How to Use Radial Shock Waves to Remove Bladder Uroliths Through a Perineal Urethrotomy

1. Introduction

Uroliths can be found throughout the urogenital tract of the horse [1,2]. Clinical signs that are caused by the urolith are based on its location, although hematuria can be seen when a urolith is in any location throughout the urinary tract. Colic is seen when uroliths are in the kidney, ureter, and urethra. Urine scalding and dribbling, as well as tenesmus and frequent posturing to urinate, are the result of irritation and partial urinary obstruction caused by uroliths in the bladder and urethra. A loss of body condition is occasionally detected in horses with uroliths [1].

Uroliths can form in adult horses of all genders, but they are most commonly detected in aged geldings. The etiology of urinary calculi is not clear, but it is in part caused by the alkaline pH and high concentration of calcium in equine urine. The diagnosis of urolithiasis in the bladder can be made by rectal palpation, ultrasonography, and cystoscopy (Fig. 1) [1].

Figure 1. Urolith in the bladder.

Surgical removal of uroliths is the only suitable therapy, because medical treatments, including dietary management, are not successful. Most equine uroliths are detected when in the bladder, and although there are some challenges, urolith removal is easiest in this location. The two approaches to a bladder urolith are a suprapubic celiotomy and a perineal urethrotomy [2,3]. The celiotomy also requires a cystotomy, and exposure of the bladder and urolith can be difficult. The perineal approach results in a small opening in the urinary tract; therefore, the urolith must be reduced in size for removal.

Historically, crushing of human uroliths has been accomplished using a lithotrite, but currently, it is more commonly accomplished by laser, electrohydraulic, or ultrasonic methods. Equine uroliths are usually crushed using a lithotrite or a mallet and chisel. Both methods are time consuming and usually result in significant urethral trauma, occasionally resulting in life-threatening complications [1]. Although laser disruption of equine uroliths has been reported [4,5], the lack of access to specialized equipment results in a search for more accessible methods. Because many equine practices now have access to shockwave therapy for the treatment of musculoskeletal disorders, this paper will discuss the use of radial shock waves to break up equine bladder uroliths through a perineal urethrotomy.

2. Technique

This procedure is performed under general anesthesia in left lateral recumbency (the procedure will be described for a right-handed surgeon). Pre-surgical medication consists of flunixin meglumine (1 mg/kg, IV) and trimethoprim-sulfadiazine (20 mg/kg, PO). For geldings, a routine perineal urethrotomy is used to approach the urolith. For mares, the large diameter of the urethra requires no surgical approach. Removing bladder uroliths through a perineal urethrotomy is not recommended for breeding stallions because of the possibility of inducing urethral damage that may compromise breeding ability.

After the perineal urethrotomy is performed, the urolith is grasped using the left hand that is introduced per rectum. The shock waves are generated by the Swiss DolorClast Vet [a], which consisting of a control unit and a pneumatic compressor; the shock waves are unfocused. A purpose-designed 6-mm-diameter, 42-cm-long applicator (Fig. 2) is soaked in disinfectant [b] and fitted to the hand piece to transmit the shock wave to the urolith.

Figure 2. Purpose-designed probe for urolith destruction.

To maintain sterility of the surgeon's right hand, a sterile rectal sleeve can be placed over the hand piece; the applicator can be brought out of a hole cut in the glove end. The end of the probe is positioned on the urolith using the hand in the rectum for guidance (Fig. 3). Moderate pressure is used to establish good applicator-urolith contact. The pressure settings for the machine is 4 bar, and the frequency is 15 Hz. The hand piece is activated on one site of the urolith until it breaks along the site of contact. Shock waves are used to break up all large (>2 cm) pieces of the urolith. Small pieces of urolith are flushed from the bladder using a 15-mm rigid thin-walled polypropylene tube fashioned from an IV catheter container as a conduit (Fig. 4). Delivery of sterile flushing fluid can be accomplished by either hand or mechanical pumping. Large pieces of the urolith (up to 2 cm in width) can be removed through the urethrotomy using a sponge forceps. After removal of all palpable pieces of urolith, the bladder is copiously flushed with sterile saline to remove any small pieces of urolith and blood clots. The perineal urethrotomy is left to heal by second intention. Systemic antibiotic and anti-inflammatories are continued at the surgeon's discretion but usually for <5 days. Exercise can be resumed in several days if recovery is uncomplicated.

Figure 3. Hand piece with probe attached that is delivering a shock wave to the urolith. The surgeon's left hand is grasping the stone at the rectum.

Figure 4. Flushing small pieces of urolith from bladder using a polypropylene conduit.

3. Horses

Four geldings (ages 6 - 26 yr) have had bladder uroliths (largest dimension ranging from 8 to 12 cm) removed through a perineal approach after disruption using shock waves. The length of time for disruption of each urolith was 5 - 10 min, and the entire procedure ranged from 45 to 90 min. Although the number of shock waves required to disrupt the urolith varied with the size and density, the absolute number of shock waves was ~10,000. Post-operative complications included self-limiting hematuria in all horses and moderate radial neuropraxia in one horse that responded to therapy. No recurrence has been reported.

4. Conclusions

Bladder urolith disruption (Fig. 5) is quickly and easily accomplished using unfocused shock waves transmitted through a perineal urethrostomy using a 42 x 6-mm applicator. This method is superior to other methods of physical destruction of uroliths, because the urolith can be reduced into small fragments and no crushing instruments need to be introduced into the bladder. Uroliths of at least 12 cm can be disrupted (we believe there is no upper size limit), and the pieces of the urolith are removed from the bladder using sponge forceps or flushed using large fluid volumes. Some trauma to the urethra using this method is expected because of the rough surface of the urolith and the sharp surfaces generated by disruption, but it is less than that caused by other methods.

Figure 5. Bladder stone after shock wave destruction.

Footnotes

1. EMS Corporation, Dallas, TX 75243.
2. Nolvasan, Fort Dodge Animal Health, Fort Dodge, IA 50501.