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In physiology, dehydration is a lack of total
body water In physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studies life and living organisms, including their anatomy, physica ...
, with an accompanying disruption of
metabolic processes
metabolic processes
. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mild dehydration can also be caused by
immersion diuresis Diuresis () is increased urination and the Renal physiology, physiologic process that produces such an increase. It involves extra urine production in the kidneys as part of the body's Homeostasis, homeostatic maintenance of fluid balance. In hea ...
, which may increase risk of
decompression sickness Decompression sickness (DCS; also known as divers' disease, the bends, aerobullosis, or caisson disease) describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurisation. DCS most common ...
in divers. Most people can tolerate a 3-4% decrease in total body water without difficulty or adverse health effects. A 5-8% decrease can cause
fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

fatigue
and
dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling such as giddiness or foolishness. Dizziness is a common medical c ...

dizziness
. Loss of over ten percent of total body water can cause physical and mental deterioration, accompanied by severe
thirst Thirst is the craving for potable fluids, resulting in the basic instinct Instinct is the inherent inclination of a living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objec ...
.
Death Death is the permanent, irreversible cessation of all biological functions that sustain a living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organi ...

Death
occurs at a loss of between fifteen and twenty-five percent of the body water.Ashcroft F, Life Without Water in Life at the Extremes. Berkeley and Los Angeles, 2000, 134-138. Mild dehydration is characterized by thirst and general
discomfort Comfort (or being comfortable'')'' is a sense of physical or psychological ease, often characterized as a lack of hardship. Persons who are lacking in comfort are uncomfortable, or experiencing discomfort. A degree of psychological comfort c ...
and is usually resolved with oral rehydration. Dehydration can cause
hypernatremia Hypernatremia, also spelled hypernatraemia, is a high concentration of sodium in the Serum (blood), blood. Early symptoms may include a strong feeling of thirst, weakness, nausea, and anorexia (symptom), loss of appetite. Severe symptoms include de ...
(high levels of
sodium ions Sodium is a chemical element with the Symbol (chemistry), symbol Na (from Latin "natrium") and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the p ...
in the blood) and is distinct from
hypovolemia Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss ...
(loss of
blood volume Blood volume is the volume Volume is a scalar quantity expressing the amount Quantity or amount is a property that can exist as a multitude Multitude is a term for a group of people who cannot be classed under any other distinct category, ex ...
, particularly
blood plasma Blood plasma is a yellowish liquid component of blood Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the Cell (biology), cells and transports metabolic waste products ...
).


Signs and symptoms

The hallmarks of dehydration include
thirst Thirst is the craving for potable fluids, resulting in the basic instinct Instinct is the inherent inclination of a living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objec ...
and neurological changes such as
headache Headache is the symptom of pain Pain is a distressing feeling often caused by intense or damaging stimuli. The defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or ...

headache
s, general discomfort, loss of
appetite Appetite is the desire to eat Eating (also known as consuming) is the ingestion of food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργα ...
, decreased
urine Urine is a liquid by-product A by-product or byproduct is a secondary product derived from a production process, process or ; it is not the primary product or service being produced. A by-product can be useful and marketable or it can be cons ...

urine
volume (unless
polyuria Polyuria () is excessive or an abnormally large production or of (greater than 2.5 L or 3 L over 24 hours in adults). Increased production and passage of urine may also be termed . Polyuria often appears in conjunction with (increased thirst) ...
is the cause of dehydration),
confusion In medicine, confusion is the quality or state of being bewildered or unclear. The term "acute mental confusion"
, unexplained
tiredness Fatigue is a feeling of tiredness. It may be sudden or gradual in onset. It is a normal phenomenon if it follows prolonged physical or mental activity, and resolves completely with rest. However, it may be a symptom of a medical condition if it ...
, purple fingernails, and
seizures An epileptic seizure, formally known as a seizure, is a period of symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temp ...
. The symptoms of dehydration become increasingly severe with greater total body water loss. A body water loss of 1-2%, considered mild dehydration, is shown to impair cognitive performance. While in people over age 50, the body's thirst sensation diminishes with age, a study found that there was no difference in fluid intake between young and old people. Many older people suffer symptoms of dehydration. Dehydration contributes to
morbidity A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Diseases are often known to be medical ...
in the elderly population, especially during conditions that promote insensible free water losses, such as hot weather. A Cochrane review on this subject defined water-loss dehydration as "people with
serum osmolality Plasma osmolality measures the body's electrolyte-water balance, electrolyte–water balance. There are several methods for arriving at this quantity through measurement or calculation. molality#Osmolality, Osmolality and osmolarity are measures ...
of 295 mOsm/kg or more" and found that the main symptom in the elderly (people aged over 65) was fatigue.


