The effect of BIS usage on anaesthetic agent consumption in high-risk patients for coronary artery bypass grafting off-pump surgery Singh S, Shaifulla P, Singh A, Okyere I,

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The effect of BIS usage on anaesthetic agent consumption in high-risk patients for coronary artery bypass grafting off-pump surgery

Sanjeev Singh¹, Pavagada Shaifulla², Arti Singh³, Isaac Okyere⁴
¹ Department of Anaesthesiology and Intensive Care, SMD, CHS, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana; Department of Anaesthesiology and Intensive Care, SAMSRI, Lucknow, Uttar Pradesh, India
² Department of Medicine, Viswabhatathi Medical College, Kurnool, Andhra Pradesh, India
³ Department of Public Health, SMD, CHS, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
⁴ Department of Surgery, SMD, CHS, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

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Date of Submission	17-Apr-2022
Date of Decision	18-May-2022
Date of Acceptance	29-May-2022
Date of Web Publication	11-Jul-2022

Abstract

Introduction: In this study, we aimed to compare whether the use of the Bispectral Index (BIS) reduces the consumption of the anaesthetic drug and improves recovery time in coronary artery bypass grafting off-pump (CABG-OP) surgery without awareness during surgery (ADS). Materials and Methods: This was a prospective, single-centre, randomised and double-blind comparative research performed on the American Society of Anaesthesiologists (PS) III patients booked for elective CABG-OP surgery under general anaesthesia. Patients received either propofol or isoflurane anaesthesia, and their consumption was calculated and compared. The conventional groups conventional propofol infusion group (CPG)-1 and conventional isoflurane group (CIG-3) received propofol and isoflurane, and haemodynamic parameters (±20% of initial values) were used to check the depth of anaesthesia. The groups BIS-guided propofol infusion group (BPG-2) and BIS-guided isoflurane group (BIG-4) received propofol and isoflurane, and BIS (value 50 ± 5) were used to check the depth of anaesthesia. In addition, haemodynamic parameters, awakening conditions, length of intubation, hospital stay and drug utilisation were recorded. To explicit ADS, patients were interviewed 24 h after extubation. Results: The quantity of propofol used was 178 ± 11 ml in CPG-1 and 117 ± 6 ml in BPG-2, with a 34.26% reduction with BIS. The isoflurane used was 39 ± 8 ml in CIG-3 and 25 ± 6 ml in BIG-4, with a 35.89% reduction in isoflurane requirement. This difference was statistically significantly low with BIS monitored anaesthesia compared to conventional anaesthesia. The length of intubation was 2.2 ± 1.27 and 2.3 ± 1.49 h in groups BPG-2 and BIG-4, respectively (P < 0.05). Conclusion: BIS monitoring aids CABG-OP surgeries by monitoring the depth of anaesthesia (BIS value 50 ± 5), preventing ADS (0%), reducing the anaesthetic agent requirement (propofol 34.26% and isoflurane 35.89%), reducing myocardial depression (mean arterial pressure maintained >74 mmHg) and aiding ultra-fast-track extubation (37% and 50% reduction in the duration of intubation in propofol and isoflurane with BIS).

Keywords: Awareness during surgery, Bispectral Index monitoring, coronary artery bypass grafting-off-pump, haemodynamic, isoflurane, propofol

How to cite this URL:
Singh S, Shaifulla P, Singh A, Okyere I. The effect of BIS usage on anaesthetic agent consumption in high-risk patients for coronary artery bypass grafting off-pump surgery. Hamdan Med J [Epub ahead of print] [cited 2023 Mar 29]. Available from: http://www.hamdanjournal.org/preprintarticle.asp?id=350632

