Can the smallest depth of ascitic fluid on sonograms predict the amount of drainable fluid?

PURPOSE: To investigate the correlation between the 'smallest fluid depth' (SFD) measured on sonography (US) at the 'paracentesis pocket' with the amount of fluid drained in patients referred for US-guided large-volume paracentesis.

METHODS: US examinations performed to guide 60 paracenteses in 29 patients with large-volume ascites were reviewed and the SFD measured at the site of the paracentesis. The SFD was measured from the most superficial bowel loop to the abdominal wall. The SFD measurements were compared with the drained fluid volume (DFV) measurements.

RESULTS: The average DFV per paracentesis was 5.2 L with an average SFD measurement of 5.4 cm. For every 1-cm increase in the measured SFD, there was an average 1-L increase in the DFV. After applying this relationship to the measured depth in each case, the comparison between the estimated fluid volume (EFV) on US and the DFV demonstrated a <1-L difference in 38 of 60 paracenteses (63.3%) and a <2-L difference in 51 of 60 paracenteses (85%).

CONCLUSION: The SFD measured at the site of paracentesis shows a correlation with the drained fluid volume and can be used for fluid volume estimation on US.