Cause

Risk factors for dehydration include but are not limited to: exerting oneself in hot and humid weather, habitation at high altitudes, endurance athletics, elderly adults, infants, children and people living with chronic illnesses. Dehydration can also come as a side effect from many different types of drugs and medications. In the elderly, blunted response to thirst or inadequate ability to access free water in the face of excess free water losses (especially
hyperglycemia Hyperglycemia is a condition in which an excessive amount of glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy fr ...

hyperglycemia
related) seem to be the main causes of dehydration. Excess free water or hypotonic water can leave the body in two ways – ''sensible'' loss such as
osmotic diuresis Diuresis () is increased urination Urination is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, ...
,
sweating Perspiration, also known as sweating, is the production of fluids secreted by the sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, f ...

sweating
,
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilat ...

vomiting
and
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
, and ''insensible'' water loss, occurring mainly through the
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differ ...

skin
and
respiratory tract The respiratory tract is the subdivision of the respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex network Network and networking may refer to: ...

respiratory tract
. In humans, dehydration can be caused by a wide range of diseases and states that impair water
homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
in the body. These occur primarily through either impaired thirst/water access or sodium excess.


Diagnosis


Definition

Dehydration occurs when water intake does not replace
free water In the physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studies life and living organisms, including their anatomy, phy ...
lost due to normal physiologic processes, including
breathing Breathing (or ventilation) is the process of moving air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of th ...

breathing
,
urination Urination is the release of urine Urine is a liquid by-product A by-product or byproduct is a secondary product derived from a production process, process or ; it is not the primary product or service being produced. A by-product can b ...
,
perspiration Perspiration, also known as sweating, is the production of fluids secreted by the sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, f ...
, or other causes, including
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery defecation, bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration of ...
, and
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach The stomach is a muscular, in the of humans and many other animals, including several s. The stomach has a dilat ...

vomiting
. Dehydration can be life-threatening when severe and lead to
seizure An epileptic seizure, formally known as a seizure, is a period of symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower tem ...
s or respiratory arrest, and also carries the risk of osmotic cerebral edema if rehydration is overly rapid. The term "dehydration" has sometimes been used incorrectly as a proxy for the separate, related condition of
hypovolemia Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss ...
, which specifically refers to a decrease in volume of
blood plasma Blood plasma is a yellowish liquid component of blood Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the Cell (biology), cells and transports metabolic waste products ...
. The two are regulated through independent mechanisms in humans; the distinction is important in guiding treatment.


Prevention

For routine activities, thirst is normally an adequate guide to maintain proper hydration. Minimum water intake will vary individually depending on weight, environment, diet, and genetics. With exercise, exposure to hot environments, or a decreased thirst response, additional water may be required. In
athlete An athlete (also sportsman or sportswoman) is a person who competes in one or more sports that involve physical strength, speed or endurance. The use of the term in several sports, such as golf or auto racing, becomes a controversial issue. A ...

athlete
s in competition, drinking to
thirst Thirst is the craving for potable fluids, resulting in the basic instinct Instinct is the inherent inclination of a living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objec ...
optimizes performance and safety, despite weight loss, and as of 2010, there was no scientific study showing that it is beneficial to stay ahead of thirst and maintain weight during exercise. In warm or humid weather, or during heavy exertion, water loss can increase markedly, because humans have a large and widely variable capacity for sweating. Whole-body sweat losses in men can exceed 2 L/h during
competitive sport Competition arises whenever two or more parties strive for a common goal A goal is an idea of the future or desired result that a person or a group of people envision, Planning, plan and commit to achieve. People endeavour to reach goals ...
, with rates of 3–4 L/h observed during short-duration, high-intensity exercise in the heat. When such large amounts of water are being lost through perspiration,
electrolytes An electrolyte is a medium containing ions that is electrically conducting Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resis ...
, especially sodium, are also being lost. In most athletes exercising and sweating for 4–5 hours with a sweat sodium concentration of less than 50 mmol/L, the total sodium lost is less than 10% of total body stores (total stores are approximately 2,500 mmol, or 58 g for a 70-kg person). These losses appear to be well tolerated by most people. The inclusion of sodium in fluid replacement drinks has some theoretical benefits and poses little or no risk, so long as these fluids are hypotonic (since the mainstay of dehydration prevention is the replacement of free water losses).


