*2.2.6 Preoperative assessment and counseling*

As with any surgical procedure, preoperative assessment and counseling are of paramount importance. It has been identified that such counseling should include discussions on possible expected side effects and adverse events of SNM therapy, such as implant site pain, infection, paresthesia, and leg and buttock pain. Moreover, the patient must understand that within the spectrum of approved devices in clinical practice, currently the Interstim® device in its two generations, there may arise a need for surgical revision of the implant or ongoing reprogramming atop an eminent and eventual need for replacement of the implantable pulse generator (IPG) once the battery wears out should treatment extend beyond an expected life-expectancy of 3 to 5 years on average. Additionally, and based on ICS recommendations, urodynamic testing is not mandatory, but phase testing is highly recommended prior to embarking on surgical implantation of the SNM IPG [4, 51].

One side effect profile that has been raised in the literature has been the psychological aspects of SNM therapy, though some authors have argued that a reverse pathology is possible with patients with chronic genitourinary and pelvic pain disorders who are potential candidates for SNM are pre-operatively burdened or have pre-existing psychological ailments. As is the limited evidence from some case reports and series, some patients encounter behavioral changes or exacerbation of preexisting psychological conditions such as depression, which has led to the argument of need for psychological assessment of certain traits that may affect SNM outcomes [52]. However, this has yet to be reflected in the guidelines and societal recommendations

and a causality has not been established. On the other hand, other researchers have shown no influence of psychological and psychiatric factors on SNM outcomes [53].

### *2.2.6.1 General considerations*

SNM implantation requires, most commonly, fluoroscopic guidance in the lead placement stage of the procedure to correctly identify the S3 foramen and the depth of lead placement and direction and correlate it with the reflex responses of the patient. Though of ongoing concern, studies have shown that radiation during SNM implantation, be it staged or office-based percutaneous nerve evaluation (PNE), is safe and within the recommended limits set by the International Commission on Radiological Protection [54]. That, however, did not alter an ongoing debate on whether "fluoroguidance" can be replaced by a less radioactive imaging modality, the ultrasound. Apart from having a far lower radiation exposure profile, if any, ultrasound-guided lead placement was found in one study to lower the number of needle punctures needed to identify the most suitable S3 foramen for patient response; however, that had minimal effects on total operative time [55].

Preoperative antibiotic administration is also advocated in both stages of implantation. The recommended antibiotic regimens should target common skin flora pathogens. Guidelines published by the French Association of Urology suggest the use of amoxycillin or broad-spectrum cephalosporins, and in case of hypersensitivity to these antibiotics, an alternative combination of vancomycin and clindamycin is suitable [56].

### *2.2.7 Technical aspects and techniques*

### *2.2.7.1 The device: lead and implantable pulse generator*

The SNM device consists of a tinned lead, connected to a stimulator, the implantable pulse generator (IPG), by insulated cords. Improvements have been made between the initial and current Interstim II device available on the market, including the tinned lead technology, deflected lead tip, and increased capacity of storage of programming and patient data, among others.

The tines allow for anchorage of the lead and prevent displacement. The quadripolar lead contains four electrical stimulation contact regions or electrodes, which are used to designate four different programmable charges on each region to provide an endless number of possible combinations of modulatory programs for patients for a variety of symptoms and effects. These are under the control of an external programming remote that allows the surgeon or programmer to store certain programs to the system of the patient. The patient can then use their own remote to initiate or shutdown certain programs at different times, or switch off the device all together, as well as control the intensity of the stimulation. An illustration of the quadripolar tinned lead can be seen in **Figure 1**.

The IPG is a battery-dependent neuromodulator that delivers electrical stimulation transmitted via the lead. It has an embedded antenna that receives signals from the operator remote controllers [42].

