What Is Hypovolemia and What Causes It?

Medically Reviewed By Darragh O'Carroll, MD
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Your body needs a certain amount of fluid to maintain its essential functions. Hypovolemia is an abnormal depletion of fluid in the body that reduces overall blood volume. This may be the result of blood loss or severe dehydration. Without treatment, hypovolemia can progress to hypovolemic shock, which is a life threatening emergency.

This article will provide an overview of hypovolemia, including what causes it, its symptoms, and how doctors treat it.

What is hypovolemia?

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Hypovolemia, or volume depletion, is a critical decrease in blood volume in your body. It can happen due to blood loss or loss of body fluids, such as water.

Blood loss can result from external injuries, internal bleeding, or specific obstetric emergencies. Diarrhea and vomiting are common causes of body fluid loss.

Extensive burns, excessive perspiration, and the use of diuretics all cause body fluid loss. Inadequate fluid intake can also contribute to dehydration and hypovolemia.

Hypovolemia vs. hypovolemic shock

Hypovolemia describes a significant loss of fluid from the body.

If you develop hypovolemia, your body first tries to compensate for the volume loss by increasing your heart rate and the strength of heart contractions. It also constricts the peripheral blood vessels, which are vessels outside of the chest or abdomen. Constricting these blood vessels helps preserve blood flow to vital organs, like the brain, heart, and kidneys.

However, when blood volume drops to a level where blood cannot reach the body’s organs, they can no longer function properly. Tissue cannot receive oxygen and nutrients, and waste is not carried away. At this stage, the condition becomes hypovolemic shock.

What causes hypovolemia?

Conditions that cause blood or body fluid loss can cause hypovolemia, as can inadequate fluid intake and dehydration.

There are several common causes of volume depletion, including:

Serious or life threatening causes of hypovolemia

Many conditions that cause hypovolemia are serious or life threatening and require emergency treatment. These include:

  • ectopic pregnancy, a life threatening pregnancy growing outside the uterus
  • internal bleeding, often from the gastrointestinal tract
  • large burns
  • ruptured aortic aneurysm or other vascular abnormalities
  • serious injury or trauma

Hypovolemic shock is a medical emergency requiring immediate intervention.

Stages of blood loss

A subset of hypovolemic shock is hemorrhagic shock, which is the loss of fluid specifically due to blood loss.

The American College of Surgeons classifies 4 stages of hemorrhagic shock based on a human body weighing 154 pounds or 70 kilograms:

Stage 1

The earliest stage refers to a loss of less than 15% or 750 milliliters (ml) of blood volume. Symptoms of this stage are:

  • pulse rate of less than 100 beats per minute
  • respiratory rate between 14–20 breaths per minute
  • blood pressure at normal limits
  • some slight anxiety, but no other change to mental status

Stage 2

Stage 2 occurs with a loss of 15–30% of blood volume, between 750–1,500 ml. Symptoms of this stage are:

  • pulse rate over 100 beats per minute
  • respirations between 20–30 breaths per minute
  • blood pressure lower than normal
  • mild anxiety

Stage 3

This stage refers to 30–40% of blood loss, between 1,500–2,000 ml. Symptoms of this stage are:

  • pulse rate over 120 beats per minute
  • respirations between 30–40 breaths per minute
  • low blood pressure
  • confusion or lethargy

Stage 4

This most severe stage means you have lost more than 40% of your blood volume, over 2,000 ml. Symptoms of this stage are:

  • pulse rate over 140 beats per minute
  • respirations over 35 breaths per minute
  • low blood pressure

What are the symptoms of hypovolemia?

Initial symptoms of hypovolemia are often nonspecific to the condition and can include fatigue, dizziness, weakness, thirst, and muscle cramps.

Because dehydration can be a cause of hypovolemia, symptoms of each condition can overlap, including loss of skin elasticity, flat veins in the neck, rapid heart rate, and low blood pressure. However, the two terms are not interchangeable.

Common initial symptoms of hypovolemia

Common initial symptoms of hypovolemia include:

  • fatigue
  • dizziness
  • thirst
  • weakness
  • leg cramps
  • dry mucous membranes
  • rapid breathing
  • rapid heart rate
  • low blood pressure
  • loss of skin elasticity
  • decreased urine output

Symptoms of hypovolemic shock

Hypovolemia that progresses to hypovolemic shock is a life threatening emergency. Call 911 to seek immediate medical care for serious symptoms of hypovolemic shock, including:

How do doctors treat hypovolemia?

Treatment for hypovolemia depends on the cause and severity of the symptoms. If hypovolemia is the result of severe dehydration, treatment focuses on replenishing fluids. In cases of hemorrhagic hypovolemia, the priority is stopping and replacing blood loss.

Treatments for hypovolemia

Because hypovolemia can quickly progress to hypovolemic shock and cause organ damage, prompt treatment for early signs of hypovolemia is critical. Treatments at this initial stage include:

  • Oral rehydration drinks: Doctors may use this treatment in cases of mild hypovolemia.
  • Colloid solutions: These are intravenous (IV) fluids that contain complex sugars and proteins.
  • Crystalloid solutions: These are IV fluids that contain electrolytes, most often sodium chloride or a mixture of sodium chloride. Other examples include sodium lactate, potassium chloride, or calcium chloride in water.
  • Vasopressors: These are medications that constrict blood vessels and increase blood pressure.

Treatments for hypovolemic shock

When hypovolemia progresses to hypovolemic shock, blood can no longer reach vital organs. This is a life threatening emergency that requires immediate treatment to prevent organ damage.

To treat hypovolemic shock, researchers recommend a rapid infusion of a crystalloid solution. Generally, doctors advise against using vasopressors once someone is in shock. However, in some cases when the shock is not responsive to crystalloid infusion, doctors may administer vasopressors as well.

Treatments for hemorrhagic shock

For hypovolemic shock due to blood loss, researchers note that replenishing blood results in better outcomes than administering crystalloid infusions.

Treatments for shock due to blood loss include:

  • blood plasma transfusion
  • cryoprecipitate transfusion, which provides fibrinogen, a protein required for clotting
  • platelet transfusion
  • red blood cell transfusion
  • crystalloid solutions
  • colloid solutions
  • tranexemic acid, a newer treatment that helps induce clotting and stop blood loss

What are the potential complications of hypovolemia?

Complications of untreated hypovolemia can be serious, becoming life threatening in cases of hypovolemic shock.

Without immediate treatment, complications of hypovolemic shock may include:

Summary

Hypovolemia refers to a serious decrease in the amount of fluid in the body. This can be the result of dehydration or loss of blood due to injury, trauma, or internal bleeding.

Treatment of hypovolemia depends on the underlying cause and the severity of the symptoms. For hypovolemia due to dehydration, doctors focus on replenishing fluids through IV infusions of colloid or crystalloid solutions. In cases of hypovolemia due to loss of blood, the primary goal is stopping the blood loss and replacing lost blood.

Hypovolemia can quickly progress to hypovolemic shock, which is a life threatening emergency. Hypovolemic shock can rapidly cause organ failure that can be fatal.

Contact your doctor as soon as you notice any signs of hypovolemia so that you can receive an early diagnosis and prompt, effective treatment.

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Medical Reviewer: Darragh O'Carroll, MD
Last Review Date: 2022 Jan 31
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