Ultrasound technology is readily available and can provide guidance for invasive abdominal procedures in multiple planes without ionizing radiation. Further, real-time guidance of the needle tip position allows the operator to avoid inadvertent puncture of vital structures during the performance of invasive and soft tissue procedures of the abdominal cavity. Recently, this technology has a demonstrated benefit in abdominal procedures such as paracentesis, liver and kidney biopsy, percutaneous gallbladder drainage, and abscess drainage.
Transducer selection for abdominal procedures most commonly includes a curved or phased array. A curved array allows the user to visualize a larger field, but the actual transducer size is larger than a phased array. Curved array is the transducer of choice for most abdominal procedures since a larger field can be visualized during the exam. A sector array is smaller and is most commonly used for abscesses that are close to the diaphragm and allows for an intercostal approach.
Ultrasound use in paracentesis improves both the ease and efficiency of the procedure and reduces unnecessary abdominal punctures in patients with scant fluid. It is particularly helpful in obese patients to assess the depth to the peritoneum and in patients with loculated effusions to define the largest locule for drainage. Ultrasound use can identify intrabdominal pathology that may increase the risk of bowel perforation during the procedure.1
Diagnostic paracentesis is indicated as a part of the initial evaluation of patients with new onset ascites and in patients with a known history of ascites secondary to liver cirrhosis who develop clinical deterioration, including the signs and symptoms of fever, abdominal pain, rapid worsening of renal function, worsened hepatic encephalopathy, leukocytosis, acidosis, gastrointestinal bleeding or sepsis, and to rule out underlying spontaneous bacterial peritonitis.2 Paracentesis can also be used for the evaluation of intraabdominal fluid in trauma patients. Therapeutic paracentesis is performed in patients with tense or diuretic-resistant ascites to alleviate difficulty with breathing or abdominal pain.
Paracentesis is contraindicated in patients with disseminated intravascular coagulation, a platelet count <50 x 109/liter, an international normalized ratio (INR) >2, and a local skin infection, visible scar, hematoma, or cutaneous vein at the site of needle entry.3 Patients with underlying renal insufficiency who have an increased tendency for bleeding should be carefully evaluated prior to the procedure.
Equipment and Procedure Tray
A 3.5–5 MHz broadband curved array is preferred for the evaluation of ascites and for assistance with ultrasound-guided paracentesis.1, 4 Prepackaged paracentesis procedure kits are commercially available and contain all necessary equipment including an aspiration catheter, catheter bag, blood collection tubing, 19-gauge introducer needle with 5 French catheter, lidocaine for skin anesthesia, skin preparation solution, and dressing pack with sterile draping (Figure 28.1). For real time ultrasound guided procedures a sterile sleeve is used to cover the ultrasound probe.
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