Define Dehydration

By Dr. Vik, MBBS, MRCP(GB), PhD

Define dehydration

The human body is mostly composed of water. A proper level of water is important to the body, since water is required for numerous physiological processes.

When the amount of water within the body gets too low, the condition is known as dehydration.

Defining Dehydration as

A Negative Fluid Balance

We can define dehydration as ‘a state of negative fluid balance’.

In simple terms, this means that the total amount of water in the body is less than what is required for normal function. This negative fluid balance can be a result of one of the following:

• A reduced intake of fluids
  
  
• An increased loss of fluid

Reduced intake

This may occur without an individual realizing that they aren’t drinking enough.

Example are:

• When a person doesn’t drink enough water in a hot climate
  
  
• Due to vigorous physical activity, especially when the day is warm and the body needs perspiration to stay cool

In these instances, it is important to increase fluid intake to compensate for the amount of water lost to sweat.

Increased loss of fluid

This can be caused by:

• Kidney disease
  
  
• Diarrhea and vomiting
  
  
• Certain medications

Another cause of dehydration is when fluids leak into a space in the body, such as the abdomen or under the skin. This is known as a fluid shift and can occur in individuals who have suffered burns or have some form of infection and sepsis.

To define dehydration, it is important to take all of these factors into consideration, since the treatment for dehydration is determined by the cause.

It is especially important to recognize when a child is dehydrated and to determine the cause, since children are more prone to developing dehydration.

A Definition Based on Sodium Levels

As we look deeper into how to define dehydration, we discover that it is not so simple as just a negative fluid balance. There are other factors that must also be considered when defining dehydration.

One such factor is the level of sodium within the blood. Sodium and water are present in a very specific ratio within the body.

Sodium levels in the blood help define ‘osmolarity’, which is the concentration of sodium in comparison with the amount of water present in the body.

In healthy individuals, the proper sodium value in the blood should be between 130 to 150 mEq/L. three different forms of dehydration can be defined based on the amount of sodium in the blood.

1. Isotonic dehydration

When we define dehydration in this form, water and electrolytes are both lost from the body in the same proportion. As a result, the dehydration that takes place affects every part of the body.

When this happens, it negatively affects the pH of the body, making it harder for blood to hold oxygen. With this type of dehydration, a person can feel run down and a little sick. This is the most common type of dehydration.

Isotonic dehydration symptoms, such as muscle cramps, an inability to concentrate, headaches and increased blood pressure can begin with as little as 1% of water loss in the body. For initial treatment, an electrolyte solution should be consumed in proper proportion with water.

To rehydrate, especially after sports and other physical exertion, mix 1/8 tsp. of sea salt and 1 tsp. of concentrated mineral electrolytes. 

2. Hypotonic dehydration

In this form of dehydration, the body has lost a greater amount of electrolytes than water.

It is often caused by drinking only water to alleviate the loss of water and electrolytes due to excessive sweating or other fluid loss. In this form of dehydration, fluid shifts from outside of cells into cells.

This condition poses a great threat to the body. Early treatment involves consuming a solution high in electrolytes, as described in point 1 above. 

3. Hypertonic dehydration

In this form of dehydration, the amount of water that is lost exceeds the amount of electrolytes lost. This results in a relative increase of electrolytes in relation to the amount of water present in the body.

Hypertonic is more prevalent in those with diabetes, but is also often found in children as a result of diarrhea and vomiting. Initial treatment is to consume water without added electrolytes.

A Definition Based on Severity

Another way of defining dehydration is to look at it according to severity. Dehydration is classified as mild, moderate or severe.

In this classification, the level of dehydration is determined by the age of the individual, as you can see below:

1. Mild dehydration

In adolescents, a loss of up to 3% of body fluid is classified as mild dehydration.

In infants, it is a loss of up to 5% of body fluid.

2. Moderate dehydration

In adolescents, it is a loss of 4% to 6% of total body fluid that is considered moderate dehydration.

In infants, it is a loss of between 6% and 10% of total body fluid.

3. Severe dehydration

In adolescents, it is a loss of 7 to 9% of total body water is considered severe dehydration.

In infants, it is a loss of 11% to 15% of total body fluid.

Measuring adult dehydration

In adults, the degree of dehydration is determined by the presence or absence of certain clinical signs and symptoms.

For example, when defining mild dehydration in adults, the heart rate is only slightly increased while in severe dehydration, the heart rate is increased significantly.

Similarly, in mild dehydration, the blood pressure and skin elasticity may be normal while in severe dehydration, the blood pressure can be significantly reduced while the skin elasticity demonstrates ‘tenting’, a phenomenon where the skin does not retract back to its normal position quickly.

Depending on the severity of dehydration, different treatment regimens are prescribed so as to correct the deficit and restore normal physiology.

Conclusion, define dehydration

Dehydration is a process where there is insufficient water present in the body to support normal physiological processes.

The causes of dehydration may differ. Defining the type of dehydration can help determine what sort of treatment options need to be undertaken to restore normal body water content.

Defining dehydration is probably the most important step before proceeding to diagnosis and management of this condition.

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