PERITONEAL FLUID: COMPOSITION, FUNCTIONS, CULTURE AND ANALYSIS - BIOLOGY - 2024

The peritoneal fluid is ultrafiltered plasma, also known as ascites. The accumulation of this fluid in the peritoneal cavity is called ascites, which can be caused by liver cirrhosis, neoplastic processes, congestive heart failure, tuberculous or pyogenic peritonitis, pancreatitis or nephrosis, among others.

Peritoneal fluid can accumulate due to an imbalance between hydrostatic and oncotic pressure, modifying the volume between the intravascular and extravascular compartments.

Patient with excess peritoneal fluid (ascites) / peritoneal fluid sample. Sources: James Heilman, MD /wikipedia.org For ascites, a sample of the peritoneal fluid can be taken through a procedure called paracentesis. The sample is collected in sterile tubes to carry out different studies, among them, cytochemical analysis, Gram, BK, culture and biopsy.

Depending on the results of the studies, it can be determined if it is a transudate or an exudate and, therefore, elucidate the possible cause of ascites.

Composition

Normal peritoneal fluid is a transudate. It is characterized by a low protein concentration, glucose similar to that of plasma, few leukocytes, no fibrin clots and red blood cells are scarce or absent.

Likewise, it contains very low concentrations of some enzymes, such as: lactate dehydrogenase (LDH), adenosine deaminase (ADA), amylase.

Features

The peritoneal fluid is located in the peritoneal cavity and is delimited between the visceral peritoneal membrane and the parietal peritoneal membrane.

The function of peritoneal fluid is to lubricate the visceral and parietal peritoneal membrane, avoiding friction of the organs in the abdominal cavity.

On the other hand, the peritoneal membrane functions as a filter, that is, it is semi-permeable and maintains a balance with the flow of the extracellular fluid.

Under normal conditions, the peritoneal fluid that diffuses into the peritoneal cavity is then reabsorbed into the subdiaphragmatic lymph nodes. This maintains a balance between how much is produced and how much is reabsorbed.

Where is it produced?

The peritoneal membrane lines the abdominal cavity. This has a visceral and a parietal leaf.

The former has a larger surface area and is supplied by the mesenteric arteries and continues towards the portal vein, while the parietal peritoneum has a smaller surface area and is supplied mainly by the arteries and veins of the abdominal wall.

Transdiaphragmatically there is a constant drainage of the lymphatic circulation that absorbs fluid.

When there is an increase in portal pressure, together with an increase in renal sodium reabsorption, plasma volume increases, which leads to excess lymph production.

The accumulated peritoneal fluid must be analyzed from the physical, biochemical and cytological point of view. These characteristics will determine whether it is a transudate or exudate.

What is a transudate and exudate? How do they originate?

Transudate

Transudate is simply the accumulation of fluid, without inflammation and / or infection. That is, there are no significant changes in its composition. There is also no involvement of the peritoneum. Example of ascites with a characteristic of transudate: cardiac ascites, ascites due to nephrotic syndrome and ascites due to cirrhosis.

In general, excess fluid with transudate characteristics is caused by a decrease in plasma proteins (hypoproteinemia), which results in a reduction in osmotic pressure and an increase in capillary permeability and venous pressure. All of this increases water retention while the lymphatic pressure decreases.

Finally, obstruction of the lymph circulation causes excess fluid in the peritoneal cavity. The volume can be as high as several liters, which significantly distens the patient's abdomen.

Exudate

In exudates there is not only accumulation of fluid, but also other factors participate that drastically modify the composition of the peritoneal fluid.

In the exudates, in addition to the lymphatic obstruction, there is a direct involvement of the peritoneum, which may be due to: an infectious and inflammatory process or infiltration or necrosis. Infections can be caused by bacteria, fungi, viruses, or parasites.

Examples of ascites with fluid with exudate characteristics include: pancreatic ascites, peritoneal carcinoma, and peritoneal tuberculosis, among others.

What is it studied for?

Peritoneal fluid should be studied to determine the etiology of excess fluid in the peritoneal cavity. The sample collection is done through a procedure called paracentesis.

The peritoneal fluid can be performed the following studies: cytochemical analysis, Gram, BK, culture and biopsy.

The cytochemical analysis clarifies if you are in the presence of a transudate or exudate. Establishing this difference is of crucial importance in order to know the possible causes and establish an accurate therapeutic procedure to follow.

On the other hand, peritoneal fluid is sterile by nature, therefore, it should not contain any type of microorganisms.

In this sense, the Gram is a quick tool to test for the possibility of an infection, being especially useful in secondary peritonitis. For its part, BK can help in the rapid diagnosis of peritoneal tuberculosis, while culture is the study that confirms the existence or absence of infection.

Culture

Sampling

Take 20-50 ml of sample depending on the number of analyzes indicated. 10 ml should be inoculated in a blood culture bottle for aerobic microorganisms, and 10 ml in a blood culture bottle for anaerobes.

