ASRA Pain Medicine Update

Spinal cord stimulation (SCS) is an evidence-based treatment modality for a number of chronic pain conditions. As with any invasive procedure, SCS is associated with its share of complications, with reported rates of approximately 30%–40%.¹ Complication rates can be generalized as device related, biologic, or programming or therapy related, with device-related complications accounting for the highest incidence. Although infection may not be the most frequent complication, it can be particularly devastating if a patient is unable to be reimplanted, thereby losing access to a beneficial therapy. Infection rates in SCS generally range from 2.45%–6%, but have been reported to be as high as 10%.^2,3 Taking efforts to minimize surgical site infections (SSI) is critical because they are associated with increased morbidity, mortality, and healthcare-related costs. In terms of SCS, an SSI is considered to be an infection in the region that occurs within one year of device implant.

Taking efforts to minimize surgical site infections (SSI) is critical because they are associated with increased morbidity, mortality, and healthcare-related costs.

Recent efforts have been made to further evaluate SSIs in the field of neuromodulation and to promote standardized practices that prevent and reduce SSIs. The Neurostimulation Appropriateness Consensus Committee (NACC) published recommendations in 2017 to establish standards to reduce infectious complications for patients receiving neuromodulation.³ Hoelzer et al. published a multicenter retrospective study of 2,737 unique implants or revisions of SCS systems which demonstrated an overall infection rate of just 2.45%, which is lower than previously reported rates and may be more indicative of contemporary SCS SSI rates.²

Implanting physicians should make every effort to decrease SSIs by using risk-reduction strategies throughout the perioperative period. Prevention measures can fall into three categories: preoperative, intraoperative, and postoperative. After the critical step of patient selection, the preoperative period starts with a thorough preoperative workup and comprehensive evaluation that considers and optimizes comorbidities. Many risk factors can increase risk for SSI, including tobacco use, uncontrolled diabetes, elevated body mass index, anemia, history of chronic obstructive pulmonary disease or congestive heart failure, immunosuppression, malnutrition, systemic infection, presence of Staphylococcus aureus, previous SSI, prolonged surgical time, lack of perioperative antibiotics, anticoagulation, and poor surgical hemostasis.^2,4

The preoperative measures that NACC³ and the Centers for Disease Control and Prevention⁵ recommend include glucose control optimization and smoking cessation for at least four weeks. NACC recommends limiting steroids in the immediate preoperative period, considering treatment of potential infection sources, and attempting to optimize nutritional status in the perioperative period prior to consideration of neuromodulation. NACC does not recommend that HIV be viewed as a contraindication, but it does recommend consulting with an infectious disease specialist to optimize the viral load. Similarly, it recommends consultation with an oncology specialist for patients with active malignancy prior to consideration of an implant.

Anticoagulation therapy should be appropriately managed based on existing guidelines. The skin in the surgical area should be carefully examined prior to surgery. The case should be cancelled or delayed until resolution of any local infections or skin abnormalities. Vital signs, including temperature, heart rate, and blood pressure, should be critically evaluated for potential indications of systemic infection. Routine decolonization of all patients is not recommended, but preoperative testing for Staphylococcus aureus (MSSA and MRSA) is recommended. If Staphylococcus aureus is found, decolonization with mupirocin ointment and chlorhexidine baths is recommended. Electrical clippers should be used immediately prior to surgery if hair removal is required. Prophylactic antibiotics should be administered preoperatively, according to preexisting guidelines.

Intraoperative measures include using a surgical scrub for two to five minutes with chlorhexidine-based products combined with isopropyl alcohol for skin preparation, taking maximal sterile barrier precautions, and double gloving. Operating room traffic should be minimized, and sterile C-arm drapes and light handles should be used. If adhesive drapes are used, they should be iodophor impregnated. Physicians credentialed for neuromodulation procedures should perform a minimum of 10 cases as the primary implanter and under supervision during training. Other surgical measures to limit infection include limiting surgical tissue trauma, performing surgical irrigation with saline through a bulb syringe before closing the surgical wound, and closing dead space with appropriate tension. Skin closure with staples or suture is at the discretion of the surgeon. Routine use of chlorhexidine-impregnated dressings is not recommended, nor is vancomycin powder; however, further studies are needed. Antimicrobial envelopes around implantable pulse generators in patients at high risk for infection can be considered.