### *2.2.7.2 Office-based percutaneous nerve evaluation*

This modality of lead testing or screening for possible responses is done in the office setting under local anesthesia and allows assessment of both sensory and motor responses of the patient to stimulation. It can be done under fluoroscopy or ultrasound guidance. It is deemed a less invasive and less resource-intensive testing phase prior to implantation. However, it is more uncomfortable to the patient since

**219**

*Neuromodulation in Urology: Current Trends and Future Applications*

only local anesthesia is being used [57]. As a matter of fact, single-staged implantation after PNE could save US \$1500–5000 depending on how high the success rate of the implantation is, an argument well utilized on part of advocates at both ends

*Quadripolar tinned lead utilized in SNM. Labeled are the electrode positions, "0" being most distal and "3"* 

*most proximal. An optimum insertion is eliciting a response on all electrodes at low voltage.*

Local anesthesia is applied subcutaneously to the mid-sacral region where testing will be performed. In the prone position, a needle harboring a single-electrode lead is advanced to correctly identify the S3 foramen. The S3 foramen can be identified fluoroscopically, or approximated anatomically as evident from cadaveric studies that showed the mean distance of the superior aspect of the S3 foramen is approximately 9 cm from the coccyx, and laterally it is 2 cm from the middle of the sacral back region, while vertical interforamenal spaces are around 1.5 cm in length [59]. The patient is asked to report any sensations felt in the perineal region or the foot, and motor responses are also examined in the buttock region and the ipsilateral foot. Stimulation is then performed at different voltages and the area is marked. Successful office-based PNE is followed by one-stage surgical tinned 4-electrode lead placement and IPG implantation. Motor responses are rechecked during implantation, and location and laterality may be modified to obtain the most appropriate response. This is probably one of the most important disadvantages and arguments against PNE in favor of staged implantation: bypassing a longer assessment or testing period that would reveal more information about the prospective

The ideal patient for PNE is a cooperative and apprehensive one who can remain

Focus has been given in current research and modifications of leads to replace current PNE leads with more functional multipolar leads that would allow a more

Under sedation or general anesthesia should the patient require it if they cannot maintain an airway in the prone position, staged SNM implantation depends

relaxed during the procedure. Patients who cannot lay prone for any reason or medical condition, and those who may need more deeper stimulation such as those morbidly obese or anyone with anatomical variations or previous sacral scars may preclude office-based PNE [57]. However, in one study by Gonssen and colleagues, the need for general anesthesia was substituted by a complete permanent SNM implantation under local anesthesia, and was reported to be both safe and tolerable

*DOI: http://dx.doi.org/10.5772/intechopen.92287*

of the debate of whether to stage or not [58].

**Figure 1.**

efficacy of the chosen S3 foramen and SNM implant.

idealistic response and minimal manipulation of the lead [57].

*2.2.7.3 Stage I testing of two-stage implantation*

with successful outcomes [60].

*Neuromodulation in Urology: Current Trends and Future Applications DOI: http://dx.doi.org/10.5772/intechopen.92287*

### **Figure 1.**

*Neurostimulation and Neuromodulation in Contemporary Therapeutic Practice*

*2.2.6.1 General considerations*

had minimal effects on total operative time [55].

*2.2.7.1 The device: lead and implantable pulse generator*

storage of programming and patient data, among others.

of the quadripolar tinned lead can be seen in **Figure 1**.

*2.2.7.2 Office-based percutaneous nerve evaluation*

the operator remote controllers [42].

*2.2.7 Technical aspects and techniques*

and a causality has not been established. On the other hand, other researchers have shown no influence of psychological and psychiatric factors on SNM outcomes [53].

SNM implantation requires, most commonly, fluoroscopic guidance in the lead placement stage of the procedure to correctly identify the S3 foramen and the depth of lead placement and direction and correlate it with the reflex responses of the patient. Though of ongoing concern, studies have shown that radiation during SNM implantation, be it staged or office-based percutaneous nerve evaluation (PNE), is safe and within the recommended limits set by the International Commission on Radiological Protection [54]. That, however, did not alter an ongoing debate on whether "fluoroguidance" can be replaced by a less radioactive imaging modality, the ultrasound. Apart from having a far lower radiation exposure profile, if any, ultrasound-guided lead placement was found in one study to lower the number of needle punctures needed to identify the most suitable S3 foramen for patient response; however, that

Preoperative antibiotic administration is also advocated in both stages of implantation. The recommended antibiotic regimens should target common skin flora pathogens. Guidelines published by the French Association of Urology suggest the use of amoxycillin or broad-spectrum cephalosporins, and in case of hypersensitivity to these antibiotics, an alternative combination of vancomycin and clindamycin is suitable [56].

