Third spacing: what it is, causes and nursing care

Third spacing is fluid that has moved out of the blood vessels into a space where it cannot help the circulation, such as the tissues, the abdomen or the bowel. The fluid has not left the body, so the client can gain weight and swell. The vessels are short of fluid, so the client shows signs of hypovolemia at the same time.

Sources checked 18 October 2026.

What third spacing is

Nursing texts often describe three spaces:

• First spacing: the normal spread of fluid inside the cells and outside them.
• Second spacing: extra fluid in the interstitial space, seen as edema.
• Third spacing: fluid trapped where it does not easily return to the circulation, such as ascites in the abdomen, fluid in an obstructed bowel, or fluid under burned skin.

StatPearls describes third spacing as fluid shifting from the intravascular space into the interstitial or "third" space, which leaves the vessels depleted and can lead to hypovolemic shock.

Why fluid leaves the vessels

Fluid stays in the capillaries when the forces on it are balanced. Third spacing happens when one of them changes:

• The capillaries leak, as in burns, sepsis and other large inflammatory responses.
• Plasma proteins fall, so less albumin holds water in the vessels. Liver cirrhosis, malnutrition and nephrotic syndrome do this.
• Pressure in the veins rises, for example when a major vein is blocked.

Common causes

The two phases

The shift phase. Fluid moves out of the vessels. The client looks hypovolemic even though weight goes up: low blood pressure, a fast and weak pulse, low urine output, thirst, and a rising hematocrit and blood urea nitrogen. Edema, ascites or a tense abdomen show where the fluid went.

The return phase. As the cause settles, often after some days, the fluid moves back into the vessels. Urine output rises and the edema goes down. Now the risk is fluid overload: a bounding pulse, rising blood pressure, crackles and shortness of breath. Clients with heart or kidney disease are at the highest risk.

What the nurse assesses

• Blood pressure, heart rate and the strength of the pulse.
• Urine output every hour when the client is unstable.
• Daily weight at the same time, on the same scale. Remember that weight includes the trapped fluid.
• Abdominal girth for ascites, and edema in dependent areas.
• Lung sounds, especially once the fluid starts to return.
• Hematocrit, blood urea nitrogen, creatinine, albumin and electrolytes.

The provider orders the fluids, usually an isotonic crystalloid such as 0.9% sodium chloride or lactated Ringer's, and treats the cause. See hypotonic vs hypertonic vs isotonic IV fluids for why.

Exam traps

• Edema does not always mean overload. Swollen tissues can sit beside empty vessels.
• Weight gain does not mean good hydration. Trust the blood pressure, pulse and urine output.
• A diuretic is wrong in the shift phase. It takes more fluid out of vessels that are already short.
• Swollen but dry is a quick way to picture it.

More on fluids and electrolytes: Chvostek and Trousseau signs, potassium and the ECG, hyperkalemia ECG changes and hypokalemia ECG changes.

Practice questions

1. Question 1Multiple choicePhysiological Adaptation
   A client with acute pancreatitis has a blood pressure of 88/50 mm Hg, a heart rate of 124 a minute and a urine output of 15 mL an hour. The abdomen is distended and the client has gained 2 kg. What explains these findings?

   Fluid has shifted out of the blood vessels into the abdomen and tissues.The client has fluid volume excess and needs a diuretic.The kidneys are retaining water normally after surgery.The weight gain proves the client is well hydrated.
   Check answer
2. Question 2Multiple responsePhysiological Adaptation
   Which conditions place a client at risk of third spacing? Select all that apply.

   Major burnsAcute pancreatitisIntestinal obstructionThe first days after major surgeryVomiting from food poisoning
   Check answer
3. Question 3Multiple choicePhysiological Adaptation
   Several days after a large burn, the client's urine output rises. Which finding needs follow-up first?

   New crackles in the lung bases and a bounding pulseUrine output of 80 mL an hourLess swelling of the armsA falling hematocrit
   Check answer
4. Question 4Multiple choiceReduction of Risk Potential
   Which laboratory change does the nurse expect while fluid is moving into the third space?

   A rising hematocritA falling blood urea nitrogenA falling hematocritA rising serum albumin
   Check answer