Introduction

Emergency physicians perform abdominal paracentesis both for diagnostic sampling of peritoneal fluid and for therapeutic drainage of symptomatic large volume ascites. Bedside ultrasound-guided paracentesis can potentially improve safety and procedural success.

Although paracentesis using the traditional landmark technique is generally safe, ultrasound allows visualization of abnormal anatomy to avoid, the deepest pocket of peritoneal fluid, and confirmation that the etiology of abdominal distention is ascites rather than another disease process. In addition it is easy to learn and has lower adverse events. Ultrasound detection of as little as 100 mL makes it the gold standard for diagnosing ascites.^1,2

Disadvantages of the traditional technique are: an effective tap depends on fluid volume, the distribution of ascites varies, and loops of bowel may impede the entry site.^3,4 Successful drainage of ascitic fluid is 44% and 78% for volumes of 300 mL and 500 mL, respectively, and never successful when volumes are less than 50 mL, using the traditional technique.³ Authors concluded in an early ultrasound-guided paracentesis study that since fluid collections were inconsistent between patients, there was no single ideal site for blind paracentesis.⁴

In a prospective randomized study performed by novice emergency medicine residents, ultrasound-guided paracentesis compared with the traditional technique had a higher success rate (95% versus 61%, P = 0.0003); moreover, ultrasound also identified other pathologies that mimic ascites or had no or little fluid, sparing the patient an invasive and potentially detrimental procedure.⁵ Another study also suggested that physical exam may not be reliable to diagnose ascites. Using ultrasound as the gold standard, physical exam had a sensitivity of 50% to 94% and specificity of 29% to 82% to diagnose ascites.⁶

In a retrospective analysis of a database of 600 hospitals, ultrasound-guided paracentesis had lower adverse events of post-paracentesis infection, hematoma, and seroma compared with traditional technique (1.4 % versus 4.7%, P = 0.01) and lower total hospitalization costs.⁷

Clinical Indications for Paracentesis

Indications for abdominal paracentesis include:

• Suspicion of a spontaneous bacterial peritonitis.
• Evaluation of new ascites or possible malignancy.
• Relieving dyspnea or discomfort from large volume ascites.

Contraindications

• A surgical abdomen is an absolute contraindication to paracentesis.

Relative contraindications are

• Thrombocytopenia (platelet count < 20 x 10 uL)
• Coagulopathy (INR > 2.0)
• Disseminated intravascular coagulation
• Primary fibrinolysis
• Pregnancy
• Distended urinary bladder
• Abdominal wall cellulitis
• Distended bowel or massive ileus
• Intraabdominal adhesions

Anatomic considerations

Although ultrasound increases success of paracentesis by allowing one to visualize a fluid-filled pocket, avoidance of certain anatomic structures decreases potential complications. The liver and spleen preclude aspiration of fluid from the upper quadrants of the abdomen and risk being punctured. The right lower quadrant contains the cecum, which can be easily perforated. This quadrant may also contain an appendectomy scar, which could interfere with the free flow of fluid. The suprapubic region contains the bladder, which may rise above the pubic symphysis when distended. The bladder should be decompressed by voiding or catheterization prior to the procedure. Aspiration lateral to the rectus muscle avoids damaging the epigastric vessels. Surgical scars may have adhesions and adherent bowel that may be inadvertently perforated.