Post-auricular Versus Frontal Bispectral Index

Twelve Patients age ≥18 years, ASA I-III patients scheduled for elective renal surgeries.

Monitoring of the depth of anesthesia will be performed using an Infinity BISx SmartPod® (Aspect Medical Systems, Newton, MA, USA) and an Infinity® Delta XL monitor (Dräger Medical, Lübeck, Germany). Two standard BISx Quatro® Sensors (Aspect Medical Systems) were placed at the forehead and post-auricular area.

Before the induction of anesthesia, 2 BIS sensors (BISTM Quatro Sensors, Aspect Medical Systems, Newton, MA, USA) will be applied to each patient, 1 across the forehead and 1 along the post auricular area and attached each sensor to each BIS monitor (BIS-VistaTM monitors, Aspect Medical Systems, Newton, MA, USA).

During induction, patients will be instructed to keep their faces relaxed (eyes closed, mouth closed, no facial expressions).

The skin on the forehead will be cleaned with an alcohol 70% swab, and 2 to 5 seconds of digital pressure applied over the sensor leads. The sensor is comprised of disposable wet gel electrodes. Electromyographic activity of the frontalis muscle is measured by lead 4, which is the ground electrode as well.

Frontal sensors will be applied with lead 1 at the center of the forehead; lead 2, 2.8 cm lateral to lead 1; and lead 3 at the temporal area between the lateral canthus and the hairline.

Post auriclar sensors will be applied to the same side of the face, with lead 1 approximately 2.5 cm medial to the mastoid area, post-auricularly next to the hairline. Lead 2 will be attached at the mastoid area and lead 3 will be attached on the same side at the temporal area between the lateral canthus and the hairline.

The titration of anesthetic depth will be maintained at BIS values between 40-60.

Sudden, high EMG scores were identified as artifacts and the associated BIS values were eliminated in data analysis.

Measurements:

From each BIS monitor, the investigators will collect 3 pieces of data at each of 6 times points: BIS score, signal quality index (SQI) score determining the strength of the signal, and electromyography (EMG) score: before the induction of anesthesia (awake), at loss of the eyelash reflex (LOC), after intubation (intubation), after the first surgical incision (incision), every 30 minutes during the intraoperative period (maintenance), and at spontaneous eye opening upon emergence from anesthesia (emergence).

Inclusion criteria

• Patients aged≥18 years
• ASA I-III
• patients scheduled for elective renal surgeries

Exclusion criteria

• Patients with disabling central nervous system
• cerebrovascular disease
• those currently taking psychiatric medication
• those with a history of neurosurgical intervention
• those with contraindications for the placement of electrodes over forehead and post-auricular area (e.g., having skin infections)