Treatment

The most effective treatment for minor dehydration is widely considered to be drinking water and reducing fluid loss. Plain water restores only the volume of the blood plasma, inhibiting the thirst mechanism before solute levels can be replenished. Solid foods can contribute to fluid loss from vomiting and diarrhea. Urine concentration and frequency will return to normal as dehydration resolves. In some cases, correction of a dehydrated state is accomplished by the replenishment of necessary water and
electrolyte An electrolyte is a medium containing ions that is electrically conducting Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resis ...

electrolyte
s (through
oral rehydration therapy Oral rehydration therapy (ORT) is a type of fluid replacement used to prevent and treat dehydration, especially due to diarrhea. It involves drinking water with modest amounts of sugar and salts, specifically sodium and potassium. Oral rehydratio ...
, or
fluid replacement Fluid replacement or fluid resuscitation is the medical practice of replenishing bodily fluid lost through sweating, bleeding, fluid shifts or other pathologic processes. Fluids can be replaced with oral rehydration therapy Oral rehydration ther ...
by
intravenous therapy Intravenous therapy (abbreviated as IV therapy) is a medical technique that delivers fluids, medications and nutrition directly into a person's vein Veins are blood vessels The blood vessels are the components of the circulatory system ...
). As oral rehydration is less painful, non-invasive, inexpensive, and easier to provide, it is the treatment of choice for mild dehydration. Solutions used for intravenous rehydration must be isotonic or
hypertonic Tonicity is a measure of the effective osmotic pressure Osmotic pressure is the minimum pressure Pressure (symbol: ''p'' or ''P'') is the force In physics, a force is an influence that can change the motion (physics), motion of ...
. Pure water injected into the veins will cause the breakdown (
lysis Lysis ( ; Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 1 ...
) of red blood cells (
erythrocytes Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

erythrocytes
). When
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in ...

fresh water
is unavailable (e.g. at sea or in a desert),
seawater Seawater, or salt water, is water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for al ...

seawater
or drinks with significant
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...

alcohol
concentration will worsen dehydration.
Urine Urine is a liquid by-product A by-product or byproduct is a secondary product derived from a production process, process or ; it is not the primary product or service being produced. A by-product can be useful and marketable or it can be cons ...

Urine
contains a lower solute concentration than seawater; this requires the kidneys to create more urine to remove the excess salt, causing more water to be lost than was consumed from seawater. If a person is dehydrated and taken to a medical facility, IVs can also be used. For severe cases of dehydration where
fainting Syncope, commonly known as fainting, is a loss of consciousness Consciousness, at its simplest, is sentience or awareness of internal and external existence. Despite millennia of analyses, definitions, explanations and debates by philos ...
,
unconsciousness Unconsciousness is a state which occurs when the ability to maintain an awareness of self and environment is lost. It involves a complete, or near-complete, lack of responsiveness to people and other environmental stimulus A stimulus is somethin ...

unconsciousness
, or other severely inhibiting symptoms are present (the patient is incapable of standing or thinking clearly), emergency attention is required. Fluids containing a proper balance of replacement electrolytes are given orally or intravenously with continuing assessment of electrolyte status; complete resolution is normal in all but the most extreme cases.


See also

*
Hydrational fluid Oral rehydration therapy (ORT) is a type of fluid replacement Fluid replacement or fluid resuscitation is the medical practice of replenishing bodily fluid lost through sweating, bleeding, fluid shifts or other pathologic processes. Fluids can ...
s * Terminal dehydration *
Dryness (medical) Dryness is a medical condition in which there is local or more generalized decrease in normal lubrication of the Human skin, skin or mucous membranes. Examples of local dryness include xerostomia, dry mouth, dry eyes, Xeroderma, dry skin and va ...


References


Further reading

* *


External links


Definition of dehydration by the U.S. National Institutes of Health's MedlinePlus medical encyclopedia
{{Authority control Causes of death Nutrition Symptoms and signs Wilderness medical emergencies