The SNM device consists of a tinned lead, connected to a stimulator, the implantable pulse generator (IPG), by insulated cords. Improvements have been made between the initial and current Interstim II device available on the market, including the tinned lead technology, deflected lead tip, and increased capacity of

The tines allow for anchorage of the lead and prevent displacement. The quadripolar lead contains four electrical stimulation contact regions or electrodes, which are used to designate four different programmable charges on each region to provide an endless number of possible combinations of modulatory programs for patients for a variety of symptoms and effects. These are under the control of an external programming remote that allows the surgeon or programmer to store certain programs to the system of the patient. The patient can then use their own remote to initiate or shutdown certain programs at different times, or switch off the device all together, as well as control the intensity of the stimulation. An illustration

The IPG is a battery-dependent neuromodulator that delivers electrical stimulation transmitted via the lead. It has an embedded antenna that receives signals from

This modality of lead testing or screening for possible responses is done in the office setting under local anesthesia and allows assessment of both sensory and motor responses of the patient to stimulation. It can be done under fluoroscopy or ultrasound guidance. It is deemed a less invasive and less resource-intensive testing phase prior to implantation. However, it is more uncomfortable to the patient since

**218**

*Quadripolar tinned lead utilized in SNM. Labeled are the electrode positions, "0" being most distal and "3" most proximal. An optimum insertion is eliciting a response on all electrodes at low voltage.*

only local anesthesia is being used [57]. As a matter of fact, single-staged implantation after PNE could save US \$1500–5000 depending on how high the success rate of the implantation is, an argument well utilized on part of advocates at both ends of the debate of whether to stage or not [58].

Local anesthesia is applied subcutaneously to the mid-sacral region where testing will be performed. In the prone position, a needle harboring a single-electrode lead is advanced to correctly identify the S3 foramen. The S3 foramen can be identified fluoroscopically, or approximated anatomically as evident from cadaveric studies that showed the mean distance of the superior aspect of the S3 foramen is approximately 9 cm from the coccyx, and laterally it is 2 cm from the middle of the sacral back region, while vertical interforamenal spaces are around 1.5 cm in length [59].

The patient is asked to report any sensations felt in the perineal region or the foot, and motor responses are also examined in the buttock region and the ipsilateral foot. Stimulation is then performed at different voltages and the area is marked. Successful office-based PNE is followed by one-stage surgical tinned 4-electrode lead placement and IPG implantation. Motor responses are rechecked during implantation, and location and laterality may be modified to obtain the most appropriate response. This is probably one of the most important disadvantages and arguments against PNE in favor of staged implantation: bypassing a longer assessment or testing period that would reveal more information about the prospective efficacy of the chosen S3 foramen and SNM implant.

The ideal patient for PNE is a cooperative and apprehensive one who can remain relaxed during the procedure. Patients who cannot lay prone for any reason or medical condition, and those who may need more deeper stimulation such as those morbidly obese or anyone with anatomical variations or previous sacral scars may preclude office-based PNE [57]. However, in one study by Gonssen and colleagues, the need for general anesthesia was substituted by a complete permanent SNM implantation under local anesthesia, and was reported to be both safe and tolerable with successful outcomes [60].

Focus has been given in current research and modifications of leads to replace current PNE leads with more functional multipolar leads that would allow a more idealistic response and minimal manipulation of the lead [57].

### *2.2.7.3 Stage I testing of two-stage implantation*

Under sedation or general anesthesia should the patient require it if they cannot maintain an airway in the prone position, staged SNM implantation depends on a primary stage I of testing done in the operative theater where the tinned lead is eventually implanted after eliciting the best motor response and insulated cord cables are tracked to the contralateral side and eventually out of the skin to be connected to a temporary pulse generator for the testing phase. These cables are later re-tunneled back the ipsilateral side where the tinned leads have been implanted and are connected to the implantable IPG.

