Dehydration

  • Medical Author:
    Benjamin Wedro, MD, FACEP, FAAEM

    Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

View Dehydration Slideshow

Dehydration facts

  • The body needs water to function.
  • Dehydration occurs when water intake is less than water loss.
  • Symptoms range from mild to life-threatening.
  • The young and the elderly are especially susceptible to dehydration.

What is dehydration?

Water is a critical element of the body, and keeping the body adequately hydrated is a must to allow the body to function. Up to 75% of the body's weight is made up of water. Most of the water is found within the cells of the body (intracellular space). The rest is found in the extracellular space, which consists of the blood vessels (intravascular space) and the spaces between cells (interstitial space).

Dehydration occurs when the amount of water leaving the body is greater than the amount being taken in. The body is very dynamic and always changing. This is especially true with water in the body. We lose water routinely when we:

  • breathe and humidified air leaves the body (this can be seen on a cold day when you can see your breath in the air, which is just water that has been exhaled);
  • sweat to cool the body; and
  • eliminate waste by urinating or having a bowel movement.

In a normal day, a person has to drink a significant amount of water to replace this routine loss.

The formula for daily fluid requirements depends upon an individual's weight. Normally, fluid and weight are calculated using the metric system; however, below is the approximation in imperial (American) units.

Body weightDaily fluid requirements (approximate)
10 pounds15 ounces
20 pounds30 ounces
30 pounds40 ounces
40 pounds45 ounces
50 pounds50 ounces
75 pounds55 ounces
100 pounds50 ounces
150 pounds65 ounces
200 pounds70 ounces

If you would like to calculate your body weight and daily fluid requirements using the metric system, please use this formula.

  • For the first 10kg (kilogram) of body weight the daily fluid intake required is 100cc (or mL) per kg.
  • For the next 10kg of body weight, the fluid required is an additional 50 cc/kg.
  • For every additional kg of body weight, an additional 10cc/kg is required

This is the basic body requirement. More fluid would be needed to replace excess sweating from exercise or fever, fluid loss from vomiting, and diarrhea or increased urine production.

Quick GuideDehydration: Causes, Symptoms & Tips to Stay Hydrated

Dehydration: Causes, Symptoms & Tips to Stay Hydrated
Are you in danger of developing hyponatremia?

Early Symptoms of Dehydration

Symptoms and signs of dehydration can be minor, such as increased thirst, or severe and life-threatening, depending on the extent of the dehydration.

The early symptoms of dehydration are

  • thirst, and
  • reduced urine output and darkening of the urine.

As dehydration progresses, other symptoms develop, including

  • dry mouth,
  • lightheadedness,
  • muscle cramps, and
  • palpitations.

What causes dehydration?

Dehydration occurs because there is too much water lost, not enough water taken in, or most commonly, a combination of the two.

  • Diarrhea: Diarrhea is the most common reason for a person to lose excess amounts of water. A significant amount of water can be lost with each bowel movement. Worldwide, more than four million children die each year because of dehydration from diarrhea.
  • Vomiting: Vomiting can also be a cause of fluid loss. Not only can an individual lose fluid in the vomitus, but it may be difficult to replace water by drinking because of that same nausea and vomiting.
  • Sweat: The body can lose significant amounts of water in the form of sweat when it tries to cool itself. Whether the body temperature is increased because of working or exercising in a hot environment or because a fever is present due to an infection; the body uses water in the form of sweat to cool itself. Depending upon weather conditions, a brisk walk may generate up to 16 ounces of sweat (a pound of water) an hour to allow body cooling, and that water needs to be replaced by the thirst mechanism signaling the person to drink fluids.
  • Diabetes: In people with diabetes, elevated blood sugar levels cause sugar to spill into the urine and water then follows, which may cause significant dehydration. For this reason, frequent urination and excessive thirst are among the early symptoms of diabetes.
  • Burns: The skin acts as a protective barrier for the body and is also responsible for regulating fluid loss. Burn victims become dehydrated because the damaged skin cannot prevent fluid from seeping out of the body. Other inflammatory diseases of the skin such as toxic epidermal necrolysis, also may be associated with significant fluid loss.
  • Inability to drink fluids: The inability to drink adequately is the other potential cause of dehydration. Whether it is the lack of availability of water, intense nausea with or without vomiting, or the lack of strength to drink. This coupled with routine or extraordinary water losses can compound the degree of dehydration.

