section name header

Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Procedure for sampling peritoneal fluid by collection through the abdominal wall
  • Abdominocentesis is usually performed at the most dependent part of the abdominal wall. The site is clipped and prepared aseptically. Either a needle or a blunt-tipped cannula can be used to enter the abdominal cavity. Using a needle is usually faster and is associated with less bleeding from vessels in the skin; the cannula is less likely to result in inadvertent enterocentesis or laceration of the intestinal wall. When using a cannula, the site is first infused with local anesthesia and a small skin incision is made
  • Transabdominal ultrasound may be used to locate fluid pockets
  • Peritoneal fluid is collected into EDTA-containing tubes for assessment of the total nucleated cell count and cytology, and into a sterile clot tube for bacterial culture or biochemical tests
  • Equine abdominal fluid normally appears clear and colorless to slightly yellow and does not clot
  • Total protein commonly is assessed by refractometer and normally is < 2.5 g/dL
  • The nucleated cells may be counted by hemocytometer or by using some hematology analyzers. The nucleated cell count in fluid from normal horses is < 5000 cells/μL, with a predominance of nondegenerative neutrophils (22–98%) and large mononuclear cells (1–68%), which include mesothelial cells and macrophages. Small lymphocytes may constitute 0–36% of the total cell count and eosinophils up to 7%; mast cells and basophils are rarely seen. Normally, few erythrocytes are present
  • Biochemical measurements in addition to total protein may include lactate as an indicator of intestinal ischemia or hypoperfusion, glucose as an indicator of septic peritonitis and creatinine, and/or potassium to aid in diagnosis of uroabdomen

Pathophysiology!!navigator!!

  • Normal peritoneal fluid is a dialysate of plasma; many of the low-molecular-weight substances in blood are present in the peritoneal fluid at similar concentrations
  • High-molecular-weight molecules (e.g. proteins) normally are not present in abdominal fluid
  • Cells in normal peritoneal fluid include mesothelial cells that line the abdominal cavity and cover visceral surfaces, and small numbers of cells from the blood and lymphatics
  • Fluid circulates constantly through the abdominal cavity and is drained via lymphatic vessels. When fluid production exceeds drainage, effusion develops. This may occur with some systemic disorders (e.g. cardiovascular disease) or with local disorders of abdominal organs or mesothelium. Changes in peritoneal fluid protein, cell numbers, and cell types may reflect those disorders
  • During inadequate intestinal perfusion and ischemia, anaerobic glycolysis can result in increased peritoneal fluid lactate concentration. A peritoneal fluid lactate concentration that is higher than the serum concentration provides evidence of intra-abdominal infection or ischemia
  • When infection is present in the abdomen, the peritoneal fluid glucose concentration is usually < 30 mg/dL, as glucose is actively consumed by bacteria. It is also reported that a difference of > 50 mg/dL between the serum and peritoneal fluid is highly diagnostic for infection in the abdomen. The glucose measurement might be most useful when timely cytologic examination is not available
  • A localized process in the abdomen, such as a walled-off abscess or a tumor, may not be reflected in a peritoneal fluid sample
  • Repeated sampling of peritoneal fluid is necessary, in some cases, to follow the course of a disease or to monitor therapy, whether it is medical or surgical

Systems Affected!!navigator!!

  • GI
  • Hepatobiliary
  • Hemic/lymphatic/immune
  • Renal/urologic
  • Cardiovascular
  • Reproductive

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

N/A

Geographic Distribution!!navigator!!

N/A

Signalment!!navigator!!

Any breed, age, or sex.

Signs!!navigator!!

  • Colic
  • Chronic weight loss
  • Abdominal distention
  • Diarrhea
  • Pyrexia

Causes!!navigator!!

  • Peritonitis caused by compromised gut wall
  • Hemorrhage (hemoabdomen)
  • Intra-abdominal neoplasia
  • Intestinal parasitism and secondary thromboembolism
  • Inflammation of abdominal organs
  • Compromised venous return due to intestinal displacement, distention, etc.
  • Breeding and foaling injuries
  • Bile or urine leakage
  • Postsurgical inflammation or other complications
  • Abdominal abscess
  • Decreased oncotic pressure
  • Congestive heart failure

Risk Factors!!navigator!!

  • Abdominal surgery
  • Pregnancy
  • Hypoalbuminemia

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Peritonitis

Peritonitis may be caused by a number of conditions, including a displaced or strangulated bowel, bowel necrosis, obstruction, bowel rupture, abscess, or thromboembolism.

  • The fluid is an exudate with an increased nucleated cell count and a predominance of neutrophils
  • The total protein usually is > 2.5 g/dL due to the presence of inflammatory proteins
  • Bacteria are present in septic peritonitis and may be intracellular or extracellular. Degenerative changes in neutrophils are usually seen and the glucose concentration of the fluid is decreased
  • With gut rupture, cells often are degenerate and mixed bacterial types, ciliated protozoa, and plant material may be seen
  • Postsurgical peritonitis also produces an exudate with increased cell numbers and total protein within 24 h and lasting up to 2 weeks. Neutrophils generally are not degenerate and no bacteria are seen. Increased RBC numbers may be seen

Hemorrhage

  • With a splenic tap, the PCV is higher in abdominal fluid than in blood, and small lymphocyte numbers may be increased
  • With hemorrhage into the abdomen, the PCV of fluid is lower than that of blood. Platelets are absent, and erythrophagocytosis or macrophages containing hemoglobin-breakdown pigments may be seen
  • With blood contamination at the time of sampling, fluid initially may look clear, with bloody streaks appearing during sampling. Phagocytosis of RBCs is not seen, and platelets may be present

Neoplasia

A diagnosis may be established on finding neoplastic cells in fluid but absence of neoplastic cells does not rule out neoplasia, because tumor cells may not exfoliate into fluid.

