To Charge or Not To Charge…
Over more than 20 years, Sacral Neuromodulation (SNM) has become one of the standard therapies for the treatment of refractory Overactive Bladder, Fecal Incontinence and Urinary Retention (when not caused by a blockage of the bladder). During that time, over 300,000 of these devices have been implanted. If you are not familiar with this therapy and want to learn more, visit our detailed page explaining its use in Overactive Bladder (OAB).
Perhaps, after discussion with your physician, you have decided that Sacral Neuromodulation therapy is right for you. But, you are still faced with additional choices. Since all patients do not respond to SNM therapy, you will need a test of the therapy before considering whether you want to have the device permanently implanted. There are two types of testing and you can decide which is best for you. Visit our Guide to SNM Choices for help in making that selection.
Rechargeable is Now an Option
Until relatively recently, that would have been the end of your choices. Sacral neuromodulators consist of two separate components. There is a lead which carries the stimulation signal to the target nerve. Connected to the lead is a generator (often just called a battery) which stores the energy and controls the signal. For most of their history, SNM batteries were not rechargeable. The battery was attached to the lead and slowly discharged over several years until it was replaced. Only the battery needed replacement and the existing lead remained in place. Today, rechargeable batteries are available. These new generators have advantages and disadvantages that may be more relevant to some people than others. The rechargeable devices are still a relatively new technology, so we have limited data to guide us as to which device is best for any individual person. But in this article, I will try to unpack some of what goes into deciding between recharge-free and rechargeable neuromodulation to try to help guide you to the best choice for you.
SNM Batteries Get Smaller
Rechargeable Generator
The evolution of SNM batteries over the last 20 years has progressed toward smaller battery size. The goal has been to create a more comfortable and less intrusive therapy. But there is a balance to strike because as battery size decreases, the capacity and the longevity of the battery decreases as well. Make a recharge-free battery small enough, and it won’t last long enough to be of much use. The application of recharge technology, first used in other medical devices, to sacral neuromodulators, eventually produced an ultra-small battery that can be useful for a very long time.
Rechargeable SNM generators are able to be quite small – the latest device is 80% smaller and 1/3 the weight of the current recharge-free device. The generator is less than 1 inch wide by 2 inches long. There are likely advantages to such a diminutive implant, though with such a short history we can’t know with certainty. Both types of SNM generators are buried in the fat of the buttocks to minimize discomfort. Most people won’t even notice either battery beneath their skin. But very thin patients may not have enough fat, even in their buttocks, to easily bury a standard SNM generator. For these patients, a very small device might decrease the risk of discomfort and reduce the noticeability of the SNM. I would like to note here that pain at the generator site is reported in only about 7% of patients, so the advantage of a small battery may not apply to most people. But, if you are very thin or have a history of pain from a previous or current neuromodulator, size may be an important consideration.
Is Smaller Always Better?
Could there be disadvantages to small size? Again, with a relatively short history to these rechargeable batteries, we can only make predictions and definitive evidence is hard to come by. However, it has been suggested that the small size might make these devices more difficult to locate. For obese patients, locating even the larger recharge-free device can be a challenge. But an advantage of the recharge-free generator in these patients is that they only need to locate their device occasionally, when they want to change a program or run a check on their device. Patients with rechargeable neuromodulators, however, will need to locate their devices much more frequently. This should not be an issue for most patients using rechargeable SNM. However, for those who may be obese, have limited use of their hands or have trouble reaching behind to where the device is located, this is a potential issue that should influence their decision.
Another potential problem might be somewhat surprising. Some patients have a tendency to move their generators below the skin. This is common enough to have a name and it’s called “Twiddler’s Syndrome”. This is a funny name for a not-so-funny problem because twisting the device like this can cause it to spin around and eventually break. It has been suggested that the smaller devices could be more likely to spin in these twiddlers. Though this is completely hypothetical, it is nonetheless interesting to consider.
How Long Do Rechargeables Last?
