Abdominocentesis or coelomocentesis may be indicated for the accumulation of fluid within one or more of the peritoneal cavities. Peritoneal fluid can accumulate with a variety of diseases, including chronic liver disease, amyloidosis in waterfowl, iron storage disease in mynah birds and toucans, coelomic tumors in budgerigar parakeets, viral infections like Marek’s disease (resulting in cardiac tumors), peritonitis, congestive heart failure, ovarian cysts, and trauma.
Depending on the underlying cause of disease and the degree of fluid accumulation, the bird may present with dyspnea secondary to compression of the air sac space, and/or non-specific signs of illness, such as weakness, depression, a fluffed and ruffled appearance, and anorexia. On physical examination, swelling may be detected within the coelom (Fig 1).
The primary indication for abdominocentesis is an enlarged, fluid-filled abdomen, but the procedure can serve both diagnostic and therapeutic purposes. Abdominocentesis can be used to relieve pressure on the air sacs and lungs of the dyspneic bird. Free peritoneal fluid can also be used for cytodiagnostics.
The presence of abdominal fluid can be an obvious finding on physical examination. Moistening feathers on the ventrum with isopropyl alcohol and using transillumination can also serve as a useful aid to confirm the presence of transudative fluid (Speer 2012). On survey radiographs there may also be loss of serosal detail, due to a characteristic “ground glass” appearance as well as a widening of the cardiohepatic silhouette. Ultrasound is extremely useful in detecting fluid and evaluating the coelomic cavity.
Where is the effusion?
The complexities of the avian peritoneal cavities means there is no single compartment in which fluid can accumulate. During embryological development, the extensive air sac system of birds effectively partitions the developing peritoneum (Taylor 2014). All birds have distinct peritoneal cavities: a central intestinal peritoneal cavity as well as left and right ventral hepatic peritoneal cavities that are separated by a ventral mesentery. There are usually two smaller left and right dorsal hepatic peritoneal cavities as well (Taylor 2014, Duncker 1979). Although birds lack a muscular diaphragm, they do have a post-pulmonary septum so there is no connection between the abdominal and pleural cavities.
Potential complications of abdominocentesis include perforation of viscera, such as the liver or gastrointestinal tract, and puncture of the air sac system, potentially flooding the respiratory tract. The smaller the patient, the higher the risk of puncturing an air sac. As in all species, removal of large volumes of fluid can create dramatic shifts in protein and/or abdominal pressure potentially causing serious or even fatal effects (Doneley 2006).
- Small gauge hypodermic needle, butterfly catheter or over-the-needle catheter (21-to-27-gauge)
- Topical antiseptic: isopropyl alcohol or chlorhexidine solution
- Sample collection tubes
- ± Stopcock
- ± Intravenous extension tubing to attach to the needle or catheter
- Firmly restrain the bird upright and slightly tipped forward. Often these birds present with dyspnea so care should be taken when handling (Jones 2007).
- Part the feathers on midline to identify the featherless tract. Pluck overlying feathers as needed.
- Aseptically prepare skin on ventral midline caudal to the point of the sternum, ideally at the level of the umbilicus, with chlorhexidine gluconate or isopropyl alcohol.
- Is the pocket of fluid visible or palpable? Insert a needle or catheter through the skin and muscle perpendicular to the skin. If an intravenous catheter is used, immediately remove the needle once the catheter pierces the abdomen.
- When an obvious pocket of fluid cannot be palpated, fluid aspiration can be performed via ultrasound guidance. Transillumination (see indications above) can also be used to guide site selection. Insert the needle from a caudoventral direction using an acute angle of entry. Insert the needle at the level of the umbilicus to avoid the liver cranially. Direct the needle just right of midline to avoid the ventriculus on the left.
- Aspirate fluid by applying negative pressure on a sterile syringe.
- Repeat as needed.
- Note: Blind four-quadrant sampling is not performed in the avian patient due to the presence of the air sacs laterally.
A form of peritoneal lavage can also be attempted with the use of a small gauge catheter and sterile saline (Jones 2007).
Birds normally produce a small amount of abdominal fluid to facilitate organ movement. This fluid should be poorly cellular with the presence of an occasional mesothelial cell or macrophage (Campbell 2007, Jones 2007).
When abdominal effusion is present, the fluid collected can be submitted for cytology, culture, and biochemical analysis. Effusions are classified as pure transudates, modified transudates, or exudates (non-septic, septic, malignant or hemorrhagic) based upon cellularity, color, total protein and specific gravity (Table 1) (Campbell 2007).
|Table 1. Nature of effusion (Tully 2013, Campbell 2007, Doneley 2006)|
|Appearance*||Yellow-pink, turbid||Clear to pale yellow|
|Specific gravity||High: >1.020||Low: <1.020|
|Protein||High: 3 g/dL||Low: 1 g/dL|
|Cytology||Many inflammatory cells, bacteria may be present with septic conditions||Low cellularity|
|*Fluid appearance will vary with the individual bird, the species, and the underlying problem. For instance, Doneley (2006a) reports that fluid associated with metritis or peritonitis in ducks is often brown-black and not the yellow-pink fluid seen in psittacine birds. Doneley (2006b) has also reported that dark brown fluid can be associated with renal or hepatic cysts as well as degenerating ovarian follicles. Thick gelatinous fluid may be associated with salpingitis (Doneley 2006b).|
In dogs, a concentration difference of greater than 20 mg/dL between blood and effusion glucose levels is considered a reliable predictor of bacterial peritonitis (Volk 2015). High abdominal fluid lactate levels (> 2.0 mmol/L) is predictive of septic peritonitis in dogs, but not cats (Volk 2015).
Coelomic drainage via a hypodermic needle or over-the-needle catheter is a minimally invasive technique when performed correctly and carefully, however the potentially serious complications must be recognized and prevented. Cytologic, biochemical, and microbiologic analyses are useful in diagnosing the underlying cause of effusion