Rajesh Geria, M.D., RDMS
I. Introduction and Indications
Ascites is defined as an abnormal collection of fluid with the peritoneal cavity. The most common cause for ascites in the United States is alcoholic liver cirrhosis. Although small collections of fluid may by asymptomatic, larger amounts may cause abdominal pain, nausea, anorexia and infection. The process of aspirating fluid from the abdomen is called paracentesis and is commonly done by emergency physicians to relieve symptoms in these patients and to retrieve fluid samples for diagnostic testing. This procedure is invasive and presents a risk for complications with high morbidity such as bowel perforation and infection. (1,2)
Use ultrasound to localize intra-abdominal fluid and for visual guidance of fluid aspiration whenever possible. It can also be employed in unstable patients with a positive FAST exam. Ultrasound guided paracentesis can help distinguish the identity of fluid in these emergent situation and expedite needed care. (3)
- Diagnostic evaluation of new-onset ascites
- Therapeutic intervention in symptomatic patients
- Diagnostic evaluation of free intra-abdominal fluid in unstable patients
Intrabdominal structures that may impede the successful aspiration of fluid include the bladder, gravid uterus, and bowel. Usually the bladder is tucked into the pelvic recess unless full. Bowel is a moving structure that may float very close to the abdominal wall. Fluid appears anechoic inferior to the echogenic abdominal wall musculature. Bowel is usually echogenic and actively moving within the fluid.
Figure 1 and 2: Large ascites with several bowel loops (Figure 2 courtesy of B. Hoffmann, M.D.).
III. Scanning Technique and Normal
A low frequency transducer (3.5 MHz) is placed in a sterile sheath. It is then positioned in saggital orientation either in the infra-umbilical or left lower quadrant of the supine patient. The deepest pocket of fluid is identified. The needle is inserted through the abdominal wall under real time ultrasound guidance. The tip of the needle is seen as a hyperechoic structure entering through the abdominal wall into the fluid and steering clear of the moving bowel and the bladder, especially with the infra-umbilical approach.
Illustration 1: Schematic view of paracentesis needle placement.
Video clip 1: The video shows the ultrasound view of a paracentesis.
Complications can include bowel perforation with infection and sepsis, puncture of bladder or cystic masses.
V. Pearls and Pitfalls
SR, Dewbre H, Miller AH.
Ultrasound-assisted paracentesis performed by emergency physicians vs the traditional technique: a prospective, randomized study. Am J Emerg Med.2005;23:363-7.
- Tibbles CD, Porcaro
Procedural applications of ultrasound. Emerg Med Clin North Am.2004;22:797-815.
Emergency diagnostic paracentesis to determine intraperitoneal fluid identity discovered on bedside ultrasound of unstable patients. J Emerg Med.2005;29:461-5.