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 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 (the breath you see in the air is water that has been exhaled);
- sweat to cool the body;
- 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.
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 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
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.
- Diarrhoea: Diarrhoea 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 diarrhoea.
- Vomiting: Vomiting can also be a cause of fluid loss. It is lost in the vomitus, but it is difficult for a person to replace water by drinking it if they have nausea and 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 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 by the thirst mechanism signalling 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 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, 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.
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 colour.
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
- Light-headedness (especially when standing)
- Decreased urine output
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, organ failure, and death eventually will occur if the dehydration remains untreated.
What about dehydration in children?
Millions of children die worldwide each year because of dehydration, often because of diarrhoea. As well, the temperature regulation and sweat mechanism of infants are not well developed and 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 diarrhoea.
In children, symptoms of dehydration increase as the level of dehydration increases. 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 interosseous (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.
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 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.
- 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 practitioner may look or feel the tongue for fluid.
- 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.
- Paediatric 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.
The purpose of blood tests is to assess potential electrolyte abnormalities (including sodium, potassium, and chloride levels) associated with the dehydration. Tests may or may not be ordered depending upon the underlying cause of dehydration, the severity of illness, the health care practitioner’s assessment of their needs and resources available. Other blood tests may be helpful in determining the level of dehydration. Haemoglobin and red blood cell counts may be elevated because the blood is more concentrated with water loss.
Kidney function tests including BUN and creatinine may be elevated, and is a sign of dehydration. Urinalysis may be ordered to determine urine concentration, the more concentrated the urine, and the more dehydrated the patient.
How is dhydration 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:
- clear broths
- 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 diarrhoea.