General anaesthesia is a carefully controlled pharmacological state characterized by unconsciousness, amnesia, analgesia, and immobility, allowing surgical procedures to be performed safely and comfortably. Achieving an appropriate depth of anaesthesia is a fundamental goal of anaesthetic practice. Insufficient anaesthetic depth may result in intraoperative awareness, autonomic responses, hypertension, tachycardia, and psychological distress, whereas excessive anaesthesia may lead to delayed emergence, haemodynamic instability, increased drug consumption, and prolonged postoperative recovery. Traditionally, anaesthesiologists have assessed depth of anaesthesia using clinical parameters such as changes in heart rate, blood pressure, lacrimation, sweating, movement, and patient response to surgical stimulation. However, these signs are indirect indicators and may be affected by several factors including opioids, vasoactive medications, neuromuscular blocking agents, and underlying patient conditions. Therefore, reliance solely on clinical signs may not provide an accurate estimation of the hypnotic component of anaesthesia. Electroencephalography (EEG)-based monitoring techniques have been developed to provide objective assessment of cerebral activity during anaesthesia. Processed EEG monitors analyze electrical activity from the cerebral cortex and convert complex EEG signals into numerical indices representing the level of consciousness and hypnotic depth. Both, the depth of anaesthesia than the required level (may result in cardiovascular depression) and light plane of anaesthesia are harmful to the patient. Here comes the importance of assessment of depth of anaesthesia. Inadequate depth during General anaesthesia can result in awareness which can result in post-traumatic stress disorder. Depth can be assessed using Bispectral index and Clinical parameters (PRST Score). Aim of the study was to compare the PRST score in patients undergoing General Anaesthesia with and without Bispectral index monitoring. Recovery time was also assessed in the two groups. Awareness is a post-operative recall of events occurring during General anaesthesia. 1 Awareness, unconscious memory formation and dreaming may happen during surgery under general anaesthesia. To ensure adequate depth of anaesthesia and to prevent awareness without inadvertently overloading the patients with potent drugs is one of the main objectives of modern anaesthesia.2 Even though there are improvements in assessment of the cardiovascular system during anaesthesia, direct determination of anaesthetic effect on the central nervous system has remained a great challenge.3 The brain condition of a patient after induction can be assessed by monitoring the patient’s physiologic signs and EEG-based index. Physiological signs include pursuit of anaesthesiologist fingers,4 oculocephalic reflex, corneal reflex, respiratory pattern,5 muscle tone, loss of responsiveness.4,6 Electroencephalogram-based indices are the most used method.7 With induction, the values get decreased from high to low values which indicates the loss of consciousness.8 These systems process EEG and provide an index value or set of values in real time ornear real time that can be used to track the level consciousness. usually, the indices are designed to decrease with decreasing level of consciousness and to increase as the level of consciousness returns. So we can use the combined effect of physiological signs and EEG based indices to assess the state of consciousness of a patient after general anaesthesia induction.9,10 Clinical scoring system for the assessment of depth of anaesthesia, the PRST score (Systolic Blood Pressure, Heart Rate, Sweating, Tears).11,12 This subjective method of assessing depth of anaesthesia is primarily based on autonomic changes with the stressful stimulus like intubation or noxious surgical stimuli. Scoring is from 0-8. Even though the method is very simple and cheap, it is not always related to the depth of anaesthesia. This method does not require sophisticated equipment, but it has been proven that hemodynamic responsiveness to noxious stimuli does not necessarily signify awareness, nor does lack of it guarantee unconsciousness. Bispectral analysis (BIS) of EEG is a non-invasive signal processing technique that quantifies the level of synchronization in the signal along with the traditional amplitude and frequency variables, thus providing a more complete description of complex EEG patterns. The BIS algorithm uses not only the conventional EEG power spectral analysis but also elements of Bispectral analysis. BIS scores indicate the level of consciousness. They continuously and objectively display in the monitor, a numerical value which indicates the level of consciousness. BIS is a dimensionless number, scaled from 100–0, with 100 representing an awake EEG and zero representing complete electrical silence. The EEG is processed and gives an index value between 0 and 100 indicating the patient’s level of consciousness. 11,12 Value of 100 corresponds to being completely awake, whereas 0 corresponds to a profound state of coma or unconsciousness which is reflected by an isoelectric or flat EEG. The BIS algorithm is proprietary, and the actual computation through which the index is derived is not of public knowledge. The BIS value is obtained from combining the information from three EEG analyses: the spectrogram, the bispectrum, and a time domain assessment of burst suppression.11-13 The spectrogram is a decomposition of the EEG into its power content by frequency as a function of time. The bispectrum measures the degree of nonlinear coupling between pairs of frequencies in the spectrogram. The BIS algorithm works by measuring specific features of the spectrogram, the bispectrum, and the level of burst suppression and uses a predetermined weighting scheme to convert these features into the index value. Intraoperative awareness can be avoided by using BIS monitoring. Intraoperative awareness can be defined as the patient having explicit recall of events that transpired during the time that he or she was under general anaesthesia.14 The Patient Safety Index (PSI) is another modality of monitoring the depth of anaesthesia in patients receiving general anaesthesia. It is also based on the EEG interpretation. The PSI is also scaled between 0 and 100 like BIS. For maintaining adequate depth of anaesthesia, PSI is to be maintained in between 25 and 50.15 In the current formulation of the PSI uses only a four-lead frontal EEG montage. The PSI strongly correlates with BIS in the assessment of level of consciousness.16-18 To track level of consciousness Entropy was developed. Entropy measures the degree of disorder or the lack of synchrony or consistency in a system. The system combines frequency domain analysis with burst suppression to measure the entropy of the EEG in patients receiving anaesthetic drugs. The EEG becomes more regularly arranged when patient goes to deeper planes of anaesthesia.19 That is, we observe an apparent decrease in the entropy of the EEG signal. There are two Entropy numbers in the entropy monitor to interpret EEG analysis namely response entropy and state entropy. Other methods to assess level of consciousness include Spontaneous surface electromyogram.20 lower oesophageal contractility, skin conductance. End tidal Anaesthetic criterion. Intraoperative awareness is a major medico-legal liability to the anaesthesiologists and can lead to postoperative psychosomatic dysfunction in the patient, and therefore should be avoided at all costs. Anaesthesia awareness is under recognized and under-treated in most health care organizations because it is clinically difficult to recognise intraoperative awareness . The common complaints include auditory recollections (48%), inability to breathe (48%), pain (28%) and unidentified number of post-traumatic stress syndrome.

