Bispectral Index Versus Minimum Alveolar Concentration Guided Anesthesia for Assessment of Intraoperative Awareness in Patients Undegoing Laparascopic Abdominal Surgery

Introduction: Intraoperative awareness with explicit recall (AWR) occurs when an individual retains memory of intraoperative events after completion of anesthesia. It is an unpleasant feeling feared by both the patients and the anesthetists. Objective: This research aims to compare Bispectral Index (BIS) versus Minimum Alveolar Concentration (MAC) guided anesthesia for assessment of intra-operative awareness in patients undergoing laparoscopic abdominal surgery. Methods: This research is a prospective comparison involving 100 patients divided into two groups of 50 patients each. Group M (MAC): Desflurane concentration was maintained at a MAC value of 1. The BIS monitor was not to be applied to this group of patients at the time of induction, but in Group B (BIS), the BIS electrode was applied on the forehead immediately before induction. Hemodynamic parameters including heart rate and mean arterial blood pressure were recorded.  After the surgery, the patients were interviewed using the Modified Brice Awareness Questionnaire and Michigan Awareness Classification score for assessment of intra-operative awareness or consciousness at two intervals: in the post-anesthesia care unit and 48 hours after surgery. Results: Demographic data were comparable between groups M and B. No significant differences in the hemodynamic parameters, which include heart rate and mean arterial blood pressure (MAP) between the M group and the B group (p value>0.05). The patient’s awareness was compared based on a modified Brice awareness questionnaire. The distribution of awareness was comparable between groups M and B (0% vs. 4% respectively) (p value=0.495). The distribution of Michigan awareness classification scores was comparable between groups M and B. Class 0 (no awareness) was 98% vs. 96% respectively, and Class 1(isolated auditory perception) of 2% vs. 4% respectively with (p value=1). Conclusion: This research found that BIS-guided anesthesia works just as well as MAC-guided anesthesia at keeping patients from waking up and keeping an eye on changes in their blood pressure while they are under general anesthesia for laparoscopic abdominal surgery.

INTRODUCTION

Laparoscopic surgeries are widely accepted and performed due to several advantages such as decreased postoperative pain, early ambulation, shorter hospital stay, cosmetically small incision, and more costeffectiveness. There are three elements of balanced anesthesia namely amnesia, analgesia, and areflexia, which must always be considered while providing general anesthesia to patients¹.

The element of amnesia should be addressed carefully while anesthetizing any patient. A multitude of surgical patients apprehendto the possibility of immobility, being awake, or being in pain due to inadequate anesthesia during the surgery (²). This inadequacy results in patients having awareness during anesthesia. Intraoperative awareness with explicit recall (AWR) occurs when an individual recalls intraoperative events after completion of anesthesia. It is an unpleasant feeling feared by the patients and the anesthetists, equally. It is an important cause of post-traumatic stress disorder (PTSD) for the patients following surgery and an important medico-legal liability for the anesthesiologist. Therefore, it is important to maintain adequate depth of anesthesia during the surgery³.

General anesthetic agents suppress cortical activity; and disrupt the connectivity of cortical areas and subcortical-cortical connections in a dose-dependent manner.

Some processing of information occurs in lighter planes of anesthesia also, even though the patients are apparently adequately anesthetized. The overall incidence of intraoperative awareness with explicit recall is approximately 0.2%-2%, but maybe >40% in some high-risk surgical patients like those with caesarean section, multiple trauma, hemodynamic instability, and cardiac surgery⁴⁵.

Depth of anesthesia refers to the progressive depression of the central nervous system and a decreased response to noxious stimuli. Adequate depth of anesthesia is achieved when the concentration of agents is sufficient to ensure both patient comfort and successful surgery. There are various somatic and clinical parameters, and devices available for anesthetists to monitor the depth of anesthesia. The two main methods frequently used are bispectral index (BIS) and minimum alveolar concentration (MAC). MAC relates to the concentration of the inhalational anesthetic agent to a single, clinically relevant endpoint of general anesthesia. It is defined as the minimum alveolar concentration of inhaled anesthetics required to prevent response in 50% of the subjects to a painful stimulus. When the MAC is approximately 0.3, 50% of the subjects do not respond to verbal commands (MAC awake), and maintaining the MAC more than 0.7 is said to reduce the incidence of AWR. It is thought that the end-tidal inhaled anesthetic partial pressure shows the partial pressure in the alveoli, which in turn shows the partial pressure of the anesthetic agent at the effect site, like the brain. This makes MAC reliable and useful. Thus, with the ease of measurement of the end-tidal anesthetic gas, MAC is considered a standard metric for comparing the potency of inhalational anesthetic agents⁶⁷.

The Bispectral Index (BIS) is a complicated number that is made up of different EEG features, such as frequency domain, time domain, and higher-order spectral features. Based on extensive clinical data, it correlates with behavioral assessments of hypnosis and sedation, regardless of the anesthetic or sedative agent used. The BIS score ranges from 0 to 100, with a target range of 40-60 recommended to prevent awareness; it also provides a reliable prediction of consciousness levels and responsiveness⁸⁹¹⁰. This research aims to compare Bispectral Index (BIS) versus Minimum Alveolar Concentration (MAC) guided anesthesia for assessment of intraoperative awareness in patients undergoing laparoscopic abdominal surgery.

METHODS

Research Design and Sample Size

This prospective, randomized, and comparative research was performed at the Atal Bihari Vajpayee Institute of Medical Sciences and Dr. Ram Manohar Lohia Hospital, New Delhi, with approval from the institutional ethical committee on October 22nd, 2019 with the certificate number TP(MD/MS)08/2019)/IEC/ABVIMS/RMLH/672/19. The research was conducted between November 1^st, 2019 and March 31st, 2021. The sample size calculation was based on the research of Alkaissi A. et al. (¹¹) which found no cases of awareness in the BIS-guided group and 4 cases (13.8%) in the control group. Based on these figures, a minimum sample size of 49 patients per group was calculated to achieve 80% power with a 5% significance level. Thus, a total of 100 patients were included, with 50 patients in each group.

Research Participants

A hundred patients were randomly divided into two groups of 50 patients each by computer-generated random sampling. The research included 100 patients classified as American Society of Anesthesiologists (ASA) grade I and II, aged 18 to 60 years, of either sex, undergoing laparoscopic abdominal surgery. Exclusion criteria were refusal of consent, allergy to research drugs, psychosis or memory impairment, and a history of brain injury.

Research Procedures

Written and informed consent was obtained from all patients. After a thorough preoperative evaluation and investigation, patients who met the inclusion criteria were included in the research. The night before surgery, all patients received premedication with a 0.25 mg tablet of alprazolam and a 150 mg tablet of ranitidine. Upon entering the operating room, routine monitoring was initiated, including a 5-lead electrocardiogram (ECG), pulse oximetry, and non-invasive blood pressure (NIBP) measurement. Baseline vital signs, such as heart rate, systolic, diastolic, mean blood pressure, and ECG rhythm, were recorded. An 18G cannula was inserted into the dorsum of the left hand, and intravenous fluid infusion was started. Patients were then randomly assigned to two groups using computer-generated random numbers. Group M (MAC): Desflurane concentration was maintained at a MAC value

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