Can we replace the catheter when evaluating urinary residuals?

To test the different formulae to calculate the bladder volume using ultrasound; the accuracy of patients hearing/feeling "bubbles" at the end of urodynamics testing as a measure of being empty; and how good we are at estimating PVR using X-ray at the end of video urodynamics testing.

This was a prospective cohort study. Using Sonosite 180 plus, bladder volumes were calculated as, height × width × depth × proportionality constant (0.52, 0.625, 0.65, and 0.7) Patients were asked whether the patient heard or felt "bubbles" at the end of the investigation. Each patient was fluoroscopically screened and the clinician estimated the volume and compared with single-use catheter volume.

A total of 85 patients were assessed. All four formulae were significantly correlated. The PC, 0.52, correlated best (r = 0.938, P < 0.001) with no significant difference with the actual volumes ( P = 0.275). The "bubbles test" had a positive predictive value of 93%. A video postvoid residual (PVR) estimation significantly correlated with catheterised bladder volume ( r = 0.842, P < 0.001). There was no significant difference between the estimated and actual bladder volumes ( P = 0.579).

This study showed that although all four formulae correlated significantly, the PC of 0.52 was the only formula without a significant difference from the actual volume. More work is needed to produce patient individualised PC. Our clinicians were able to accurately estimate the PVR on X-ray. This study has identified the best formula to accurately estimate bladder volume and that video estimation along with the "bubbles" test can avoid unnecessary intervention.