Complications of Peripheral Nerve Stimulation: Open Technique, Percutaneous Technique, and Peripheral Nerve Field Stimulation

Chapter 2 Complications of Peripheral Nerve Stimulation


Open Technique, Percutaneous Technique, and Peripheral Nerve Field Stimulation




Chapter Overview


Chapter Synopsis: Peripheral nerve stimulation (PNS) has emerged as an effective treatment for chronic neuropathic pain with the advantages of being cost effective, reversible, nonaddictive, and nonpharmacologic. Several approaches may be used for implantation and stimulation, including an open surgery technique (PNS:OT), a percutaneous implantation technique (PNS:PT), and a nonperineural technique called peripheral nerve field stimulation (PNfS). As the neuromodulatory techniques have evolved, side effects have become uncommon but should be considered as the treatments become more prevalent. Certain areas of implantation, notably the nerves of the brachial plexus, present greater risks than others. Infection ranks as the most common side effect, but technical problems such as lead migration or lead fracture can also arise. The risk of biologic complications is usually immediate; technical complications usually occur within 2 years of implant. Whereas surgical implantation (PNS:OT) of a stimulating electrode requires exploration and nerve visualization, PNS:PT relies on fluoroscopic imaging for guidance. PNfS places a stimulating device in the peripheral subcutaneous area of pain. As with any neurostimulation technique, a thorough patient selection process can increase the chances for success of the procedure and lower associated risks. A psychological assessment may be required in advance of implantation, but screening by response to nerve block is no longer indicated as predictive of success. Risk can be minimized with vigilance by the physician.


Important Points:













Introduction


Peripheral nerve stimulation (PNS) is a neuromodulation technique in which an electrical current is applied adjacent to peripheral nerves to diminish pain. For the sake of this chapter, PNS techniques will describe stimulation of structures that are anatomically outside of the spinal canal. There are three main variants of PNS: PNS performed with an open surgical technique (PNS:OT); PNS executed with a percutaneous technique (PNS:PT); and a subcutaneous, nonperineural technique called peripheral nerve field stimulation (PNfS). No matter which technique is chosen, PNS is used for chronic, intractable, debilitating neuropathic pain conditions that are refractory to less invasive treatments.


Using PNS:OT, a lead, often a paddle lead, is surgically placed directly adjacent to the target nerve. An example is placement of a paddle lead along the sciatic nerve for a person with neuropathic sciatica. Using PNS:PT, a percutaneous lead is placed through a needle that is usually guided via a nerve stimulator or by ultrasonography. An example is placement of a percutaneous lead through a needle under ultrasound guidance along nerves of the brachial plexus for a painful brachial plexopathy. Using PNfS, which is also called subcutaneous field stimulation, a lead is typically placed through a needle into the subcutaneous tissue in the direct area of pain experienced by the patient, remote to named peripheral nerves. An example is a lead placed in the subcutaneous tissues for axial low back pain in a patient with postlaminectomy syndrome.1


Neuromodulation has a fascinating history that long predates modern understanding of electricity. The Egyptians used electric stimulation to treat pain as early as 2500 bc, as seen on stone carvings depicting placement of electric catfish on people. In ancient Greece and Rome, torpedo fish were used to deliver electric shocks of as many as 200 volts (which may be sufficient to kill a human adult) to combat pain and common maladies such as headache, gout, and arthritis.


In contemporary times, PNS techniques, which are reversible, cost effective, nonaddictive, and nonpharmacologic, are based on delivery of low-level electric impulses to pain-generating nerves via an implantable system, consisting of a programmable generator connected to electric transmission leads. Over the past decade, they have been used increasingly to treat a wide range of conditions involving pain in peripheral or cranial neural distributions. In particular, they may be an effective treatment for neuropathic pain that is not accessible or effectively treated by spinal cord or spinal nerve root stimulation. Common neural targets amenable to PNS include cranial nerves (e.g., trigeminal peripheral terminal branches), occipital nerves, segmental truncal nerves (e.g., nerve root, intercostal, ilioinguinal, iliohypogastric, genitofemoral), and upper and lower extremity plexus and peripheral nerves (e.g., ulnar, median, radial, lateral femoral cutaneous, sciatic, anterior and posterior tibial nerves).2


