How does the 2020 revised definition of pain impact nursing practice?

The widely used and acknowledged universal definition of pain developed by the International Association for the Study of Pain (IASP) in 1979 has been revised in 2020. The 2020 IASP definition states pain is ‘an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage’. The 2020 IASP definition of pain reinforces the importance for nurses to have an understanding of the pathophysiology of pain and highlights the crucial role pain assessment plays in overall pain management, which nurses are pivotal in driving and delivering.


Introduction
The widely used and acknowledged universal definition of pain that states pain is 'an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage' was developed by the International Association for the Study of Pain (IASP) in 1979. This definition has been accepted broadly by health care professionals and researchers in the pain field and adopted by several professional, governmental and non-governmental organisations including the World Health Organization (WHO). Some in the pain field have postulated that advances in our understanding of pain justified a re-evaluation of this broadly accepted definition and proposed the definition be reviewed 1 .

IASP definition
The discussion prompting the proposed modifications to the 1979 IASP definition of pain stimulated considerable and often passionate discussion with strong arguments for and against the review 1,2 . One benefit of the 1979 IASP definition of pain is that it was universally accepted for decades; however, at its inception the definition was always intended to 'serve as an operational framework, not as a constraint on future development' 1,3 .
To review this 1979 IASP pain definition, a 14-member presidential task force was established by the IASP, taking two years to evaluate the definition and recommend changes based on current evidence-based knowledge. The revised IASP pain definition in July 2020 now states pain is 'an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage' 1,4 (Table 1). Table 1 Year IASP definition

1979
An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.

2020
An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.

IASP definition
The new 2020 IASP pain definition has been modified to be more inclusive of individuals experiencing pain but who cannot describe their pain, such as neonates, the elderly, intubated or critically ill patients, persons with intellectual disabilities or others who are unable to self-report their pain; the new pain definition is also inclusive of animals 5 .
The 2020 IASP definition is intended to be applied to pain conditions arising from different pathophysiology origins including nociceptive, neuropathic and nociplastic pain 6 . It can be applied to acute, persistent or chronic pain and relates to the varied and individual experiences of pain while recognising its diversity and complexity with biological, psychological and social factors 7 .

Implications for nursing practice
Nurses' understanding of the pathophysiology of pain The 2020 IASP definition of pain reinforces the importance for nurses to have an understanding of the pathophysiology of pain and highlights the crucial role pain assessment plays in overall pain management. The notes accompanying the 2020 IASP pain definition highlight the key areas of focus and clinical considerations to guide nursing practice for the future 5 .
Pain is always a personal experience influenced to varying degrees by biological, psychological and social factors as each individual learns the term 'pain' through experiences of physical and emotional injury or encounters in their early life. Many people report pain in the absence of tissue damage or any likely pathophysiological cause as pain and nociception are different phenomena 5 .
Nociception relates to the neural pathway of a noxious stimuli where high threshold sensory receptors of the peripheral somatosensory nervous system are activated via our intrinsic nociceptive pain pathway 4 , whereas pain is the individual experience and description of a sensation or feeling.

Nursing assessment of pain
A structured, reliable and accurate pain assessment using a validated pain measurement tool has long been considered crucial in undertaking a comprehensive pain assessment to ensure effective pain management. There are a number of verbal, non-verbal, behavioural and multidimensional pain assessment tools widely used and accepted 8,9,10 . Pain in the critically ill is associated with adverse physiological and psychological outcomes and nurses are the link between the patient and the health care system 11 . As patient advocates, nurses undertake an important role in accurately assessing a patient's pain in order to initiate effective management strategies 12 .
The 2020 IASP definition of pain seeks to include and highlight the importance of pain assessment in patients who are unable to describe or report their pain, a patient group nurses play a significant role in advocating for. A verbal description is only one of several behaviours to express pain; others may include grimacing, frowning, physical restlessness, splinting areas of the body, as well as haemodynamic changes such as elevated blood pressure or heart-rate. An inability to communicate does not negate the possibility that a human or an animal experiences pain 5,8,13 .
Under-recognition and undertreatment of pain in these patient groups occurs, emphasising the importance of accurate and valid pain assessment by nurses for effective pain interventions 9,14,15 . It is important that nurses try to understand not only the individual patient experiencing pain but also explore personal perception factors related to the nurse assessing and managing the patient's pain so as to be able to mitigate further barriers to effective pain assessment and management 9 .
Accurate and reliable pain assessment is not only crucial to advocate for the patient but pain assessment also aids in determining the subsequent management and treatment strategies for the patient 8 . The assessment helps to identify the causal origins of the pain such as nociceptive, neuropathic or neuroplastic factors. A biopsychosocial pain assessment then analyses the cause of a patient's pain to aid in selecting an appropriate analgesic therapy or management strategy for the patient's individual needs as well as evaluating, then modifying, that therapy according to the patient's response 8 .
Another commonly used definition of pain is McCaffery's 1968 definition 'Pain is whatever the experiencing person says it is, existing whenever he/she says it does' 15 . As clinicians who provide continuous and diverse care to patients, nurses are pivotal in supporting the subjective pain assessment with their objective assessments relating to daily activities, function and movements that may be impacted by pain. The patient's report of an experience of pain should be respected and objective assessments, such as the functional activity score, aim to ensure that pain interventions and treatments correspond with the pain experience of the patient being subjectively reported 8,10 .
Nursing role in pain management in the future An ageing population and the occurrence of chronic pain worldwide will continue to generate significant ongoing physical and psychological distress, having impacts on people's daily function and ability to work, and increasing health service utilisation and economic burden 16 . Chronic pain impacts approximately 20 per cent of people worldwide, with detrimental impacts on quality of life 17,18 . Nurses are vital in implementing a biopsychosocial model of care for patients and are essential members of interdisciplinary teams delivering holistic pain management.
An interdisciplinary team approach to chronic or persistent pain using evidence-based practice is an established standard of care and an area where nurse involvement has been shown to be effective 18,19 . The nursing role in interdisciplinary pain management care is useful for providing accessible and expanded health care delivery via a biopsychosocial model of care to improve function, provide continuity of care, implement nonpharmacological interventions and provide a holistic pain assessment 20,21,22,23 .
The 2020 IASP definition of pain will also be supported in the future by the inclusion of chronic pain in the 2019 WHO International Classification of Diseases (ICD-11) 4 . The ICD-11 is intended to be adopted by several countries in the future when it comes into effect in 2022 with the ICD codes commonly used to report target diseases and comorbidities of participants in clinical research. The inclusion of chronic pain in the recent ICD-11 update is an important step for recognising pain as an important health condition, transforming pain research by the acquisition of accurate epidemiological data, enhancing adequate billing for painrelated treatments and encouraging the development of care and pain treatments worldwide 17 . These recent developments by the IASP and WHO provide greater awareness and expanded recognition of the importance of pain management and pain assessment, creating opportunities for advanced nursing roles in the future from expanded service delivery and pain-focused care.

Conclusion
The 2020 IASP definition aims to be inclusive of all types and presentations of pain to provide scope for management, research and awareness in the coming years. The updated 2020 IASP definition of pain provides an opportunity for nurses to focus on the importance of their roles in assessing pain and advocating for their patients and for optimal pain management strategies to be implemented. The aspirations of pain management in the future support an interdisciplinary, biopsychosocial model of care for patients, an area in which nurses can continue to provide holistic care.