Sacral Nerve Stimulation (Interstim™)
Sacral Nerve Stimulation, also known as Interstim™ is a technology developed by Medtronic,Inc for the treatment of overactive bladder, urge incontinence, and incomplete bladder emptying. It is approved by the FDA, and is safe and effective. It is used for patients who have failed conventional medical treatments for these conditions. The Sacrum is the lowest part of the spine, and has holes on both sides that nerves pass through. The spinal cord is not involved in this process. The object of the treatment is to electrically stimulate the nerve passing through the 3rd hole in the Sacrum, also known as the S-3 foramen. Stimulation with a low level pulse of electrical current blocks abnormal signals to the bladder, and seems to "reset" bladder function. The mechanism of this is not completely understood, but it has proven efficacy in approximately 75% of patients selected for the therapy.
The process begins with an investigation of the urinary tract to make sure there are no other conditions that may affect the results of the treatment, such as obstruction of the urinary tract, infection, stress incontinence, or high-pressure bladder. This is accomplished by office tests such as urinalysis, urodynamic studies, cystoscopy and a thorough physical exam. Once any confounding factors have been eliminated, a test stimulation is performed in the office.
The test stimulation takes usually 20 minutes to an hour to perform. It involves the patient lying on a table in the prone position, with the buttocks and feet exposed. The skin and tissues overlying the S-3 foramen are anesthetized with a local anesthetic, and a needle is placed into the foramen when it is found. Once the foramen is entered with the needle, electrical stimulation is applied and certain reflexes are sought. These are flexion of the large toe, movement of the muscles around the anal sphincter, and a feeling of pulsation in the vagina/penis and or rectum. The presence of these reflexes establishes that the needle is in the proper location. Once in proper position, a thin electrical lead(wire) is placed through the needle, and the needle is withdrawn. The wire is secured, and the same process is repeated on the other side of the sacrum. When both leads are in, the patient gets dressed and one of the leads is plugged into a battery-powered stimulation device. A voiding diary is given to the patient so we can assess the results, and the patient can control the level of stimulation at home by adjusting the energy levels. Both leads are tested at home over the next 7 days.After the trial period, the electrical leads are simply pulled out in the office and the response is assessed. If no change was noted with stimulation, no further action is taken. If the test stimulation was unsuccessful due to leads falling out, or the patient thinks there may have been a benefit but isn't totally sure, a "Stage I" implantation may be used. If a definite benefit was shown due to the electrical stimulation, the patient often decides to proceed to implantation of the generator, which is essentially a pacemaker for the bladder.
The generator implantation is the final and permanent part of the process. This is performed in the operating room under IV sedation with local anesthesia. The leads that are placed in this situation have teeth known as "tines" that hold the lead in place securely. Only one side of the sacrum receives a lead. This is then connected to the pacemaker, which is placed into a small pocket made in the buttock. Everything is now inside, and the patient can control the energy level with a remote that is placed over the region of the generator. The battery life is 5-7 years for the older model generator, which is the larger device. The smaller, newer device has a battery life of 3-5 years.
The risks of these procedures are primarily bleeding and infection. All blood thinners and Aspirin products should be stopped 5-7 days before the procedure. The patient may undergo MRI if needed, but the unit should be turned off by the remote before the exam.