Some authors recommend using a needle insertion site in the midline,¹ whereas others advocate a left lower quadrant insertion site.^4,6 Paracentesis has also been successfully performed via a right lower quadrant or infraumbilical insertion site. Regardless, percussion should be utilized to help select the most appropriate site. If it is difficult to localize the area of dullness with percussion, ultrasound should be employed to help guide the site selection. In modern intensive care units and surgical floors, the liberal use and wide availability of ultrasound should facilitate its routine use in this setting as well.

A variety of metal needles have been used to perform routine paracentesis, typically ranging in size from 16 to 22 gauge.^1,4 Although in an average-sized patient, a 1.5-inch (3.8-cm) needle is generally sufficient, for obese patients, a 3.5-inch (8.9-cm) needle may be necessary to successfully penetrate the pannus. For large-volume paracentesis, other options include multiple-hole blunt cannulas with sharp removable inner trocars⁸ or a 10-Fr Teflon peritoneal dialysis catheter, which can be connected to a Foley bag and drained to gravity.⁶

The bowel, bladder, and pregnant uterus are the anatomic obstacles most commonly encountered when performing paracentesis (Fig. 12-1). Whereas under normal circumstances, the intestine tends to float away from the advancing paracentesis needle, the presence of adhesions or other anatomic impediments can prevent this from occurring. The bladder is more likely to be breached in cases of neurogenic bladder or other causes of distention. An abnormal position of abdominal structures could lead to a failed attempt to localize fluid or a more difficult needle placement. It could also lead the operator to inadvertently traverse adjacent organs or structures, potentially leading to further complications. In one large series of diagnostic paracenteses, two bowel perforations were reported.⁹