Prospective observational study was done in willing ASA PS 1,2 patients undergoing elective surgery under General Anaesthesia in age group 18-65 years. Exclusion criteria included patients with dementia, impaired cardio-vascular status, emergency surgery, patients with history of substance abuse. With approval of the Hospital Ethics committee and written informed consent, 100 patients who presented to our hospital from January 2019 to January 2020 were enrolled for the study. They were assessed and categorised into 2 groups of 50 each by drawing lots. First group was monitored with PRST score alone, second group with PRST score and BIS index. Patients with dementia, impaired cardiovascular status and substance abuse were excluded. All patients were premedicated with midazolam. Before induction, in group 2 patients, a unilateral BIS sensor that records EEG waves were secured on cleaned and dried forehead. Induction was done with Propofol and Vecuronium. Anaesthesia maintained with O2, N2O and Isoflurane. PRST score and BIS index were assessed at 5 points. Baseline reading before general anaesthesia T0, at intubation T1, at first skin incision T2, 30 minutes after first skin incision T3, 30 minutes after T3 reading T4, immediately after placing last skin suture T5. A PRST score of more than 3 was considered as inadequate anaesthetic depth. BIS values in the range of 40 – 60 was considered as adequate depth of anaesthesia. BIS was monitored continuously, but values recorded at same intervals as group 1. With both groups, an interview was conducted 24 hours after surgery to assess the awareness according to Modified Brice questionnaire. Sample size calculation N = 2(Zἀ + Zβ )² σ² d² • Where Zἀ = 1.96 for ἀ = 0.05 • Zβ = 0.84 for β = 0.20 • d = μT – μC (difference in mean) • σ = Standard deviation Here N = 2 (1.96 + 0.84)2 x 8.52 = 21 (7.46)2 Minimum sample size was 21. For the study total of 100 patients were included. For the study, the parameters were age, gender, comorbid illness, duration of surgery, requirement of intravenous propofol intraoperatively, PRST score, bispectral index, Modified Brice questionnaire. Statistical Analysis Student t test was used to find out the significance of study parameters on continuous scale within each group. Chi – square test was used to find out the significance of study parameters on categorical scale between two or more groups. Significance was assessed at 5% level of significance (P<0.05) and P<0.001 highly significant. Statistical analysis was done using Statistical Package for Social Studies (SPSS).

