Validation of an ultrasound scanner for determing urinary volumes in surgical patients and volunteers

Objective. As bladder distension related to anaesthesia puts patients at risk for permanent dysfunction, perioperative determination of bladder volume is of great importance. The aim of this study is to validate an ultrasonic imaging device for determing bladder urine volume. Method.To evaluate a broad volume range, ultrasonically scanned volumes were compared to true urinary volumes both in surgical patients and in volunteers. After institutional approval and informed consent 60 healthy volunteers were asked not to void for as long as possible. After ultrasound measurements (BladderScan BVI 2500, Diagnostic Ultrasound, Redmond WA, U.S.A.) they voided and true urinary volumes were measured. Fifty surgical patients scheduled for procedures requiring urinary catheterisation were studied. Pre- and post-induction of anaesthesia ultrasound measurements were recorded, followed by urinary catheterisation and measurement of true urinary volume. Urine volumes were compared using Student t-tests and Wilcoxon Rank Tests (p <0.05). For validation linear regression was used together with Bland-Altman analyses. Results. Ultrasonic scanning underestimated the true urine volume by about 7% over the whole volume range (17 ml to 970 ml). Underestimation was larger in females than in males (p <0.02). R-2 values for correlation of measured and scanned urinary volumes ranged between 0.92 and 0.95. Bland and Altman analyses showed a bias of 31 ml in volunteers and of 19 ml in patients and a precision of 110 ml and 80 ml, respectively. Conclusions. The ultrasonic imaging device can be used peri-operatively to establish bladder volume, taking into account the 7% underestimation of the bladder volume.