Understanding Hypovolemia

Hypovolemia is the loss of 15% or more of the fluid circulating in the body, specifically blood or water. Because your organs need these fluids to function, their depletion can cause organs to malfunction and fail. Symptoms include dizziness, rapid heartbeat, clammy skin, confusion, and fainting.

There are many possible causes for hypovolemia from extreme dehydration or massive bleeding. In severe cases, hypovolemia can lead to shock and death.

This article describes the symptoms and causes of hypovolemia. It also explains how this potentially serious condition is diagnosed and treated.

How Hypovolemia Occurs

Hypovolemia literally means low (hypo-) volume (-volemia). It involves a decrease in the volume of extracellular fluids. Extracellular fluids are those that exist outside of cells, such as the fluid part of blood (known as plasma) or the fluid circulating in lymphatic vessels (known as lymph).

Hypovolemia is ultimately caused by either a loss of blood or a loss of water. In either instance, the depletion of fluid decreases the volume of whole blood in the body. This, in turn, reduces the amount of oxygen being delivered to cells and tissues throughout the body.

When hypovolemia becomes severe, the low volume of blood in arteries and veins will cause your blood pressure to drop. When it drops to where organs are unable to function, the body goes into shock.

Shock caused by hypovolemia is specifically known as hypovolemic shock.

What Are the Symptoms of Hypovolemia? 

Hypovolemia causes systemic symptoms, meaning that the whole body is affected by the reduced flow of blood. The symptoms worsen as fluid volumes in the body continue to drop.

Hypovolemia symptoms may not be recognized in the early stages and may only become apparent when the volume depletion approaches 30%.

Hypovolemia is categorized into stages 1 through 4, which denote the percentage of fluid volumes lost. Symptoms develop in a characteristic pattern from stage to stage, as follows:

Hypovolemic Shock

In medical terms, shock is the body's response to a sudden drop in blood pressure.

Hypovolemic shock is a type of shock in which severe blood or fluid loss makes the heart unable to pump enough blood to service the body's needs. Other types include cardiogenic shock (related to the dysfunction of the heart) and anaphylactic shock (caused by a severe allergic reaction).

Hypovolemic shock is a medical emergency that develops in a progressive pattern. It technically starts with stage 1 hypovolemia and progresses to stage 4, at which point the insufficient flow of blood can start to damage the heart, lungs, liver, kidneys, and other vital organs.

If left untreated, multiple organ failure can occur. If treatment is not delivered quickly, the risk of irreversible damage and death is high.

What Causes Hypovolemia? 

Hypovolemia can range from mild to severe depending on the underlying cause. Common causes include:

• Severe dehydration: Caused by a lack of fluid intake, malnutrition, severe vomiting or diarrhea, or extreme sweating (hyperhidrosis)
• External bleeding: Caused by severe injuries, cuts, or burns
• Internal bleeding: Caused by a traumatic injury or medical conditions like an aortic aneurysm, ruptured spleen, ectopic pregnancy, or peptic ulcer disease
• Kidney problems: Caused by excessive urination (polyuria), acute kidney failure, or the overuse of diuretics ("water pills")
• Fluid accumulation in body cavities: Caused by illnesses like acute pancreatitis, liver cirrhosis, advanced heart failure, nephrotic syndrome, and intestinal obstruction that draw water out of tissues and into the abdomen and other cavities
  

How Is Hypovolemia Diagnosed? 

The diagnosis of hypovolemia starts with a review of your symptoms and medical history. A physical exam would then be performed and would involve the following baseline evaluations:

• Skin and mucous membranes: The healthcare provider will check your skin and the inside of your mouth. The loss of fluid volume will cause your skin to lack turgor (elasticity) and the mucous membranes in your mouth, tongue, and nose to become notably dry.
• Blood pressure: One sign of hypovolemia is a narrow pulse pressure. This is when your upper and lower blood pressure readings are not all that different (unlike a normal blood pressure reading of 120/80).
• Body temperature: A lower-than-normal body temperature is characteristic of hypovolemia.
• Pulse rate: Hypovolemia causes a faster heart rate (tachycardia) when the body has to work harder to pump lower volumes of blood throughout the body.
  

Other lab and imaging tests can help confirm the diagnosis, including:

• Kidney function tests: These blood and urine tests can establish if hypovolemia is the result of a kidney problem.
• Sodium tests: With hypovolemia, more sodium is proportionally lost than water. Blood and urine tests can check sodium levels and diagnose hyponatremia (low sodium).
• Hematocrit (HCT): This blood test measures the percentage of red blood cells in your blood. As fluid volumes decrease with hypovolemia, hematocrit values will invariably increase.
• Arterial blood gasses (ABG): This blood test can help confirm hypovolemia and diagnose its severity based on an imbalance of oxygen and carbon dioxide in the blood.
• Ultrasound: This non-invasive imaging test can estimate blood volumes by assessing the diameter of the major blood vessels and whether there are any signs of collapse. A similar test called an echocardiogram can do the same.
  
• Nuclear medicine blood volume analysis: This method measures blood volume by injecting a radioactive tracer that tags specific components in your blood. After the tracer circulates around the bloodstream, blood volume can be determined by measuring the concentration of the tracer in a blood sample.

How Is Hypovolemia Treated? 

Hypovolemia can quickly lead to shock and requires urgent care to restore fluids and normalize blood pressure. An aggressive response is needed to avoid permanent organ damage caused by the lack of oxygen to tissues. The treatment is also focused on resolving the underlying cause.

The standard of care is intravenous (IV) fluid resuscitation which involves the delivery of fluids through a vein. Crystalloid solutions comprised of water and water-soluble electrolytes like sodium and chloride are the preferred choice. Lactated Ringer's solution is one form of this.

Colloid solutions made up of synthetic compounds can also be used and have the advantage of quickly restoring blood pressure. But studies suggest that colloid solutions pose significant health risks, including a one-in-500 risk of a potentially life-threatening, whole-body allergy called anaphylaxis.

If blood loss is the cause of hypovolemia, a blood transfusion would be needed.

How Hypovolemic Shock Is Treated

In cases of hypovolemic shock, you would first be given fluids and then blood through an IV drip. One or several of the following drugs would also be administered by injection or intravenously to quickly restore blood pressure:

• Epinephrine (adrenaline): This is a synthetic form of a naturally occurring hormone that causes blood vessels to narrow (referred to as a vasoconstrictor),
• Levophed (norepinephrine): This is a vasoconstrictor similar to epinephrine.
• Intropin (dopamine): This is a synthetic hormone that acts as a precursor to norepinephrine.
• Inotrex (dobutamine): This is typically used to treat heart failure and cardiogenic shock.

Treatment is delivered in an intensive care unit. If an accident caused blood loss, you may need surgery to repair the injury.

Summary

Hypovolemia is the loss of 15% or more of circulating fluids in the body. Causes include severe dehydration, internal or external blood loss, and severe illnesses that cause fluids to accumulate in the body cavities. Symptoms can progress from fatigue, clammy skin, and dizziness to rapid heartbeats, changes in consciousness, and fainting.

Depending on the cause, hypovolemia may be treated with intravenous or oral fluids or with a blood transfusion. Severe cases can lead to a medical emergency known as hypovolemic shock.