In our study, there were 26 males and 24 females in each group. There is no significant difference between the two groups regarding age distribution and gender. When the PRST score was compared between the two groups, the mean PRST score was higher during all the points in the first group indicating a shallower anaesthesia (table1). BIS values varied with various stages of anaesthesia but showed a very mild increase because of use of adequate analgesia and depth of anaesthesia. There was a transient increase in BIS values following tracheal intubation. Post induction, BIS values were 43.8+6.1. During recovery phase, BIS values were maintained in 65.7+9.5. (Table 2). Group 2 required a lesser quantity of Propofol.(table 3).The mean propofol requirement in group 1 was 18.7+18.6mg.In group 2 it was much lower, around 6.5+7.3mg.The study was clinically significant with p value<0.01. Group 2 had a faster recovery. The anaesthesia recovery time after the surgical procedure was 14.4+4.6 minutes in group 1 while in group 2 it was 8.8+3minutes only which was clinically significant with p value<0.01.(figure 1). Assessment was done with Modified Brice questionnaire (figure2). Table 1. Comparison of PRST score between two groups during T1 to T5 Groups T1 T2 T3 T4 T5 Group one 1.54±0.68 1.56±0.64 1.3 ± 0.51 1.3±0.51 1.86±0.7 Group two 0.28±0.45 0.26±0.6 0.24 ±0.52 0.26±0.53 1.68±0.51 There was a transient increase in BIS values following tracheal intubation. Post induction BIS values was 43.8+- 6.1. During recovery phase, BIS values were maintained in 65.7+-9.5. Table 2. Descriptive statistics of BIS score in group 2 BIS Mean SD Median Minimum Maximum T0 43.4 4.8 44 31 56 T1 43.8 6.1 43 31 56 T2 44.1 6.1 43.5 33 66 T3 43.3 4.5 43 32 56 T4 43.8 4.7 43 32 54 T5 65.7 9.5 68.5 43 78 Table 3.: Comparison of propofol requirement based on group Group Mean N T P Group 1 18.7 50 4.34 <0.01 Group 2 6.5 50 The mean propofol requirement in group 1 was 18.7 ±18.6mg. In the second group it was much lower, around 6.5 ± 7.3 mg. The study was clinically significant with p value of <0.01.

In our study, PRST score of group 2 was consistently lower than the PRST score of group 1 at all the time intervals. The respondents who had BIS values between 42 – 48 showed minimal or no change in heart rate or blood pressures. Group 2 required a lesser quantity of drugs when compared to first group and a faster recovery. Our findings reflect the observation made by Davidson A et al. 22 In this study, where immediate post extubation, the BIS values were 87.48± 5.27 and it increased to 93.4 ± 2.82 within 15 minutes. In a study by Gan T J et al patients who were observed with BIS showed faster recovery than the control group. 13 Sebel P S et al revealed that in a study population of 20000 patients, only 25 patients i.e around 0.13% experienced awareness.23 Myles et al found that BIS reduced the incidence of intraoperative awareness 102. As found by Sandrin et al. 24, out of 11785 patients, awareness was observed in 0.15%. There is correlation with a study by Natividad Quesada et al where BIS monitoring reduced Anaesthesia the dosage of propofol and thereby adverse events.14 Sharon Lewis et al found that BIS anaesthesia compared to clinical signs reduces the risk of intraoperative awareness and improves anaesthesia recovery times which is in close agreement to our study.25 Very similar to ours, Punjasawadonga et al found BIS guided anaesthesia reducing awareness in patients at high risk of developing it in comparison to clinical signs for assessment of anaesthetic depth.26 All the EEG based indices are designed to decrease with decreasing loss of consciousness and to increase as it returns.15 Adesanya et al found BIS to be consistently better at predicting oversedation which is very similar to our study.27 Jasmina Smajic et al found that BIS monitoring with clinical assessment allows a precise decision making in balancing and dosage of anaesthetic drugs. 28. Gunter N Schmidt et al in a comparative study revealed Narcotrend and BIS index as more reliable indicators for assessment of anaesthesia status.29 Shepherd et al in a systematic review of depth of anaesthesia indices by Entropy, Narcotrend and BIS showed a close correlation.16 Alejandro Recart et al showed the anaesthetic sparing effect of cerebral monitoring with BIS or auditory evoked potentials resulting in shorter PACU stay and improved quality of recovery.17 In a comparative study by Prichep et al, PSI (Patient State Index) and BIS performed equally well in predicting depth of anaesthesia.18 Both are effective predictors of unconsciousness as found by Chen X, Tan J et al. 30 Vierto Oja et al showed that loss of consciousness was best predicted by BIS and response entropy. 31 EEG and SEMG (Spontaneous Electromyography) monitoring during induction and maintenance with propofol are comparable as studied by Herregods et al. 32 Schneider et al found BIS and PSI to be equally effective in detecting awareness.33 All currently available monitors need varying time periods to calculate a new index when reacting to changes in anaesthetic depth. The exact time delay for calculation is unknown. In our study none of the participants had conscious recall of events during surgery. This may be due to the relatively small sample size. Hemodynamic parameters like heart rate and blood pressure were measured non-invasively. More accurate results could have been obtained if this study was done using invasive monitors like continuous arterial blood pressure. Sample size was only 100 in this study. More accurate results would have been possible if a larger sample size was used.

Bispectral monitoring helps the anaesthesiologists to monitor the depth of anaesthesia. Thus will help to prevent unwanted sedation and other side effects of the hypnotic drugs. Along with the clinical parameters, BIS helps in decision making, facilitates titration of anaesthetics and achieve the best possible outcome for the patient.

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