Introduction

Coronary artery bypass grafting off-pump (CABG-OP) is an old technique first used in 1960 by Kuwahara and Tashiro.^[1] CABG-OP is a minimally invasive surgery performed without cardiopulmonary bypass (CPB). Neither needs cross-clamping of the aorta nor its cannulation. However, in recent years, it has been recognised that the systemic inflammatory response caused by CPB leads to substantial post-operative dysfunction of organs.^[2] CABG-OP reduces perioperative morbidity and mortality such as stroke, renal failure, large blood transfusion and coagulation disorders caused by CPB.^[3],[4],[5] Furthermore, OP surgery reduces the risk of cognitive changes that have been reported in many CPB-CABG cases.^[5],[6] Encouraged with outcomes of CABG-OP, approximately 65% of CABG procedures are currently performed OP in Japan. In contrast, approximately 15% of CABG-OP is performed in Western countries.^[1]

Too deep anaesthesia leads to hypotension, delayed awakening, increased morbidity and mortality and light anaesthesia leads to the risk of awareness during surgery (ADS).^[7] ADS has many long-term psychological sequelae such as depression, insomnia, post-traumatic stress disorder and anxiety.^[6],[8],[9] Unintended accidental ADS reported 0.2% to 2% during general surgery.^[10],[11] However, ADS is significantly higher in cardiac surgery, up to 23%.^[12] ADS has been a concern among anaesthesiologists and the subject of numerous studies during the past few decades in cardiothoracic surgeries.

Bispectral Index (BIS) monitors the depth of general anaesthesia (GA), and values range from a hundred to zero. A BIS value of a hundred means a fully awake state, and zero means the absence of brain activity. A BIS value below 60 decreases the incidence of awareness during anaesthesia.^[13] One anaesthetic agent may be less sedated than another, and the combination of drugs responds differently. Certain anaesthetics influence BIS values, such as nitrous oxide and ketamine.^[13],[14] After administration of neuromuscular blocking drugs (NMBDs), patients are immobile during surgery, but after surgery, provide evidence of ADS. Many previous studies proved the association between NMBD and ADS.^[15],[16] BIS monitoring decreases anaesthetics requirements during surgery, as reported with sevoflurane, desflurane, alfentanil and propofol anaesthesia.^[17],[18] On the contrary, Karaca et al. reported that injection (inj) propofol consumption was more in the BIS group than without BIS (control) group in patients operated on for supratentorial mass under GA.^[19] Literature reviews initiate an academic debate on the utility of the BIS in reducing the requirement of anaesthetic agents in high-risk patients without ADS.^{[17],[18],[19]}

In CABG-OP surgeries, GA is usually administered by an intravenous (IV) agent and then maintained with an inhalational agent till the end of surgery. However, a recent trend is to maintain GA solely with an IV agent, such as etomidate, propofol, or dexmedetomidine;^[8] this delivery method is called total IV anaesthesia. Propofol (2, 6-diisopropyl phenol) is a γ aminobutyric acid (GABA) receptor agonist used IV ly for sedation and hypnosis of patients during procedures. It has a fast onset and offset and demonstrated that a continuous infusion of the standard rate of propofol reduces the occurrence of ADS.^[20]

Isoflurane, a volatile anaesthetic used to induce and maintain GA, inhibits neurotransmitter-gated ion channels in the central nervous system, including N-methyl-d-aspartate, GABA and glycine receptors. Due to weak-adrenergic stimulation, it has little effect on left ventricular function and lowers systemic vascular resistance. However, the cardioprotective effect of isoflurane through ischaemia preconditioning outweighs the risk of myocardial dilation and coronary steal.^[21]

This study aimed to compare conventional anaesthesia without BIS- and BIS-guided anaesthesia in terms of the use of anaesthetic drugs, haemodynamic parameters, recovery time after anaesthesia, length of intubation, awareness during anaesthesia, duration of stay (DOS) in the cardiac care unit (CCU), and DOS in hospital among patients undergoing CABG-OP surgery.

