Effect of Subanaesthetic Dose of Ketamine on Depth of Anaesthesia Consistency

General Anaesthesia (GA) is a medical state of controlled unconsciousness that inhibits two dimensions of consciousness: the content and the level of consciousness. This state is achieved using various anaesthetic agents, with propofol being one of the most commonly used intravenous anaesthetics. Propofol is a gamma amino butyric acid (GABAA) receptor agonist, which affects both the content and level of anaesthesia. In some cases, anaesthesiologists may choose to use an adjuvant drug, ketamine, in subanaesthetic doses during inhalation GA and propofol total intravenous anaesthesia (TIVA). Ketamine is an N-methyl D-aspartate (NMDA) receptor antagonist and is primarily employed for its analgesic properties. Unlike propofol, ketamine selectively affects only the content of consciousness. The combination of propofol and ketamine appears to have dual effects on the dimensions of consciousness, with propofol affecting both content and level, and ketamine affecting only the content. This combination is likely to complement and improve the consistency of intraoperative anaesthesia depth. However, studies have shown that the administration of ketamine with propofol TIVA, delivered through an automated anaesthesia delivery system using electroencephalogram (EEG) feedback signals from NeuroSENSE processed electroencephalogram (pEEG) monitor, has not demonstrated any significant benefit over the use of propofol alone. Till now, the only study on propofol-ketamine co-administration used an uncommon NeuroSENSE pEEG monitoring system. Closed loop anaesthesia delivery system (CLADS) is a more precise, efficient, and robust mechanism to facilitate automated administration of propofol TIVA which employs the standard bispectral index (BIS) pEEG monitoring to control propofol TIVA delivery. Further evidence is desirable on depth of anaesthesia consistency when ketamine is co-administered with propofol TIVA, using CLADS This randomised controlled study will compare the effect of subanaesthetic dose of ketamine versus placebo (normal saline) on anaesthesia depth consistency in patients undergoing elective laparoscopic surgery under automated propofol TIVA using CLADS. All patients undergoing elective laparoscopic surgery will be screened, and those found eligible will be enrolled. Enrolled patients will receive CLADS-controlled propofol TIVA as standard. In intervention are, patients will additionally receive subanaesthetic dose of ketamine (0.25-mg/kg bolus followed by maintenance infusion 0.25-mg/kg/h) (ketamine group); in control arm, patients will receive normal saline as placebo in addition to propofol TIVA (placebo group).