Intraoperative nociceptive responses and postoperative complications in patients undergoing laparoscopic colorectal surgery under general anaesthesia - A prospective observational study

Nociception is the neural process of encoding and processing noxious stimuli. In conscious state, noxious stimuli cause the sensation of pain as response. Response to noxious stimuli during unconsciousness i.e., during general anaesthesia, however, are different from those in the awake state.Surgical invasion which activates peripheral nociceptors, induces autonomic responses, including increase in blood pressure and heart rate, and decrease in peripheral blood flow, under general anaesthesia.Intraoperative surgical stimulation also increases inflammation and tissue damage during surgery by producing various cytokines and chemokines.C - Reactive protein is a biomarker for such inflammatory process.The nociception produced by surgical invasiveness should be effectively balanced by anaesthesia.Monitoring nociception is an important growing area of investigation. Nociceptive response index (NRI), a recently proposed index is a dimensionless number between 0 & 1. It was developed based on appropriate mathematical models representing autonomic activation responses to noxious stimulation and considering heart rate, systolic blood pressure and perfusion index in calculating the numerical value. Hirose et al., evaluated its utility to discriminate nociceptive responses to a small and large skin incision in laparotomy and found that NRI quantitatively discerned the differences. They suggested that NRI could be used to assess either real time nociceptive responses or averaged nociceptive responses throughout surgery without special equipment.

A higher level of surgical stimulus is associated with more physiological responses which in turn is thought to be associated with incidence of postoperative morbidity and mortality.This study is based on the hypothesis that intraoperative nociceptive responses can add on to postoperative complications in patients undergoing colorectal surgery under general anaesthesia.

Postoperative complications can be classified as per modified Clavien – Dindo classification system.