Dehydration pictures

The body is able to monitor the amount of fluid it needs to function. The thirst mechanism signals the body to drink water when the body is dry. Moreover, hormones like anti-diuretic hormone (ADH) work with the kidney to limit the amount of water lost in the urine when the body needs to conserve water (diuretic = increased excretion of water).

Dynamic Picture of Rehydration
Dynamic Picture of Dehydration

What are the signs and symptoms of dehydration?

The body's initial responses to dehydration are thirst to increase water intake, and decreased urine output to try to conserve water loss. The urine will become concentrated and more yellow in color.

As the level of water loss increases, more symptoms can become apparent. The following are further signs and symptoms of dehydration.

The body tries to maintain cardiac output (the amount of blood that is pumped by the heart to the body); and if the amount of fluid in the intravascular space is decreased, the body compensates for this decrease by increasing the heart rate and making blood vessels constrict to try to maintain blood pressure and blood flow to the vital organs of the body. The body shunts blood flow away from the skin to internal organs, for example, the brain, heart, lungs, kidneys, and intestines; causing the skin to feel cool and clammy. This coping mechanism begins to fail as the level of dehydration increases.

With severe dehydration, confusion and weakness will occur as the brain and other body organs receive less blood flow. Finally, coma, organ failure, and death eventually will occur if the dehydration remains untreated.

Quick GuideDehydration: Causes, Symptoms & Tips to Stay Hydrated

Dehydration: Causes, Symptoms & Tips to Stay Hydrated

What about dehydration in children?

Millions of children die worldwide each year because of dehydration, often because of diarrhea. As well, the temperature regulation and sweat mechanism of infants are not well developed, and this increases their risk of heat-related illness.

It is important to remember that infants and children are dependent upon others to provide them with water and nutrition. Infants cannot tell their parents or care providers when they are thirsty. Enough fluid needs to be provided so that the dehydration can be prevented. This is especially true if increased water loss occurs because of fever, vomiting or diarrhea.

In children, symptoms of dehydration increase as the level of dehydration increases.

Level of dehydration Estimated fluid loss Signs and Symptoms in Children
Level of dehydrationEstimated fluid lossSigns and symptoms
Minimal<3% of body weightnone
Mild to moderate<10% of body weightFussy, tired, irritable child. Dry mucous membranes (mouth, tongue), increased heart rate, increased breathing rate, decreased urine output, increased thirst
Severe10% of body weight or moreListless, lethargic, unconscious. Too weak to cry. Sunken eyes, sunken fontanelle (soft spot of skull). Increased heart rate, weak pulses, and rapid shallow breathing. Cool, mottled skin. No urine output (dry diapers). Too weak to suckle or drink fluids. Loss of muscle tone with the child appearing "floppy."

Infants and children respond well to fluid replacement, and often oral rehydration therapy (ORT) can treat dehydration. Small, frequent sips of fluid replacement solutions such as Pedialyte or Gatorade may be enough to prevent the need for intravenous fluids. In ORT, replacement begins with 5cc or one teaspoon of fluid every 5-10 minutes. If this is tolerated without vomiting, the amount of fluid is doubled, again providing small amounts every few minutes. However, if the child is too ill to drink or cannot tolerate even small sips of fluid, medical care should be accessed immediately.

Intravenous fluids can rehydrate the infant or child while the underlying illness is evaluated and treated. Occasionally, there is difficulty in placing an intravenous line and an intraosseous (inside the bone) needle can be placed, usually in the tibia (shin bone) that allows fluid resuscitation.

In children who are markedly dehydrated, blood tests may be used to monitor electrolytes, kidney function, and acid-base balance in the body.

It is important to find the reason for the illness because dehydration is the result of a disease process, not the cause of it.

How is dehydration diagnosed?

