Paracentesis, or peritoneal tap, involves inserting a needle through the abdominal wall into the peritoneal cavity and aspirating fluid. The peritoneum is bathed in a small amount of fluid normally. Ascites, derived from the Greek word “askites,” meaning bag or bladder, is a collection of fluid in the peritoneal cavity whose volume is in excess of the normal amount. Paracentesis may be used as a diagnostic tool in the evaluation of ascites and/or as a therapeutic procedure for the relief of respiratory distress secondary to large accumulations of ascites. An understanding of the patient’s anatomy and the pathophysiology of ascites is essential to the correct performance of this procedure. Treatment rooms in the hospital, office, or clinic are appropriate settings for a diagnostic peritoneal tap. For the relief of respiratory distress, paracentesis should be performed in a facility equipped with monitoring and resuscitative equipment, such as an emergency department (ED) or intensive care unit, because the patient has the potential to rapidly deteriorate.

No one pediatric age group is predisposed to the development of ascites. Unlike adults, who often develop ascites secondary to acquired diseases, ascites in children is more often the result of congenital defects. Obstructive urinary tract anomalies are the most common cause of neonatal ascites (1). Other forms of ascites can be seen with a diverse group of conditions, including hydrops fetalis, occult perforations of the gastrointestinal tract, lymphatic obstruction, cardiac abnormalities with associated congestive heart failure, portal hypertension, peritonitis, metabolic diseases, malnutrition, neoplasias, and ventriculoperitoneal shunt obstruction. The basic pathologic mechanisms resulting in ascites include (a) high venous hydrostatic pressure (congestive heart failure, portal hypertension), (b) decreased plasma colloid oncotic pressure (hypoproteinemia), (c) lymphatic obstruction, (d) genitourinary obstruction, (e) inflammation (peritonitis), and (f) ruptured viscus (2,3).

Marked ascites is clinically noted by a protuberant abdomen and bulging flanks in the supine position. Shifting areas of dullness may be noted by percussion of the abdomen as the patient moves from a supine to a decubitus position. The clinician can appreciate fluid waves by placing the hands on a supine patient’s opposing flanks, gently thumping with one hand, and palpating the resulting wave on the opposite flank. (4). Regardless of the etiology of ascites, infants and small children may develop clinical symptoms by both direct and indirect effects on respiratory function. With marked ascitic fluid collections, restriction of diaphragmatic movement and compression of lower lung fields occur, resulting in decreased functional residual capacity, increased ventilation-perfusion mismatch, and resulting respiratory compromise.

In adult patients with cirrhosis and ascites, rapid removal of peritoneal fluid (8 L, or approximately 120 mL/kg, over 1 hour) has been associated with increased cardiac output 1 hour after paracentesis (5). However, prerenal azotemia, hyponatremia, decreased central venous pressure, decreased pulmonary capillary wedge pressure, and decreased cardiac output subsequently developed 24 hours later. Albumin replacement (8 g albumin for every 1 L of peritoneal fluid removed) prevented these effects.

Paracentesis for therapeutic purposes is often temporizing until the etiology is determined and treated. In some situations,

ascitic fluid is difficult to locate, and a radiologist should be consulted. Ultrasound may detect as little as 10 mL in an optimal setting and can discern loculated areas of fluid (6,7). Radiographic films of the abdomen reflect indirect findings and only are helpful if a large amount of fluid is present.

Paracentesis should never be performed through an area of cellulitis. In addition, relative contraindications include a history of prior abdominal surgeries due to the possibility of perforating a bowel loop that is adherent to the abdominal wall. In these patients, paracentesis should be performed in consultation with a pediatric surgeon. Patients with abnormal coagulation studies are at risk of developing an expanding abdominal wall hematoma, and the clinician should be cognizant of this possibility (8). Coagulopathy, however, is not a contraindication to performing paracentesis. Pregnant patients also can undergo paracentesis with proper selection of the puncture site (see “Procedure”).