EEG from the PATHFINDER control cohort (n = 2) and MMGA cohort (n = 18) was recorded intraoperatively and analyzed postoperatively for retrospective analysis. EEG data were recorded with a pre-amplifier bandwidth of 0.5 to 92 Hz, sampling rate of 178Hz, with 16-bit, 29 nV resolution. The standard Sedline (Masimo Corporation, Irvine, CA, United States) electrode array records from electrodes located approximately at positions Fp1, Fp2, F7, and F8, with ground electrode at Fpz, and reference electrode approximately 1 cm above Fpz. Electrode impedance was less than 5 kΩ in each channel. The EEG was analyzed using the multi-taper spectrogram intraoperatively to manage unconscious and nociceptive state, and postoperatively to retrospectively observe unconsciousness (see Figure 3 ). EEG was also analyzed for suppression events, which are common during coma-like deep states of unconsciousness. Suppression identification was achieved using a recursive variance tracking algorithm (27 (link)) with an adaptive threshold that was determined by a second estimate of the variance evolving on a slower timescale. Suppressions are thus characterized as segments of EEG where the local variance is small relative to the long-term baseline variance. All data analyses were performed using the scientific Python stack (28 (link)).
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