“Third spacing” is an older term that healthcare professionals used to describe the movement of fluid. Some healthcare professionals might still use the term to refer to movement of fluid out of body tissues.

The term “third space” was coined to describe an area where fluid was thought to pool during surgery. The idea was that this fluid was no longer part of the body’s fluid system and became non-functional. However, scientists did not agree upon the exact location of this space and studies did not find one particular “third space.”

Body fluids that are outside of your cells are known as extracellular fluids. Extracellular fluid (outside cells) may be:

  • intravascular (inside blood vessels)
  • interstitial (in between cells)

Some scientists used the term “third space” to include all extracellular fluids, whereas some argued that it should be limited to certain areas, such as:

  • the bowel lumen, the space within the intestine
  • the peritoneum, the membrane lining the abdomen and abdominal organs
  • pleura, the membrane lining the lungs and chest cavity

Though some health care professionals might still use the term “third spacing” to describe fluid moving out of where it should be, health care professionals generally favor more specific terms to describe exactly where fluid has built up.

Fluid movement may happen in one organ, one area of the body, or multiple organs or areas.

The loss of fluid from the blood leads to a decrease in overall blood volume, which can affect blood pressure and may lead to hypovolemic shock.

A wide range of conditions can lead to fluid buildup, usually those that cause severe trauma, obstruction, or inflammation, including:

  • intestinal obstructions
  • vein obstructions
  • pancreatitis, or inflamed pancreas
  • trauma
  • infection
  • radiation
  • sepsis
  • allergic reactions
  • surgery
  • a decrease in plasma proteins
  • lymphatic blockages
  • increased capillary permeability

During or after surgery or a major disease or trauma, third spacing may trigger symptoms that doctors, nurses, or medical monitoring may pick up on, such as:

  • reduced blood pressure
  • swelling or fluid accumulation, known as edema, in the abdomen or other dependent areas of the body
  • dehydration or electrolyte imbalances
  • swelling in the neck or lymph nodes
  • swelling in the abdomen
  • feeling faint, dizzy, or losing consciousness

Contact a doctor if you experience any of these symptoms, especially during or after surgery, trauma, or major disease.

Conditions that cause fluid buildup may include:

Third spacing from milder conditions or localized inflammation may not be as obvious on examination but doctors expect it to be present with certain conditions and treat it accordingly.

The best treatment for third spacing usually depends on the underlying cause of the condition, such as:

Fluids are not given to treat these conditions as it worsens the condition. Only if a person has true fluid loss, for example, through the skin from burns, will fluids be given.

Healthcare professionals will monitor various vital signs, including:

If severe symptoms occur, healthcare professionals may administer a diuretic, such as furosemide.

Third spacing is an outdated term that medical professionals sometimes still use to refer to fluid movement.

The term can refer to the movement of fluid from the blood vessels into interstitial spaces. Or it can describe intravenous fluids accumulating in areas that typically contain minimal fluid, often during surgery or in response to major trauma or inflammation.

Speak with a doctor if you experience fluid accumulation, neck or abdomen swelling, dehydration, or dizziness, particularly after surgery or major trauma.