This is the method utilized at our center, where we deem it and it has been proven to be more comfortable for the patient in a controlled setting where even sedation can be switched to anesthesia should the patient become restless. Nevertheless, muscle relaxation is not administered to maintain the ability to assess motor response on lead placement and testing. One particular population of patients which are ideal candidates for this mode of testing are morbidly obese patients where local anesthesia administered subcutaneously may not be sufficient for the deep layer manipulation necessary to deliver the lead to the sacral foramens [57].

Some researchers have continuously advocated staged testing and implantation despite PNE being a more resourceful alternative. Arguments included the increased comfort of the patient allows for better identification of ideal patients for therapy and less likely to result in a misleading positive screening but unsuccessful subsequent implantation. It also allows the employment of a longer testing trial period and has the added potential of fine-tuning stimulation parameters. It has been advocated as the ideal modality of screening for responses in patients with NOUR, sensory urgency and CPPS [57].

The two-stage implantation technique depends on a 2–4 weeks arbitrary period of testing for improved responses in patients planned for implantation. This period has been contested in literature, as are the arguments in favor of office-based PNE. The range of reported successful test phases is around 60% [61]. However, the length of this period has been also up for debate. One group of researchers studied a group of patients who underwent stage I SNM implantation test phase and found that the mean time needed to identify potential successful outcomes of the test was 3 days, ranging from 1 to 9 days in total. This was not different between patients implanted for OAB and those for NOUR, and thus they concluded that a test stage I period of two or more weeks may not be necessary [61].

The importance of such an argument lays in the potential morbidities of a prolonged test period, with partially exposed external leads liable for displacement and a possible route for infection, though the literature does not report on either. The length of stage I has been suspected to be a risk factor for SNM implant infections, but the evidence is lacking, and the identifiable association if any may be the result of improper antibiotic regimens or assessment of small sample sizes of patients [62].

Disadvantages of staged screening and implantation include that only motor responses are assessed during lead placement. Sensory responses cannot be assessed in the presence of even light sedation. However, two formal studies have found that motor responses more importantly surpass sensory responses in predicting SNM successful outcomes [57]. These are in addition to the logical added financial and time requirements for testing in the operation theater and the need for anesthesia.

### *2.2.7.4 Lead placement*

In SNM, the lead is placed in the S3 foramen, either on the right or left side, and rarely bilateral lead placement is undertaken. The S3 foramen has been identified to be relevant to the target nerve fibers required to achieve the effect of SNM [15]. Patients exhibit and experience typical motor and sensory responses to lead placement in the S3 foramen, depending on the setting of lead placement under local or general anesthesia. This is further summarized in **Table 1**, along with responses

**221**

**Figure 2.**

*motor responses.*

*Neuromodulation in Urology: Current Trends and Future Applications*

S3 Perineal paresthesia or pulling sensation in rectum,

**Foramen Sensory response Motor response**

of adjacent S2 and S4 foramens, which surgeons utilize to correctly identify the S3

S4 Pulling sensation in rectum only Anal bellows only without leg or

The placement of the actual tinned lead is preceded by testing or screening using a conductive long needle that is introduced first in the correct foramen, and a conductor is used to elicit the best response possible on the most number of electrodes (optimum being four-out-of-four positive electrodes at the lowest stimulatory voltage possible). Once finalized, a small skin incision around the needle facilitates for the introduction of the tinned lead in the chosen foramen. This tracking is aided by an introducer stylet [42, 63, 65, 66]. **Figures 2**–**5** show an illustration of the steps on the introduction of the tinned lead and implantation of the IPG, while **Figure 6** shows how the inserted tinned lead looks like and is confirmed to be correctly placed on fluoroscopy.