Dehydration is often a clinical diagnosis. Aside from diagnosing the reason for dehydration, the health care professional's examination of the patient will assess the level of dehydration. Initial evaluations may include:

  • Mental status tests to evaluate whether the patient is awake, alert, and oriented. Infants and children may appear listless and have whiny cries and decreased muscle tone.
  • Vital signs may include postural readings (blood pressure and pulse rate are taken lying down and standing). With dehydration, the pulse rate may increase and the blood pressure may drop because the blood is depleted of fluid. People taking beta blocker medications for high blood pressure, heart disease, or other indications, occasionally lose the ability to increase their heart rate as a compensation mechanism since these medications block the adrenaline receptors in the body.
  • Temperature may be measured to assess fever. While it is common to measure temperature in the ear (tympanic) or by mouth (orally), a rectal thermometer may be used to assess core body temperature if the patient appears warm, but no fever is noted tympanically or orally.
  • Skin may be checked to see if sweat is present and to assess the degree of elasticity (turgor). As dehydration progresses, the skin loses its water content and becomes less elastic. The amount of sweat is often felt in the armpit or groin, two areas that tend to have moisture normally.
  • The mouth can become dry and the health care professional may look at or feel the tongue to see how wet it is.
  • Infants may have additional evaluations performed, including checking for a soft spot on the skull (sunken fontanelle), and assessing the suck mechanism, loss of sweat in the armpits and groin, and muscle tone. All are signs of potential significant dehydration.
  • Pediatric patients are often weighed during routine child visits, thus a body weight measurement may be helpful in assessing how much water has been lost with the acute illness. This is very rough estimate because all scales are not the same, and for infants and children, it is important to know what clothing they were wearing when the original weight was taken.

Laboratory testing

The purpose of blood tests is to assess potential electrolyte abnormalities (including sodium, potassium, chloride, and carbon dioxide levels) associated with the dehydration. Other tests may or may not be ordered depending upon the underlying cause of dehydration, the severity of illness, and the health care professional's assessment of their needs and resources available.

Other blood tests may be helpful in determining the level of dehydration. Hemoglobin and red blood cell counts may be elevated because the blood is more concentrated with water loss from the intravascular space.

Kidney function tests including BUN and creatinine may be elevated, and this is one way of measuring the severity of dehydration.

Urinalysis may be ordered to determine urine concentration; the more concentrated the urine, the more dehydrated the patient.

Quick GuideDehydration: Causes, Symptoms & Tips to Stay Hydrated

Dehydration: Causes, Symptoms & Tips to Stay Hydrated

How is dehydration treated?

As is often the case in medicine, prevention is the important first step in the treatment of dehydration. (Please see the home treatment and prevention sections.)

Fluid replacement is the treatment for dehydration. This may be attempted by replacing fluid by mouth, but if this fails, intravenous fluid (IV) may be required. Should oral rehydration be attempted, frequent small amounts of clear fluids should be used.

Clear fluids include most things you can see through.

  • Water (please note that water alone is not necessarily safe to use in infants and can lead to significant electrolyte problems. For this reason, Pedialyte or other balanced electrolyte solutions should be used.
  • Clear broths
  • Popsicles
  • Jell-O
  • Other replacement fluids that may contain electrolytes (Pedialyte, Gatorade, Powerade, etc.)

Decisions about the use of intravenous fluids depend upon the health care professional's assessment of the extent of dehydration, the ability for the patient to drink fluids by mouth, and the ability for the patient to recover from the underlying cause.

The success of the rehydration therapy can be monitored by urine output. When the body is dry, the kidneys try to hold on to as much fluid as possible, urine output is decreased, and the urine itself is concentrated. As treatment occurs and if it is successful, the kidneys sense the increased amount of fluid within the intravascular space and urine output increases.

Medications may be used to treat underlying illnesses and to control fever, vomiting, or diarrhea.

Can I treat dehydration at home?

Dehydration occurs over time. If it can be recognized in its earliest stages, and if its cause can be addressed, home treatment may be beneficial and adequate.

Steps a person can take at home to prevent severe dehydration include:

  • Individuals with vomiting and diarrhea can try to alter their diet and use medications to control symptoms to minimize water loss. Clear fluids are recommended as the diet of choice for the first 24 hours, with gradual progression to a regular diet as tolerated.
  • Loperamide (Imodium) may be considered to control diarrhea. If the affected individual has a fever, or if there is blood in the diarrhea, medical advice should be obtained before administering medications to control diarrhea.
  • Acetaminophen (Tylenol and others) or ibuprofen (Advil, Motrin, and others) may be used to control fever. Ibuprofen may irritate the stomach and cause nausea and vomiting, so it should be used with caution in patients who already have these symptoms.
  • Fluid replacements may be attempted by small, frequent amounts of clear fluids (see clear fluids information in previous section). The amount of fluid required to maintain hydration depends upon the individual's weight. The average adult needs between 2 and 3 liters of fluid per day.

