Dehydration is defined as a state of negative fluid balance in the body that may be caused by various physiological or pathological reasons. The most common causes are diarrheal illnesses.

Water is vital for human survival. When the body loses more water than it takes in, a negative fluid balance is created in the body, which results in and is usually a mild problem, which reverses on intake of more fluid intake, orally or intravenously. However, severe dehydration can be fatal if not addressed and treated promptly. dehydration and its symptoms.

It is commonly seen in clinical practice

  • A 3 to 4% decrease in total body water causes no symptoms or adverse health effects.
  • A 5-8% decrease can cause weakness fatigue and giddiness.
  • More than 10% loss of total body water can cause worsening physical and mental symptoms such as severe thirst.
  • 15 to 25% loss of body fluid can cause hypovolemic shock, which ultimately results in organ failure and death.

The negative fluid balance that occurs in dehydration can result from various reasons such as

  • decreased fluid intake
  • increased fluid loss from the body due to renal, gastrointestinal, or insensible losses such as from the respiratory system and skin
  • fluid shift, which occurs in conditions such as ascites, effusions, burns, and sepsis.


The total water in the body is distributed into extracellular and intracellular compartments. The decrease in total body water in dehydration occurs in both the intracellular and extracellular compartments.

The extracellular compartment comprises the intravascular, interstitial, and transcellular spaces and contains one-third of the total body water. The intracellular compartment (within the cells) contains two-thirds of the total body water.

When dehydration develops, fluid from the extracellular compartment is lost first, followed by intracellular fluid. The intracellular loss causes the cells to shrink and lose function.

Dehydration can occur due to decreased water intake, increased fluid loss, or both.

For example, impaired thirst awareness (as in the elderly), chronic illnesses, and fever are common causes of less water intake.

Increased fluid loss occurs in vomiting, diarrhea, diuresis (excessive urination), and excessive sweating as in workers doing physical activity in hot weather without water.


Dehydration is classified according to existing sodium concentration in blood.

Dehydration can be

  • Isonatremic (Serum sodium levels between 130-150 mEq/L) ,
  • Hyponatremic (sodium < 130 mEq/L), or
  • Hypernatremic (sodium >150 mEq/L

Isonatremic dehydration is the most common accounting for 80%  of the cases. Hypernatremic and hyponatremic dehydration each comprise 5-10% of cases.

  • Isonatremic (isotonic) dehydration occurs when the lost fluid has the same sodium concentration as that of blood. Sodium and water losses are equal in both the intravascular and extravascular fluid compartments.
  • Hyponatremic (hypotonic) dehydration occurs when the lost fluid contains more sodium than blood. More sodium is lost from the body due to which serum sodium levels fall. As a result, water from the intravascular compartment shifts to the extravascular space, causing a fall in intravascular volume.
  • Hypernatremic (hypertonic) dehydration occurs when more water and less sodium are lost. As a result, the concentration of sodium in the blood increases due to which extravascular water shifts to the intravascular space, minimizing the depletion of intravascular fluid volume.

Besides changes in sodium concentration, other electrolyte imbalances may also occur:


As mentioned above, dehydration occurs when you are not taking in enough water, losing too much water, or a combination of both.

Determining the cause of dehydration is essential for successful management. Poor fluid intake, excessive fluid loss, or a combination of the above may cause depletion of intravascular volume.

Common causes of dehydration include the following:

  • Gastroenteritis: This is the most common cause of dehydration in which dehydration may progress rapidly due to vomiting and diarrhea.
  • Stomatitis: Due to the inflamed and sore mouth, you may severely limit oral intake of food and water due to pain.
  • Diabetic ketoacidosis (DKA): DKA leads to osmotic diuresis and dehydration if oral intake is insufficient. Weight loss is caused by both excessive fluid losses and tissue catabolism.
  • Febrile illness: An increase in body temperature (fever) increases your metabolism rate and your respiratory rate, leading you to more insensible water loss.
  • Pharyngitis: Due to sore throat and pain, there is a tendency to drink and eat less.
  • Burns: Burns can cause extreme fluid loss through the burnt areas of the skin and the blisters filled with fluid that form.
  • GI obstruction: This condition is often associated with poor intake and recurrent vomiting.
  • Heat exhaustion: This occurs due to excessive physical activity in the hot sun leading to excessive loss of fluid through sweating.
  • Diabetes mellitus: One of the symptoms of diabetes is polyurea, which is excessive urination. This can cause you to become dehydrated if your water intake is low.
  • Diabetes insipidus: This condition causes excessive production of very dilute urine, which can result in huge water losses and severe hypernatremic dehydration.
  • Thyrotoxicosis: In this condition, dehydration occurs due to diarrhea. In spite of increased appetite, there is weight loss.
  • Cystic fibrosis. This condition is a genetic defect, which changes the way in which a salt moves in and out of cells. There is excessive formation of sticky mucus in the respiratory, digestive, and reproductive systems.

Risk factors

Although dehydration can develop in anyone, some people are at a greater risk. Babies, children, and older adults are more at risk of dehydration.

