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

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Objectives for this module

• Discuss the ways pain can be characterised– Duration– Mechanism– Origin– Situation

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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)

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Different mechanisms of pain

Why are they important?• Pathophysiology is different• Presentation is different• Management is different

Introductory Palliative Care Course for Health Care Professionals (Uganda); PCAU/MOH (2013) 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

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Duration: acute vs. chronic pain

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Gradual or vague onset– Continues and may become progressively more severe– Patient may appear depressed and withdrawn– Usually no signs of sympathetic over-activity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)

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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).

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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)

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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)

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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

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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)

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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 painB. Chronic, visceral pain C. Acute, neuropathic painD. Acute, incident pain

Beating Pain, 2nd Ed. APCA (2012)

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Take home message

• Knowing the differences in the mechanisms of pain is important to adequately and appropriately treat the pain

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References

• African Palliative Care Association. Beating Pain: a pocketguide for pain management in Africa, 2nd Ed. [Internet]. 2012. Available from: http://www.africanpalliativecare.org/images/stories/pdf/beating_pain.pdf

• African Palliative Care Association. Using opioids to manage pain: a pocket guide for health professionals in Africa [Internet]. 2010. Available from: http://www.africanpalliativecare.org/images/stories/pdf/using_opiods.pdf

• Amery J, editor. Children’s Palliative Care in Africa [Internet]. 2009. Available from: http://www.icpcn.org/wp-content/uploads/2013/08/Childrens-Palliative-Care-in-Africa-Full-Text.pdf

• Kopf A, Patel N, editors. Guide to Pain Management in Low-Resource Settings [Internet]. 2010. Available from: http://www.iasp-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. 2013.