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Abst rac t

About 230 million general surgeries are performed worldwide every year in which

efficient administering and control of anesthesia is required. Balanced Anaesthesia hasbeen defined as that state which ensures the suppression of the somatic and visceralsensory components and thus the perception of pain [1]. It is basically GeneralAnesthesia (GA) that balances the depressing effects of the motor, sensory, reflex andmental aspects of nervous system. Anesthesiologists are multi-skilled physicians whoapply their experience based knowledge of medicine to keep the patient in balancedanesthesia state throughout the surgery.

Necessity to assess and monitor the Depth of Anesthesia (DoA) is obvious to ensurepatients safety during surgery. In conventional methods, DoA is measured based onclinical assessment through empirical measurement of autonomic signs such as

respiration pattern, blood pressure, body temperature, tearing, sweating, heart rate etc. These parameters do not prove to be good predictors of exact anesthetic state of thepatient [2]. Moreover, modern anesthesia practice involves a number of other drugssuch as vasodilators, vasopressors, neuromuscular blockers etc. Each one of themaffects these clinical signs in its own manner making it difficult to associate these signswith anesthetic depth. Also, factors like induction agents, patient illness, age, generalhealth, site and extent of surgical stimulus may modify these signs to a large extent [3].As a result, the decisions made by anesthetists inside the operation theatre are heuristic[4] and cases of patient awareness during surgery with an average of 1:1000 andoverdosing with anesthetic agents are major clinical concerns of anesthesia [5]. Inaddition to this, anesthesiologist has to perform other important tasks in the operation

theater (OT) such as to achieve haemodynamic stability, airway management etc whichcreate a lot of mental as well as physical pressure on anesthetist.

The role of anesthesiologist is not limited to OT only. It extends to the Post AnestheticCare Unit (PACU) for the management of postoperative pain. Statistics shows that 80%of the patients experience pain postoperatively and about 20% experience severe pain[6-8]. No such Gold standard is available for clinical assessment of pain. Despite theavailability of different measures, analgesics and guidelines as per World HealthOrganisation (WHO) [9], negligible work has been done in this direction over the pastdecade. Pain associated with surgical and diagnostic procedures is a commonoccurrence in hospitals [5].

Pain intensity measures are based on physiological monitoring and a numeric rating iscommonly used which classifies pain as mild, moderate or severe. Pain is a sensoryand emotional experience. Intensity, pattern and perception of pain are subjective;therefore, psychological, physiological and patient ratings may not be true measures forassessment of pain intensity. Also when the patient is a pediatric or unconscious, thesemethods are not reliable [10-12]. Sensory receptors of pain (nociceptors) becomesensitive and active after an injury (surgery or other disease) and communicate

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sensations to the cerebral cortex (brain) [11].

Research establishes that 80% of human brain activity is related to sensationperception and being the target organ of different anesthetic agents, brain activity i.e.electroencephalogram (EEG) can be used as the best clinical monitoring tool for pain

assessment. Although, extensive studies have been carried out on EEG of patientsduring surgery in the past [14-25], solution to the problem of maintaining the patient indesired balanced anesthetic state still remains elusive.

The present study addresses the issues related to determination of EEG parameterswhich are correlated with hypnosis and analgesia components of balanced anesthesia,optimizing them and classifying them to estimate independent indices for thecomponent of balanced anesthesia. Objective is to assist the anesthesiologist so thatthe actual condition of the patient can be assessed and drugs can be administeredaccordingly.