Materials and Methods

The study was conducted in the Department of Anaesthesiology and Intensive Care after approval from the Ethical Clearance Committee on Human Research (Number: AH/127/C/2021) SAMSRI, Lucknow, India, as per the Helsinki declaration and revised guidelines of 2000. SAMSRI is the second-largest referral hospital with a bed capacity of more than 1000 beds in the capital of Uttar Pradesh (UP), Lucknow. UP is India's largest state, with a population of >200 million. This was a single-centre, prospective, randomised and double-blind study that recruited 100 patients from August 2021 to February 2022 of both genders below the age of 60 years, belonging to physical status III of the American Society of Anaesthesiologists, planned for elective CABG-OP surgery under GA. After explaining study protocols, informed written consent was obtained from participants. Exclusion criteria for the study were patients with left ventricular ejection fraction (LVEF) <40%, New York Heart Association class IV, LV aneurysms, carotid stenosis, recent/unstable angina, cerebrovascular accident, emergency surgery, body mass index (BMI) >40, on catecholamines or vasodilators before anaesthesia, hepatic/renal dysfunction, psychological/neurological disorders, allergy to propofol, with alcohol intake and drug abuse. In addition, patients requiring pre-operative intra-aortic balloon pumps were also excluded from the study.

We hypothesised that the anaesthetic requirement would be less in the BIS group than in the conventional (non-BIS) group. We derived a mean difference of 8.3% with a standard deviation (SD) of 10.5% from the pilot study. Two-sided α error of 0.05 and power of 0.8 with G*power 3.1 (flexible statistical power analysis programme) calculated a sample size of 21 patients per group.^[22] We included a dropout rate of 15% to make up for withdrawals or surgeries converted to on-pump CABG, which is 3.15. Therefore, the required sample size for each study group is (21 + 3.15 = 24.15) =25 patients per group. A study nurse, with the help of a computer-generated randomisation programme, distributed participants to any one group from the conventional propofol infusion group (CPG-1), BIS-guided propofol infusion group (BPG-2), conventional isoflurane group (CIG-3) and BIS-guided isoflurane group (BIG-4) of 25 each. The drug, patient and BIS allocation were concealed in an envelope. This envelope was opened on the day of surgery before the procedure. The patient and outcome assessor were blinded regarding drug allocation and the BIS monitoring group. The anaesthesiologist who anaesthetised and monitored the patient had all information. In groups (CPG-1 and CIG-3) and (BPG-2 and BIG-4), the depth of anaesthesia was maintained with conventional haemodynamics monitoring and BIS monitoring, respectively. The anaesthesiologist provided anaesthesia according to the study protocol.

The patients were pre-medicated with tablet diazepam 10 mg and advised to take antihypertensive and antianginal medications as prescribed during the night and the morning of the operation. As per study protocol patients were kept nil per os (NPO) prior to surgery. After arrival in the operating room on the day of surgery, IV access was obtained. Non-invasive blood pressure, electrocardiography (ECG), pulse oximetry (SpO₂), temperature, urine output, BIS and neuromuscular monitoring were performed. Baseline haemodynamics such as systolic blood pressure, diastolic blood pressure, mean arterial blood pressure (MAP), SpO₂ and heart rate (HR) were recorded. BIS was obtained with disposable sensors of BIS^TM Covidien Nellcor Medtronic, Minneapolis, USA monitoring system. BIS monitor was used in all study groups, but anaesthesia was maintained with BIS values in BPG-2 and BIG-4 groups. In the (CPG-1), anaesthesia was maintained with inj propofol 1 mg/kg as a bolus, then infusion at 7–8 mg/kg/h was maintained till sternotomy and after that maintained 5–6 mg/kg/h while keeping blood pressures and HR within the range of ± 20% of baseline values as per the study protocols. In BPG-2, anaesthesia was maintained with inj propofol 1 mg/kg as a bolus, then titrated to a BIS of 50 (±5). Propofol used from Claris Life Sciences Limited (Gujarat, India)-Profol.