Foot: plantar flexion, foot rotation Anal sphincter "clamp movement"

Anal bellows "winking" Great toe dorsiflexion

foot movement

There is no agreed upon definition of optimal lead placement, and many factors have been speculated to alter placement and SNM outcomes, including position and depth of lead, angle, and deflection (straight, lateral or medial related to the foramen), but none shown to have any relation to SNM outcome. Lateral deflection is the only factor found to be associated with identifying more active electrodes, although the number of active electrodes itself has not been shown to correlate with a better motor response. Thus, the concentration during lead placement especially under general anesthesia should be on identifying the best motor response rather

In the quest for optimal lead positioning and how to facilitate this process, some researchers have advocated for the use of a curved stylet during the introduction of

*Test needle insertion into the S3 foramen. The needle position is confirmed fluoroscopically or by ultrasound. An electrostimulation probe is then used in contact with the distal end of the needle to test for appropriate* 

*DOI: http://dx.doi.org/10.5772/intechopen.92287*

Leg sensation

scrotum or vagina

S2 Buttock sensation

*Hubsher et al. [63] and Thompson et al. [64].*

**Table 1.**

foramen and avoid the formers [63, 64].

*Expected responses from SNM at different sacral levels.*

than on anatomical details [67].

*Neuromodulation in Urology: Current Trends and Future Applications DOI: http://dx.doi.org/10.5772/intechopen.92287*


### **Table 1.**

*Neurostimulation and Neuromodulation in Contemporary Therapeutic Practice*

and are connected to the implantable IPG.

NOUR, sensory urgency and CPPS [57].

period of two or more weeks may not be necessary [61].

on a primary stage I of testing done in the operative theater where the tinned lead is eventually implanted after eliciting the best motor response and insulated cord cables are tracked to the contralateral side and eventually out of the skin to be connected to a temporary pulse generator for the testing phase. These cables are later re-tunneled back the ipsilateral side where the tinned leads have been implanted

This is the method utilized at our center, where we deem it and it has been proven to be more comfortable for the patient in a controlled setting where even sedation can be switched to anesthesia should the patient become restless. Nevertheless, muscle relaxation is not administered to maintain the ability to assess motor

response on lead placement and testing. One particular population of patients which are ideal candidates for this mode of testing are morbidly obese patients where local anesthesia administered subcutaneously may not be sufficient for the deep layer

Some researchers have continuously advocated staged testing and implantation despite PNE being a more resourceful alternative. Arguments included the increased comfort of the patient allows for better identification of ideal patients for therapy and less likely to result in a misleading positive screening but unsuccessful subsequent implantation. It also allows the employment of a longer testing trial period and has the added potential of fine-tuning stimulation parameters. It has been advocated as the ideal modality of screening for responses in patients with

The two-stage implantation technique depends on a 2–4 weeks arbitrary period of testing for improved responses in patients planned for implantation. This period has been contested in literature, as are the arguments in favor of office-based PNE. The range of reported successful test phases is around 60% [61]. However, the length of this period has been also up for debate. One group of researchers studied a group of patients who underwent stage I SNM implantation test phase and found that the mean time needed to identify potential successful outcomes of the test was 3 days, ranging from 1 to 9 days in total. This was not different between patients implanted for OAB and those for NOUR, and thus they concluded that a test stage I

The importance of such an argument lays in the potential morbidities of a prolonged test period, with partially exposed external leads liable for displacement and a possible route for infection, though the literature does not report on either. The length of stage I has been suspected to be a risk factor for SNM implant infections, but the evidence is lacking, and the identifiable association if any may be the result of improper antibiotic regimens or assessment of small sample sizes of patients [62]. Disadvantages of staged screening and implantation include that only motor responses are assessed during lead placement. Sensory responses cannot be assessed in the presence of even light sedation. However, two formal studies have found that motor responses more importantly surpass sensory responses in predicting SNM successful outcomes [57]. These are in addition to the logical added financial and time requirements for testing in the operation theater and the need for anesthesia.

In SNM, the lead is placed in the S3 foramen, either on the right or left side, and rarely bilateral lead placement is undertaken. The S3 foramen has been identified to be relevant to the target nerve fibers required to achieve the effect of SNM [15]. Patients exhibit and experience typical motor and sensory responses to lead placement in the S3 foramen, depending on the setting of lead placement under local or general anesthesia. This is further summarized in **Table 1**, along with responses

manipulation necessary to deliver the lead to the sacral foramens [57].

**220**

*2.2.7.4 Lead placement*

*Expected responses from SNM at different sacral levels.*

of adjacent S2 and S4 foramens, which surgeons utilize to correctly identify the S3 foramen and avoid the formers [63, 64].

