Indications: Determination of residual urine.
Measurement: Calculate bladder volume using the formula for an ellipsoid (see below).
x Have the patient empty the bladder completely.
x Measure the residual urine volume sonographically using the formula (Fig. 69):
volume (mL) = width (cm) q depth (cm) q length (cm) q 0.5.
a Measurement in transverse section. W = width, D = depth.
b Measurement in sagittal section. L = length
x A residual urine volume I 50mL is still within the normal range.
x Bear in mind that the residual urine values calculated for small volumes are too
large, and that those calculated for large volumes are too small.