In the CIG-3, isoflurane with oxygen (O₂) was used, and isoflurane end-tidal concentration (Et Iso) was adjusted to 1 or 2 minimum alveolar concentration (MAC) during the procedure while keeping haemodynamic changes within the range of ± 20% of baseline values. In the BIG-4, isoflurane with O₂ was used to maintain anaesthesia. The inspired concentration of isoflurane was maintained to a BIS of 50 (±5). Isoflurane was administered in CIG-3 and BIG-4 groups through a calibrated isoflurane anaesthetic vaporizer-Jupiter (MNLife Care Products Private Limited, Kolkata, West Bengal, India). Isoflurane USP was used in our study from Piramal Healthcare (Andhra Pradesh, India). During procedure, the total dose of isoflurane as liquid consumed was calculated by the formula:^[23] Total dose of isoflurane as liquid (ml) = Fresh gas flow (ml/min) × volatile anaesthetic concentration (Vol%) × Anaesthesia duration (min)/Saturated vapour volume (ml/ml) × 100 (Vol%)

Anaesthesia was induced with fentanyl 2 μg/kg, midazolam 0.1 mg/kg, lignocaine 50 mg, propofol (1–2.5 mg/kg), isoflurane with MAC 1 and for tracheal intubation vecuronium dose, 0.1–0.2 mg/kg was used. For ventilation of the lungs, the intermittent positive pressure ventilation technique was used with 100% O₂. The end-tidal CO₂ of 33 (±3) mmHg was maintained by adjusting tidal volume (Vt) and respiratory rate. Diclofenac sodium 100 mg suppository was administered for perioperative analgesia. An arterial line and central venous catheter were inserted to monitor invasive blood pressure and central venous pressure. Anaesthesia during the procedure was maintained with propofol or isoflurane as per study protocols. Phenylephrine, glyceryl trinitrate and dopamine were used to maintain haemodynamics within 15% of the baseline value. To prevent intraoperative hypothermia warming blanket and warm airflow at 35° C–40° C (Bear Hugger warmer EP, MN, US) was used. The total amount of fentanyl use was restricted to 10 μg/kg during the entire procedure. Vecuronium (0.01–0.02 mg/kg) was repeated for muscle relaxation. The patient received heparin 100–200 IU/Kg, so activated coagulation time (ACT) maintained greater than 300 s before graft anastomosis. Every 30 min, the ACT is repeated during the procedure, and heparin is added if ACT is recorded below 300 s. During surgery, ST-segment analysis was carried out in I, II and V5 ECG leads; any elevation or depression >1 mm of ST-segment was considered significant. BIS scores were recorded throughout the surgery, but the BIS values were not considered during electrocautery. Patients were reversed with inj neostigmine 25 μg/kg at the end of the operation, and reversal was confirmed after achieving a TOF ratio >0.9. Propofol/isoflurane administration was stopped as per study protocol. Patients were mechanically ventilated and monitored for 2–3 h before tracheal extubation in CCU. Removal of the endotracheal tube after ensuring haemodynamic stability, temperature 36°C, no bleeding and sufficient spontaneous ventilation indicated by Vt >6 ml/kg and negative inspiration pressure < -20 cmH₂O. The patient's observer assessment alertness and sedation (OAA-S) score of more than two was recorded.^[24] Awareness is the presence of memory of any event from induction of anaesthesia to the time of emergence from GA. Using the Brice Questionnaire, a structured interview was conducted to rule out ADS after 24 h of tracheal extubation in the CCU:^[25] (1) The last thing remembered after anaesthesia for the surgery? (2) The first thing remembered after the operation? (3) Is anything recalled between these two periods? While answering these questions, if the patient stated “had no specific memory of event during surgery,” further patients were not questioned. If the patient indicated memory of intraoperative events, then detailed information was gathered by a senior anaesthesiologist to assess the patient and answer their questions and, if required, then refer them for psychological counselling.

