Basics of Pain Physiology

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The Basics
Dr Antonita D. Macaraeg – De Pano
DPBA, FPSA, DPBM, Mmed, FPSMS
Pain Physiology:

Pain is a …..
PAINFUL REALITY

STATISTICS
• Jones et al…
• 32% of patient ranked pain as their
greatest worry
• 73% of hospitalized patients stated
that their pain was inadequately
treated.
• ACS, NCCN
• 2/3 advanced cancer: pain

WORLWIDE STATISTICS
• Market research report :
– more than 1.5 billion people worldwide suffer
from chronic pain
• approximately 3- 4.5% of the global
population
– neuropathic pain, with incidence rate increasing
in complementary to age.

PHILIPPINE STATISTICS
• Lu et al 2013
-10.4% of the general adult population
- annual incidence rate of 3.4%
- chronic pain : women and elderly
- more than 50% reported inadequate control
- Cancer is the 3rd most frequent cause
- >200,000 Filipinos are suffering from cancer pain

The Problem of Pain
• American Pain Foundation:
• - a major health crisis
• - tremendous impact on healthcare
costs
• -rehabilitation ($261-$300B)
• - lost worker productivity ($279-$336 B)

Review of terminologies:
• Nociception – perception of a potentially tissue
damaging stimulus
• Nociceptor- a receptor preferentially sensitive to a
noxious stimulus
• Pain threshold- lowest intensity at which a given
stimulus is perceived as painful; constant
• Pain tolerance- greatest level that a subject is
prepared to endure; varies among individuals
• Hyperalgesia-increased response to a stimulus that
is normally painful
• hypoalgesia-diminished sensitivity to a noxious
stimulus

Pain Terms
• allodynia-pain due to a stimulus that does not
normally provoke pain
• Paresthesia- any abnormal sensation w/c may be
spontaneous or evoked; pins & needles
• Dysesthesia- painful paresthesias; “unpleasant
• Adjuvant analgesics - drugs that are available for
indications other than pain but are analgesic in
select circumstances.

Pain terms:
• Peripheral sensitization – increased or
excitability of peripheral nociceptors
• Central sensitization – increased sensitivity or
excitability of nerves within the central
nervous system . Normal inputs begin to
produce abnormal responses; such as spread
of pain beyond an area of tissue damage

Doorbell theory of Pain:
NERVE IS
NEVER THE
SAME

Chronic Pain
Is a biopsychosocial phenomenon

Management of Pain:
• Understanding the definition of pain
• Mastery of the neural pathways that transmit and
modulate pain
• Taking into consideration the psychological
aspects of pain.

IASP:
PAIN is an unpleasant sensory and
emotional experience associated
with actual or potential tissue
damage or described in terms of
such damage.

Types of Pain
 Acute Pain– a complex physiologic
reaction to tissue injury, visceral
distention or disease, alerts
 Chronic Pain – a multi-faceted
medical problem that does not
resolved after medical treatment,
persists

Classification of Pain as to Pathophysiology
 SOMATIC PAIN – well localized *achy, dull, exacerbated by movement
, relieved by rest
 Activation of nociceptors in cutaneous and deep tissue.
 VISCERAL PAIN – poorly localized *, deep, squeezing, crampy,
frequently associated with autonomic symptoms and with radiation sites
 Activation of nociceptors in visceral organs, stretching, distention.
 NEUROPATHIC PAIN – arises from nerve injury, persists; burning,
stabbing, with allodynia, associated with electrical sensations
 Injury to peripheral / central nervous system

NEURAL PATHWAY TO PAIN
TRANSMISSION & MODULATION:
• 1. transduction – a process by which
noxious stimuli lead to electrical activity in the
appropriate nerve ending
• 2. transmission – process by which the
coded information is relayed to the structures
of the Central Nervous System

Neural Pain Pathway
• 3. modulation – refers to the neural activity
leading to control of pain. Modification occurs at
several levels :
– a) spinal cord – neurotransmitter substances in the dorsal
horn or spinal reflexes that convey different efferent
impulses
– b) could be described by gating mechanisms
– Ex: binding of substance P or glutamate to NMDA receptors
 “central sensitization”
• 4. perception – final process (cortex) where the
individual experiences the subjective correlates of
pain.

Diagram of the Pain System:

PAIN PATHWAY:
• A. Peripheral System:
• B. Spinal Dorsal Horn / Ascending System
• C. Supraspinal System
• D. Descending System

Dorsal Horn:
• Excitatory neurotransmitters:
• 1. Glutamate ) excite large myelinated
• 2. Aspartate ) fibers
• 3. Substance P - excite A delta & C afferents
•
• Inhibitory substances:
• 1. Endorphins
• 2. Enkephalins
• 3. GABA
• 4. opioid receptors

Supra-spinal System
• Involve in the processing of nociceptive
information
• 1. Reticular formation - mediates motor,
autonomic and sensory functions
• affective dimensions of pain
• 2. Thalamus - refined cutaneous awareness of
pain
• 3. Hypothalamus and limbic system - integrates
and regulates autonomic and neuroendocrine
responses

Pain Pathway

Factors affecting the severity of
Pain
Age
Culture, mores, races, beliefs
Psychological factors and previous
experiences
History of drug abuse
Site, extent and length of surgery
Anesthetic techniques and medication

Why Relieve Pain?
 Reduced length of hospitalization
 Reduced post-operative complications
 Early ambulation and rehabilitation
 Better respiratory parameters
 Less incidence of hospital acquired infection
 Reduced stress and anxiety
 Better psychological and emotional gratification
 Beneficial effects on immune response

Assessment of Pain
• P - palliative and provocative
factors
• Q - quality
• R - region and radiation
• S - severity
• T - timing

Measurement of Pain:
1. Verbal descriptive Scale
- Mild-discomforting-distressing-
horrible-excruciating
2. Numeric Rating Scale
- Choose a number 0 to 10 to
indicate severity of pain

3. VAS (Visual Analogue
Scale)

Principles of Pain
Management:
1. Psychological preparation
2. Not all pain can be eliminated always.
3. Pre-emptive treatment
4. Around the clock analgesia – multimodal
approach

Principles of pain
management:
5. Provide rescue doses
6. Pain intensity and relief must be
assessed at regular intervals
7. Treat the side-effects
8. Respect patient’s preferences.

WFSA Analgesic ladder to treat
Acute Pain
Paracetamol
+ NSAIDs
+ strong, potent
opioid
Paracetamol
+ NSAIDs
+ weak
opioid
Paracetamol
+ NSAIDS
Paracetamol
Slight
mild
moderate
severe

Summary:
ACUTE PAIN:
• Duration
• Serves as a warning
• Treatment
modalities
– Know the type of pain
– NSAIDS
– Opioids
– PCA
– Regional techniques
CHRONIC PAIN:
• Duration – persists
beyond the usual
course
• Varied and complex in
manifestations
• with significant
behavioral changes
• Treatment modalities
– Know the type of pain
– Same as acute pain plus
anti-depressants or
anticonvulsants

Basics of Pain Physiology

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