URINE-UREA EXCHANGE PROCEDURE FOR URINARY BLADDER RESIDUAL VOLUME DETERMINATION

In some children, small residual bladder volumes may predispose to urinary tract infections but current methods for determining small residual urine volumes are relatively inaccurate and impractical. A urine-urea exchange procedure was developed to determine full-bladder volume prior to voiding. Subtracting the volume voided from the full-bladder volume gives the residual volume. This procedure consists of injecting suprapubically a small volume of concentrated urea solution, and measuring the increase in osmolality; the larger the urine volume prior to the injection, the smaller will be the increase in urine osmolality following the injection. A mathematical error analysis to determine the overall statistical standard deviation of the full-bladder volume, the voided volume and the residual volume showed the standard deviation of each to be 0.929cc, 0.401cc and 1.33cc, respectively. With trials, using an in vitro laboratory model, the mean error of the full-bladder volume was 1.1cc and the mean error of the residual volume 1.14cc. In vivo dog experiments confirmed that the procedure is safe and practical. Clinical trials have been started.