In this study, statistical tests such as the Chi-squared test, Student's t-test, Wilcoxon-Mann–Whitney U-test and ANOVA test are used to analyse the data. The study data are expressed as mean ± SD, median (interquartile range)/percentage/and absolute numbers. In this analysis, a P < 0.05 was considered statistically significant. SPSS-23.0; IBM, Armonk, NY, the USA, for Windows was used for statistical analyses.

Results

One hundred patients were enrolled in this study as per our study's inclusion criteria. Study participants were randomly divided into four Groups (CPG-1), BPG-2), CIG-3 and BIG-4 of 25 each. These four groups were comparable, the study age 57 ± 13.17 years, weight 82.9 ± 9.21 kg, height 165 ± 5.21 cm, BMI 30.2 ± 4.43 kg/m² and gender ratio of 1:18 between females and males [Table 1].

Table 1: Demographic profile

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Patients' pre-operative characteristics such as LVEF, the number of grafts and previous myocardial infarction showed no difference between the groups. In addition, the prevalence of comorbidities such as hypertension and diabetes mellitus were 60% and 27%, respectively, in this study [Table 2]. These were comparable in all 4 groups.

Table 2: Distribution of patient's pre-operative characteristics

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No difference was noticed between the groups regarding pre-operative antihypertensive medications received. Patients on β-blockers, calcium channel blockers and ACEI were 93%, 35% and 21%, respectively, in the study. None of the study participants was on digoxin or diuretics. There was also no difference between the groups receiving oral hypoglycaemic medications and insulin, and in the study were 85% and 15%, respectively [Table 3].

Table 3: Distribution of patient's pre-operative medications

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The study groups BPG-2 and BIG-4 average MAP prior to induction and after extubation (85.45 ± 8 and 87.62 ± 6 mmHg) and post-intubation and after sternum closure were (76.47 ± 7 and 74.51 ± 8 mmHg), respectively [Figure 1]. The study groups mean BIS values prior to induction, post-intubation, skin closure and after extubation were 95.64 ± 6.75, 51.32 ± 11.92, 54.16 ± 10.25 and 83.10 ± 13.14 [Figure 2]. In addition, the mean BIS values during CABG-OP surgery in the groups CPG-1, BPG-2, CIG-3 and BIG-4 were 38 ± 8, 49 ± 5, 32 ± 12 and 51 ± 6, respectively, which were statistically significant in both the study groups with BIS monitoring compared to conventional anaesthesia during CABG-OP surgeries [Table 4] and [Table 5].

Figure 1: MAP between study groups. MAP: Mean arterial pressure

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Figure 2: BIS scores between study groups. BIS: Bispectral Index

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Table 4: Bispectral index value and propofol used in study groups

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Table 5: Bispectral index value and isoflurane used in study groups

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The mean quantity of propofol used for CABG-OP surgery was 178 ± 11 ml in CPG-1 and 117 ± 6 ml in BPG-2. On calculating, there was a reduction of 34.26% in propofol requirements with BIS-guided anaesthesia for CABG-OP surgeries compared to conventional anaesthesia for CABG-OP surgeries, which was statistically significant in both the study groups [Table 4].

The quantity of isoflurane used to perform CABG-OP (the formula to derive the amount of isoflurane in ml is mentioned in methods) was 39 ± 8 ml in CIG-3 and 25 ± 6 ml in BIG-4. On calculating, there was a reduction of 35.89% in isoflurane requirement with BIS monitored anaesthesia compared to conventional anaesthesia for CABG-OP, and this difference was statistically significant with the use of BIS.

All patients completed CABG-OP surgeries without converting them into an on-pump procedure. In groups, BPG-2 and BIG-4 lengths of endotracheal intubation were 2.2 ± 1.27 and 2.3 ± 1.49 h, respectively. The extubation time was reduced by 37% and 50% for propofol and isoflurane with BIS, which was statistically significantly lower for the BIS groups. The OAA-S > 2, DOS in CCU, and DOS in the hospital had no significant difference among the four groups. None of our participants had ADS when interviewed 24 hours after extubation in CCU [Table 6] and [Table 7].

