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 × a × b × c. If the dimensions are given in cm, the result is in ml. This 93-year old man had a large residual of 0.6 × 10.7 × 11.1 × 14.6 = 1040 ml. The retention was caused by prostatic carcinoma that obstructed the urethra. The patient had hydronephrosis and hydroureter (video ). The patient was treated with long-term suprapubic cystostomy (video ).
Residual urine volume (ultrasonography)