Median Nerve Stimulation to Detect Awake and Anesthetized States with Riemannian Classifiers
Résumé
Among all the operations with general anesthesia worldwide, some patients have had the terrible experience of Accidental Awareness during General Anesthesia (AAGA), an unexpected awakening during surgery [1], potentially leading to pain, recall of surgical events and post-traumatic stress disorders [2]. The inability to predict AAGA using only clinical signs, leads to the use of brain activity monitors [3]. Given AAGA patients’ first reflex to move, impeded by neuromuscular-blocking agents, we propose using a new Brain Computer Interface (BCI) with Median Nerve Stimulation (MNS) to detect their movement intentions (MI). Combining MI and MNS significantly impacts MNS-generated patterns, leading to better MI detection accuracy. MNS also provides a trigger, resulting in better classification (+18%) compared to asynchronous BCI [4].
To continue in this direction, we analyzed the MNS patterns of 13 patients receiving propofol, an intravenous anesthetic, during surgery at CHU Brugmann, Belgium [5]. Two conditions were examined: EEG activities of preoperative MNS while the patient is awake (MNS-awake), and intraoperative MNS during various stages of anesthesia (MNS-anesthesia). Then, a Riemannian Minimum Distance to the Mean classifier achieved 97% test balanced accuracy in distinguishing awake and anesthetized states. We also observed the classifier’s response evolution with anesthesia depth, in terms of distance between the MNS-awake class centroid and covariance matrices of other trials throughout the surgery (Fig. 1). This distance appears to track the patients’ awareness level: it is greater during the maintenance phase, at deeper anesthetic concentrations, than during the induction or emergence phases. This holds potential for creating a one class classifier using this distance, only relying on MNS-awake data, as MNS-anesthesia data are usually unavailable for calibration during regular surgeries.
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