Risk factors include:

  • People staying at higher altitudes.
  • Athletes, especially those in long-distance endurance events, such as marathons, triathlons, and cycling tournaments.
  • People with chronic conditions such as diabetes, kidney disease, cystic fibrosis, and alcoholism.
  • Infants and children – most commonly due to diarrhea and vomiting.
  • Older people – old people drink less water because of the reduced sensation of thirst and also so that they do not need to get up for the toilet as often.

How do you reduce the risk of dehydration?

Drinking water regularly can reduce the risk of dehydration. Water or sweetened diluted fruit juices are good choices.

You should drink enough to ensure that your urine is clear and pale in color. You should drink more when the risk of dehydration is higher.

For example, you could be having a fever, or you are sweating more due to hot weather or exercise, or when you have diarrhea.

Children especially those under the age of 5 years should get plenty of fluids to avoid dehydration.

The thirst sensation is reduced in the elderly after the age of 60 years. They may not feel thirsty even when mildly dehydrated. Such people should particularly down at least 10 to 12 glasses of water spaced out during the day.


Dehydration is often mild and mild dehydration usually does not cause any symptoms. Even your urine color may not be dark. However, if untreated, it progresses and can present these symptoms and signs. which are seen in men and women:

  • Feeling thirsty
  • Having a dry mouth and nose
  • Cracked lips
  • Fatigue and weakness
  • Muscle pain
  • Headache
  • Dizziness or lightheadedness
  • Weakness and fatigue
  • Having dark-colored urine
  • Increased heart and respiratory rate
  • Confusion
  • Wrinkled skin in severe dehydration

Symptoms of severe dehydration in infants and children:

  • Absence of tears when crying
  • No wetting of diapers for four hours or more
  • Sunken abdomen, eyes, cheeks, or fontanel
  • High fever
  • Lethargy
  • Irritability

Symptoms of severe dehydration in adults

  • Not passing urine or having very dark-colored one
  • Dry skin with poor elasticity that does not immediately return to normal shape after pinching and letting go
  • Feeling dizzy
  • Fast heartbeat
  • Rapid breathing
  • Sunken eyes
  • Feeling drowsy
  • Lack of energy
  • Confusion or irritability
  • Fainting


Untreated dehydration can lead to serious complications:

  • Low blood volume seen in dehydration produces low blood pressure. This causes less oxygen to reach throughout the body, which can be life-threatening.
  • Seizures are caused by an imbalance of electrolytes.
  • Kidney problems, which include kidney stones, urinary tract infections, and eventually kidney failure
  • Heat-related issues such as mild cramps, heat exhaustion, and even heat stroke.
  • Extreme cases of dehydration, if left untreated, can lead to kidney failure, stroke, and death.

Laboratory tests for dehydration

There is no definitive laboratory test for dehydration. Appropriate treatment can be given if the etiology is identified and in mild-to-moderate dehydration.

With moderate to  severe dehydration, the doctor may ask for the following laboratory studies:

  • Serum sodium is done to determine hyponatremia (< 130 mEq/L) and hypernatremia (> 150 mEq/L) because they require specific treatments.
  • High serum potassium levels may be elevated in congenital adrenal hyperplasia, renal failure, marked acidosis, and low in pyloric stenosis and alkalosis.
  • Low serum chloride levels may be seen in pyloric stenosis or tubercular meningitis.
  • Low bicarbonate levels have been correlated with increased severity of dehydration.
  • Serum glucose levels may be low due to poor intake or poor absorption, or very high in DKA.
  • BUN and creatinine levels may be elevated because of renal insufficiency.
  • Urinalysis may show the presence of ketones and glucose in DKA


Replacing the lost fluids and lost electrolytes and moving the person or child to a cool area is the only effective treatment for dehydration. Treatment guidelines depend on age, the severity of dehydration, and its cause.

Oral rehydration solution (ORS) is the cornerstone of treating diarrhea in low-resource settings. You can prepare it at home by adding six teaspoons of sugar and a half teaspoon of salt to one liter of water. This simple mixture has saved millions of lives and hardly costs anything.

WHO has formulated ORS powder, which you should add to water and drink. The formula is described here.

Treatment of children with mild to moderate dehydration

For infants and children in whom dehydration has occurred due to diarrhea, vomiting, or fever, an over-the-counter oral rehydration solution (ORS) is ideal. ORS contains water and salts in specified proportions to replenish the lost fluids and electrolytes.

Older children can be given diluted sports drinks in equal proportions of one part of a sports drink to one part of water.

Treatment of adults with mild to moderate dehydration

Most adults with mild to moderate dehydration caused by diarrhea, vomiting, or fever should drink more water with ORS or juices and soups. Do not drink full-strength fruit juice and soft drinks.

Cool water is best if your dehydration is due to outdoor physical work or exercise in hot or humid weather. Sports drinks containing electrolytes and a carbohydrate solution can also help.

Treatment of children and adults with severe dehydration

Children and adults who are severely dehydrated should be treated in a hospital on an emergency basis. Fluids and electrolytes delivered intravenously are the fastest way to cure dehydration and give a speedy recovery. Most people recover completely from dehydration once it is addressed.

The prognosis is excellent if the child is promptly and effectively treated. However, if treatment is delayed in a child with severe dehydration and hypovolemic shock, morbidity, and mortality rates are significantly high. If rapid and appropriate treatment is initiated, morbidity and mortality are low.