Intraoperative awareness, hemodynamic instability, myocardial ischemia, and postoperative delirium are major concerns in elderly patients with cardiovascular and cerebrovascular disease. Traditional clinical signs (blood pressure, heart rate, movement) are unreliable measures of consciousness under neuromuscular blockade and volatile anesthesia.
The Bispectral Index (BIS) provides a validated electroencephalography (EEG)-derived measure of hypnotic depth, transforming complex EEG waveforms into a simple numerical scale from 0 (isoelectric EEG) to 100 (fully awake). Maintaining BIS values between 40–60 is associated with adequate anesthesia while avoiding awareness or excessive cortical suppression.
In this chapter, BIS findings and their implications are analyzed in a 74-year-old post-CABG patient with cerebrovascular disease and Parkinsonism, undergoing extended gastrectomy under sevoflurane anesthesia.
References
Rampil IJ. A primer for EEG signal processing in anesthesia. Anesthesiology. 1998;89(4):980–1002.
Avidan MS, Mashour GA. Prevention of intraoperative awareness with explicit recall. N Engl J Med. 2013;368:1189–1201.
EEG records cortical postsynaptic potentials. Awake states are dominated by beta activity (13–30 Hz). With anesthetic induction, cortical neurons hyperpolarize, generating alpha (8–13 Hz) and theta (4–8 Hz) rhythms. Deep anesthesia enhances delta (<4 Hz) and may progress to burst suppression.
The BIS index integrates three EEG dimensions:
Power spectrum – distribution of EEG frequencies.
Bispectral analysis – phase relationships between frequency components.
Time-domain features – detection of burst suppression.
100: Awake.
80–100: Sedation.
60–80: Deep sedation/analgesia.
40–60: Surgical anesthesia (target).
<40: Deep anesthesia/burst suppression.
0: Isoelectric EEG.
BIS reduces the risk of intraoperative awareness, optimizes anesthetic titration, shortens recovery, and prevents excessive brain suppression that predisposes to delirium and cognitive dysfunction.
References
3. Sigl JC, Chamoun NG. An introduction to bispectral analysis of the EEG. J Clin Monit. 1994;10:392–404.
4. Myles PS, Leslie K, McNeil J, et al. BIS monitoring to prevent awareness: the B-Aware trial. Lancet. 2004;363:1757–1763.
The patient was a 74-year-old male, scheduled for extended total gastrectomy.
Cardiac: Post-CABG; mild LV systolic dysfunction (EF 45%); grade II diastolic dysfunction; regional wall motion abnormalities (inferior/inferolateral hypokinesia).
Neurological: Old right cerebellar, occipital, and left capsulo-ganglionic infarcts; multiple intracranial vessel stenoses.
Medications: Syndopa Plus (Levodopa/Carbidopa) 125 mg TID.
Intraoperative: Sevoflurane MAC 1; atracurium infusion; BIS ~54; BP 136/69; HR 69.
This multimorbid profile placed him at high risk of myocardial ischemia, perioperative stroke, autonomic instability, and postoperative delirium.
Recorded BIS:...
