Description

Case Summary

A 36-year-old male, 185 cm tall, previously operated for right renal cell carcinoma (nephrectomy 5 years ago), presented for exploration and repair of two tendons following leg trauma (RTA).
Pre-anesthetic evaluation was unremarkable apart from a solitary kidney. Routine investigations and airway examination were normal.

Medications administered:

• Glycopyrrolate 0.2 mg

• Midazolam 1 mg

• Fentanyl 200 µg

• Dexamethasone 8 mg

• Propofol 80 mg for induction

• Atracurium 40 mg (plus 10 mg top-up every 30 min)

• Dexmedetomidine 30 µg infusion

• Magnesium sulfate 1 g

• Paracetamol 1 g

Anesthesia was maintained with oxygen–nitrous oxide–sevoflurane mixture (FiO₂ 0.52, N₂O 0.46, Sevo 1.2–1.8 vol%) in volume-controlled ventilation (VT 520 mL, RR 12, PEEP 3, FiO₂ 0.52, EtCO₂ 46 mmHg).
Hemodynamics: HR 112/min, BP 138/90 mmHg, SpO₂ 100%, core temperature 23.2°C (Tskin low).
BIS monitoring (Covidien) was used with real-time DSA display.

1. Understanding BIS and DSA: Conceptual Overview

1.1 BIS (Bispectral Index)

• BIS is a dimensionless EEG-derived parameter (0–100) quantifying cortical electrical activity.

• It processes raw EEG using bispectral, time-domain, and frequency-domain analysis to estimate hypnotic depth.

• Interpretation:

  • 100 = Awake

  • 80–90 = Sedated, but responsive

  • 40–60 = Optimal hypnotic depth for general anesthesia

  • < 40 = Deep hypnosis or burst suppression

1.2 Density Spectral Array (DSA)

• DSA is a two-dimensional color spectrogram displaying EEG frequency content over time.

• X-axis = Time; Y-axis = Frequency (0–30 Hz); Color intensity = Power of each frequency band.

• Helps identify transitions in cortical states (alpha dominance, burst suppression, EMG interference).

2. Phase 1: Pre-Induction (BIS 98, DSA with Beta Dominance)

• Observation: BIS = 98, strong high-frequency (beta > 20 Hz) pattern on DSA, evident EMG activity.

• Interpretation: Awake cortical state, alert patient, dominant frontal EMG interference, minimal alpha or delta activity.

• Significance: Confirms functional sensor placement and baseline calibration before induction.

Clinical insight:
A high BIS (~98) with a bright beta-band streak indicates arousal and muscle tone, validating good EEG electrode impedance and absence of burst suppression or artifact.

3. Phase 2: Post-Induction and Maintenance (BIS 63, DSA with Alpha–Theta Dominance)

After induction with propofol 80 mg and fentanyl 200 µg, followed by sevoflurane 1.8 % + N₂O + dexmedetomidine, the monitor shows:

• BIS 63

• DSA: Reduced beta power, appearance of alpha (8–13 Hz) and theta (4–8 Hz) bands

• SEF 18 Hz, MF 07 Hz

Interpretation:

• BIS 63 → adequate depth for surgical incision, possibly in light-to-moderate hypnotic range.

• Alpha–theta dominance → thalamocortical synchronization typical of volatile anesthesia or propofol hypnosis.

• SEF (Spectral Edge Frequency) ~ 18 Hz → upper EEG boundary consistent...