• Jason Chui, Alex Freytag, Greydon Glimore, Shalini Dhir, Max Rachinsky, and John Murkin.
• Department of Anesthesia and Perioperative Medicine, Schulich School of Medicine and Dentistry, University of Western Ontario, C3-106, University Hospital, 339 Windermere Road, London, ON, N6A 5A5, Canada. Jason.chui@lhsc.on.ca.
• Can J Anaesth. 2021 Jul 1; 68 (7): 1018-1027.

PurposeIntraoperative nerve dysfunction has been difficult to investigate because of its rarity and unpredictable occurrence. The diagnostic test attributes of nerve function monitors have not been clearly defined. This proof-of-concept study aimed to assess the feasibility of using brachial plexus blockade (BPB) in awake patients as an experimental model for nerve dysfunction to characterize the diagnostic test attributes of somatosensory evoked potentials (SSEPs).MethodsWe obtained baseline SSEPs and neurologic function in patients and subsequently placed BPBs (experimental model) to generate progressive states of nerve dysfunction. We monitored SSEP changes (index test) and neurologic symptoms (reference standard) simultaneously during the onset of BPB to determine the temporal relationships and diagnostic test attributes of SSEPs.ResultsBrachial plexus blockade produced differential motor and sensory dysfunction that allowed simultaneous clinical and neurophysiologic assessment. One hundred and fifty-seven pairs of multiple data points from 14 patients were included for final analysis. The onset of abnormal SSEP signals almost always preceded the onset of neurologic symptoms. The sensitivities and specificities of SSEP to detect the impairment of power (motor rating score ≤ 4/5), cold sensation, and two-point discrimination were 100% and 67%, 99% and 55%, and 100% and 46%, respectively.ConclusionThis study found that BPB can produce sufficient differential nerve dysfunction to allow adequate evaluation of the diagnostic test attributes of SSEPs as a nerve monitor. The results of this study may stimulate further work on refining intraoperative nerve dysfunction models and diagnostic nerve function monitors.Trial Registrationwww.clinicaltrials.gov (NCT03409536); registered 24 January 2018.

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