Ultrasound devices that only focus on determining the volume of residual urine are also available on the market. They are able to perform the measurement accurately enough, but a regular ultrasonic device provides significantly more information, which is why using the latter is recommended.
Urinary retention (obstruction to urinary outflow or anuria?)
Increased serum creatinine (to rule out obstruction)
Ensuring that the bladder is sufficiently empty before removing a percutaneous cystostomy.
The tube is kept closed for at least 4 hours, and the residual urine is measured after the patient has voided urine the natural way. The residual urine volume should be under 200 ml.
Techniques
The patient voids.
Keep the ultrasonography probe in a transverse position and find a view that shows the bladder in its maximum size. Freeze the view and measure the horizontal (a) and vertical (b) dimensions of the bladder.
Move the probe to a longitudinal position, find the maximum longitudinal dimension (c) of the bladder and measure it.
The (minimum estimate of) residual urine volume = 0.6 × width × height × length. If the dimensions are given in cm, the result is in ml. See pictures F1 and F2.
A volume exceeding 100 ml is abnormal, a volume exceeding 200 ml is usually an indication of pharmacological treatment in male patients, and a volume exceeding 500 ml even in long-term retention is an indication for percutaneous cystostomy or catheterization.
If you intend to determine the position and depth of the bladder before bladder puncture (video Urine Aspiration Sampling in a Child) or percutaneous cystostomy (video Suprapubic Cystostomy), do not ask the patient to void, but perform ultrasonography with a full bladder.