An important advantage for rechargeable devices is the longevity or life of the battery. Recharge-free devices eventually discharge and need to be replaced, though this can be done fairly easily under a local anesthetic. Current recharge-free devices are rated for a longevity of 5-6 years at standard patient settings. Rechargeable devices, on the other hand, can probably be used for 15 years or more. A limit for any rechargeable battery is fading. Think about your smartphone battery. Over hundreds of charging cycles, does it still hold a charge as well? It would be a real problem if your sacral neuromodulator generator had as much trouble holding a charge after a few years as your smartphone. The loss of recharge capacity of the battery over time is called cycle-fading. The most current SNM device, however, is essentially immune to cycle-fading because it does not use a traditional lithium-ion battery. The new rechargeable battery technology also appears to resist the loss of capacity that occurs over time and is independent of the number of charge cycles (called calendar fading). Thus, at its rated 15-year lifespan, the newest rechargeable devices are expected to show no decrease in their ability to recharge to their full capacity. The manufacturers make no specific claims beyond 15 years. However, it is possible that these new generators may continue to function adequately even beyond that predicted lifespan.
Recharge-free Longevity
Recharge-Free Generator
It is tempting to look at the battery life of rechargeable and recharge free devices and simply say that “rechargeable generators will last about three times longer”. But it is not obvious that the true lifespan of a recharge-free device is actually as short as 5-6 years. There are a couple of developments that may allow these devices to remain useful well beyond that range. As experienced implanters become better and better at lead placement (called lead optimization), the lead is placed closer to the nerve with more options for how we stimulate. With lead optimization, we are able to treat patients with lower and lower levels of energy. The less energy used to signal the nerve, the longer the battery will last.
The second reason why recharge-free generators may have utility beyond 5-6 years is suggested by recent studies on the amplitude or “volume” of stimulation. Traditionally, when adjusting the stimulation of the sacral neuromodulator in a patient, the amplitude was increased until patients were just able to feel the stimulation to the nerve. The point at which you first begin to sense the signal is called the sensory threshold. In the past, people were told to maintain their stimulation near the level of sensory threshold. But over the years it was noted that many people who did not feel a sense of nerve stimulation still had an acceptable response to therapy. The results of a recent clinical trial I was involved with suggest that, early in therapy, people who are stimulated at as little as half of sensory threshold still see similar benefits as those who have the therapy turned up to where they can feel it. If future studies confirm this finding over a longer time, it could lead to lower stimulation levels, considerably increasing the life of recharge-free batteries. Between improvements in how well we place leads and possible decreases in the necessary level for successful stimulation, we may find that even recharge-free SNM may last for many years.
Therapy Over Time
Whenever I discuss the longevity of rechargeable versus recharge-free devices with patients, I am always concerned that they may misinterpret battery longevity as meaning they are guaranteed to be free from any further surgery for at least 15 years. It is certainly fair to say that some patients who have placement of a rechargeable generator will experience successful therapy without a return to the operating room for 15 or more years. However, not all patients will see this benefit and it is probably also fair to say that the majority of patients will not be able to have satisfactory therapy for 15 years without any further procedures.
The first issue is that there is so much that can happen to a patient over a 15-year treatment period. As they age, some patients may have changes in memory and thinking that would make it difficult to remember to charge the device on a regular basis. Someone who could easily place the charging pad over their device at age 70 may have more difficulty at 80 or 85. Switching to a recharge-free device because a patient is no longer able to reliably maintain their rechargeable device could be problematic because a new lead would also have to be placed, under anesthesia.
Battery Life Isn’t Everything
Though a rechargeable battery may last 15 years, a sacral neuromodulator includes both a generator and a lead. Issues other than running out of charge can occur with generators and problems can also arise with the lead itself. In a study of over 300 SNM device implants, 38% of patients had to undergo a replacement of the lead at an average of 7 years. The same study also found that, over the same time, 39% of patients had dropped out of the study for a number of reasons including device infection, malfunction of the device or lack of response. So, while a generator that will last at least 15 years may sound like the best choice, many patients, unfortunately, will not see a full 15-year benefit from a rechargeable sacral neuromodulator. This should not discourage you from considering this type of neuromodulator but can help to inform your decision.
