SONOGRAPHIC ASSESSMENT OF POSTVOID RESIDUAL URINE VOLUMES: DISCUSSION
DISCUSSION
Significant postvoid residuals can result in symptoms of urinary frequency, nocturia, overflow incontinence, and recurrent urinary tract infections. Measurement of this residual volume is important to rule out both neurologic abnormalities and/or obstructive voiding disorders. In managing patients with prostatic gland enlargement, it is very useful in the initial assessment and monitoring of clinical progress.
With an increase in the scope of pharmacological treatment options in cases of such urinary problems, there is a growing need for a rapid and noninvasive as well as accurate evaluation. Over the years, residual urine has been measured by catheterization of the urethra, which is generally accepted as accurate. It, however, carries the risk of infection and trauma to the urethra. In the past three decades, ultrasonography has been an alternative method of evaluating the urinary bladder volume. Its accuracy has, however, remained contentious. Although several studies’ have been done using different types of scanners, clinical conditions, and subjects, controversies still exist over the accuracy of this method when compared with the traditional bladder catheterization. Orgaz et al. attributed the inaccuracy of some of the previous reports to the assumption that the urinary bladder has a fixed geometric shape. For instance, the bladder was assumed ellipsoid by Simpson. This assumption can only be true within a particular range of bladder volume, as the shape changes with the volume. Since the urinary bladder is not a rigid, hollow viscus and is surrounded by other pelvic structures that may limit its expansion in certain directions, we considered that an increase in size would lead to an increase in at least one out of the three dimensions. We therefore decided to use the average of the three dimensional measurements ({L+T+ Dl}/3). A review of the literature further showed that efforts at deriving a simple empirical formula not based on geometric shape resulted in wider range of errors. Our formula—[PVRCUBIC =374.057+(-196.94+Vl)+(32.5539+Vl2)+(-1.1480 +V13) where Vl=average of the length (L), width (T), and depth (Dt) of the postvoid urinary bladder]—which does not describe any known measurement or geometrical figure but seems highly accurate in the calculation of bladder volume, was obtained by cubic regression analysis. This yielded the most accurate PVR measurements by a portable general-purpose ultrasound machine to date when compared with previous studies. We attribute these results to a dynamic three-dimensional vol-umetry rather than a fixed geometric formula. canadian pharmacy viagra
Our equation, though complex, is most accurate over a wider range of bladder volume than any of the pre-existing formulas, and can be integrated into the memory of modern ultrasound machines for easy and faster computation. Hence, we consider conventional transabdominal ultrasonography a reliable, safe, and rapid method for assessing the residual urine volume in patients with benign prostatic hyperplasia. With an increase in demand for pharmacological treatment for benign prostatic enlargement, this examination can be repeated as often as necessary as an office-based procedure to monitor progress of treatment without the risk of trauma or infection to the urinary tract.
