Physiology of pain—a narrative review on the pain pathway and its application in the pain management

Abstract

Background and Objective: Pain is perhaps the commonest symptom for which patients seek medical care and represents a major socioeconomical burden on healthcare systems globally. Pain-related conditions were shown to be the leading causes of disability in 10–49 years old in a recent study on the global burden of disease [2019]. Despite a great deal of research into pain and analgesic strategies the effective management of pain remains challenging. An appreciation of the physiology of pain is therefore essential for understanding how to correctly assess, diagnose and manage it. There is no up-to-date review article on the physiology of pain, which taking into account the latest scientific evidence. It is written as part of a series of articles looking at ‘Analgesia for major surgery’ and therefore principally focuses on post-surgical pain. Methods: We performed a literature search on PubMed and google scholar using the terms ‘pain physiology’, ‘acute pain’, ‘chronic pain’, ‘chronic post-surgical pain’, ‘nociception’, ‘peripheral and central sensitisation’, ‘descending modulation pathway’, ‘pain management’ and ‘multimodal analgesia’. We included studies, review articles and editorials published in English from 1st Jan 2000 to 1st Dec 2021. All papers reviewed and their key references are crossed checked to ensure a balanced and high quality literature review on the subjects. We also referenced the ‘physiology of pain’ chapter from the textbook— Fundamentals of anaesthesia (3rd ed.) and the International Association for the Study of Pain (IASP) website. Key Contents and Findings: Better understanding of pain physiology has been achieved through research and clinical studies with numerous new targets identified to add new tools for clinicians to manage pain. There is still a significant gap between research and successful clinical applications due to the complex nature of pain. Conclusions: The pain pathway is a complex process with multiple interdependent processes and under modulations from neuronal, endocrine, and inflammatory systems. This better understanding of the pain physiology guide our clinical approach in targeting pain more aggressively in the peri-operative period and more opportunities for multimodal analgesia approaches as we can target many sites on the pain pathways simultaneously.