Although most studies demonstrate high accuracy using transabdominal point-of-care ultrasound or bladder scanners with automated measurement of bladder volume, other recent studies have questioned the accuracy of these methods. ĭata on the accuracy of transabdominal ultrasound for determining the PVR is mixed. This method is recommended as the standard calculation because it is fast and easy. The bladder is measured at its maximal transverse (width), longitudinal (length), and anterior-posterior (height) diameters. The prolate ellipsoid formula has more than one acceptable correction factor. There are multiple mathematical methods to calculate volume, and the prolate ellipsoid formula below is one accepted method. The volumes can be calculated using the prolate ellipsoid formula if this function is unavailable. Most ultrasound machines have a function to automatically calculate volumes from the measurements used with the ultrasound calipers. The probe is then rotated 90 degrees to measure the width or axial dimension. ![]() Measurements are from the longest anteroposterior dimension and the craniocaudal dimension. The probe is inserted into the vagina, and bladder identification is in the sagittal plane. The patient should be supine with the legs in stirrups or a pad under the pelvis. Ensure the probe is clean, has a probe cover, and has gel placed onto the end of the probe. įor transvaginal bladder volume evaluation, an intracavitary transvaginal probe with frequencies between 7 to 9 MHz is used. The greatest transverse (width), anteroposterior (depth), and superior-inferior (height) distances are recorded. Bladder images are recorded in both the sagittal and transverse planes. įor transabdominal bladder volume evaluation, the probe is placed over the suprapubic area while the patient is prone. Transvaginal ultrasound appears especially accurate for measuring low bladder volumes. The PVR is measured using the ultrasound machine's internal volume calculations or the mathematical equation below. Ĭonventional ultrasound is used to visualize the bladder directly, using either a transabdominal or transvaginal approach. Abdominal ascites may cause a falsely elevated measurement. ĭifferent bladder scanner machines may have slightly different procedures, but the basics of the technique are similar across devices.īladder scanning is unsuitable for patients with severe abdominal scarring, prolapse of the uterus, or if currently pregnant. The process can be repeated to optimally align the bladder in the center of the display. The result is displayed on a screen for the operator to see. A simple button is depressed, which initiates the examination of the bladder volume. The probe is placed on the gel and directed toward the bladder. With the patient supine, ultrasound gel is placed on the suprapubic area. The technique of PVR measurement using a bladder scanner is straightforward. The device is easily portable on a movable stand, and a single instrument can serve an entire office or department. However, the device must be calibrated periodically, and the initial financial outlay may be significant. Nevertheless, while moderately expensive, the device has proven cost-effective over time and facilitates patient care in primary care facilities and specialist offices. In addition, the technique is simple to learn and takes only a few minutes to perform. It is a simple, noninvasive approach to measuring the PVR and is usually the preferred approach when available. Portable Dedicated Bladder Ultrasound DeviceĪ portable dedicated bladder ultrasound device, commonly known as a bladder scanner, uses ultrasound to measure the three-dimensional volume of urine in the bladder. ![]() ![]() Urinary catheterization is the gold standard for measuring the PVR but is invasive and has several other disadvantages compared to ultrasound. Measurement of the PVR determines the quantity of urine remaining in the bladder shortly after a voluntary void this measurement can be obtained using a portable dedicated bladder scanner, a formal bladder ultrasound examination, or by directly measuring the urine volume via urinary catheterization. ![]() Measurement of the post-void residual volume (PVR) immediately after voiding is crucial for an accurate result, with delays of as little as 10 minutes from bladder emptying to PVR determination potentially causing clinically significant overestimation of the volume.
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