1. Mechanisms of pain
Disclaimer: This presentation contains information on the general principles of pain management. This presentation cannot account for individual variation among patients and cannot be considered inclusive of all proper methods of care or exclusive of other treatments. It is the responsibility of the treating physician, or health care provider, to determine the best course of treatment for the patient. Treat the Pain and its partners assume no responsibility for any injury or damage to persons or property arising out of or related to any use of these materials, or for any errors or omissions. Last updated on January 12, 2015

2. Objectives for this module
Discuss the ways pain can be characterised
Duration
Mechanism
Origin
Situation

3. Characterisations of pain
Pain can be described by its:
Duration – acute or chronic
Mechanism – nociceptive or neuropathic
Origin – somatic or visceral
Situation – incidental pain, breakthrough pain, procedural pain
Beating Pain, 2nd Ed. APCA (2012)

4. Different mechanisms of pain
Why are they important?
Pathophysiology is different
Presentation is different
Management is different

5. Duration: acute vs. chronic pain
Acute pain
Presentation: characterized by help-seeking behavior such as crying and moving about in a very obvious manner
Cause: definite injury or illness
Signs/symptoms:
Definite onset with limited and predictable duration
Clinical signs of sympathetic over-activity: tachycardia, pallor, hypertension, sweating, grimacing, crying, anxious, pupillary dilation
Example: trauma, surgery, or inflammation
Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

6. Duration: acute vs. chronic pain
Presentation: Patients may not show signs of distress seen in acute pain
Cause: chronic pathological process
Under-treatment of acute pain can lead to changes in the central nervous system that result in chronic pain
Signs/symptoms:
Gradual or vague onset
Continues and may become progressively more severe
Patient may appear depressed and withdrawn
Usually no signs of sympathetic over-activity
Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

7. Mechanism: nociceptive pain
Nociceptive pain: caused when nerve receptors called nociceptors are irritated. Nociceptors exist both internally (visceral) and externally (somatic)
Indicates that nerve pathways are intact
Beating Pain, 2nd Ed. APCA (2012); Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013).

8. Nociceptive pain: somatic pain
Somatic pain: stimulation of nociceptors in the skin, soft tissues, muscle, or bone
Pain usually is in a particular location
Aching, throbbing, or persistent pain
Causes: bone or soft tissue infiltration
Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

9. Nociceptive pain: visceral pain
Visceral pain: stimulation of nociceptors in internal organs and hollow viscera organs
Pain is often not in a single location
Described as pressure, cramping, or squeezing pain
Causes: blockage, swelling, stretching, or inflammation of the organs from any cause
Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013)

10. Mechanism: neuropathic pain
Neuropathic pain: caused by damage to nerve pathways
Described as burning, prickling, stinging, pins and needles, insects crawling under skin, numbness, hypersensitivity, shooting, or electric shock
Causes: infiltration by cancer, HIV infection, or herpes zoster, drug-related peripheral neuropathy, central nervous system injury, or surgery
Introductory Palliative Care Course for Health Care Professionals (Uganda). PCAU/MOH

11. Situation
Incident pain – occurs only in certain circumstances (e.g. after a particular movement)
Breakthrough pain – a sudden, temporary flare of severe pain that occurs on a background of otherwise controlled pain
Procedural pain – related to procedures or interventions
Beating Pain, 2nd Ed. APCA (2012)

12. Assessment
Jane has come to your clinic with pain she’s describing as constant shooting pain in her feet for the past four days. How would you classify her pain? A. Procedural pain B. Chronic, visceral pain C. Acute, neuropathic pain D. Acute, incident pain
Answer C:
Beating Pain, 2nd Ed. APCA (2012)

13. Take home message
Knowing the differences in the mechanisms of pain is important to adequately and appropriately treat the pain

14. References
African Palliative Care Association. Beating Pain: a pocketguide for pain management in Africa, 2nd Ed. [Internet] Available from:
African Palliative Care Association. Using opioids to manage pain: a pocket guide for health professionals in Africa [Internet] Available from:
Amery J, editor. Children’s Palliative Care in Africa [Internet] Available from: Africa-Full-Text.pdf
Kopf A, Patel N, editors. Guide to Pain Management in Low-Resource Settings [Internet] Available from: pain.org/files/Content/ContentFolders/Publications2/FreeBooks/Guide_to_Pain_ Management_in_Low-Resource_Settings.pdf
The Palliative Care Association of Uganda and the Uganda Ministry of Health. Introductory Palliative Care Course for Healthcare Professionals