Accuracy of peritoneal fluid measurements by transvaginal ultrasonography

To assess the accuracy of the assessment of peritoneal fluid volumes of up to 1 L by transvaginal ultrasonography and to re-evaluate the formula used to calculate total volume from the dimensions of the largest pocket.

Patients (n = 13) enrolled for a minor laparoscopic procedure were prospectively recruited. At the end of the procedure, with the patient in the 30 degrees anti-Trendelenburg position, Ringer's lactate was instilled into the abdomen in discrete steps up to 1 L. Following equilibration the diameters of the single pocket of fluid were measured by transvaginal ultrasonography in order to calculate the volume, and regression models were used to determine the relationship between this and the instilled volume. The body mass index (BMI) of the patient was evaluated as a parameter for predicting the instilled volume more accurately.

The intra-abdominal fluid volume could be calculated from the measured volume using a quadratic regression equation with an overall coefficient of variation of 19%. In individual patients, changes in volume could be assessed with a coefficient of variation of 7.3%. BMI was not found to be a significant parameter in relating the measured to the instilled volume.

Transvaginal ultrasound in a standardized setting can accurately estimate the volume of peritoneal fluid, with the accuracy consistent for small and large volumes. Changes in peritoneal fluid volume over time in the same individual can be measured more accurately than the total volume present.