The placement of the actual tinned lead is preceded by testing or screening using a conductive long needle that is introduced first in the correct foramen, and a conductor is used to elicit the best response possible on the most number of electrodes (optimum being four-out-of-four positive electrodes at the lowest stimulatory voltage possible). Once finalized, a small skin incision around the needle facilitates for the introduction of the tinned lead in the chosen foramen. This tracking is aided by an introducer stylet [42, 63, 65, 66]. **Figures 2**–**5** show an illustration of the steps on the introduction of the tinned lead and implantation of the IPG, while **Figure 6** shows how the inserted tinned lead looks like and is confirmed to be correctly placed on fluoroscopy.

There is no agreed upon definition of optimal lead placement, and many factors have been speculated to alter placement and SNM outcomes, including position and depth of lead, angle, and deflection (straight, lateral or medial related to the foramen), but none shown to have any relation to SNM outcome. Lateral deflection is the only factor found to be associated with identifying more active electrodes, although the number of active electrodes itself has not been shown to correlate with a better motor response. Thus, the concentration during lead placement especially under general anesthesia should be on identifying the best motor response rather than on anatomical details [67].

In the quest for optimal lead positioning and how to facilitate this process, some researchers have advocated for the use of a curved stylet during the introduction of

#### **Figure 2.**

*Test needle insertion into the S3 foramen. The needle position is confirmed fluoroscopically or by ultrasound. An electrostimulation probe is then used in contact with the distal end of the needle to test for appropriate motor responses.*

### **Figure 3.**

*Introductory stylet inserted in chosen S3 foramen. The stylet guides enclosed lead. Once removed, tines allow for anchorage of lead in proper position.*

#### **Figure 4.**

*Tined lead position after removing of stylet and introductory sheath. Note position of electrodes deep to foramen and in proximity to nerve root.*

**223**

**Figure 6.**

*Neuromodulation in Urology: Current Trends and Future Applications*

the tinned lead into the foramen. The tip of this stylet has an 18° bend that allows it to follow the natural pathway of the sacral root nerve. This is thought to allow for identification of an ideal response on all 4 electrodes at low voltage, subsequently

identification of the S3 foramen, but also to eliciting the best response from the patient on stimulation at the lowest voltage possible. Researchers have argued for years for unilateral or bilateral lead testing. What is evident from studies to date is that the side that tests with the best motor response (or sensory response if patient can relay it) does not necessarily translate into the best outcome for therapy on the long-term. However, bilateral testing has the advantage of allowing patients to

choose the side that they find more beneficial or comfortable [57].

*Fluoroscopic confirmation of position of lead and electrodes in relation to sacral spine.*

*2.2.7.5 Implantation of internal pulse generator/stage II procedure*

*2.2.8 Post-implantation programming and troubleshooting*

During lead placement and testing, the requirement is not only limited to correct

Implantation of the internal or implantable pulse generator (IPG) can be in the setting of a single-stage along with lead placement following successful PNE testing, or the second stage of a staged implantation after a successful trial period following stage I lead implantation. Regardless of the staging, the IPG is implanted in a subcutaneous pocket on the same side the tinned lead has been placed in the S3 foramen. Sterility of the IPG device must be maintained to avoid acute or chronic infections. After skin preparation and administration of necessary local anesthesia, a subcutaneous pocket is created under the skin in the patient's buttock. This pocket should be high enough away from the seating area of the patient, and deep enough to avoid superficial sensation of the IPG by the patient as well. Preoperative marking is helpful in such scenarios, keeping in mind distance from the employed S3 foramen as well to avoid tension on the connection between the tinned lead and the IPG. The cord is tunneled from the lead to the IPG subcutaneously and the connections are made. Before wound closure, wash with a sterile water-based antibiotic solution has been described by some authors. It is important to avoid saline-based solutions that may cause electronic malfunction of the device [41, 42, 63, 65, 69].

Programming is done after IPG implantation when the patient is fully awake and conscious to provide feedback on different modes and programs as they are being

providing greater flexibility with programming [68].

