Practical urology techniques

Retrograde urohydropropulsion

Nonsurgical stone removal: voiding urohydropropulsion

Until recently, most uroliths in the urinary bladder were either medically dissolved or surgically removed. However, at the University of Minnesota, we developed a new technique to remove urocystoliths, called voiding urohydropropulsion (table 1). By taking advantage of the effect of gravity on urolith position in the urinary bladder and dilation of the urethral lumen during the voiding phase of micturition, this simple technique allows uroliths to be rapidly flushed out of the urinary tract.

Over the past 5 years, voiding urohydropropulsion has been used to remove uroliths in over 100 dogs. We have found voiding urohydropropulsion to be an effective and safe method to remove small to moderately sized urocystoliths of any mineral composition. What follows are answers to the questions that we believe are most important to effectively perform voiding urohydropropulsion in your patient.

How can I determine what size of urolith can be voided?

Proper selection of patients for voiding urohydropropulsion will enhance removal of urocystoliths. The relationship of the size, shape, and surface contour of urocystoliths to the luminal diameter of the urethra are important factors. Uroliths that are larger than the smallest diameter of any portion of the distended urethral lumen are unlikely to be voided. In our clinical experience, diameters of the largest uroliths expelled from the urinary bladder were 7 mm from a 7.4 kg female dog, 5 mm from a 9 kg male dog, 5 mm from a 4.6 kg female cat, and 1 mm from a 6.6 kg male cat. It is logical to hypothesize that uroliths greater than 1 mm in diameter could be voided from a male cat with a perineal urethrostomy. As a guideline, we assume that smooth uroliths, less than 5 mm in diameter can be removed by voiding urohydropropulsion in any dog weighing more than 18 pounds.

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