Spinal Cord stimulation (SCS) and intrathecal drug delivery systems (IDDS) are becoming increasingly important in the management of chronic pain. It will be progressively more common for the anesthesia team to encounter patients with these devices. This article aims to discuss possible concerns regarding the management of patients with SCS and IDDS in the perioperative period.
Spinal Cord Stimulation
The SCS is FDA approved for the treatment of chronic neuropathic pain of the trunk and limbs, radicular pain from failed back surgery syndrome, and complex regional pain syndrome. It has also been used in the treatment of peripheral nerve pain, peripheral vascular disease, and chronic intractable angina (1). With SCS, wire leads with electrical contacts at the distal portion are placed in the epidural space over the dorsal columns. The wire is then connected to a pulse generator. Prior to implantation, patients undergo an approximately one-week SCS trial period with percutaneously placed leads; those who experience significant pain relief or increased functional status progress to permanent implantation.
There are two options for permanent implantation. Wire leads can be placed percutaneously through a needle or a paddle can be placed via an open laminectomy. For both approaches, the leads will be tunneled beneath the skin and connected to the pulse generator (IPG) which can reside in the back, buttock, or abdomen.
There are five main companies offering SCS in the United States currently:
- Boston Scientific,
- St. Jude/Abbott,
- and Stimwave.
General Intraoperative Management
When a patient with an SCS presents for anesthesia, it is recommended that the device be reprogrammed to the lowest amplitude and turned off; patients can do this with their device controller as long as the battery has been charged and the patient has their controller present (1). Reprogramming ensures that in the event of inadvertent activation, the stimulation will be low and likely unnoticed. Turning off the device reduces the risk of accidental reprogramming via electromagnetic interference (2-6). The patient should be able to turn the device back on post-operatively via their controller. The device generally does not need to be interrogated immediately post operatively.
Electrocautery used in surgery can potentially damage any implanted electronic medical device through four main mechanisms by creating electromagnetic interference (EMI):
- Turning device on/off
- Resetting IPG to different frequencies or amplitudes
- Allowing high levels of current to pass through electrodes to target tissue causing inappropriate simulation or injury
- Allowing high current to permanently damage battery (7).
Bipolar cautery is less likely to create EMI than monopolar cautery as bipolar passes radiofrequency current through 2 tips of the instrument at a very short distance apart. All 5 SCS companies recommend use of bipolar electrocautery (2-6). If care is taken to ensure the device does not come between the 2 electrodes on the bipolar cautery device, no harm should come to the device or the patient (8).
If monopolar electrocautery is necessary, it should be used on the lowest effective setting and grounding pad should be placed as far as possible from the SCS on the opposite side of the IPG (9). If using monopolar electrocautery, it is recommended that the device be interrogated post-operatively to ensure proper functioning.
Neuraxial and Regional Anesthesia
The presence of SCS is not an absolute contraindication to neuraxial anesthesia. There have been case reports in which patients who developed postdural puncture headache after SCS lead placement were successfully treated with epidural blood patches with the leads in situ (10). However, depending on the desired level, placement of an epidural without fluoroscopy can be difficult or impossible. Placement of an epidural catheter for post-operative analgesia often requires placement at the T7-T12 levels for adequate coverage of the surgical site. These levels are also the most common levels for placement of SCS for coverage of low back and leg pain. At these levels, there is significant risk to damaging the SCS system. It is our opinion that the benefits usually do not outweigh the risks at certain levels.
Spinal anesthesia should not be influenced by the presence of a SCS device as long as pre-procedure x-ray is available to ensure that leads are not present at the desired neuraxial level (1). There is no contraindications to regional anesthesia for acute pain management in patients with SCS.
Infection risk is often cited as a concern and reason to avoid neuraxial and regional anesthesia in a patient with SCS. However, the risks of causing significant seeding of infection to the device are negligible during these procedures.
Seeding to the SCS device requires systemic bacteremia and has been reported from sources such as bowel perforation; infection of the SCS caused by seeding from neuraxial or regional anesthesia has not been reported. Of note, the mortality rate associated with infection of spinal implantable electronic devices (including both SCS and intrathecal drug delivery systems) is 1.83%.
This is significantly lower than the mortality rates associated with infections of CIEDs, knee replacements, and hip replacements (4.39%. 4.33%, and 4.22% respectively), yet neuraxial and regional anesthesia are routinely performed in patients with these hardware (11).
Both spinal and epidural anesthesia are reasonable at the levels required for OB anesthesia and analgesia, well below the level of SCS lead entry. While there is always the potential to damage the SCS system during placement of spinal or epidural, the risk is dramatically decreased with prior knowledge/x-ray imaging of implant location and technique used. It may be wise for patients with SCS to present for early anesthesia evaluation to provide adequate time for anesthetic planning.
