Cognitive and Neurophysiological Outcomes Associated With EEG-Guided Administration of General Anesthesia

Everyday in the United States, nearly 100,000 patients undergo general anesthesia and
sedation for surgical and diagnostic procedures. Approximately 35% of all surgical procedures
are performed on adults older than 65 years. Advanced age has been identified as a
predominant risk factor for postoperative cognitive dysfunction (POCD) as well as
postoperative delirium (POD), a more acute complication of major surgery. POD and POCD are
commonly reported as being part of the same continuum. Although many factors, such as
surgical stress, inflammation, and other comorbidities may contribute to POCD, there is
evidence that anesthetic exposure plays a major role. Pre-clinical studies have demonstrated
that exposure to anesthetic drugs is neurotoxic, and that older animals are particularly
vulnerable. It is also generally understood that the elderly are more sensitive to
anesthetics meaning that lower doses of anesthetic drugs are required to induce and maintain
unconsciousness.

Propofol and sevoflurane, two of the most commonly-used anesthetic drugs, induce a
stereotyped sequence of brain oscillations with increasing drug concentration. These brain
oscillations are directly related to the states of sedation and unconsciousness induced by
anesthetic drugs, and readily observed using the EEG. At high concentrations, propofol and
sevoflurane produce a pattern referred to as burst suppression, a deep state of brain
inactivation in which brain activity is punctuated by long periods of neuronal and EEG
silence. Elderly patients are far more likely to be in burst suppression, even when
age-adjusted anesthetic dosing is used. Recent studies have shown compelling evidence that
EEG burst suppression during anesthesia is an independent risk factor for POD and predicts
deficits in cognitive function after surgery. Since burst suppression occurs at higher
anesthetic doses, and is not required to maintain unconsciousness, an obvious implication is
that cognitive outcomes might be improved if anesthesiologists used the EEG to maintain
unconsciousness but avoid burst suppression.

Although anesthesiologists and researchers have advocated the use of the unprocessed EEG and
EEG spectrogram as tools to manage a patient's state of consciousness during general
anesthesia for many decades, few anesthesiologists use the EEG in their routine practice. A
major limiting factor has been the absence of training programs to teach anesthesiologists
how to interpret the EEG in the context of their clinical practice. Alongside this problem,
to date no studies have been conducted to measure the benefits, if any, of using the
unprocessed EEG and EEG spectrogram for anesthetic management. In this study the
investigators hypothesize that: 1) Anesthesiologists can be trained to read the unprocessed
EEG and EEG spectrogram to manage general anesthesia; and 2) EEG-based anesthetic management
to maintain unconsciousness but avoid burst suppression can improve patient outcomes.

Inclusion Criteria:

- 65 years old or above (male and female) American Society of Anesthesiologists (ASA)
physical status classification of I, II or III.

- Candidates scheduled for open or laparoscopic general surgical procedures under
general anesthesia

- Montreal Cognitive Assessment (MoCA) (Nasreddine et al., 2005) score ≥ 26

Exclusion Criteria:

- Preoperative delirium (based on 3D-CAM)

- Dementia (MoCA < 26)

- Prior history of psychiatric or neurological diseases including:

- Schizophrenia

- Parkinson's Disease

- Epilepsy

- Brain injury

- Brain tumors/metastases

- Encephalitis

- Stroke

- Drug or alcohol abuse

- Hearing or visual impairment

- Comorbidities:

- Renal failure

- Hepatic failure

- Heart failure

- Respiratory diseases (COPD)

- Poorly controlled hypertension

- Severe obesity (BMI ≥40 kg/m2)