Parasitism

Migration of parasitic larvae may be associated with increased eosinophils, but this does not occur often and is not diagnostic for parasitism.

Uroabdomen

  • Typically, peritoneal fluid creatinine and potassium concentrations are increased compared with serum concentrations
  • Hyperkalemia, marked hyponatremia, and hypochloremia are typical but are not present in all cases

Ascites

  • A transudate with low cell numbers and low protein content may be present with hypoalbuminemia or lymphatic or vascular obstruction or stasis
  • Serum biochemical profile and history contribute to this diagnosis

Congestive Heart Failure

Increased hydrostatic pressure within vessels may result in a modified transudate with a higher cell count and protein level than a transudate, but these values may be normal for equine abdominal fluid.

CBC/Biochemistry/Urinalysis!!navigator!!

  • Inflammatory causes of abdominal effusion may be associated with leukocytosis or hyperfibrinogenemia if disease is systemic
  • Left shift or toxic changes in neutrophils indicate systemic inflammation
  • Serum biochemistries help in assessing causes of transudate, e.g. panhypoproteinemia is consistent with GI protein loss; elevated liver enzymes suggest hepatic disease
  • Serum electrolyte concentrations and comparison of serum and fluid creatinine concentrations aid in diagnosis of uroperitoneum

Other Laboratory Tests!!navigator!!

Bacterial culture is helpful in some cases, such as abdominal abscess.

Imaging!!navigator!!

Ultrasonography

  • May be useful in identifying a subjective increase in peritoneal fluid, hemoabdomen, GI distention or wall thickening, intussusception, masses, adhesions, abnormal liver/spleen/kidney, and enteroliths
  • Ultrasonographic location of peritoneal fluid might help in performing abdominocentesis

Abdominal Radiography

In adult horses, may aid in establishing the diagnosis of diaphragmatic hernia, sand enteropathy, and enteroliths.

Other Diagnostic Procedures!!navigator!!

  • Palpation per rectum might aid in the diagnosis of GI abnormalities or abdominal effusion
  • Laparoscopy may be used to establish the diagnosis in cases of chronic colic or weight loss
  • Gastroscopy can be useful in establishing the diagnosis of gastric ulcers, impaction, and neoplasia
  • Exploratory laparotomy is necessary for definitive diagnosis in some cases

Pathologic Findings!!navigator!!

As described.

Treatment ⬆ ⬇

TREATMENT

Directed at the underlying cause.

Medications ⬆ ⬇

MEDICATIONS

Based on the underlying cause.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

No specific monitoring procedures are indicated following an uncomplicated abdominocentesis.

Prevention/Avoidance!!navigator!!

N/A

Possible Complications!!navigator!!

  • Subcutaneous swelling at the site may be more commonly observed when a blunt cannula is used for the procedure
  • Accidental enterocentesis is rarely associated with clinical disease but causes an increased nucleated cell count in abdominal fluid within 4 h. When the gut is tapped, there will be few, if any, cells, large numbers of bacteria, and plant material on cytologic examination. Also, the physical condition of the horse is relatively normal compared with one with a gut rupture
  • Puncture of a compromised intestinal wall could cause leakage and rapid development of severe peritonitis. Sand impaction is associated with increased risk of intestinal puncture
  • Accidental amniocentesis may occur in pregnant mares. This has not been reported to be associated with any specific sequelae

Expected Course and Prognosis!!navigator!!

Dependent on the underlying cause.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Age-Related Factors!!navigator!!

Foals normally have peritoneal fluid protein concentrations similar to those of adults, but total nucleated cell counts (< 1500 cells/μL) that are lower than those of adults.

Pregnancy/Fertility/Breeding!!navigator!!

There are no significant differences between fluid from mares that are pregnant or have recently foaled and fluid from nonperipartum mares.

Synonyms!!navigator!!

  • Abdominal paracentesis
  • Belly tap
  • Intraperitoneal tap

Abbreviations!!navigator!!

  • GI = gastrointestinal
  • PCV = packed cell volume
  • RBC = red blood cell

Suggested Reading ⬆ ⬇

Brownlow MA, Hutchins DR, Johnston KG. Reference values for equine peritoneal fluid. Equine Vet J 1981;13:127–130.

Duesterdieck-Zellmer KF, Richl JH, McKenzie EC, et al. Effects of abdominocentesis technique on peritoneal fluid and clinical variables in horses. Equine Vet Educ 2014;26:262–268.

Latson KM, Nieto JE, Beldomenico PM, Snyder JR. Evaluation of peritoneal fluid lactate as a marker of intestinal ischaemia in equine colic. Equine Vet J 2005;37:342–346.

Parry BW, Brownlow MA. Peritoneal fluid. In: Cowell RL, Tyler RD, eds. Cytology and Hematology of the Horse. Goleta, CA: American Veterinary Publications, 1992:121–151.

Van Hoogmoed L, Snyder JR, Christopher M, Vatistas N. Evaluation of peritoneal fluid pH, glucose concentration, and lactate dehydrogenase activity for detection of septic peritonitis in horses. J Am Vet Med Assoc 1999;214:1032–1036.

Author(s) ⬆

Author: Susan J. Tornquist

Consulting Editor: Sandra D. Taylor