What is Dehydration

Water is a critical element of the body, and adequate hydration 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 what is referred to as the extracellular space, which consists of the blood vessels (intravascular space) and the spaces between cells (interstitial space).

Total body water = intracellular space + intravascular space + 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;
sweat to cool the body; and
urinate or have a bowel movement to rid the body of waste products.
In a normal day, a person has to drink a significant amount of water to replace this routine loss.

If intravascular (within the blood vessels) water is lost, the body can compensate somewhat by shifting water from within the cells into the blood vessels, but this is a very short-term solution. The body lives within a very narrow range of normal parameters, and signs and symptoms of dehydration will occur quickly if the water is not replenished.

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. As well, 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.

What causes dehydration?

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

Diarrhea: Diarrhea is the most common reason for a person to loose 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 and it is difficult for a person to replace water by drinking it if they are unable to tolerate liquids.

Sweat: The body can lose significant amounts of water when it tries to cool itself by sweating. Whether the body is hot because of the environment (for example, working in a warm environment), intense exercising in a hot environment, or because a fever is present due to an infection; the body uses a significant amount of 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) to allow body cooling, and that water needs to be replaced.

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: Burn victims become dehydrated because the damaged skin cannot prevent fluid from seeping out of the body. Other inflammatory diseases of the skin are also associated with 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 or the lack of strength to drink adequate amounts, this, coupled with routine or extraordinary water losses can compound the degree of dehydration.

What are the signs and symptoms of dehydration?
The body’s initial responses to dehydration are thirst to increase water intake along with decreased urine output to try to conserve water. 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:

dry mouth,
the eyes stop making tears,
sweating may stop,
muscle cramps,
nausea and vomiting,
heart palpitations, and
lightheadedness (especially when standing).

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 tries to compensate 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. 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. Finally, coma and organ failure, and death eventually will occur if the dehydration remains untreated.

How is dehydration diagnosed?
Dehydration is often a clinical diagnosis. Aside from diagnosing the reason for dehydration, the health care practitioner’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 intravascular space 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.

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.
Infants may have additional evaluations performed, including checking for a soft spot on the skull (sunken fontanelle), assessing the suck mechanism, muscle tone, or loss of sweat in the armpits and groin. 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.
Laboratory testing

The purpose of blood tests is to assess potential electrolyte abnormalities (especially sodium levels) associated with the dehydration. Tests may or may not be done on the patient depending upon the underlying cause of dehydration, the severity of illness, and the health care practitioner’s assessment of their needs.

Urinalysis may be done to determine urine concentration – the more concentrated the urine, the more dehydrated the patient.

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:

water,
clear broths,
popsicles,
Jell-O, and
other replacement fluids that may contain electrolytes (Pedialyte, Gatorade, Powerade, etc.)
Decisions about the use of intravenous fluids depend upon the health care practitioner’s assessment of the extent of dehydration 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, the kidneys sense the increased amount of fluid, 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 often recommended as the diet of choice for the first 24 hours, with gradual progression to a BRAT diet (bananas, rice, apples, toast) and then adding more foods as tolerated.
Loperamide (Imodium) may be considered to control diarrhea.
Acetaminophen or ibuprofen may be used to control fever.
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 dehydration, and/or because of the underlying disease or situation that causes the fluid loss.

Kidney failure

Kidney failure is a common occurrence, although if it is due to dehydration and is treated early, it is often reversible. As dehydration progresses, the volume of fluid in the intravascular space decreases, and blood pressure may fall. This can decrease blood flow to vital organs like 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. If enough organs begin to malfunction, the body itself may fail, and death can occur.

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.

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 fail from running). As fluid loss increases, the patient may be so dehydrated that there is not enough water to sweat and heat exhaustion or heat stroke may occur. 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 and potassium) 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 practitioner is often aware of the fluid and electrolyte balance in the dehydrated patient and may decide to monitor electrolyte levels by checking blood tests. Some 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. In many patients with dehydration, the kidneys are able to compensate and regulate electrolyte levels.

It is reasonable 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 die.

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. Of course, people should be monitored to make certain they are safe. Those working in hot environments need to take care to rehydrate often.
Exercise: People exercising in a hot environment need to drink adequate amounts of water.
Age: The young and elderly are most at risk. 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.

Dehydration at A Glance
The body needs water to function.
Dehydration occurs when water intake is less than water loss.
Symptoms range from mild to life-threatening.
Prevention is the important first step in treating dehydration.
The young and the elderly are especially susceptible to dehydration.


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