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.

Complications from paracentesis are uncommon but include hemorrhage (0% to 0.93%), abdominal wall hematoma, mesenteric hematoma, bladder or bowel perforation, inferior epigastric artery aneurysm, vessel laceration (aorta, mesenteric artery, iliac artery), hypotension, infection (0.58% to 0.63%), and persistent ascitic fluid leak (5%).⁸

Patient Positioning And Landmarks

Typically, the patient is either supine or in a slight lateral decubitus position with the head raised to maximize drainage. The areas recommended for the traditional technique are midline and 2 cm below the umbilicus or 4-5 cm superior and medial to the anterior superior iliac spine in either lower quadrant. Use these landmarks with ultrasound to find the deepest fluid pocket. The abdominal scan should be done immediately before the procedure with the patient remaining in the same position for the procedure.

Scanning for Ascites

Ultrasound may be used statically to mark the entry site prior to paracentesis or dynamically to observe the needle entering the peritoneal cavity. The latter is helpful for smaller fluid collections.

Use a 2-5 MHz low-frequency curvilinear transducer under the abdominal setting to scan the abdomen. Simple transudative ascites is anechoic and extraperitoneal. Loops of bowel appear hyperechoic and will float and peristalse within the fluid. The bowel may have dirty shadowing, depending on how much intraluminal gas is present, and have a mesenteric stalk. Complex ascitic fluid has varying echogenicities depending on its composition, including protein, fibrin, leukocytes and erythrocytes.

The bladder is located in the midline infraumbilical abdomen with a hyperechoic dome and anechoic urine. Locate where the largest pocket of ascitic fluid and the thinnest abdominal wall are. A fluid pocket that is at least 3-cm deep is adequate for the procedure. Mark this pocket in two orthogonal planes if using ultrasound statically.

Equipment

Most of the equipment required can be found in a peritoneal lavage kit.

• Gloves, gown
• Mask, cap
• Ultrasound probe cover
• Ultrasound machine
• Antiseptic
• Fenestrated drape
• Gauze
• Lidocaine
• Syringes: 10 mL, 60 mL
• Injection needles: 25 ga, 22 ga
• Scalpel, #11 blade
• Catheter 8 F over 18 ga x 7.5” needle
• 3-way stopcock
• Tubing set
• Drainage bag or vacuum container
• Specimen vials (3)

Technique

• Prep and drape the patient aseptically.
• Anesthetize the skin by making a wheal. Anesthetize down to the peritoneum along the catheter tract. Apply negative pressure when advancing the needle.
• Make a small nick in the skin with the scalpel.
• With your nondominant hand, apply traction to the entry site caudad or cephalad, creating a “Z track.” Once the catheter is removed at the end of the procedure and the skin returns to its normal position, the track will be indirect, decreasing persistent leak.
• Insert the catheter over needle.
• If using ultrasound statically, insert the catheter over needle perpendicular to the entry site while applying negative pressure in the syringe.
• If using ultrasound dynamically, have another person center the nick in the middle of the sterile dressed probe. Insert the catheter over needle at 45 degrees to the probe. Visualize the catheter entering the abdominal wall and fluid while applying negative pressure in the syringe.
• Once the syringe fills easily, insert the catheter over needle 3 mm.
• Hold the hub of the needle and advance the catheter.
• Withdraw the needle.
• Attach the 3-way stopcock to the catheter.
• Obtain laboratory samples with the 60 mL syringe for a diagnostic tap.
• Connect the tubing and attach the drainage bag or vacuum bottle for a therapeutic tap.
• Remove the catheter after collecting the desired amount of fluid. Apply firm pressure and a bandage to the entry site.

Laboratory

Depending on the clinical picture, the following may be sent to the laboratory: Routine:

• Cell count and differential
• Bacterial culture
• Albumin
• Protein
• Optional
• Gram stain
• Triglycerides
• Bilirubin
• Glucose
• Amylase
• Lactate dehydrogenase
• Cytology

Disease

The most common cause of ascites is cirrhosis (81%), followed by malignancy (10%), heart failure (3%), tuberculosis (2%), hemodialysis (1%), pancreatic disease (1%) and other (2%).¹⁰ Approximately 5% of patients have mixed ascites, that is, fluid due to more than one cause.¹⁰

In new onset ascites, the serum-ascites albumin gradient (SAAG) helps determine the presence of portal hypertension. The difference between the serum albumin level and ascites albumin level is the gradient. A gradient > 1.1 g/dL suggests a transudative ascites from portal hypertension, whereas a gradient <1.1 g suggests an exudative etiology.