In the past decade, Boston Scientific, Medtronic, Nevro, St. Jude/Abbott, and Stimwave have all developed SCS models that are labeled full body MRI conditional. However, MRI safety recommendations continue to vary significantly between SCS models and companies (12-16). Therefore, prior to any MRI the device manufacturer and model should be identified, and the appropriate device manual should be consulted. Elective MRIs should be postponed until appropriate documentation can be obtained. In cases of emergent MRI without available documentation, the risks and benefits should be weighed and alternative imaging modalities should be considered.
IDDS consists of a metal housing, usually implanted in the abdomen, that holds a bellow containing the drug, battery, and pump. Drug is delivered from the metal housing via a catheter into the intrathecal space (17). Currently IDDS are FDA approved for the delivery of baclofen, morphine, and ziconotide, however many other medications are used off label. Most pumps are designed to last 5-7 years and are refilled every 1-6 months depending on drug concentrations and dosing.
General Intraoperative Management
Prior to any procedure that might interfere with the IDDS, communication with the physician managing the pump is recommended. The age of the device, current pump medication and dosing, and the date of most recent pump interrogation should be determined. Contact information for the device representative and the patient’s pain management physician should be available in case any issues arise. As device malfunction may cause inadvertent over or underdosing of intrathecal medications, it is important to be familiar of the signs and symptoms of overdose or withdrawal of relevant medications.
Intraoperatively, temperature and positioning must be approached more carefully to avoid unwanted alterations in dosing. At body temperatures over 39℃, pump temperatures can be impacted, and patient can be at risk of increased drug delivery rates and overdose. When positioning, avoid excessive bending or twisting as this can kink, occlude, or damage the intrathecal catheter (17). According to manufacturer documentation, electrocautery is safe and unlikely to interfere with device function (18).
Peri-operative pain control in patients with IDDS can be challenging. In patients receiving intrathecal opioids at baseline, the addition of peri-operative opioids can cause respiratory depression. Unfortunately, there is not a reliable method to convert intrathecal opioids dosing to IV or PO dosing. Therefore, all patients should have opioid medications titrated carefully and receive appropriate monitoring. Of note, patients receiving intrathecal baclofen may have a greater than expected response to opioids due the synergistic nature of the drugs (17). Multimodal analgesia and regional anesthesia should be considered.
Neuraxial and Regional Anesthesia
Neuraxial anesthesia is not absolutely contraindicated in patients with IDDS. However, care must be taken to identify and avoid the entry point of the catheter into the spinal canal via review of prior imaging. Efforts should be made for multidisciplinary planning, utilization of imaging, and post-operative monitoring and device interrogation. Despite the challenges, a case series has been published describing the successful placement of epidural catheters in children with intrathecal baclofen pumps in situ. Sixteen children undergoing planned orthopedic surgery met inclusion criteria. The neurosurgical, pain, and regional anesthesia teams determined the appropriateness of epidural placement. Epidurals were placed fluoroscopically on the day of the procedure. Pumps were interrogated prior to discharge (19).
There are no contraindications to the use of regional anesthesia for acute pain management in patients with IDDS. In fact, the use of opioid sparing pain management modalities is often more important in these complex patients. An example of this a case report published describing the successful use of a lumbar plexus and sciatic nerve block as the primary anesthetic for left total knee arthroplasty in a patient with cerebral palsy with intrathecal baclofen pump. A continuous lumbar plexus catheter was used postoperatively for successful pain control (20).
Several case reports describe successful placement of labor epidurals in patients with intrathecal pumps. An article published in 1997 describes a 23-year-old G2P0 with a morphine intrathecal pump implanted via direct surgical exposure through a midline incision from the level of L1 to L3. Epidural catheter was placed below the level of her scar at the L3-4 level without imaging guidance. Patient had adequate labor analgesia without any significant complications (21).
Another study describes at 28-year-old G2P0 at 28 weeks who received an uncomplicated epidural. This patient was evaluated by the anesthesia team in the antenatal clinic where review of x-ray imaging, operative notes, and consultation with her neurosurgeon were completed. Epidural placement was performed without imaging guidance at the level below her IDDS insertion site at L4-5 without complications (22).
Interestingly, ultrasound can be used as a tool in these cases. A 44-year-old G1 P0 received an uncomplicated epidural for labor analgesia. Ultrasound of the lumbar spine (transverse and longitudinal views) were used to determine epidural depth and to ensure the pump catheter was not in the pathway of the Touhy. In this case, patient also had significant pre-labor planning including review of x-ray imaging to confirm location and entry point of intrathecal catheter, discussion with neurosurgeon, and planned placement of epidural early in labor (23).
