Bispectral Index (BIS) Monitoring in Abdominal Surgery

Patients undergoing major abdominal surgery under general anesthesia in University Hospital Dubrava, were eligible if there were aged 18 years or older, and ASA (American Society of Anesthesiologists) physical status II or III. Study included 40 patients enroled in the six months period (between February 2011. and July 2011.). Exclusion criteria were memory impairment, psychosis, known or suspected electroencephalograph abnormality (eg, epilepsy, previous brain operation), chronic use of psychoactive medication, and operation time exceeding six hours.

The protocol was approved by Institutional Ethics Committee of University Hospital Dubrava. All participating elective surgical patients were given brief description of the trial, and gave written informed consent before enrolment.

According to a computer generated randomisation list, patients were randomly assigned to receive BIS-guided anesthesia (group 1) or routine anesthesia care as a non BIS-guided group (group 2). The non BIS-guided group was studied while the BIS monitor was attached to patient, but the screen was blinded to the anesthesiologist in charge. All values were recorded by the younger anesthesiologist, who was not involved in the anesthesia maintenance. All other aspects of perioperative treatment were similar, including choice of anesthetic agents and monitoring.

The operation was performed under general anesthesia using midazolam (0.15 mg/kg), fentanyl (2 µg/kg) and pancuronium (0.1 mg/kg) to facilitate endotracheal intubation, and 1.5-2.5 MAC of sevoflurane, nitrous oxide 50% in oxygen, boluses of fentanyl and pancuronium for maintenance. Intraoperatively, after induction doses of fentanyl, anesthesia was mainly balanced with sevoflurane. Electrocardiography (EKG), invasive blood pressure (IBP), peripheral oxygen saturation (SpO2), and end-tidal CO2 (etCO2) were monitored.

A BIS sensor was applied to patient's forehead before induction of anesthesia and connected to A-2000 BIS monitor (Aspect Medical Systems, Newton, MA, USA). It records the electroencephalogram from 4 electrodes and after processing it with mathematic algorithms it generates a number from 0 to 100. When the BIS value is lower than 40, the patient is in deep anesthesia state, when the value is over 80, the patient is under light sedation [3].

After the surgery and recovery from anesthesia, patients were transferred to intensive care unit for continuous monitoring of vital functions and homeostasis.

At the induction of anesthesia, and every 15 minutes during operation, BIS levels were recorded. Also, at the end of the operation, extubation time and analgesics consumption were recorded.