A bladder scanner is a handheld, non-invasive ultrasound device designed to quickly estimate the volume of fluid within the urinary bladder. This portable technology uses sound waves to create a three-dimensional image, which it then processes using an internal algorithm to calculate the total fluid volume. Its primary clinical application is measuring Post-Void Residual (PVR) volume, which is the amount of urine remaining in the bladder immediately after a person has attempted to empty it.
Preparing the Patient and Device
Before initiating the scan, proper preparation of the patient and device is necessary to ensure an accurate reading. The patient should be positioned comfortably, ideally lying flat on their back (supine), which helps the bladder settle and provides better access for the probe. The lower abdomen must be fully exposed from the navel down to the pubic bone, and the patient should relax their abdominal muscles.
The scanner requires specific configuration before use, particularly regarding gender settings. Many devices include distinct modes for male, female, or female with a hysterectomy, as these variables affect the internal algorithm used to calculate volume. Selecting the correct mode is important to ensure the final reading is accurate. Finally, a small amount of ultrasound gel must be applied to the lower abdomen, typically about one inch above the pubic bone, to facilitate the transmission of sound waves.
Step-by-Step Scanning Procedure
With the patient prepared, the transducer (probe) should be placed directly onto the gelled skin in the midline of the lower abdomen, positioned just above the pubic bone. The device must be aimed slightly downward toward the tailbone, directing the ultrasound beam into the pelvic cavity where the bladder is situated. Maintaining firm but gentle contact with the skin ensures optimal transmission of the sound waves.
Once the probe is in place, the operator must focus on the scanner’s display screen to locate the bladder structure. The bladder typically appears as a dark, fluid-filled oval or round shape. Most modern scanners feature a target reticle, which must be centered over the largest diameter of this dark area to achieve the most accurate measurement.
Adjustments to the probe’s angle are often necessary to maximize the bladder image on the screen. This involves gently rocking, or “fanning,” the probe side-to-side and tilting it slightly up or down until the dark bladder shape fully encompasses the targeted area. The goal is to capture the entire organ within the ultrasound view, avoiding shadows or partial views that would lead to an underestimation of the volume.
After the bladder has been successfully centered within the reticle, the operator presses the designated scan or measure button. The scanner automatically calculates the volume based on the three-dimensional data it collects. The final calculated volume, usually displayed in milliliters (mL), appears on the screen within a few seconds. If the initial reading is unusually low or inconsistent with the visual image, the device should be reset, the probe slightly repositioned, and the procedure repeated to confirm the result.
Interpreting the Scan Results
The final numerical reading displayed on the scanner represents the Post-Void Residual volume in milliliters (mL). This measurement provides an objective indicator of bladder emptying efficiency. A PVR value under 50 mL is generally considered acceptable in adults, indicating efficient emptying.
Readings between 50 mL and 100 mL may warrant closer monitoring. A PVR reading consistently greater than 100 mL, particularly in older adults, is viewed as abnormal and indicates an underlying issue with bladder function. These elevated volumes suggest incomplete bladder emptying, a condition known as urinary retention, which can predispose a person to urinary tract infections.
Significant urinary retention, often defined as volumes exceeding 200 mL, can be a symptom of conditions like benign prostatic hyperplasia (BPH) in men, neurogenic bladder disorders, or certain medications. The presence of a high PVR volume signals the need for further diagnostic evaluation to determine the cause of the retention. The PVR measurement helps healthcare providers decide on appropriate management, which can range from lifestyle changes to medication or catheterization.