Up to 5% of total shoulder arthroplasty patients experience transient or permanent nerve injury during surgery. In this study, we will monitor the nerve transmission of the patients' arm to detect whether the nerve is functioning normally. This techniques is called somatosensory evoked potential (SSEP) monitoring. In this study, we will assess whether SSEP monitoring could detect nerve abnormalities, alerts the surgical team enabling optimize their surgical intervention and prevent surgical related nerve injury.

Perioperative PNI is a well-recognized but seriously under-investigated complication of general anesthesia. Arguably, such nerve injury may be viewed as being as devastating as spinal cord and cerebral injury, as the resultant functional disabilities may be very comparable.(1) Many such nerve injured patients require prolonged recovery and rehabilitation, while some result in long-term disability and/or litigation due to motor deficits and chronic pain.(2-5) In ASA Closed Claims Analysis PNI was the second most common cause of claims other than death.(6, 7) However, little progress has been made in the past three decades in developing a reliable intraoperative monitoring technique for early detection and prevention. SSEP monitoring is a potential option for preventing PNI. Abnormal SSEP is widely used as a surrogate outcome for PNI in research studies (8-11). Additionally, previous studies (12-17) investigating the use of SSEP for spinal cord or cerebral injury during neurosurgical procedures have incidentally found high incidences of abnormal SSEP (4-7%) due to mal-positioning that was corrected with repositioning; this suggested SSEP could be used to detect intraoperative PNI and that prompt intervention can reverse PNI. However, there have been no further prospective studies to evaluate the diagnostic value of SSEP, or its outcome benefit. This is largely because conventional SSEP is a bulky, expensive and labor-intensive monitoring modality, requiring a technologist for operation and interpretation.(18) Because of these budgetary and logistical limitations, as well as the relative lack of clinical evidence, SSEP is not performed routinely in most surgical centres solely for the purpose of PNI detection. The recent introduction of the Evoked Potential Assessment Device (EPAD®, SafeOp Surgical, Hunt Valley, MD) may be able to overcome these practical barriers. It is a novel, simplified, automated SSEP monitoring device (FDA approved). The key features of EPAD® are its compactness, ease of connectivity via Bluetooth, and its use of surface adhesive electrodes that remove the potential for needle-stick injuries. This device also incorporates an automated progressive signal optimization algorithm, several newly developed artifact rejection and electrocautery suppression technologies as well as an auto-interpretation diagnostic system. It eliminates the need for a designated technician and permits simplified and direct interpretation of the SSEP data for clinicians in the operating room. This device also enables display and storage of raw SSEP data permitting post hoc area-under-curve analysis. (Fig. 3) We have previously evaluated the clinical utility of this automated SSEP device in 33 cardiac surgical patients (19). This pilot study found that automated SSEP monitoring can be performed readily in a busy cardiac operating room. The raw signal quality is reliable and comparable to the conventional SSEP machine. These results indicate that this device is able to eliminate the practical challenges of performing SSEP monitoring and confirmed its feasibility for routine use.(REB# 104826) Surgical-related nerve injury during TSA is one of the highest risk subspecialties leading to postoperative upper limb peripheral neuropathy with reported incidences of 1-4% (20-22). A previous cohort study10, using motor evoked potential and EMG to evaluate the nerve injury during TSA, reported an exceedingly high incidence of intraoperative alerts (56.7% of patients). Importantly, 76.7% (23 of 30) of nerve alerts were reversed with repositioning of the patients' arm and removal of the retractor. Another cohort study11 in shoulder rotator cuff repair reported an even higher incidence of nerve alert (76.5%). Both studies were received Neer research awards from the Orthopedic Society, however neither study has informed the outcome benefit nor has assessed the relationship between cumulative injury, baseline nerve reserve and postoperative neuropathy. Accordingly, we propose to perform single blinded, superiority, parallel design, prospective randomized controlled study to assess the efficacy of the automated SSEP device in preventing PNI during TSA and explore the dose-response relationship of PNI.

Inclusion Criteria:

• Adult elective patients undergoing total shoulder arthroplasty surgery using general anesthesia

Exclusion Criteria:

• Patients unable to perform complete neurological examination
• Patients who refuse to participate
• Unable to obtain informed consent.
• Patients who are contraindicated for (or unable to perform) SSEP monitoring
• Patients who have known pre-existing peripheral neuropathy or brachial plexus injury
• Patients who are contraindicated to brachial plexus block

The patient and the outcome assessor will be blinded. The physicians and operating room nurses, anesthesiologists could not be blinded due to the nature of the intervention