If the person becomes confused or lethargic; if there is persistent, uncontrolled fever, vomiting, or diarrhea; or if there are any other specific concerns, then medical care should be accessed.

Emergency medical system (EMS) or 911 should be activated for any individual with altered mental status - confusion, lethargy, or coma.

What are the complications of dehydration?

Complications of dehydration may occur because of the consequences of dehydration, and/or because of the underlying disease or situation that causes the fluid loss.

Kidney failure

Kidney failure is a common occurrence and often is reversible, if it is due to dehydration and is treated early. As dehydration progresses, the volume of fluid in the body decreases, and blood pressure may fall. This can decrease blood flow to vital organs including the kidneys, and like any organ with a decreased blood flow; it has the potential to fail to do its job.

Coma

Decreased blood supply to the brain may cause confusion and even coma. 

Shock

When the fluid loss overwhelms the body's ability to compensate, blood flow and oxygen delivery to the body's vital organs become inadequate and cell and organ function can begin to fail. If enough organs begin to malfunction, the body itself may fail and death can occur.

Heat-related illnesses and associated complications

In heat-related illness, the body's attempt to cool itself by sweating may cause dehydration to the point that muscles may go into spasm (heat cramps). It is often the muscles that are being stressed that will spasm (for example, in people who work outside in a hot environment, arm and leg muscles may spasm from lifting and moving heavy objects or equipment; in athletes, leg muscles may cramp from running). As fluid loss increases, the symptoms of heat exhaustion can occur and include weakness, lightheadedness, nausea, and vomiting. If the symptoms are recognized and the patient isn't moved from the heat and rehydrated, the situation may progress to heat stroke. The patient will stop sweating, have a change in mental status that includes confusion and coma, and the body temperature may spike to 106 F (41 C) or higher. Heat stroke is a true medical emergency and 911 or the emergency response system should be activated immediately in this situation.

Electrolyte abnormalities

In dehydration, electrolyte abnormalities may occur since important chemicals (like sodium, potassium, and chloride) are lost from the body through sweat. For example, patients with profuse diarrhea or vomiting may lose significant amounts of potassium, causing muscle weakness and heart rhythm disturbances. The health care professional may decide to monitor electrolyte levels by checking blood tests. Examples of symptoms caused by abnormal electrolyte levels include muscle weakness due to low potassium, heart rhythm disturbances due to either low or high potassium, and seizures due to low (hyponatremia) or high sodium (hypernatremia). In many patients with dehydration, the kidneys are able to compensate and regulate electrolyte levels.

It is important to remember that dehydration does not occur quickly, and sometimes it may take hours to slowly correct the fluid deficit and allow the electrolytes to redistribute themselves appropriately in the different spaces in the body. If rehydration is done too slowly, the patient may remain hypotensive and in shock for too long. If done too quickly, water and electrolyte concentrations within organ cells can be negatively affected, causing cells to swell and eventually become damaged.

Can dehydration be prevented?

  • Environment: Dehydration due to the weather is a preventable condition. If possible, activities should not be scheduled in the heat of the day. If they are, adequate fluids should be available, and cooler, shaded areas should be used if possible. People should be monitored to make certain they are safe. Those working in hot environments need to take care to drink plenty of fluids and be self-aware of their condition. In heat waves, it is important to routinely check on neighbors, especially the elderly or those that do not have air conditioning.
  • People exercising and working in a hot environment need to drink adequate amounts of water. People can become dehydrated while playing in the ocean, lakes, or pools if the water and environmental temperatures are warm enough.
  • Age: The young and elderly are most at risk because of poor temperature regulation systems. During heat waves, attempts should be made to check on the elderly in their homes. During the Chicago heat wave of 1995, more than 600 people died in their homes from heat exposure.
  • Heat related conditions: Know the signs and symptoms of heat cramps, heat rash, heat exhaustion, and heat stroke. Preventing dehydration is one step to avoid these conditions.

Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine

REFERENCES:

Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.

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Reviewed on 10/5/2016
References
Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine

REFERENCES:

Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.

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