Non-invasive bladder volume measurement for the prevention of postoperative urinary retention: validation of two ultrasound devices in a clinical setting

Ultrasound scanning of bladder volume is used for prevention of postoperative urinary retention (POUR). Accurate assessment of bladder volume is needed to allow clinical decision-making regarding the need for postoperative catheterization. Two commonly used ultrasound devices, the BladderScan (R) BVI 9400 and the newly released Prime (R) (Verathon Medical (R), Bothell, WA, USA), with or without the pre-scan' option, have not been validated in clinical practice. The aim of this study was to assess the performance of these devices in daily clinical practice. Between June and September 2016 a prospective observational study was conducted in 318 surgical patients (18years or older) who needed a urinary catheter perioperatively for clinical reasons. For acceptable performance, we required that the volume as estimated by the BladderScan (R) differs by no more than 5% from the actual urine volume after catheterization. The Schuirmann's two one-sided test was performed to assess equivalence between the BladderScan (R) estimate and catheterization. The BVI 9400 (R) overestimated the actual bladder volume by +17.5% (95% CI +8.8 to +26.3%). The Prime (R) without pre-scan underestimated by -4.1% (95% CI -8.8 to +0.5%) and the Prime (R) with pre-scan underestimated by -6.3% (95% CI -11.6 to -1.1%). This study shows that while both ultrasound devices were able to approximate current bladder volume, both BVI 9400 (R) and Prime (R) with and without pre-scanwere not able to measure the actual bladder volume within our predefined limit of +/- 5%. Using the pre-scan feature of the Prime (R) did not further improve accuracy.