A bladder scanner is a specialized, portable ultrasound device used by healthcare professionals to quickly and non-invasively estimate the volume of urine inside a patient’s bladder. This diagnostic tool provides an objective measurement, typically expressed in milliliters, replacing older, less reliable methods like physical palpation. The primary function of the scanner is to assess how well the bladder is emptying and to determine if an abnormally large volume of urine is being retained. Because the procedure relies on harmless sound waves rather than radiation, it is a safe and efficient way to gather immediate data at the patient’s bedside.
How the Scanner Measures Volume
The bladder scanner operates using the principles of ultrasound technology, which involves transmitting high-frequency sound waves into the body through the lower abdomen. These sound waves travel through the tissues until they encounter a boundary, such as the wall of the fluid-filled bladder, and reflect back to the device’s handheld probe as echoes. The probe contains piezoelectric crystals that convert these returning sound waves into electrical signals. The device’s internal computer processes the time and strength of the echoes to determine the size and shape of the bladder. Algorithms then translate these dimensions into a calculated volume reading, usually in milliliters.
Key Clinical Reasons for Use
The most common clinical application of the bladder scanner is the measurement of Post-Void Residual (PVR) volume. PVR refers to the amount of urine that remains in the bladder immediately after a patient has attempted to void completely. An elevated PVR volume suggests that the bladder is not emptying effectively, which can be an early sign of a urinary tract issue.
Measuring PVR is a primary method for diagnosing urinary retention, a condition where urine is unable to leave the bladder fully. While a PVR volume under 100 milliliters is typically considered normal, a measurement exceeding 200 milliliters often indicates inadequate emptying and may require intervention. Urinary retention can be caused by various factors, including mechanical blockages like an enlarged prostate, nerve dysfunction, or certain medications.
The data provided by the scanner also helps prevent unnecessary invasive procedures. By confirming that a patient’s bladder is empty, healthcare providers can avoid inserting a urinary catheter solely for diagnostic purposes. Catheterization, while sometimes necessary, carries risks such as discomfort and the potential for introducing infection, specifically Catheter-Associated Urinary Tract Infections (CAUTIs).
Bladder scanning is also frequently used to monitor bladder function in patients with specific risk factors. This includes individuals recovering from surgery, those with neurological conditions like multiple sclerosis or spinal cord injury, and patients who are experiencing incontinence or a frequent urge to urinate. Consistent high PVR volumes can lead to chronic bladder overstretching, which may cause long-term damage to the bladder muscle or contribute to kidney problems.
What to Expect During a Bladder Scan
The procedure itself is straightforward, comfortable, and takes only a few minutes to complete. The patient is typically asked to lie down in a relaxed position, exposing the lower abdomen. Minimal preparation is usually required, though for a PVR measurement, the scan must be performed shortly after the patient has tried to urinate.
A small amount of clear, water-based gel is applied to the skin over the lower stomach, just above the pubic bone. This gel enhances the transmission of the sound waves from the handheld probe into the body. The healthcare provider then gently moves the probe over the area, aiming it toward the bladder.
The device displays the calculated volume on a screen almost immediately, and the patient feels no pain or sensation from the sound waves. Once the measurement is complete, the excess gel is simply wiped away.