The Nerve Desk

Tag: neurosurgery

  • Case Example #1 – Positional Saphenous Nerve SSEP Changes During L3-4 XLIF

    Case Example #1 – Positional Saphenous Nerve SSEP Changes During L3-4 XLIF

    The femoral nerve is the largest branch of the lumbar plexus. It originates from posterior L2 divisions to L4, and innervates the surfaces of the medial and anterior thigh. The saphenous nerve is monitored as the largest cutaneous branch of the femoral nerve to reflect femoral nerve sensory function during indicated procedures. For the lateral lumbar and eXtreme lateral interbody fusion (LLIF and XLIF) procedures, which are mostly performed between the L2-L5 levels, this main branch is mostly at risk by way of retraction systems in situ. This case presents an example of saphenous nerve SSEP changes with relatively stable tibial nerve SSEPs, further reinforcing the importance of saphenous nerve monitoring during lateral procedures.

    NuVasive XLIF Procedure Animation – NuVasive

    This patient was a 45-year old female, presenting with complaints of excruciating lower back and left-sided leg pain with associated numbness through her hip and into her foot. She was also beginning to experience these symptoms on the right. She had no weakness. She states she had no history of diabetes, hypertension, seizure, or stroke. Her prior surgical history included a lumbar fusion at L4-5 and a cervical fusion.

    She was positioned in the lateral decubitus position with her left side up and knees bent towards her chest. Tape was wrapped around the hips, just above the knee, and across the lower legs to keep her in place on the bed. Pillows were placed between the knees. Anesthetic protocol included a total intravenous method, utilizing between 100- 150mcg/kg/min of propofol and a steady 0.30mcg/kg/min of remifentanil. Surgeon requested SSEP monitoring (Saphenous + Posterior Tibial + Ulnar) with NuVasive EMG for dilator / nerve stimulation. Needle electrodes were placed in the standard placements for PTN, SN (Fig 1), & UN stimulation with additional needles behind the popliteal fossa and sticky pads over the femoral nerve as back-up for saphenous nerve.

    Figure 1: Stimulation placement for saphenous
    nerve SSEPs (figure from Silverstein et al. 2015)

    Baseline SSEPs were monitorable from all extremities except for RPTN, which was just barely marginally present. (Fig 2). Initial RPTN SSEPs were monitorable but quickly appeared to wash out following additional traces. PTN SSEPs were stimulated at 60mA 0.5ms 2.09Hz, SN SSEPs at 70mA 0.5ms 2.09Hz, and UN SSEPs at 30mA 0.3ms 2.09Hz. PTN + SN SSEPs were interleaved on the same timeline to more quickly acquire lower extremity data.

    Figure 2: Baseline PTN & SN SSEPs

    A change in the LSN SSEPs was reported almost immediately after setting baselines and prior to any implant sizing or placement (Fig 3). Some decompression work had begun but it was believed based on stimulation trials that the surgeon was well away from any significant nerve roots or groups. No problems in SSEP stimulation delivery were apparent based on movement during stimulation in all 4 extremities.

    The recommendation therefore was made to maintain an elevated blood pressure (declined due to surgeon preference for lower mean blood pressure for less bleeding) and to remove any distraction down at the legs. The surgeon declined this at the time as well, stating that he had a good deal of retraction in place and that it would interfere with surgical maneuvers. For the time being, the legs were only gently moved around and shaken to attempt to restore some blood flow to the legs.

    Figure 3: Loss of Left SN SSEP (Bottom Left)

    Immediately after instrumentation was in place, the tape across the hip, knee, and foot was cut away and removed. The left leg was lifted off the right and set back into its original position, only without tape. Within one data set, LSN SSEPs were within baseline parameters (from 90%+ reduced) and Right PTN SSEPs were much more reliable in cortical channels (Fig 4). Some improvement was seen in LSN subcortical responses as well.

    Figure 4: Recovery of Left SN SSEP after tape removal. Mild improvement also seen in R PTN SSEP (slightly more repeatable).

    The patient was then flipped to prone for posterior instrumentation with no significant events. She woke up with no additional deficits, and not much psoas pain which is very common following lateral spine surgeries. Because the actual data changes occurred in only LSN SSEPs, this case demonstrates the usefulness of saphenous and/or femoral nerve SSEPs in not only directly assessing L2-L4 nerve root function, but also as a reflection of possible malpositioning during lateral spine surgery.

    Monitoring PTN + SN/FN SSEPs on the same timeline can be helpful to evaluate most at-risk sensory pathways simultaneously. Positioning effects can occur prior to any monitoring and must therefore be approached quickly in the absence of monitorable baselines in patients with no pre-operative deficits.

    Figure 5: History stack of SN SSEPs illustrating loss + recovery. Change reported @ 12:24, Tape Removed @ 12:54.

    For more reading, please see the always-fantastic Dr. Silverstein’s article:

    Silverstein J, Mermelstein L, DeWal H, Basra S. Saphenous nerve somatosensory evoked potentials: a novel technique to monitor the femoral nerve during transpsoas lumbar lateral interbody fusion. Spine (Phila Pa 1976). 2014 Jul 1;39(15):1254-60. doi: 10.1097/BRS.0000000000000357. PMID: 24732850.

