Clinical evaluation of a novel ultrasound-based bladder volume monitor

Objective. Bladder volume monitors may be useful for surveillance of bladder volume and urine production in urologic patients. Therefore, we designed an ultrasonic bladder volume monitor and evaluated it in vitro using phantoms and in vivo in one male volunteer. The purpose of this study was to perform a more thorough in vivo evaluation of our monitor in urologic patients to investigate biological effects and variance over a wide range of bladder volumes. Material and methods. Thirty urologic patients of either gender were examined using the bladder volume monitor, which is based on seven phased array ultrasonic transducers arranged in a circular pattern to optimize detection of the bladder walls. The monitor was set up to record bladder volume every 30 s during two sequential cystometries with infusion rates of 30 and 60 ml/ min. The measured volumes were analyzed using regression analysis to determine volume increments ( slopes), offset volume ( intercept) and correlation ( Pearson's correlation coefficient). Results. In the male patients, the median correlation coefficient between the infused and measured volumes was 0.97 and the slope was 0.68 ml/ ml, thus warranting a correction factor of approximate to 1.47 with no general volume offset. In the female patients, small bladders were generally outside the field of view of the monitor. Consequently, the correlation coefficients and slopes were 0.834 ( median) and 0.43 ( mean), respectively, whereas volume offsets were generally negative. Conclusions. For examinations in male patients, the performance of the bladder volume monitor was adequate. However, for examinations in female patients, a minor redesign of the transducer unit is necessary to insure proper operation.