Percutaneous Peripheral Nerve Stimulation for the Management of Postoperative Pain

Acknowledgments

This work was supported in part by the National Institute on Aging (1R44AG052196-01). The content of this chapter is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute on Aging.

Postoperative pain is often severe, not easily treated with existing analgesics, which might produce undesirable side-effects, and may increase the risk of persistent (“chronic”) pain lasting months or even years. Moderate or severe pain is reported by over 70% of patients following surgery and over 60% of patients after discharge ( ). Various surgical procedures are prone to cause persistent moderate–severe postoperative pain, such as total joint replacement (e.g., hip, knee), limb amputation, thoracotomy, and mastectomy ( ). Postoperative pain in the acute period prolongs hospital duration of stay, reduces quality of life (QoL), delays functional recovery, increases the risk of chronic pain, and increases medical costs ( ). Postsurgical pain is a major factor in the decision to discharge patients to rehabilitation centers (e.g., skilled nursing, acute inpatient rehabilitation), and pain increases length of stay in hospitals and/or rehabilitation centers by 17%–33%, increasing costs by approximately $1000–$2000 per day per patient ( ).

Existing Treatments for Postoperative Pain

Currently, the predominant interventions to provide postoperative pain control are oral and/or intravenous analgesics. Nonopioid analgesics, such as acetaminophen or nonsteroidal antiinflammatory drugs, are commonly used with minimal risk of side-effects, but are often insufficient by themselves for treating acute postoperative pain. Nonopioid analgesics are typically paired with opioid analgesics, which do provide greater pain relief than when used alone. However, opioids carry risks of dependence and debilitating side-effects (e.g., sedation, dizziness, nausea, constipation, urinary retention, sleeping problems, respiratory depression) that can greatly impair QoL and delay recovery ( ). Anticonvulsants (e.g., gabapentin, pregabalin) are also commonly used to reduce the neuropathic component of postoperative pain ( ). However, anticonvulsants also carry risks of side-effects that can delay recovery, reduce QoL, and interfere with activities of daily living (impaired cognition, sedation, dizziness, headache, blurred vision) ( ).

Because these analgesics have significant limitations or adverse side-effects, local anesthetic-based central and peripheral nerve blocks are often added as part of a multimodal analgesic strategy to reduce postoperative pain. Unfortunately, the longest-acting local anesthetic still provides less than 16 h of analgesia when administered through a single injection. Although a continuous local anesthetic infusion via a percutaneous perineural catheter may prolong pain control for multiple weeks, practically speaking these modalities are limited to just a few days’ duration due to induced motor, sensory, and proprioception blockade (possibly increasing the risk of falls and limiting early rehabilitation), relatively high consumption of local anesthetic, hemodynamic effects (e.g., hypotension), infection risk from the percutaneous catheter, and increasing incidence of catheter dislocation. Considering that most surgical procedures result in multiple days or weeks—and sometimes months—of pain, an analgesic technique avoiding these pitfalls would be highly valuable to patients and the surgical community.

Following hospital discharge, patients are given oral analgesics (including opiates) to use for several days to weeks as the primary intervention to relieve their pain. This can be problematic, as approximately one in four patients prescribed opioids for the first time will continue receiving prescriptions in the long term (at least 90 days) ( ), which may increase the risk of opioid dependence and misuse. Single-injection nerve blocks cannot be delivered outside the clinical setting, and continuous infusions generally are not used long term due to the infection risks from indwelling catheters. Furthermore, pumps used to administer continuous nerve blocks are inconvenient to use long term because they are bulky, must be carried by the patient, and are often noisy. Thus patients are often left with unsatisfactory pain control at home following hospital discharge.

History: Treating Postoperative Pain With Electrical Stimulation

The use of electrical current to treat pain was first described by the ancient Romans using live torpedo fish ( ). For nearly two millennia after the Romans first described its use to treat pain, applications for the use of electrical current were exclusively chronic pain states such as gout ( ), sciatica, and lumbosacral neuralgia ( ). Following the publication of Melzack and Wall’s “gate-control theory” in the 1960s ( ), Reynolds noted that rats could undergo surgery with little discernable pain during periventricular brain stimulation ( ).

The decade after the introduction of the gate-control theory and Reynold’s observation of electro-anesthesia in rats, transcutaneous electrical nerve stimulation (TENS) was employed to provide postoperative analgesia in patients ( ). TENS uses surface (patch) electrodes placed on the skin around the regions of pain to generate pain relief locally. It has been used to treat postoperative pain following numerous types of surgeries, but reports on the effectiveness of TENS have been mixed at best. While some studies have found statistically significant reductions in postoperative pain scores and/or analgesic usage ( ), the majority of reports conclude that insufficient analgesia is provided to justify its use following surgery ( ). The success of TENS is highly dependent on the stimulation intensity (i.e., amplitude and/or pulse duration). The analgesic effect of TENS is commonly believed to be due to the activation of subcutaneous afferent nerve fibers rather than superficial cutaneous nerve fibers ( ). Accordingly, TENS delivered with low stimulation intensities may not activate sufficient numbers of the deeper subcutaneous fibers to provide adequate analgesia ( ). Large stimulation intensities can activate the deeper subcutaneous fibers but can irritate the skin and activate cutaneous nerve endings, causing discomfort and/or pain ( ). Consequently, TENS has been limited in practice by its inability to activate deep nerve fibers comfortably and effectively, resulting in low patient compliance.

Spinal cord stimulation (SCS) and conventional (i.e., fully implanted) peripheral nerve stimulation (PNS) can activate nerve fibers from both superficial and deep tissues of the regions of pain by stimulating spinal/peripheral nerves with implanted electrodes, avoiding the cutaneous discomfort of TENS ( ). SCS and conventional PNS may be effective for treating persistent/chronic postoperative pain, where the long duration may justify the invasiveness and cost of the permanent implantable system. For example, SCS produced highly clinically significant reductions in chronic postoperative pain of more than 50% following total knee replacement in two patients refractory to other analgesic methods ( ). Another case report described the use of SCS to provide complete relief of chronic postoperative pain that had lasted 3 years following thoracotomy ( ). In addition, SCS is frequently used to treat failed back surgery syndrome ( ), although the etiology of this pain is not always clear (e.g., pain from the surgical procedure vs. misdiagnosis of original cause of low back pain). However, these stimulation modalities require invasive surgery to implant costly and permanent stimulation systems (i.e., electrodes and stimulator). As a result, they are highly unsuitable as a temporary therapy for acute postoperative pain, which usually requires only a few weeks of stimulation.

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