Causes of portal hypertension are cirrhosis, alcoholic hepatitis, congestive heart failure, and liver metastases. Less common considerations are fulminant hepatic failure, Budd-Chiari syndrome, portal vein thrombosis, venous occlusive disease, fatty liver of pregnancy, myxedema, and mixed ascites.

Causes of a low gradient include nephrotic syndrome, peritoneal carcinomatosis, tuberculous peritonitis, pancreatic ascites, and connective tissue disease serositis. History of breast, colon, gastric or pancreatic cancers or signs and symptoms of malignancy raise suspicion for peritoneal carcinomatosis. The tap may be sanguinous. Cytology may differentiate among malignancies.

Patients with uncomplicated ascites from cirrhosis have an ascitic white blood cell (WBC) count < 500 cells/mL. In spontaneous bacterial peritonitis, the patient will have symptoms of fever and abdominal pain and a WBC count > 250 cells/mL with greater than 50% polymorphonuclear leukocytes (PMN). The ascitic fluid may be turbid. A Gram stain is usually not helpful, but cultures are useful.

Pitfalls

• Allowing the patient to move after marking the entry site, resulting in a dry tap or bowel perforation.
• Not mapping or identifying abdominal structures, such as bowel and bladder, leading to perforation.

Conclusion

Ultrasound may be used statically for paracentesis to mark the largest pocket of ascitic fluid or used dynamically for small fluid collections, increasing procedural success. It may also be used to identify anatomic structures to avoid.

References

1. Williams JW, Simel DL. The rational clinical examination. Does this patient have ascites? How to divine fluid in the abdomen. JAMA. 1992;267(19):2645-2648.
2. Goldberg BB, Clearfield HR, Goodman GA, et al. Ultrasonic determination of ascites. Arch Intern Med. 1973;131(2):217-220.
3. Giacobene JW, Siler VE: Evaluation of diagnostic abdominal paracentesis with experimental and clinical studies. SurgGynecolObstet1960;110:676-686.
4. Bard C, Lafortune M, Breton G. Ascites: ultrasound guidance or blind paracentesis? CMAJ. 1986;135(3):209-210.
5. Nazeer 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(3):363-367.
6. Cattau EL Jr, Benjamin SB, Knuff TE, Castell DO. The accuracy of the physical examination in the diagnosis of suspected ascites. JAMA. 1982;247(8):1164.
7. Patel PA, Ernst FR, Gunnarsson CL. Evaluation of hospital complications and costs associated with using ultrasound guidance during abdominal paracentesis procedures. J Med Econ. 2012;15(1):1-7. Epub 2011 Oct 19.
8. Runyon BA. Diagnostic and therapeutic paracentesis. UpToDate. 8 Sep 2011. Web. 15 June 2012.
9. Runyon BA; AASLD Practice Guidelines Committee. Management of adult patients with ascites due to cirrhosis: an update. Hepatology. 2009 Jun;49(6):2087-107.
10. Runyon BA, Montano AA, Akriviadis EA, Antillon MR, Irving MA, McHutchison JG. The serum-ascites albumin gradient is superior to the exudate-transudate concept in the differential diagnosis of ascites. Ann Intern Med. 1992 Aug 1;117(3):215-20.
11. Shlamovitz GZ, Paracentesis. Medscape. 9 May 2012. Web. 10 June 2012.
12. Hwang JQ, Kimberly HH, Liteplo AS, Sajed D. An Evidence-Based Approach To Emergency Ultrasound. Emergency Medicine Practice. Mar 2011.
13. Promes SB. Chapter 54. Paracentesis. In: Reichman EF, Simon RR, eds. Emergency Medicine Procedures. New York: McGraw-Hill; 2004. http://www.accessemergencymedicine.com/content.aspx?aID=51430. Accessed June 11, 2012.
14. Dewitz A, Jones R, Goldstein J. Chapter 20. Additional Ultrasound-Guided Procedures. In: Blaivas M, Ma OJ, Mateer JR, eds. Emergency Ultrasound. 2nd ed. New York: McGraw-Hill; 2008. http://www.accessemergencymedicine.com/content.aspx?aID=105418. Accessed June 11, 2012.