*DOI: http://dx.doi.org/10.5772/intechopen.92287*

**Figure 5.** *Final position of implanted pulse generator (IPG) and connections.*

*Neurostimulation and Neuromodulation in Contemporary Therapeutic Practice*

*Tined lead position after removing of stylet and introductory sheath. Note position of electrodes deep to foramen* 

*Introductory stylet inserted in chosen S3 foramen. The stylet guides enclosed lead. Once removed, tines allow for* 

**222**

**Figure 5.**

*Final position of implanted pulse generator (IPG) and connections.*

**Figure 4.**

**Figure 3.**

*anchorage of lead in proper position.*

*and in proximity to nerve root.*

**Figure 6.** *Fluoroscopic confirmation of position of lead and electrodes in relation to sacral spine.*

the tinned lead into the foramen. The tip of this stylet has an 18° bend that allows it to follow the natural pathway of the sacral root nerve. This is thought to allow for identification of an ideal response on all 4 electrodes at low voltage, subsequently providing greater flexibility with programming [68].

During lead placement and testing, the requirement is not only limited to correct identification of the S3 foramen, but also to eliciting the best response from the patient on stimulation at the lowest voltage possible. Researchers have argued for years for unilateral or bilateral lead testing. What is evident from studies to date is that the side that tests with the best motor response (or sensory response if patient can relay it) does not necessarily translate into the best outcome for therapy on the long-term. However, bilateral testing has the advantage of allowing patients to choose the side that they find more beneficial or comfortable [57].

### *2.2.7.5 Implantation of internal pulse generator/stage II procedure*

Implantation of the internal or implantable pulse generator (IPG) can be in the setting of a single-stage along with lead placement following successful PNE testing, or the second stage of a staged implantation after a successful trial period following stage I lead implantation. Regardless of the staging, the IPG is implanted in a subcutaneous pocket on the same side the tinned lead has been placed in the S3 foramen. Sterility of the IPG device must be maintained to avoid acute or chronic infections.

After skin preparation and administration of necessary local anesthesia, a subcutaneous pocket is created under the skin in the patient's buttock. This pocket should be high enough away from the seating area of the patient, and deep enough to avoid superficial sensation of the IPG by the patient as well. Preoperative marking is helpful in such scenarios, keeping in mind distance from the employed S3 foramen as well to avoid tension on the connection between the tinned lead and the IPG. The cord is tunneled from the lead to the IPG subcutaneously and the connections are made. Before wound closure, wash with a sterile water-based antibiotic solution has been described by some authors. It is important to avoid saline-based solutions that may cause electronic malfunction of the device [41, 42, 63, 65, 69].

### *2.2.8 Post-implantation programming and troubleshooting*

Programming is done after IPG implantation when the patient is fully awake and conscious to provide feedback on different modes and programs as they are being

tested and tried out and allows them to choose their preferred settings. At our center this is done on the next day postoperatively and ensues removal of the urinary catheter placed during the procedure to allow for trials of voiding [41, 70]. Patient follow-up is periodic thereafter, during which voiding and stimulation parameters are checked and patient compliance is evaluated [42].

Good communication between the patient, surgeon and the programmer are necessary to obtain the optimum results and efficacy of SNM. In cases where any unforeseeable event occurs, such as sudden loss of efficacy or any of the adverse events that will be discussed as follows, proper testing of the programs and circuit impedance, as well as efforts at reprogramming operational electrodes should be utilized extensively before reaching the morbid decision of revision or explantation [42, 71, 72].

### *2.2.9 Adverse events and complications*

Adverse events associated with SNM are numerous and well-documented. The majority of such events are anticipated and even counseled for preoperatively, with a documented range of 16–30% between the test and final implantation stages. Unanticipated or unexpected adverse events and complications are rare and are limited to isolated case reports and limited series [73].

### *2.2.9.1 Pain*

Implant site pain is pain perceived at the site of the IPG. This could be the result of many reasons. A too-superficial implant may be cutaneously felt and pose a source of discomfort especially if implanted at a lower gluteal point and as such would be "sat on" by the patient. In one review, the most commonly cited reason for explantation was site pain [74]. Another series reported this to occur in 7% of implants, with the majority presenting beyond 30 days of implantation and some associated with trauma.