Table 6: Distribution of patient's post-operative characteristics in propofol groups

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Table 7: Distribution of patient's post-operative characteristics in isoflurane groups

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Discussion

Nowadays, many anaesthesiologists monitor haemodynamic responses and/or measure MACs of inspired inhalation anaesthetics to adjust the doses of anaesthetic agents during GA. However, these adjustments do not always reflect anaesthesia's hypnotic component and lead to ADS. Deep anaesthesia may develop complications such as delayed awakening, hypotension, increased morbidity and mortality, and awareness may occur through superficial anaesthesia.^[7] The ADS reported in the literature and incidence of ADS varies between 0.2% and 2%.^[10],[11] The incidence of ADS, especially in cardiac surgery, is significantly higher, with an older report of up to 24%.^[12] In cardiac surgeries, the incidences of awareness are more common due to the longer duration of surgery and frequent use of muscle relaxants. The heart's compression and displacement are ubiquitous during CABG-OP, resulting in a significant increase in atrial pressures and a marked decrease in cardiac output. Patients with low cardiac output and pulmonary arterial hypertension become vulnerable to haemodynamic compromise with deep anaesthesia. Anaesthesiologists, therefore, try to minimise anaesthetic drug utilisation among these patients resulting in ADS. The exact amount of the anaesthetic required to guarantee lack of recall is unknown. A reliable monitor that can ensure unconsciousness is highly desirable in high-risk patients. Many electroencephalographies based machines have been marketed for this purpose, and the most common are M-entropy (G. E. Health-care), Narcotrend (MonitorTechnik) and BIS (Medtronic Ltd). The most broadly studied and FDA approved is the BIS, used to titrate anaesthetic agents to maintain a loss of consciousness and prevent ADS.^[17],[18]

While comparing ADS in the BIS group and without the BIS (conventional) group patients, the B-Aware study reported that BIS utilisation reduces the risk associated with the incidence of ADS by 82%.^[26] However, Avidan et al. performed a more extensive BAG-RECALL study and could not demonstrate BIS's superiority over end-tidal anaesthetic gas concentration in preventing ADS.^[10] Karaca et al. compared the effects of BIS monitoring with the conventional anaesthesia approach and reported no incidence of awareness in their study.^[19] These differences may be due to differences in the study designees, the dose of anaesthetic drugs used, and the patients' condition. In addition, Karaca et al. underreported cases of ADS, as they ruled out awareness of intraoperative events at 20 min after surgery in the recovery unit, which was too early. Although previous literature has acknowledged that the structured post-operative interview is the most appropriate method to investigate ADS, the interview's actual timing is debatable. Some studies advocated interviewing patients as soon as they regain consciousness. Others suggest interviewing patients after 24 h or even as long as 30 days after surgery.^[3] However, most patients will be drowsy during the early interview and may give unreliable information. Interviewing after 1-week would eliminate patients already discharged from the hospital with an ultra-fast-track (UFT) strategy involving early hospital discharge for more cost-effective quality health care.^[27] Interview 24 h after extubation was the interview timing in our study due to the UFT extubation strategy.

In a study, Leslie et al. disclosed that a BIS value < 40 maintained for 5 min during surgery increases morbidity and mortality of patients.^[7] Furrthermore, Monk et al., in a retrospective study, reported deep hypnotic time with a BIS < 45 as a risk factor for 1-year mortality.^[28] Therefore, to reduce the deep hypnotic time and avoid ADS, we used BIS monitoring in these high-risk patients going for OP-CABG and kept the BIS value 50 ± 5. On the other hand, Karaca et al. compared the effects of BIS monitoring with the conventional anaesthesia approach and reported that BIS monitoring does not bring much benefit.^[19] This was maybe due to the wide range of BIS values used in their study, from 40 to 60.