Postoperatively, precautions include using sterile occlusive dressings for 24–48 hours, considering discontinuing antibiotics within 24 hours following SCS implants, educating patients and families for signs and symptoms of SSIs, promptly recognizing SSIs, and implementing appropriate management strategies. Although NACC recommends discontinuing postoperative antibiotics within 24 hours following surgery, Hoeltzer et al. found a statistically significant decrease in the infection rate in patients who received antibiotics beyond 24 hours postoperatively.² The majority of patients in their study received cephalexin (78.3%). Additionally, they found that patients with permanent SCS implantations after a previous trial of more than five days had a significantly higher infection risk pertaining to the permanent implant and not the trial itself. They found a decreased rate of infection for staged trials followed by immediate implant versus the traditional trial approach. Finally, they also found an increased rate of infection in patients who underwent SCS implants at an academic institution. They postulated the presence of larger perioperative teams and increased operating room traffic as reasons. See Table 1 for a complete list of surgical site infection prevention measures and their associated levels of evidence support.

A majority of infections occur at the generator site, with lower infection rates at the SCS electrode implant and lumbar incision sites.³ The most common causative organism is Staphylococcus species. Hayek et al. previously found a median time from implant to occurrence of infection of two months.⁴ Superficial SSIs involve the skin and subcutaneous tissue surrounding the incision and are defined as infections occurring within 30 days after the operation, whereas deep SSIs involve the deep soft tissue including the muscle and fascia and occur up to one year postoperatively. Deep SSIs are reported less frequently than superficial infections and can have a more insidious onset.⁵ Although C-reactive protein (CRP) levels predictably elevate following surgery, these levels typically normalize within two to three weeks postoperatively.⁶ Failure of the CRP levels to normalize or an acute increase in the CRP levels is a sensitive predictor of an SSI. Physical exam findings in the setting of SSIs can include temperature fluctuations, tachycardia, hypotension, chills, pruritus, pain or warmth over the surgical site, purulent drainage, wound dehiscence, and swelling.

Empiric antibiotics should be promptly initiated once an infection is suspected, with narrowed antibiotic coverage employed once the microbial culture has resulted. An infectious disease consult should be obtained, and neuraxial imaging should be considered if physicians have a high suspicion for a deep infection including epidural involvement. Superficial infections can be treated more conservatively with antibiotics and close monitoring; however, they can track along the device over time and progress to a deeper infection. When a deep SSI is identified, whether by imaging or clinical evaluation, explantation of the device is recommended in most cases. Once the device is removed and purulent material is drained, copious irrigation is recommended to clear all of the infected material. Considerations should also be made for drain placement and a primary closure versus serial packing.³

SSIs related to SCS trials and implants remain a significant complication that can cause significant morbidity. All physicians implanting these devices should have a strong knowledge of methods of infection prevention and management guidelines to help minimize infection risk as much as possible. Even with appropriate preventative measures, infections may still occur, and the physician must be able to promptly identify and treat these infections.

References

1. Cameron T. Safety and efficacy of spinal cord stimulation for the treatment of chronic pain: a 20-year literature review. J Neurosurg. 2004;100:254–267. https://doi.org/10.3171/spi.2004.100.3.0254
2. Hoelzer C, Bendel MA, Deer, TR, et al. Spinal cord stimulator implant infection rates and risk factors: a multicenter retrospective study. 2017;20:558–562. https://doi.org/10.1111/ner.12609
3. Deer TR, Provenzano DA, Hanes M, et al. The neurostimulation appropriateness consensus committee (NACC) recommendations for infection prevention and management. 2017;20:31–50. https://doi.org/10.1111/ner.12565
4. Hayek SM, Veizi E, Hanes M. Treatment-limiting complications of percutaneous spinal cord stimulator implants: a review of eight years of experience from an academic center database. 2015;18:603–609. https://doi.org/10.1111/ner.12312
5. Berrios-Torres S. et al. Centers for disease control and prevention guideline for the prevention of surgical site infection, 2017. JAMA 2017;152(8):784-791.
6. Mok JM, Pekmezci M, Piper SL, et al. Use of C-reactive protein after spinal surgery: comparison with erythrocyte sedimentation rate as a predictor of early postoperative infectious complications. 2008;33:415–421. https://doi.org/10.1097/BRS.0b013e318163f9ee