  • Communication in Neuromonitoring

    Communication in Neuromonitoring

    Effective communication and teamwork is essential for the delivery of high quality, safe patient care.

    Failures to communicate are the leading cause of inadvertent patient harm.

    Closed-loop communication (CLC) is essential for safety and precision in healthcare, particularly during complex surgeries involving intraoperative neuromonitoring (IONM). The neuromonitoring clinician cannot effectively do their primary function without clearly and confidently communicating baseline data, early changes, wave loss, or stimulation results.

    (I would say in the context of an “early change”, anything that is an immediately noticeable trace-to-trace difference that I can’t attribute to a technical or anesthetic factor warrants at least a brief notification.)

    In surgical environments, situational awareness is vital. CLC enhances this awareness by ensuring that all information is not only shared but acknowledged and confirmed by the appropriate team members.

    Phrases like “Dr, I have a complete loss of right leg and foot MEP responses” or “Responses have returned after increasing the MAP” must be acknowledged aloud by the surgeon or anesthesiologist to confirm shared understanding and coordinated action.

    Teams should use effective tools and structured communication behaviors, such as the SBAR technique (Situation, Background, Assessment, Recommendation). For example:

    • S: “We’ve lost MEPs in the left lower extremity.”
    • B: “Signals were stable prior to osteotomy.”
    • A: “This may indicate some level of spinal cord compromise.”
    • R: “Recommend surgical pause, increase in MAP, and re-testing after a few minutes.”

    Using critical language – clear, standardized phrases that denote urgency or required action – also supports rapid response. Terms like “Signal loss,” or “Absent after…,” convey priority issues that must be addressed without delay. Hinting and hoping that you have been heard is fraught with hazard.

    There is a hierarchy in medicine, and while it may be difficult to speak up with concerns due to certain power structure, cultural norms, or uncertainty, the ability to get everyone to stop and listen is essential for safe care. The reliability of IONM is threatened when the clinician’s role is neglected, and the decision to change course of a surgery relies heavily upon the communicator.

    Checklists can be extremely useful to ease cognitive burden when faced with potential significant changes. And while there’s no substitute for being having situational awareness, we must all be cognizant and anticipate “the next steps” when dealing with waveform loss. See the following from Vitale 2014, a classic in the IONM world.

    As neuromonitoring clinicians, we must overcome the heavy cognitive bias of the surgeon when there is a change. They will (understandably) want to see their carefully planned procedure through to the end, and experience with changes and patients waking with no or extremely minimal deficit can prohibit taking action when there is potentially serious change.

    Maintaining team alignment through frequent communication about patient history, surgical milestones, and frequency of testing ensures the neuromonitoring clinician is integrated – not isolated – in the care process.

    Ultimately, we must all be accountable for the patient. Every team members commitment to structured, reliable communication, shared awareness, and mutual respect ensures the best possible outcome for the patient.

    For more reading, I suggest:

    Dormans JP: Establishing a standard of care for neuromonitoring during spinal deformity surgery. Spine (Phila Pa 1976). 35:2180–2185, 2010

    Leonard M, Graham S, Bonacum D: The human factor: the critical importance of effective teamwork and communication in providing safe care. Qual Saf Health Care; 13 (Suppl 1):i85-i90, 2004

    Vitale MG, Skaggs DL, Pace GI, Wright ML, Matsumoto H, Anderson RC, et al: Best practices in intraoperative neuromonitoring in spine deformity surgery: development of an intraoperative checklist to optimize response. Spine Deform 2:333–339, 2014

  • Clinical Tip #1: Be Early

    Clinical Tip #1: Be Early

    It sounds simple enough.

    But being early permits you to take advantage of a lot.

    First, the earlier you are, the more likely you are to learn that your case has canceled because your patient had coffee with cream and you can go back to bed. Kidding. Sort of.

    Many of us performing IONM are not employed by a hospital system, but rather are contracted clinicians through a third-party company. Technically, we can show up basically whenever, as long as we get the job done. But…

    The best advantages, in my mind, come from the reduced stress and anxiety of setting things up. Ask yourself: “Do I have all of the tools I need for today? Probes, check. Stimulator clips, check. Electrodes, check.”

    Do I have ample time to turn on my system and confirm its proper functioning? There’s nothing worse than a patient rolling in the room and your MEP stimulator isn’t connecting and you need a new one. You could have figured that out before anesthesia started!

    Being early allows you to shape your workspace and mentally prepare your flow. Early hours are often quieter, offering better concentration and fewer interruptions. Preparedness is confidence, and confidence is calming. Not just to you, but to everyone in the room.

    I recently did monitoring for a case where I called before I left for an afternoon start, confirmed on-time, showed up, and the patient was being positioned. It happens. I was wholly unprepared, and although I knew what I was doing, the setup was extensive and I was definitely not calm. In fact – I could’ve been better. Luckily I had a patient surgeon and good data, but I did not know what I was walking into because I had nothing prepared and hadn’t spoken to the patient.

    After that case, I remained on high stress for a little while after. I feel that when your workday begins slowly and smoothly, you are much less likely to carry that tension home, which enhances work-life balance.

    In general, my rule of thumb is: Clothes changed into scrubs 1 hour before first-start cases, 1.5 hours before afternoon starts. Let me know when you like to show!