Ultrasound for the detection of intraperitoneal fluid: the role of Trendelenburg positioning.

A prospective, observational study was performed to evaluate the role of Trendelenburg positioning in improving the sensitivity of the single-view ultrasound examination. Hemodynamically stable patients undergoing diagnostic peritoneal lavage (DPL) were assigned to one of two groups: supine or 5 degrees of Trendelenburg positioning. Baseline right intercostal oblique images of Morison's pouch were obtained followed by additional images for each 100 cc of lavage fluid instilled into the peritoneal cavity. The initial volume of fluid required to identify an anechoic stripe was recorded for each patient. Patients were excluded if they had (1) a positive DPL for hemoperitoneum (defined as 10 cc of gross blood or >100,000 red blood cells/microL), (2) positive baseline ultrasound study, (3) hemodynamic instability, or (4) lack of documentation (ie, baseline/subsequent hard copy images were not obtained or inadequately demonstrated anechoic stripe). The mean quantity of fluid for visualization of the anechoic stripe was 443.8 cc in the Trendelenburg group (n = 8) and 668.2 cc in the supine group (n = 11). These means were statistically different (P < .05, t test). The median amount of fluid needed for visualization of the anechoic stripe was 400 cc and 700 cc for the Trendelenburg and supine groups, respectively.