The volume of urine the bladder can be determined very easily with Point of care ultrasonography. Determining this can be very relevant when you are concerned that a restless patient near the end of life is restless because of urinary retention. Thus the focussed question being asked is:
Does the patient have a very full bladder?(I.e. is the patient in urinary retention?)
The bladder appears as an anechoic balloon in the suprapubic region. It is very easy for the human eye to tell the difference between ascites and a full bladder whereas a“bladder scanner” may misinterpret urine volume in the presence of ascites.
The bladder can be viewed initially in the transverse plane to measure the length across +/- depth back and then the sagittal plane to measure the height +/- depth back. A good approximation or urine volume for most people is:
Bladder volume(in ml) = length across(in cm) x depth back x height x 0.72
Images
Images measuring bladder volume:
Transverse bladder view using a Signostics RT
Sagittal bladder view of the same patient. Total urine volume of about 9.4 x 11.5 x 4.3 x 0.72 = 335ml
Miscellaneous bladder images:
Bladder ultrasound showing a large echo bladder cancer anteriorly
Technique
The structures to identify:
Bladder
The probe to use:
A 1-5 MHZ transducer
Technique
Place the probe in the midline directly above the pubic symphasis in the sagittal plane
Identify the bladder and measure the its height(z) by measuring across ways(horizontally)
Turn the probe 90 degrees into the transverse plane
Measure the length across(x) by measuring across ways(horizontally)
Measure the depth back(y) by measuring downwards(vertically)
There are various formulae the approximate the bladder volume such as the one noted above
Images
Technique
Resources