The rest of the peritoneal fluid sample is deposited in several sterile tubes to perform Gram and BK, cytochemical, etc.

Sown

The blood culture bottles are incubated for 24-48 hours. The contents of the bottle should be seeded in enriched culture media, such as: blood agar and chocolate agar, where most microorganisms grow.

A Mac Conkey plate for Gram negatives and a Sabouraud agar plate for fungal research can also be attached.

If peritoneal tuberculosis is suspected, the sample can be collected in a sterile tube and from there inoculated directly onto the Löwenstein-Jensen medium.

Cytochemical analysis

The sample is collected in sterile tubes. The cytochemical analysis includes the physical aspects, the biochemical analysis and the cytological study.

The parameters observed in the physical study are: appearance of the liquid, color, density. The basic biochemical study includes glucose, proteins and LDH. However, other metabolites can be attached such as: amylase, albumin, ADA, among others.

Normal values ​​(transudate)

Physical appearance

Density: 1.006-1.015.

Appearance: Transparent.

Color: light yellow.

Biochemical study

Rivalta reaction: negative.

Proteins: <3 g%.

Albumin: <1.5 g / dl.

Glucose: normal, similar to plasma.

LDH: low (<200 IU / L).

Amylase: value similar to or less than plasma.

ADA: <33 U / L.

Fibrinogen: absent.

Coagulation: never.

Cytological study

Cell count: <3000 cells / mm ³

Neoplastic cells: absent.

Bacteria: absent.

Leukocytes: few.

Red blood cells: scarce.

Pathological values ​​(exudate)

Physical aspects

Density: 1.018-1.030.

Appearance: cloudy.

Color: dark yellow or whitish.

Biochemical study

Rivalta reaction: positive.

Proteins:> 3 g%.

Albumin:> 1.5 g / dl.

Glucose: decreased.

LDH: increased, especially in neoplastic processes (> 200 IU / l).

Amylase: increased in case of pancreatitis.

ADA (adenosine deaminase enzyme):> 33 U / L in case of tuberculous ascites.

Bilirubin: increased (indicated only when the color of the liquid is dark yellow or brown).

Fibrinogen: present.

Coagulation: frequent.

Cytological study

Cell count:> 3000 cells / mm ³

Neoplastic cells: common.

Bacteria: frequent.

Leukocytes: abundant.

Red blood cells: variables.

Pathologies

Chylous ascites

It has been noted that the peritoneal fluid can become cloudy, white (chylous), but with low cell counts. This is due to the administration of certain calcium antagonist drugs, such as: lercanidipine, manidipine, dihydropyridines, nifedipine, without associated infection.

Chylous ascites (increased triglycerides and chylomicrons) can have other causes, such as: neoplasms, nephrotic syndrome, pancreatitis, liver cirrhosis, among others. It is also called lymphatic ascites.

Bacterial peritonitis

If the fluid is cloudy and there are a large number of leukocytes, peritonitis should be considered. Peritonitis can be spontaneous, secondary, or tertiary.

Spontaneous or primary peritonitis is caused by microorganisms that come from a bacterial translocation (passage of bacteria from the intestine to the mesenteric ganglia). This is how the bacteria pass into the lymph, the peritoneal fluid and the systemic circulation.

This process is favored by a significant increase in the intestinal microbiota, an increase in the permeability of the intestinal mucosa and a decrease in local and systemic immunity.

Bacterial peritonitis occurs in a large percentage in patients with liver cirrhosis.

The most isolated microorganism is Escherichia coli, however, others can be found, such as: Staphylococcus aureus, Enterobacter cloacae, Klebsiella pneumoniae, Enterococcus faecalis, Enterococcus faecium, among others.

Secondary peritonitis is caused by the passage of septic content into the peritoneal cavity through a fissure in the gastrointestinal wall. The causes of wall rupture can be traumatic, post-surgical, gastric ulcer perforation, acute appendicitis, among others.

Whereas, tertiary peritonitis is difficult to diagnose. It can be caused by unresolved or persistent primary or secondary peritonitis. Occasionally, low pathogenic bacteria or fungi are isolated, but without finding the primary focus of infection. It can also be diffuse, without an infectious agent.

Tertiary peritonitis has a poor prognosis, it tends to have a high mortality despite the installation of aggressive treatment.

Bacteriazitis

Presence of bacteria in peritoneal fluid with low white blood cell count. It may be due to the onset of spontaneous bacterial peritonitis, or a secondary infection with an extraperitoneal origin.

Tuberculous peritonitis

The main cause is previous pulmonary tuberculosis. It is believed that it can affect the peritoneum mainly by lymphatic dissemination and secondly by hematogenous route.

Mycobacterium tuberculosis can reach the intestine by swallowing infected sputum. This involves the intestinal submucosa, the intramural, regional and mesenteric nodes.

References

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