These cases demonstrate that epidural placement is feasible in patients with IDDS. X-ray imaging should be reviewed to confirm position and entry level of the intrathecal catheter. Consultation with patient’s neurosurgeon or interventional pain physician should be considered. Imaging is not necessary, but ultrasound can be used.
The Medtronic Syncromed ER, Syncromed II, and the Prometric Flowonix are MRI conditional.
Prior to any MRI the device manufacturer and model should be identified and the appropriate device manual should be consulted as significant differences exist. For example, Prometric states that the Flowonix pump should be emptied prior to MRI; failure to do so can result in drug overdose and significant morbidity or mortality. In contrast, Medtronic does not recommend emptying the pump prior to MRI with the Syncromed ER or Syncromed II (17).
It is important to know that MRI exposure temporarily halts the pump and suspends delivery of intrathecal medications for the duration of the scan (24). Prior to any scan it is important to determine if drug delivery can be safely suspended or if drug needs to be supplied via an alternate route. After completion of the MRI, the IDDS should resume normal drug delivery automatically. The device should be interrogated after completion of the MRI to ensure that drug delivery has restarted appropriately. Special attention should be paid to patients receiving intrathecal baclofen as withdrawal can be life threatening (17).
- Hardman MI, Hagedorn JM. Perioperative Spinal Cord Stimulation Management: A clinical scenario of device loss and recommendations for Anesthesiologists. Pain Physician. 2020 February; 21(4):865-867.
- Nevro. Physician implant data: www.accessdata.fda.gov/cdrh_docs/pdf13/P130022d.pdf.
- Medtronic Pain Therapy. http://manuals.medtronic.com/wcm/groups/mdtcom_sg/@emanuals/@era/@neuro/ documents/documents/contrib_199974.pdf.
- St. Jude Medical. Power over your pain. www.poweroveryourpain.com/safety/SCSSafety.
- Precision Spectra™ Spinal Cord Stimulator System. http://hcp.controlyourpain.com/scs-safety-information/precisionspectra.
- Stimwave Technologies. Freedom spinal cord stimulator trial kit manual. http://stimwave.com/mobile/wp-content/uploads/2016/01/LA-FR8A-1-869-TrialInstructions-for-Use.pdf
- Srejic U, Larson P, Bickler P. Little Black Boxes: noncardiac Implantable Electronic Medical Devices and their Anesthetic and Surgical Implications. Anesthesia-Analgesia. 2017 July;125(1):124-138.
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- Simopoulos TT, Sharma S, Amer M, Gill JS. The incidence and Management of Postdural Puncture headache in Patients undergoing Percutaneous Lead Placement for Spinal Cord Stimulation. Neuromodulation 2016; 19:738-743
- Goel V, Kumar V, Agrawal SN, Patwardhan AM. Outcomes Associated with Inrection of Chronic Pain Spinal Implantable Electronic Devices: Insights from a Nationwide Inpatient Sample Study. Neuromodulation 2020; E-pub ahead of print. DOI:10.1111/ner.13263
- Medtronic SureScan‡ MRI Manuals. 2018. http://www.mrisurescan.com/index.html
- Abbott MRI Ready Systems Manual. 2018. https://www.sjm.com/mriReady
- Boston Scientific ImageReady‡ MR-Conditional Systems. 2018. http://www.bostonscientific.com/imageready/en-US/scsmriinfo.html
- Nevro MRI Guidelines for Senza‡ System. 2018. https://www.nevro.com/English/Physicians/MRI/default.aspx
- Abbot. MRI parameters by company. 2018. PDF file
- Nadherny W, Anderson B, Abd-Elsayed A. Perioperative and Periprocedural Care of Patients with Intrathecal Pump Therapy. Neuromodulation 2019; 22:775-780.
- Medtronic. SyncroMed, IsoMed: implantable Infusion Systems. Minneapolis, MN: Medtronic 2017; p. 1-35
- Eklund S, Samineni A, Koka A. Epidural Catheter Placement in Children with Baclofen Pumps. Pediatric Anesthesia 2020.
- Bojaxhi E, Salek D, Sherman C, Greengrass R. Regional anesthesia for a total knee arthroplasty on an adult patient with spastic diplegia and an intrathecal baclofen pump. Romanian Journal of Anesthesia and Intensive Care 2017; 24 (1):69-72.
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- Ali Sakr Esa W, Toma I, Tetzlaff E. Epidural analgesia in labor for a woman with an intrathecal baclofen pump. International Journal of Obstetric Anesthesia 2009; 18:64-66.
- Badve M, Shah T, Jones-Ivy S, Vallejo MC. Ultrasound guided epidural analgesia for labor in a patient with an intrathecal baclofen pump. Int J Obstet Anesth. 2011 Oct; 20(4):370-2. doi: 10.1016/j.ijoa.2011.06.009. Epub 2011 Aug 12. PMID: 21840204.
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