Another reason PNS therapies have increased in popularity may be their lower incidence of complications. In spite of reported complications including infection, lead migration, and device failure, the risk of serious problems resulting from PNS or PfNS therapies appears to be relatively low in clinical practice. Although there has been no formal comparison of PNS versus spinal cord stimulation (SCS) complications, when compared with intrathecal drug delivery, electrical neuromodulation techniques rarely impact morbidity or mortality significantly.3


Notwithstanding the preceding, PNS therapy is not without risk, and lead placement along specific target areas may be more challenging technically than SCS therapy. For example, placement of PNS leads using an open or closed technique to treat nerves of the brachial plexus, which lie in close proximity to the subclavian and axillary vessels, might be associated with comparable or greater risks than SCS lead placement in the cervical epidural space to treat upper extremity neuropathic pain.



Selected Complications


Perhaps one of the most significant advantages of PNS is its relatively low rate of complications (Table 2-1). Mobbs et al4 mention relatively minor complications in their retrospective study (currently the largest in the literature), which examines the role of the implantable PNS device in the chronic pain patient. In 38 patients who received implanted PNS devices, six stimulators were removed after implantation (15%). Two were removed due to infection, representing a 5% infection rate. One of these patients had hemophilia despite factor VIII cover, and an episode of bleeding that was further complicated by infection, necessitating stimulator removal. Despite a positive result during the trial period, one stimulator was removed after one month because of minimal effect post-implantation. This patient subsequently improved again after his workers’ compensation issues were resolved. One stimulator was removed at 4 years post-implantation since the patient maintained it was no longer needed. Two stimulators in one patient had an initially positive effect, lasting 3 months, followed by a rapid decline in effect. The patient did not wish to have the stimulators re-trialed or re-implanted. A single lead had to be replaced as it was fractured following a fall from a tree. The stimulator continued to function following revision of the lead. During the follow-up period, two battery generators were replaced because of battery failure and a further two generator/lead combinations were repositioned as they were uncomfortable and restricted arm movement. One electrode was relocated during the trial period due to a substantial, uncomfortable motor effect in an adjacent muscle. A further 8 electrodes were resutured during the second operation due to electrode lead migration.


Table 2-1 Complications of PNS (OT; PT, fS)





























































Complication Reported Rate (If Reported)
Overall revision rate 27%32
Requiring explant 15%4
Procedural
Tissue trauma Theoretical
Allergic reactions Case reports,33* 0.8%34
Specific anesthesia-related complications Anecdotal evidence
Hemorrhage Theoretical
Peripheral nerve trauma 60%4
Organ trauma Theoretical
Post-Procedural
Infection 5%,4 3%-5%,17 4.5%,18 1%35
Seroma 2.5%36
Lead migration 27%-33%,34,37 2%35
Skin erosion 12.5%,21 7%35
Pain at generator site 0.9%-5.8%38,39*
Excessive bleeding Theoretical
Sepsis Theoretical, unpublished case report at the Cleveland Clinic
Battery failure/hardware failure 1.6%,40* 2%35
Lead migration 33%,27 24%30

* Extrapolated from spinal cord stimulation devices.


The overall risk of complications associated with PNS therapies appears to be very low. In contrast to SCS, PNS techniques target nerves external to the spinal canal, eradicating potential development of bleeding and infection within the epidural space, catastrophic central neurologic deficit, and emergent spine surgery. However, there exists a risk of a range of procedural, postprocedural, device-related, and infectious complications even when PNS is performed by the most experienced practitioners. Consequently, any physician who undertakes a PNS procedure must be prepared to manage any unexpected sequelae.


Before undertaking a PNS procedure, several factors should be considered, according to a review of surgical procedures pertaining to implantable neuromodulation technology.5 These factors include the incidence, severity, and time to resolution of complications, as well as the net impact on the patient given that complications may detract from the beneficial effect of the procedure.


