The intraoperative administration of opioids was considered as a foundation of anaesthesia. It is used to stabilize the hemodynamics during anaesthesia. Opioids are met with adverse effects, such as respiratory depression, nausea/ vomiting, constipation, tolerance and hyperalgesia. This in turn results in delayed recovery and prolonged hospital stay.

Opioid-free anesthesia (OFA) have been introduced in order to overcome these adverse effects. In OFA, both central and peripheral pathways, are blocked by drugs acting on sodium channels, G-protein-coupled receptors, and N-methyl-D-aspartic acid (NMDA) receptors, some of which also have anti-inflammatory activity.

Inhalational anaesthetics contributes significantly to healthcare-related greenhouse gas emissions, ozone depletion. Prolonged exposure to inhalational agents have shown risks of health hazards, potential to cause genetic damage and oxidative stress among health care personnel in working environments with poor or inadequate scavenging of inhaled anaesthetics. Anaesthetic drugs account for upto 6% of total pharmacy costs, out of which inhalational agents contributes upto 20%.Monitoring depth of anaesthesia partly helps to deliver appropriate dose of anaesthetic agents and helps to overcome these burdens. One such measure is patient state index (PSI) which measures the effect of anaesthesia and level of consciousness.