Bladder volume ultrasound is a non-invasive imaging technique that uses sound waves to create images of the bladder, allowing for the calculation of its volume. It is a valuable method for evaluating bladder function and assessing the quantity of urine it holds.
Performing the Ultrasound Scan
To perform a bladder ultrasound, patients are advised to arrive with a full or partially full bladder, as fluid enhances visibility. Once positioned comfortably, a trained professional applies ultrasound gel to the lower abdomen, just above the pubic bone. A handheld transducer, which emits and receives sound waves, is then gently pressed onto the gel-covered skin and moved in various directions. This allows the operator to visualize the bladder from different angles, capturing images for measurement.
Obtaining Key Measurements
From the acquired ultrasound images, specific dimensions of the bladder are measured to determine its volume, including the maximum length, width, and depth. The length refers to the superior-inferior dimension, extending from the bladder’s dome (top) to its base (bottom). The width, or transverse measurement, is taken from one side of the bladder wall to the opposite side. The depth, also known as the anterior-posterior measurement, spans from the front to the back wall of the bladder. These dimensions are captured from the largest observable points in their respective planes.
Applying Calculation Formulas
The most common method for calculating bladder volume from these measurements utilizes the ellipsoid model. This formula is expressed as Length x Width x Depth x a constant, often 0.523 or 0.5. The constant is included because the bladder’s shape is approximated as an ellipsoid, a three-dimensional oval. While variations exist, automated calculations are often performed by modern ultrasound machines. For example, if a bladder measures 8 cm in length, 7 cm in width, and 6 cm in depth, the volume would be approximately 8 cm x 7 cm x 6 cm x 0.523, resulting in about 175.8 mL.
Understanding the Results
The calculated bladder volume provides important information for assessing bladder function. It is frequently used to determine post-void residual (PVR) volume, the amount of urine remaining in the bladder immediately after urination. This measurement helps evaluate bladder emptying efficiency and can indicate conditions like urinary retention. A PVR volume greater than 50 mL in adults under 65 years old or over 100 mL in those over 65 years old is considered elevated, with volumes over 200 mL suggesting inadequate emptying. Understanding these volumes assists healthcare providers in diagnosing issues such as urinary tract infections, bladder stones, or problems with bladder capacity.