One of the cornerstones of iatrogenesis avoidance in PNS is patient selection. This includes restricting PNS eligibility to patients with neuropathic pain who have failed to gain relief from more conservative therapies. Because infection is one of the most common complications of PNS procedures, patients must be free of serious skin and systemic infections and must not be immunocompromised. Furthermore, patients receiving PNS must be able to tolerate weaning from nicotine, steroids, and blood thinners and must be thoroughly prescreened to determine their psychological suitability for undergoing PNS procedures.



Procedural Complications


Common potential procedure-related complications surrounding PNS procedures involve tissue trauma, infection, allergic reactions, and anesthesia-related complications. In general, avoidance of such complications necessitates high-quality fluoroscopic guidance to promote optimal lead placement, as well as meticulous surgical technique to prevent infection from contaminated skin, implanted equipment, and other causes. However, development of complications from PNS procedures is still possible even with extensive preventive measures, use of technologically advanced equipment, and years of practitioner expertise.


Harm caused to tissues during PNS procedures may consist of bleeding, peripheral nerve trauma, and damage to vital structures (e.g., vessels and organs). Because vital internal structures are vulnerable in PNS, the use of high-quality fluoroscopy is indicated; for example, pneumothorax, a potential organ-related complication of PNS device installation in the thoracic region, is best circumvented by high-quality imaging.6 In deeper tissues, damage to vessels can be evaded by using an open rather than percutaneous technique, which may help to prevent blind injury of vasculature, embolism, and other negative sequelae.


Hemorrhage is a potential adverse outcome in any surgical procedure. In PNS, bleeding can occur in the region of the generator or lead incision, promoting hematoma and wound dehiscence. In some instances, serosanguineous fluid rather than blood may accumulate, leading to seroma. Both of these problems are limited to the area of surgery and do no usually result in life-threatening disorders.


Because the risk of excessive bleeding and seroma development exists, standard precautions against hemorrhage and fluid leakage should be exercised. Specifically, in the preoperative period, patients should discontinue medications likely to promote bleeding, and patients with a history of excessive bleeding should have a coagulation profile performed. During the procedure, the practitioner should focus on careful tissue dissection, containment of bleeding, and thorough inspection of the wound before closure. In addition, expert surgeons recommend irrigation and complete closure of surgical wounds to diffuse any sources of infection and restriction of pocket size to no larger than necessary to inhibit seroma formation.


The use of PNS therapy was commonly used to treat pain after previous nerve damage as described by Mobbs et al4 in their retrospective study (currently the largest in the literature) of 38 patients implanted with 41 nerve stimulators. The previous nerve damage included blunt and or sharp nerve trauma (in 14 of 38 patients) and inadvertent injection of a nerve (in nine of 38 patients). The incidence of nerve damage from PNS therapy itself is unknown and believed to be rare. To avoid nerve damage, practitioners should maintain excellent knowledge of relevant anatomy and watch for patient neuralgia and radicular pain in the postoperative period. Treatment of suspected nerve injury may include steroid protocol, anticonvulsants, and referral for neurologic consult.


Allergic events in PNS procedures can range from mild topical reactions to full anaphylaxis. Allergic events generally surround the use of preoperative skin preparations, antibiotics, local anesthetics, latex, and sedative medications (e.g., midazolam). Rarely, patients have reported allergic events to the PNS equipment itself, although this seems to be a delayed reaction.


