Ascites is the accumulation of free fluid in the peritoneal cavity and is typically caused by portal hypertension due to hepatic failure. Other common causes of ascites include renal failure, congestive heart failure, infection, or malignancy. Ascites may be extremely uncomfortable when large amounts of fluid are present, and may be life threatening if it becomes infected or compromises respiratory efforts or venous return. Physical examination is not sensitive for ascites and cannot reliably determine the optimal location for drainage. Bedside ultrasound can reliably detect ascites and aid in the removal of fluid.
Both critical care and emergency medicine physicians have long performed bedside paracentesis. The traditional blind approach to remove intraperitoneal fluid has been employed until the recent introduction of ultrasound-guided techniques. Ultrasound-guided paracentesis is now the standard of care amongst both critical care and emergency medicine physicians. When compared to the older blind approach, ultrasound-guided paracentesis may increase the success of the procedure and decrease the risk of vascular injury or bowel perforation.
Paracentesis can be diagnostic or therapeutic and sometimes both, depending on the patient's presentation. Diagnostic paracentesis may be required to rule out an infection or malignancy. Ascitic fluid is always at risk for bacterial translocation which can lead to peritonitis. Therapeutic paracentesis can also be performed to relieve abdominal pain or shortness of breath. When massive, ascitic fluid can inhibit excursion of the diaphragm and cause respiratory distress, or compress the inferior vena cava (IVC) impairing right heart filling which lead to hemodynamic instability. In these patients, removal of fluid can relieve cardiopulmonary distress and provide significant symptomatic relief.
- Assessment of new onset ascites and/or ascites of unclear etiology
- Concern for spontaneous bacterial peritonitis in a patient with known ascites (may present with abdominal pain, fever, or altered mental status)
- Relief of symptomatic ascites, particularly if cardiovascular or respiratory compromise is present
Curvilinear Probe with a Frequency of 3.5–5.0 MHz
The initial probe for detection of fluid should be a large footprint curvilinear probe in the 3.5–5.0 MHz range. This probe is best for identifying large pockets of fluid in the upper and lower quadrants, explained fully in Chap. 9.
Linear-Array Probe with a Frequency of 8–12 MHz
Following the identification of the optimal fluid pocket for aspiration, a higher-frequency linear probe, in the 8–12 MHz range, should be used for actual procedural guidance. This will provide better resolution, improving identification of the inferior epigastric vessels and visualization of the needle entering the fluid pocket.
The standard equipment required for a sterile procedure, including appropriate local anesthesia (1%–2% lidocaine with or without epinephrine), is needed for a paracentesis. In addition, if available, a packaged "paracentesis kit" or similar supplies are required which include: