EEG phase synchrony and variability has had limited investigation during transition from coma to wakefulness in response to sedation and analgesia. Studying changes in phase synchrony and variability during and after sedative-induced coma is an exciting opportunity to better understand EEG changes during transitions in states of arousal. It is expected that consciousness should be higher in entropy and greater in complexity in the number of configurations of pairwise connections as compared to sedative-induced coma. If sufficiently sensitive, it may be possible to identify states of lower entropy and fewer configurations when patient are aroused but with altered sensorium (e.g. delirium).

Aim 1: To quantify EEG phase synchrony changes, both globally and locally by brain region, during emergence from medically induced coma required for performance of a cardiovascular related operation (deep sedation defined as a Riker Sedation-Agitation Scale [SAS] of 1-2).

Hypothesis: The global R-index will be increased above baseline at multiple frequency bandwidths and the magnitude of R-index will correlate with the sedative dosage (as a crude measure of depth). The rate of fluctuations of the R-index will decrease with deeper sedation.

Aim 2: To compare the magnitude of the EEG phase synchrony globally and locally in patients emerging from coma; a patient's pre-anesthesia phase will serve as a control.

Hypothesis: Fluctuations in R-index will vary; fluctuations will be greater in awake adults as compared to while comatose or emerging from coma.

Aim 3: To determine EEG phase synchrony changes in patients with and without delirium during their CVICU stay.

Hypothesis: Lower scores of R-index consistent with increased phase synchrony and lower spatio-temporal variability will be seen while delirious as compared to days when patients are not delirious.

Inclusion criteria:

• Age 30 - 65 years
• Scheduled for first-time CABG or single valve replacement

Exclusion criteria:

• Previous stroke
• Severe pre-existing cognitive impairment (TICS score < 24)

Population: Adults aged 30 - 65 years, invasively mechanically ventilated for a first-time CABG or single valve replacement surgery; Exposure: R-index measured at different states of consciousness (awake, emerging from comatosed state, and transitional states between) after standardized induction with opioid and benzodiazepine with or without propofol; postoperative sedation in CVICU with propofol or other; Outcome: Delirium as measured by the Confusion Assessment Method-ICU (CAM-ICU).