Dehydration overview and Definition

Dehydration occurs when body does not have adequate water and it gets deprived from the story.


Severe hydration shrinks the blood vessels in the brain. When there aren’t high enough fluid levels in your brain, that affects your memory and coordination.

The heart should works faster than normal to compensate the water loss.

Beverages causing dehydration:

The beverages such as the coffee, tea and colas tends to pull the water away from the body and increases the chances for dehydration. Hence it is safer to avoid these drinks during strenuous exercises or other activities. Fruit juices and Fruit drinks are rich in carbohydrate and they have little amount of sodium content in it causing dehydration. During strenuous exercises or during sports activity sports drink are must since they contains both sodium and potassium which prevents the dehydration. Lime water or cumcumber water prevents the dehydration.


The negative fluid balance that causes dehydration results from decreased intake of water, increased output such as renal, gastrointestinal or fluid shift such as ascites, pleural effusion and capillary leak state such as burns and sepsis. The decrease in the total body water causes reductions in both the intracellular an extracellular fluid volumes.

Clinical manifestations of dehydration are closely related to intravascular volume depletion and the physiologic compensation attempts that takes place. As dehydration progresses, hypovolemic shock ultimately ensues, resulting in end organ failure and death.


Young children are more susceptible to dehydration due to larger body water content, renal immaturity and inability to meet the own needs independently. Older children shows sign of dehydration earlier than infants due to lesser amount of extracellular fluid.


Dehydration can also be evaluated according to osmolarity and severity. Serum sodium is a good surrogate marker of osmolarity assuming the patient has a normal serum glucose. (Osmolarity = [2 × sodium] + [glucose/18] + [blood urea nitrogen/2.8]) Dehydration may be isonatremic (130-150 mEq/L), hyponatremic (< 130 mEq/L), or hypernatremic (>150 mEq/L). Isonatremic dehydration is the most common (80%). Hypernatremic and hyponatremic dehydration each comprise 5-10% of cases. Variations in serum sodium reflect the composition of the fluids lost and have different pathophysiologic effects, as follows:


  • Isonatremic (isotonic) dehydration occurs when the lost fluid is similar in sodium concentration to the blood. Sodium and water losses are of the same relative magnitude in both the intravascular and extravascular fluid compartments.
  • Hyponatremic (hypotonic) dehydration occurs when the lost fluid contains more sodium than the blood (loss of hypertonic fluid). Relatively more sodium than water is lost. Because the serum sodium is low, intravascular water shifts to the extravascular space, exaggerating intravascular volume depletion for a given amount of total body water loss. [12]
  • Hypernatremic (hypertonic) dehydration occurs when the lost fluid contains less sodium than the blood (loss of hypotonic fluid). Relatively less sodium than water is lost. Because the serum sodium is high, extravascular water shifts to the intravascular space, minimizing intravascular volume depletion for a given amount of total body water loss. [234]

Neurologic complications can occur in hyponatremic and hypernatremic states. Severe hyponatremia may lead to intractable seizures, whereas rapid correction of chronic hyponatremia (>2 mEq/L/h) has been associated with central pontine myelinolysis. During hypernatremic dehydration, water is osmotically pulled from cells into the extracellular space. To compensate, cells can generate osmotically active particles (idiogenic osmoles) that pull water back into the cell and maintain cellular fluid volume. During rapid rehydration of hypernatremia, the increased osmotic activity of these cells can result in a large influx of water, causing cellular swelling and rupture; cerebral edema is the most devastating consequence. Slow rehydration over 48 hours generally minimizes this risk (not to exceed 0.5 mEq/L per hour; 10-12 mEq/L in 24 hours).


Clinical signs & symptoms




Muscle cramps

Head ache

Not peeing very much

Dark yellow pee

Thirsty mouth

very dry skin

Feeling dizzy

Rapid heartbeat

Rapid breathing

Sunken eyes

Sleepiness, lack of energy, confusion or irritability


Differential Diagnosis

The following test includes the test for dehydration:

Basic metabolic panel:

This panel can offer information on a person’s general health in addition to the kidney function.

The acid base balance and electrolytes are checked. The electrolytes includes bicarbonate, chloride, potassium and sodium.

Blood urea nitrogen: it is used for detection of kidney function test.

Urinanalysis: it evalutes the amount of urine, its concentration and colour.

Complete blood count:

It is used for evaluating blood cells as well as the balance inbetween the liquid and solid parts of the blood. The haematocrit with dehydration may be used to evaluate.

Glucose: checked for the presence of diabetes.

Blood and urine osmolality: evaluate the water balance of the body.

Stool culture is used to check for presence of bacteria

Cortisol levels are checked for the presence of Addison’s disease

Liver panel: it is used for detecting the liver disease

Blood ketones are used for the evaluation of diabetic ketoacidosis.



 The prognosis is excellent but make sure to consume fluids in larger amounts atleast 24 hrs after the symptoms subside.