Dr David Grant
Although it is relatively easy to access a mare's bladder, it is harder in geldings because of the length of the urethra.
In the past, it has been necessary to open into the urethra below the anus to gain access to gelding's urethra.
But using an endoscope to transmit the laser beam means that the procedure can be carried out without the need for epidural or local analgesia.
An optical fibre is passed through the biopsy channel of the endoscope. This is used to direct the laser beam on to the bladder stone.
The surgeon sweeps the fibre across the surface of the stone to produce a crater or groove until eventually a fragment breaks off. This process is repeated as many times as necessary until the remaining pieces of stone are small enough to pass out through the urethra.
Larger fragments are removed by grasping them with a wire basket passed through the endoscope. Smaller fragments are flushed out.
The clinicians make sure they can always see the tip of the optical fibre when the laser is activated so as to prevent it coming in contact with the bladder wall and causing accidental damage.
The report, published in the Journal of Veterinary Internal Medicine, carries details of seven cases of urinary calculi that were treated using laser lithotripsy.
In all cases, the procedure was performed by Dr David Grant, of the Virginia-Maryland Regional College of Veterinary Medicine.
Successful cases took 101 to 150 minutes to complete.
All stones in this series of cases were composed of calcium carbonate.
There were no serious complications directly related to the laser lithotripsy procedure. Two horses had small burns of the inner lining of the bladder. These were superficial, and did not cause detectable signs.
On one occasion, the tip of the optical fibre broke off and had to be retrieved from within the bladder using forceps passed through the endoscope's biopsy channel.
The procedure was not successful in two cases. The authors suggest that if no progress is made within the first 30 minutes, the case will have to be managed by other means.
"Uroliths (stones) in which only small pieces can be dislodged or in which only holes can be made in the surface of the urolith - are not suitable for management by laser lithotripsy."
The technique was successful for removing all stones and fragments in five of seven cases.
The authors concluded that laser lithotripsy, combined with lavage and retrieval of larger fragments using the endoscope, was a safe procedure.