Description

Understanding BIS, SEF, and TP After Induction During Controlled Hypotensive Anesthesia in a Morbidly Obese Female Undergoing Sleeve Gastrectomy with Ventral Hernia Repair

Clinical Overview

Patient: 39-year-old female
BMI: 41 kg/m² (morbid obesity)
Planned procedure: Laparoscopic sleeve gastrectomy with ventral hernia repair
Surgeon’s request: Controlled hypotensive anesthesia for a bloodless surgical field

Anesthetic Technique: General anesthesia with endotracheal intubation and controlled ventilation.

Drugs Administered During Induction

• Glycopyrrolate 0.2 mg – antisialagogue, attenuates vagal response

• Midazolam 1 mg – anxiolytic, enhances GABAergic tone

• Fentanyl 200 µg – blunts sympathetic response to laryngoscopy

• Propofol 150 mg – induction agent (lipophilic, rapid CNS penetration)

• Atracurium 40 mg – neuromuscular blockade

• Dexamethasone 8 mg – antiemetic, anti-inflammatory

• Dexmedetomidine 30 µg – α₂ agonist, sympatholytic and sedative

• Magnesium sulfate 1 g – NMDA blockade, enhances analgesia

• Paracetamol 1 g and Diclofenac suppository 100 mg – multimodal analgesia

Post-Induction Monitor Readings

1. Clinical Context: The Post-Induction Window

The period after induction and before surgical incision is a critical transition zone where:

• Drugs are at peak plasma and effect-site concentrations.

• Airway is secured and controlled ventilation initiated.

• Cerebral electrical activity stabilizes after rapid GABAergic surge.

• Hemodynamics are adjusting to both anesthetic depression and surgical preparation.

In this patient, BIS 35, SEF 15 Hz, and TP 69 µV² represent the neurophysiologic equilibrium of a deep but perfused hypnotic state—ideal before incision in a controlled hypotensive setup.

2. BIS 35 — Deep Hypnosis and Sympatholytic Stability

A BIS value of 35 reflects a deep hypnotic plane of anesthesia — slightly beyond the surgical target range (40–60), but desirable immediately post-induction before noxious stimulation begins.

At this stage:

• The brain is heavily suppressed by propofol and opioid synergy.

• Sympathetic activity is minimized, producing the desired controlled hypotension (MAP 57 mmHg).

• Dexmedetomidine augments cortical inhibition through α₂ receptor activation in the locus coeruleus, lowering BIS further.

Clinical meaning:
The patient is unresponsive, hemodynamically stable, and metabolically suppressed — the optimal foundation for controlled hypotension.

3. SEF 15 Hz — Slowed Cortical Oscillation

Spectral Edge Frequency (SEF) represents the upper boundary of the EEG power spectrum — the frequency below which 95% of cortical activity resides.

• SEF 15 Hz indicates that most neuronal firing is slow (alpha–theta range).

• This corresponds to thalamocortical synchronization, a state of deep sleep–like sedation.

• The shift from beta (awake) to...