Somatosensory Evoked Potential (SSEP) Monitoring for Brachial Plexus Injury
Condition: Brachial Plexus Injury; Peripheral Nerve Injuries
MeSH terms: Peripheral Nerve Injuries; Wounds and Injuries
Study type: Observational

Summary: 
      Brachial plexus block is a common regional anesthesia technique which is performed by
      anesthesiologists to anesthetize the arm for surgery. In this study, we are investigating the
      relationship between the nerve conduction (induced by brachial plexus block) and the
      patients' symptoms before and after the brachial plexus block. We will attach a nerve
      conduction device (SSEP device) to monitor the patients' arm conduction and we will assess
      the patients' symptoms simultaneously.
    

Detailed description: 
      Perioperative peripheral nerve injury (PNI) is an under-recognized and under-investigated
      complication of general anesthesia and continues to impact postoperative recovery resulting
      in patient disability malpractice claims.(1-5) In the American Society of Anesthesiologists
      (ASA) Closed Claims Analysis (published in 1999), PNI was the second most common cause of
      claims other than death. (6-7) This claim pattern has remained essentially unchanged over the
      past 3 decades and the average settlement was $123,000 US Dollar/claim (unpublished data from
      ASA closed claims analysis). The overall incidence of PNI varies across different surgical
      procedures, and it is significantly affected by the underlying patient comorbidities and
      pre-existing peripheral neuropathy. Despite considerable implications of PNI to both the
      patients and clinicians, little progress has been made in the past three decades in
      developing a reliable intraoperative monitoring technique for its early detection and
      prevention. SSEP monitoring has long been used in neurology as a means to diagnose peripheral
      neuropathy and has been used for the early detection of intraoperative PNI caused by improper
      patient positioning. A few retrospective studies have found that reversal of intraoperative
      SSEP signal changes (e.g. correct the patient's arm position in the event of a positioning
      related peripheral nerve compromise) prevented postoperative neuropathy, suggesting SSEP
      could be used to detect intraoperative PNI and that prompt intervention could reverse
      neurological injury (8-10). However, to date, there has not been a study that clearly defines
      how the magnitudes of SSEP changes relate to the severity of peripheral nerve dysfunction.
      Due to this lack of information, the current thresholds that are used for diagnosing PNI in a
      variety of surgical procedures are largely based on the results of SSEP monitoring in spinal
      cord injury. The traditional diagnostic criteria (used in spinal cord injury) might not be
      applicable for PNI. Fundamentally, there is also a lack of a clinical study that defines
      significant and non-significant changes for PNI. Most current available evidence regarding
      SSEP in PNI is retrospective and mainly derived from patients being monitored for spinal cord
      or cerebral injury during neurosurgical procedures. The lack of well-validated diagnostic
      criteria is one of the key issues in preventing the use of SSEP for monitoring peripheral
      nerves during surgery. As such, further studies are required to characterize the relationship
      between SSEP changes and peripheral nerve dysfunction and re-define the threshold (or cut-off
      values) for significant SSEP change for PNI.

      This is a prospective cohort study to evaluate the relationship between the peripheral nerve
      dysfunction, and SSEP signal changes in patients who will receive a brachial plexus block for
      their surgical procedure. Brachial plexus block is a regional anesthesia technique routinely
      performed by anesthesiologists where the nerves in the arm are blocked with local anesthetics
      to prohibit movement and sensation. In LHSC, the average brachial plexus block performed is
      around 10-15 patients/day for various upper limb surgeries. In this study, the patients with
      brachial plexus block will be used as a model of brachial plexus injury to assess the
      relationship between intraoperative brachial plexus injury and the SSEP changes. Brachial
      plexus block in awake patients is an attractive model to study brachial plexus injury,
      because it provides transient and progressive de-afferentation state of brachial plexus
      dysfunction (mimicking brachial plexus injury), allows for real-time assessment of the
      relationship between clinical symptoms and SSEP changes (awake patients), and overcomes
      obvious practical limitations of investigating intraoperative PNI (small sample size of
      patients with intraoperative brachial plexus injury). In this study, 50 consecutive patients
      who required a brachial plexus block for their surgery, will be recruited. This study will be
      performed in the "Block Room" of either London Health Science Centre or St Joesph Hospital,
      London, Ontario. After obtaining informed consent, an independent assessor (hand specialist)
      will perform a baseline assessment of the sensory and motor function of the upper limb. The
      sensory function will be quantified by a two-point discrimination test in each dermatome. The
      motor function will be quantified by the motor score in each myotome. The patients will be
      attached to the automated SSEP monitor to obtain baseline upper limb SSEP signals. Median,
      ulnar and radial nerves will be monitored. After satisfactory baseline SSEP recordings have
      been obtained, a brachial plexus block will be performed in the usual fashion to achieve
      complete sensory and motor blockage (approx. 30 min). This provides a unique experimental
      condition to assess the relationship between the brachial plexus dysfunction and the SSEP
      signal changes. An independent assessor (hand specialist) will re-assess the patients'
      sensory and motor function every 5 minutes (up to 30 minutes during the onset of the block).
      SSEP recording will be concomitantly obtained. A total of 300 data pairs (6 data pairs for
      each patient) will be obtained for analysis. In this study, the Evoked Potential Assessment
      Device (EPAD®, SafeOp Surgical, Hunt Valley, MD) SSEP machine will be used. It is a novel,
      simplified, automated SSEP monitoring device (FDA approved), designed to detect
      intraoperative PNI. The key features of EPAD® are that only the surface adhesive electrodes
      (i.e. no subdermal needle electrodes) will be used, as well as there is newly artifact
      rejection and optimization algorithm that permit SSEP recording in awake patients.

      Prior to performing the brachial plexus block in the "Block room", a complete neurological
      examination will be performed including motor score and 2-point discrimination test. Eligible
      patients will be recruited after obtained informed consent. The baseline SSEP of the
      participants will be recorded using the EPAD@ device. After the participants received the
      brachial plexus block (as part of their standard of care), the participants will be
      monitoring the progressive changes of SSEP signals while the effect of brachial plexus block
      gradually onset (usually takes around 30 minutes). An independent assessor (hand specialist
      blinded to the SSEP results) will concomitantly re-assess the patients' sensory and motor
      function every 5 minutes (up to 30 minutes during the onset of the block).

      The primary analysis will be on describing the relationship between the severity of the
      neurological deficits (impaired sensory and/or motor function) and SSEP changes (amplitude
      and/or latency changes). Secondarily, an optimal cut-off limit using Youden index and/or
      logistic regression-derived likelihood ratio functions will be determined. A
      Receiver-operating-curve for the new cut-off limits will be assessed. REDCapTM will be used
      for electronic data collection and STATA (version 14) will be used for statistical analysis
      in all the studies. These new cut-off limits in comparison with conventional criteria in our
      subsequent clinical studies will be compared.
    

Intervention name(s): SSEP monitoring
Intervention type(s): Device
Intervention description(s): Participants will be monitored using the SSEP device both before and after induction of a brachial plexus block.
Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        All adult patients who are scheduled to have elective upper limb surgeries and require a
        brachial plexus block as part of their standard of care.
      
Keywords: SSEP Monitoring; Diagnostic threshold