A bench model was created to measure and analyze pressures in a simulated
bladder and an actual urine drainage system. Fluid-filled dependent (generally
U-shaped) loops in the urine drainage tubing generated back-pressure (in units
of cm H2
O), directly related to the difference in fluid meniscus heights (in units of
cm) across the dependent loop that interfered with emptying of the simulated
bladder. If the results obtained with a simulated bladder occur in actual bladders
with indwelling urinary catheters, retained urine volume (that can promote urinary
tract infection) will increase with larger differences in meniscus heights across the
dependent loop due to increased back-pressure. Dependent loops in urine
drainage tubing should be avoided. If the dependent loops cannot be avoided or
a configuration without dependent loops cannot be maintained, they should be
routinely emptied of urine, especially if the bag-side meniscus is higher than the
bladder-side meniscus.