BIS monitoring enables one to titrate anaesthesia to meet patients' requirements without awareness, especially in high-risk patients with cardiovascular disease, haemodynamic instability, or renal failure. In our study groups, BPG-2 and BIG-4 showed average MAP before induction and after extubation (85.45 ± 8 and 87.62 ± 6 mmHg) with average BIS values (92 ± 6 and 87 ± 11) and post-intubation and after sternum closure showed average MAP (76.47 ± 7 and 74.51 ± 8 mmHg) and average BIS values (52 ± 4 and 54 ± 3), respectively. BPG-2 and BIG-4 reductions in MAP were noticed in groups along with BIS values. Our haemodynamic findings are inconsistent with Thomas et al., who reported hypotension incidences correlated with low BIS values.^[29] Our study recorded no hypotension as a BIS value of 50 ± 5 was titrated with blood pressure.

Many researchers compared BIS versus haemodynamic-based anaesthesia practices.^{[17],[18],[19]} The use of propofol in the BIS and control groups varied between 2.8 and 8.0 mg/kg/h and 4.9–11.9 mg/kg/h, respectively. Using BIS monitoring during CABG-OP surgery, we reduced the requirement of propofol by 34.26% and isoflurane by 35.89%. Our findings support Gan et al., that the BIS monitoring reduces the requirement for anaesthetic drugs compared with conventional anaesthesia practice and this may result in potential economic benefits.^[8],[18] In contrast, Karaca et al. reported that propofol consumption was more in the BIS group than in the control group.^[19] However, in their study, difference between the two groups was not statistically significant. We believe that the disparity in results is related to methodological discrepancies, as they used a BIS value of 40 compared to our 50. Likewise, titrating anaesthetic agents with BIS monitoring decreases anaesthetic drug requirements. The reduced use of anaesthetic drugs during CABG-OP in patients with poor LV function causes less myocardial depression and reduces the requirement for inotropic support and arrhythmias.

In a study, Gan et al. reported that using BIS than the conventional anaesthesia practice reduces propofol requirement and leads to faster recovery.^[18] The length of post-operative intubation in the groups BPG-2 and BIG-4 were (2.2 ± 1.27) and (2.3 ± 1.49) compared to the groups CPG-1 and CIG-3 were (3.5 ± 4.51) and (4.6 ± 3.72), respectively. The length of post-operative intubation was significantly less in BIS groups BPG-2 and BIG-4 in our study, supporting the study of Gan et al.^[18] The authors believe that the extubation time was impacted by factors other than the propofol or isoflurane dose.

Conclusion

Our study raised an important question: High-risk OP-CABG patients get more anaesthetic drugs than required without BIS monitoring. In this era of UFT anaesthesia with early extubation and CCU discharge, minimising unnecessary exposure to anaesthetic agents using BIS monitoring is crucial. Furthermore, many anaesthesiologists would prefer to limit excessive use of anaesthetic agents due to their myocardial depressing property, particularly while grafting the distal vessels when haemodynamic instability is pervasive. Thus, BIS monitoring aids CABG-OP surgeries by monitoring the depth of anaesthesia (BIS value 50 ± 5), preventing ADS (0%), reducing anaesthetic requirement (propofol 34.26% and isoflurane 35.89%), reducing myocardial depression (MAP >74 mmHg) and aiding UFT extubation (37% and 50% reduction in the duration of intubation in propofol and isoflurane with BIS).

Data availability

All the data are available within the manuscript. In addition, the datasets used and analysed during the current study are available from the corresponding author based on reasonable request.

Ethical approval

Ethical clearance and approval were obtained through the Department of Anaesthesiology and Intensive Care at the SAMSRI, Lucknow, after approval from the Institutional Ethical Clearance Committee on Human Research (Number: AH/127/C/2021) SAMSRI, Lucknow, India, as per the Helsinki Declaration of 1975 and revised guidelines of 2000.

Consent

The study was explained to the patients, and written informed consent was obtained from them. Patients were informed that the care would not be compromised in any way, and their confidentiality was assured. Name and other identifying information were not used in the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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