDI) and nephrogenic DI (NDI). Both conditions result in the kidneys being unable to concentrate urine, leading to polyuria, nocturia, and polydipsia. Diabetes Insipidus (DI): genetic or acquired condition of impaired urinary concentrating ability due to either the lack of ADH (central DI) or resistance to it by the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys (nephrogenic DI). Both conditions result in the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys being unable to concentrate urine, leading to polyuria and polydipsia. Diagnosis is by measurement of ADH levels and response to the water-deprivation test. Central DI is treated with desmopressin; nephrogenic DI is treated with diuretics and dietary salt restriction.

References

  1. Mandel, J. & Palevsky, P.M. (2019). Treatment of severe hypovolemia or hypovolemic shock in adults. UpToDate. Retrieved March 13, 2021, from https://www.uptodate.com/contents/treatment-of-severe-hypovolemia-or-hypovolemic-shock-in-adults
  2. Sterns, RH. (2020). Etiology, clinical manifestations, and diagnosis of volume depletion in adults. UpToDate. Retrieved March 13, 2021, from https://www.uptodate.com/contents/etiology-clinical-manifestations-and-diagnosis-of-volume-depletion-in-adults
  3. Somers, M.J. (2020). Clinical assessment and diagnosis of hypovolemia (dehydration) in children. UpToDate. Retrieved December 15, 2021, from https://www.uptodate.com/contents/clinical-assessment-and-diagnosis-of-hypovolemia-dehydration-in-children
  4. Santillanes, G., Rose, E. (2018). Evaluation and management of dehydration in children. Emerg Med Clin North Am 36:259–273. DOI: 10.1016/j.emc.2017.12.004
  5. Lacey, J., et al. (2019). A multidisciplinary consensus on dehydration: definitions, diagnostic methods and clinical implications. Ann Med 51:232–251. DOI: 10.1080/07853890.2019.1628352

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