peritoneal fluid
Meaning of peritoneal fluid: A thin film of lubricant between the sheets lining the abdomen, normally so scant that finding it on a scan is itself a finding.
Definition of peritoneal fluid
Peritoneal fluid is the small volume of clear liquid held between the two layers of the peritoneum, the smooth membrane that lines the abdominal wall and wraps the organs inside it. It works as a lubricant, letting loops of bowel slide over one another and against the wall without friction. Normally only a few tablespoons are present.
Where does it come from?
The membrane consists of two sheets, one lining the wall and one covering the organs, with the peritoneal cavity as the potential space between them. Fluid seeps continuously from small blood vessels in the membrane and is reabsorbed by lymphatic channels, chiefly on the underside of the diaphragm. Production and drainage stay in balance, so the volume remains tiny. Bowel movement pushes fluid toward the diaphragm, which is why material released anywhere in the abdomen tends to travel upward and why irritation there can be felt in the shoulder tip.
What does an excess mean?
A large collection is called ascites, and the reason usually falls into one of a few groups.
| Cause | Mechanism |
|---|---|
| Liver scarring | Raised pressure in the portal system and low blood protein |
| Heart failure | Back pressure through the veins draining the abdomen |
| Cancer in the abdomen | Deposits leak fluid and block lymphatic drainage |
| Infection of the membrane | Inflammation increases leakage |
| Low blood protein | Fluid escapes vessels in kidney or nutritional disease |
What can be learned from a sample?
Fluid drawn through a needle in the abdominal wall is examined for cell counts, protein, and bacteria, and for cancer cells. Comparing the albumin concentration in the fluid with that in blood separates fluid driven by raised portal pressure from fluid caused by disease of the membrane itself, and that single comparison narrows the diagnosis considerably. A high white cell count points to infection of the fluid, which can arise without any obvious source. Malignant cells in the sample indicate peritoneal cancer or spread from an organ nearby.
Is the cavity used for anything else?
Its lining is rich in blood vessels and behaves as a natural filter, which is the basis of peritoneal dialysis. Fluid is run into the cavity through a catheter, waste products cross from the bloodstream into it, and the fluid is drained and replaced. The same access route allows drug treatment to be delivered directly into the cavity in some abdominal cancers.
Also known as
Used in a sentence
Peritoneal fluid was sent for cell count, culture and albumin measurement.
Good to know
Comparing albumin in the fluid with albumin in blood separates ascites caused by raised portal pressure from ascites caused by disease of the peritoneum itself.
Word origin
Where “peritoneal fluid” comes from
Peritoneal comes from the Greek peritonaion, meaning stretched around, describing a membrane wrapped about the organs.