BACK TO BASICS: THE ACUTE ABDOMEN IN THE FIELD


1.5” needle may be sufficient. Body walls thicker than 2.5 cm require one of the alternative options. The risk for penetrating a viscus is believed to be lower with the more blunt-ended teat cannula and bitch catheter, and the proper use of these blunt instruments results in a higher likelihood of obtain- ing a diagnostic sample. Abdominocentesis using a teat cannula or bitch catheter is also slightly more difficult and time consuming. Use of needles is con- traindicated when taut, fluid-filled loops of small intestine are immediately adjacent to the body wall or palpated per rectum as inadvertent puncture or laceration of small intestine is likely to result in septic peritonitis.


Fig. 1. Local anesthesia with 2.5 mL 2% lidocaine prior to abdominocentesis.


Technique with Needles


optimize a location and limit the potential for en- terocentesis or inadvertent puncture of the spleen. A good starting point for application of the ultra- sound probe is in the most cranioventral abdomen, just to the right of midline, behind the xiphoid pro- cess and just caudal and axial to the deep pectoral muscles. A measurement of the depth of the body wall at the proposed site of abdominocentesis can also be readily performed with any ultrasound probe to assist with determination of which supplies are needed for successful entry into the peritoneal cavity. Once the location for abdominocentesis has been optimized via ultrasound, clipping of hair fol- lowed by a sterile prep of the area should be per- formed. Local anesthesia using a 25-gauge, 5/8” needle with 2.5–3 mL of 2% lidocaine solution can then be applied to the subcutaneous tissue, follow- ing a track vertically to the depth of the needle, through the external rectus fascia (Fig. 1). This step may not be necessary depending on the sup- plies used for abdominocentesis. Ultrasonographic findings favorable for abdomi- nocentesis are free peritoneal fluid at the site, al- though fluid acquisition may be successful in the absence of sonographically evident peritoneal fluid accumulation. Other ultrasonographic features to look for when free fluid is limited, is the presence of visibly mobile viscera. The presence of large colon haustra (sacculations) indicates the absence of heavy colonic content (e.g., sand or gravel) making the risk of enterocentesis lower. Lastly, avoid the spleen to limit the potential for blood contamination.


Choosing Supplies


There are generally 4 options to obtain a sample of peritoneal fluid. These include an 18-gauge, 1.5” needle, an 18-gauge, 3.5” spinal needle, a teat can- nula, and a bitch catheter. If abdominal ultra- sound was used to determine the depth from the skin surface to the peritoneal cavity and that dis- tance was equal to or less than 2.5 cm, the 18-gauge,


110 2020  Vol. 66  AAEP PROCEEDINGS


Following site selection and aseptic preparation, the 18-gauge needle is inserted through the skin, sub- cutaneous tissues, and external rectus fascia using sterile gloves to handle the needle. The needle should then be advanced a few millimeters at a time, with a spin of the needle to encourage fluid move- ment. The 1.5” needle will often need to be inserted to its full length prior to entering the peritoneal cavity. Occasionally, a vacuum effect due to the negative pressure within the abdomen will prevent fluid from exiting via the needle, and insertion of a second needle immediately adjacent to the first may allow flow of peritoneal fluid. Alternatively, a small volume 2–3 mL of air may be injected through the needle using a sterile 3-mL syringe. It may be difficult to discern whether the tip of the needle has reached the peritoneal cavity. Gentle movement of the needle hub is common when within the perito- neal cavity due to movement of intestinal viscera against the tip of the needle. Fluid should be col- lected into an ethylenediaminetetraacetic acid (EDTA) blood collection tube unless a septic process is suspected where samples should be collected in both EDTA and sterile red top tubes. Lactate con- centration can be measured from EDTA or heparin- ized tubes.


Technique with Teat Cannula or Bitch Catheter


The following supplies are required following aseptic preparation and local anesthesia prior to initiating abdominocentesis: sterile #15 scalpel blade, sterile 3  3or4  4 gauze, teat cannula or bitch catheter, and collection tubes (EDTA  red top tube) (Fig. 2). Following site selection, aseptic preparation and ap- plication of local anesthetic, a stab incision is made through the skin, subcutaneous tissue, and external rectus fascia by the examiner wearing sterile gloves. Avoid injury to small vessels in the skin. In over- weight horses, this may require deep insertion of the #15 blade beyond the primary cutting edge. The external rectus fascia is palpable with the tip of the blade and should be recognized and then pene- trated to a depth of 0.5 cm before extracting the blade (Fig. 3). The teat cannula or bitch catheter should be pushed through the center of a sterile


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