Safer urethral catheters: how study of catheter balloon pressure and force can guide design

To better define urethral catheter balloon pressures and extraction forces during traumatic placement and removal of urethral catheters. To help guide design for safer urethral catheters.

Measurements of balloon pressure were made upon filling within the urethra vs the bladder. Extraction forces were measured upon removal of a catheter with a filled balloon from the bladder. Models for the bladder and urethra included an ex vivo model (funnel, 'bladder', attached to a 30 F tube, 'urethra') and fresh human male cadavers. The mean (SEM) balloon pressures and extraction forces were calculated.

In the ex vivo model, the mean (SEM) pressures upon filling the balloon with 10 mL were on average three-times higher within the ex vivo'urethra' (177 [6] kPa) vs 'bladder' (59 [2] kPa) across multiple catheter types. In the human cadaver, the mean balloon pressure was 1.9-times higher within the urethra (139 [11] kPa) vs bladder (68 [4] kPa). Balloon pressure increased non-linearly during intraurethral filling of both models, resulting in either balloon rupture (silicone catheters) or 'ballooning' of the neck of the balloon filling port (latex catheters). Removal of a filled balloon per the ex vivo model 'urethra' and cadaveric urethra, similarly required increasing force with greater balloon fill volumes (e.g. 9.34 [0.44] N for 5 mL vs 41.37 [8.01] N for 10 mL balloon volume).

Iatrogenic complications from improper urethral catheter use is common. Catheter balloon pressures and manual extraction forces associated with urethral injury are significantly greater than those found with normal use. The differences in pressure and force may be incorporated into a safer urethral catheter design, which may significantly reduce iatrogenic urethral injury associated with catheterization.