“Third spacing” is an outdated term that healthcare professionals used to describe the movement of bodily fluid from the blood into the spaces between the cells. Numerous conditions can lead to third spacing.

The term “third spacing” also describes the accumulation of fluid from the blood within body cavities, intestinal areas, or areas of the body that normally contain little fluid.

Keep reading to learn more about third spacing, including the causes, phases, diagnosis, and treatment.

Person in a hospital bed.Share on Pinterest
SimpleImages/Getty Images

Third spacing occurs when intravenous fluid shifts out of circulation in the blood and into the space between cells in organs and tissues, also known as interstitial space.

Third spacing can also describe the accumulation of fluid from the blood into interstitial space, body cavities, or body areas that usually hold minimal fluid.

Once intravenous fluids move into the interstitial space, they no longer impact the body’s fluid balance and become non-functional. Third spacing may affect one organ, an area of the body, multiple organs.

Healthcare professionals initially coined the term “third space” to describe a non-functional compartment in the body where intravenous fluids would pool during major surgery.

However, experts have never formally identified or localized these areas. Tracer studies have also been unable to confirm the space’s existence.

Some research calls for the terms “third space” and “third spacing” to be abandoned, arguing that intravenous fluid can exist within the vascular system or interstitial spaces. Therefore, there is no organ or void space to fill.

Other researchers believe they should only use the term “third space” to refer to anatomical spaces where extracellular volume — the fluids outside of the body’s cells — can accumulate, such as within the:

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

A wide range of conditions can lead to third spacing, usually those that cause severe trauma, obstruction, or inflammation, such as:

  • 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

There are two distinct phases of third spacing.

Phase 1

Phase 1 is also called fluid loss. In this phase, fluid moves from the blood into the interstitial spaces or body cavities. This typically occurs directly following surgery, trauma, or any other cause of severe inflammation, and lasts for 48–72 hours.

During Phase 1, the smallest blood vessels, the capillaries, become more fragile and permeable. When this occurs, they allow fluids and proteins to leak into areas where inflammation, trauma, or obstructions develop.

Phase 2

Phase 2 is also called reabsorption. In this phase, capillaries start to heal and regain their normal permeability, blockages clear, and fluid volume shifts back into the blood. Once in the blood, the kidneys eventually excrete these fluids. Phase 2 usually occurs once someone is recovering in the hospital.

Symptoms of phase 2 include:

  • increased urine output
  • urinating more fluids than are being consumed
  • weight loss

Healthcare professionals may monitor someone for signs that the circulatory system has become overwhelmed, such as:

  • shortness of breath
  • increased central venous pressure, the blood pressure in the heart’s right atrium
  • distended or swollen neck veins
  • electrolyte imbalances or dehydration
  • changes in heart rhythm or electrical abnormalities

If surgery leads to third spacing, most people complete phase 2 and recover on the third day after surgery.

It is usually difficult to tell whether someone is experiencing third spacing. This makes it harder to diagnose the condition early and reduce the risk of complications.

During or after surgery or a major disease or trauma, third spacing may trigger some 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

The best treatment for third spacing usually depends on the underlying cause and phase of the condition.

Managing phase 1 typically includes administering intravenous fluids, often crystalloid or colloid fluid. Doctors may also give people hypertonic fluids before undergoing anesthesia and isotonic fluids during surgery.

During Phase 1, healthcare professionals will monitor various vital signs to avoid complications, such as:

Treatments for phase 2 typically involve medical monitoring. If severe symptoms occur, healthcare professionals may administer a diuretic, such as furosemide.

Third spacing is an outdated term that medical professionals sometimes use, especially among the nursing community.

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

Third spacing is almost impossible to detect, while even healthcare professionals often miss or misdiagnose it.

Contact a doctor if the following symptoms occur, especially during or after surgery, trauma, or major disease:

  • low blood pressure
  • dehydration
  • swelling in the neck or lymph nodes
  • swelling in the abdomen
  • feeling faint, dizzy, or losing consciousness