Taking a thorough patient history is beneficial in determining whether the patient is allergic to any of the agents used in PNS therapies. Because the patient may be unaware of any allergies surrounding these products, the physician should remain vigilant for development of allergic sequelae during PNS. For example, local anesthetics are common elicitors of adverse reactions with clinical symptoms such as anaphylaxis with tachycardia; hypotension; and subjective feelings of weakness, heat, or vertigo.7 Furthermore, during general anesthesia or sedation, anaphylactic response to IV hypnotics and other drugs can occur; cardiovascular collapse and bronchospasm are frequent in immunoglobulin E–dependent reactions.8 In addition, latex can produce allergic reactions as serious as anaphylaxis.9


Although the incidence of allergic or toxic reactions to skin preparations is unusual, practitioners should remain aware that iodine tincture and chlorhexidine can produce adverse outcomes in some patients. It is advisable to take a thorough patient history to avoid cutaneous manifestations, particularly in patients with skin sensitivity or other drug allergies. Iodine is associated with adverse effects ranging from minor skin irritation to anaphylaxis, with symptoms occurring within minutes and up to 8 hours after contact.10 In addition, the incidence of contact dermatitis to chlorhexidine in atopic patients is approximately 2.5% to 5.4%, and acute hypersensitivity reactions to chlorhexidine are often not recognized and therefore may be underreported.11


Skin preparations are a topic of concern not only because of their allergic potential but also because of choice of agent (e.g., iodine tincture vs. chlorhexidine). According to a 2010 study published in the New England Journal of Medicine,12 preoperative cleansing of the patient’s skin with chlorhexidine–alcohol was superior to cleansing with povidone–iodine for preventing surgical site infection (SSI) after clean-contaminated surgery. Chlorhexidine–alcohol was significantly more protective than povidone–iodine against both superficial incisional infections (4.2% vs. 8.6%; P = 0.008) and deep incisional infections (1% vs. 3%, P = .05), although it was not effective against organ space infections (4.4% vs. 4.5%). Furthermore, according to Barenfanger et al,13 in choosing a skin preparation for surgical site antisepsis in PNS, it should be noted that although iodine tincture has been called the “gold standard” in preoperative skin preparation, it does not provide statistically greater utility than chlorhexidine in terms of contamination rates, and chlorhexidine may be safer, less expensive, and preferred by staff members. Furthermore, iodine tincture has the disadvantage of being toxic when used repeatedly, but toxicity or sensitization caused by chlorhexidine is very uncommon. However, Barenfanger et al13 found that the average contamination rate with chlorhexidine was found to be slightly greater than with iodine (3.13%, or 186 contaminants in 5936 cultures, vs. 2.72%, or 158 contaminants in 5802 cultures).


Numerous randomized, controlled trials in the literature underscore the benefits of giving prophylactic antibiotics to the patient immediately before surgical procedures such as PNS to inhibit development of infection, although the risk of allergic reaction to antibiotics exists. Classen et al14 prospectively monitored the timing of antibiotic prophylaxis and development of surgical wound infections in 2847 patients undergoing surgical procedures. Among patients who received antibiotics up to 24 hours before surgery, 2 hours before surgery, 3 hours after surgery, and more than 3 hours after surgery, those who received antibiotics 2 hours before surgery had the lowest rates of subsequent surgical wound infections. Furthermore, according to a surgeon’s perspective by Nichols,15 it is generally recommended in elective clean surgical procedures using a foreign body and in clean-contaminated procedures that IV antibiotics should be administered in the operative suite immediately before incision.


Although innumerable clinical trials demonstrate the efficacy of preoperative administration of antibiotics against subsequent infection, physicians should remain mindful of the possibility of unexpected antibiotic allergy in these patients. Although allergic reactions to antibiotics account for only a small proportion of reported adverse drug reactions and estimates of their prevalence vary widely, they are associated with substantial morbidity and mortality and increased health care costs.16


Although infectious complications of PNS and PNfS techniques have generally been associated with less morbidity and mortality as compared to spinal cord stimulation, serious infectious complications have been described. In an unpublished case at the Cleveland clinic, a patient underwent PNfS for somatic abdominal pain, placing the lead in transversus abdominal plane using US guidance. Six weeks later the patient presented with an acute abdomen and sepsis secondary to erosion of the leads into the peritoneal cavity, with subsequent death from septic complications.

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Aug 28, 2016 | Posted by in PAIN MEDICINE | Comments Off on Complications of Peripheral Nerve Stimulation: Open Technique, Percutaneous Technique, and Peripheral Nerve Field Stimulation

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