Another cause of pain could be stimulation program related. Turning off the IPG can differentiate between IPG-related and program-related pain, the latter usually requiring changes in stimulator settings by the programmer [42]. In the most debilitating cases, and often, this complaint would require surgical revision of the pocket or implant [73].

Pain could also be felt at the site where the stimulatory sensation is perceived, and this too, could often be differentiated by turning off the stimulator, and subsequently altering the settings [42].

### *2.2.9.2 Undesirable change in stimulation*

Perhaps one of the most unfortunate adverse events is an undesirable change in stimulation that leads to loss of a successful SNM effect or subjective dissatisfaction with an objectively successful implant. In one series, researchers reported this to occur in 12% of their surveyed adverse events in SNM implants for OAB. The majority of such incidences can be corrected with simple or sometimes more complex reprogramming of the neuromodulator, and rarely requires revision or explantation [73]. However, decrease in efficacy of stimulation is a major reason for reoperation and explantation should reprogramming in absence of lead migration fail to correct the deficiency [42, 75].

Checking the impedance can be useful to assess for any possible lead breakage or dislodgement which would show high impedance, but if the impedance is less than 50 ohms, this may indicate a short circuit that could be due to a wet connection.

**225**

colocutaneous fistula [80].

*Neuromodulation in Urology: Current Trends and Future Applications*

or alternative solution, but lead revision is often necessary [71].

target potential and common skin organisms such as *S. aureus* [62].

Reprogramming electrodes with acceptable impedances could provide a temporary

In a multicenter retrospective case–control assessment of risk factors for explantation of the SNM device due to infection, researchers reported on an almost 2–3% incidence of infection and identified that hematoma formation and IPG pocket depth of greater than 3 cm were independently associated with development of infection, while implant infection was the leading cause of device explantation at 1 year follow-up in another large trial [68, 73, 76]. The most common pathogen reported on cultures obtained from these explants was the skin flora resident *S. aureus*. Infection is probable both early in the postoperative period within 30 days of implantation, or later beyond 30 days and sometimes up to 10 months post-implantation [73, 76].

Risk factors associated with SNM implantation infection have been studied, and some have been refuted. The choice of preoperative antibiotic regimen is of importance in both stage I and final IPG implant, and the antibiotic administered should

Prevention of such infections has also been reviewed. One group of researchers reported on the use of an antibiotic-coated collagen layer placed over the IPG before wound closure with noticeable results. Skin preparation is also important, particularly with chlorhexidine-based solutions per international recommendations [62, 68]. And although many surgeons still do administer certain courses of post-implantation antibiotics, this is not supported by any clinical evidence of benefit, though further research may better define its role as is the case with other prosthetic or implantable

Lead fracture, migration or dislodgement are a rare occurrence reported at around 1% of adverse events and eminent needs for device and lead replacements. The introduction of the tinned leads has aided in lowering the incidence of lead

be needed, though the latter may not always prove successful [42, 71, 77].

*2.2.9.5 Unanticipated adverse events and complications*

Patients may have, against better judgment and counseling, engaged electively in physically demanding exercises, or it may be the result of sudden acute movements or trauma. The result is a sudden loss of or major change in stimulation. On testing, high impedance (>4000 ohms) is found on all 4 electrodes [73]. Additionally, sacral x-ray imaging can help determine if any lead displacement or dislodgement is present. If evident, especially in the presence of complete loss of efficacy and all other alternative reprogramming efforts have been extorted, replacement of the lead is necessary, and sometimes contralateral placement or even bilateral stimulation may

It is important to understand that although rare, complications are an important

predictor of SNM reoperation and may result in severe morbidity [75, 78]. Rare complications of lead placement and implantation have been reported in separate case reports and limited series, including one case of retroperitoneal hemorrhage after SNM implanted for urge incontinence [79]. Another case of lead migration into the sigmoid colon during implantation was complicated by and presented as a

*DOI: http://dx.doi.org/10.5772/intechopen.92287*

*2.2.9.3 Implant infection*

devices [62].

migration [41].

*2.2.9.4 Lead fracture and displacement*

Reprogramming electrodes with acceptable impedances could provide a temporary or alternative solution, but lead revision is often necessary [71].