Patient Commitment
A final consideration when contemplating recharge versus recharge-free neuromodulation is the amount of your maintenance of the device required for each. Recharge-free devices have sometimes been thought of as a low-maintenance therapy. After 6-12 weeks, further adjustment of the stimulation is usually unnecessary. Many patients can go for years without adjusting their settings. However, I am reluctant to endorse this “set it and forget it” mindset. While recharge-free neuromodulation may not require frequent adjustment, I always emphasize that Overactive Bladder, Fecal Incontinence and Urinary Retention are life-long diseases that require lifetime therapies. Neuromodulation therapy is always more successful when patients and their doctors maintain a continued commitment to additional measures including behavioral therapies like diet changes and fluid moderation. We may spend less time managing the device with a recharge-free neuromodulator, but we never stop managing the disease.
Regardless of how you view long-term therapy, it is clear that rechargeable devices will always require more patient commitment to the device due to the need for regular charging. The time burdens for charging are not excessive with the latest device able to be charged weekly in about 20 minutes or reaching a full charge that can last two weeks in less than an hour. This regular interaction with the device could have varying effects on each individual. I could imagine some patients who would find reassurance and comfort from regularly charging their device. It may give them a sense of control and empowerment to be an active participant in their therapy. It could even be a regular reminder to stick with the behavioral therapies that can make sacral neuromodulation even more effective.
However, one can also envision patients who do not want to be frequently reminded of their dependence on neuromodulation. The charging pad for rechargeable devices is fairly convenient and allows patients to move around freely even while charging. But some patients may find even this minimal burden to be cumbersome. This is suggested by data on rechargeable spinal cord stimulators. In these studies, patients with a rechargeable stimulator were more likely to terminate therapy early than those with a recharge-free device. In one of these studies, but not in others, there was an indication that patients older than age 74 may be less satisfied with rechargeable devices than those under 56.
Making the Decision
For some, the decision to proceed with sacral neuromodulation may be an easy one. After suffering for years with Urinary Incontinence or Fecal Incontinence or Urinary Retention, you may be relieved to have finally found a potentially successful treatment. But the choice to use a recharge-free versus a rechargeable generator may not be as simple. It may help to first focus on those who are likely to see the most benefit from a rechargeable device. This includes someone who is extremely thin, has a prior history of pain at a generator site or has a desire to be very active in their therapy. There may be people who are at a high risk for complications, such as infection, with generator replacement. Occasionally, people will require very high stimulation energy that would quickly drain a recharge-free battery. All of these people may see enough benefit from a rechargeable battery that the choice is an easy one.
Other people may have a high likelihood of problems with a rechargeable generator or may see more benefit from a recharge-free device. This could include those who are very obese or have limited dexterity of their hands, making it difficult to regularly place the charging pad over their neuromodulator. Patients with problems of thinking and memory or who are at risk of having such problems in the next 15 years may gravitate toward a recharge-free device. Anyone who is anxious about frequently interacting with their device, has difficulty with technology or has trouble keeping up with previous therapies may want to avoid a rechargeable device that requires a considerable patient commitment. Based on limited data, those in their 60’s or 70’s may be more dissatisfied with a rechargeable than those who are much younger. Other factors such as frequent travel or a busy lifestyle are not so clear as to whether how much they should be taken into consideration.
Choosing between a recharge-free or rechargeable sacral neuromodulator seems to present a challenge. But it is reassuring to remember that, in many ways, we are fortunate to be in a position to even choose. For over 20 years, people who wanted the considerable benefits that can come from SNM had no choice. Their only option was the recharge-free device. But our days of only having a single option for neuromodulation are over. Now, patients are free to consider the pros and cons of both types of device and choose the best one for them. This is less a dilemma than an opportunity.
