Week 4 Flashcards
Types of pain
Common terminology of overall types (time)
* Acute
* Persistent (previously chronic)
Related Pathways for different classifications
* Nociceptive
* Neuropathic
Nociceptive Pain
Nociceptive pain response
* Transduction
* Transmission
* Perception
* Modulation
Pathophysiology- pain
Nervous system has key three areas related to sensation and perception of pain:
1. Afferent pathways
2. Central nervous system
3. Efferent pathways
Afferent pathway
a) nociceptors (pain receptors)
b) afferent nerve fibres
c) spinal cord network
- Afferent pathways terminate in the dorsal horn of the spinal cord
CNS pathway
The portions involved in the interpretation of the pain signals:
* the limbic system
* reticular formation
* thalamus
* hypothalamus
* cortex
Efferent pathways
Composed of the fibres connecting:
* reticular formation
* midbrain
* substantia gelatinosa in dorsal horn
Nociceptors
- Sensory receptors (nerve endings) activated by noxious stimuli, transmit impulses via C fibre and A‐delta fibres
Distributed in: - somatic structures (skin, muscles, connective tissue, bones, joints);
- visceral structures (visceral organs such as liver, gastro‐ intestinal tract)
Transduction
- Response to tissue injury
- Release of chemical mediators
- Conversion of energy types
- Generation of action potential
Chemical mediators in pain
- Prostaglandins
- Substance P
- Histamine (Mast cells)
- Bradykinins
- Serotonin
- Potassium
- Others
Transmission
Three phases:
* Injury site to spinal cord
- A‐delta and C fibres
* Spinal cord to brain stem and thalamus
* Thalamus to cortex
Action potential
Action potentials are generated by voltage-gated ion channels embedded in a cell’s plasma membrane
Pathways: ascending = sensory
- From nociceptors to brain
- Complex transmission from periphery to dorsal root of spinal cord
- Terminate in dorsal horn
- Signals communicate with local interneurons
- Neurons with long axons ascend to brain
Pathways: descending = motor
From brain to spinal dorsal horn
* Can be modulated
- Chemical substances
- Gate theory
- Actions
* Selective response to stimuli
Perception
Conscious experience of pain
* Reticular activating system (RAS)
* Somatosensory system
* Limbic system
* Cortical structures
Modulation
- Signals from brain travelling downwards
- Release of chemical substances o Endogenous opioids
- Encephalins
- Endorphins
- Serotonin
- Noradrenaline (norepinephrine)
- Amplification of dampening of the pain system
- Occurs at all levels of the nervous system
- Signals enhanced or inhibited
- Influences pain perception
- Helps explain variability in pain experience
- The “Gate Theory”
Nerve fibres- A delta fibres
- Thinly myelinated
- Large diameter
- Fast-conducting fibres
- Transmit well-localised, sharp pain
- Sensitive to mechanical and thermal stimuli
- Transmit signals rapidly: associated with acute pain
Nerve fibres- C fibres
- Unmyelinated, small diameter
- Slow-conducting
- Transmit poorly localised, dull and aching pain
- Sensitive to mechanical, thermal, chemical stimuli
- Activation associated with diffuse, dull, persistent pain.
Nerve fibres- A beta fibres
- Highly myelinated
- Large diameter
- Rapid-conducting
- Low activation threshold
- Respond to light touch, transmit non-noxious stimuli
- Gate theory: tactile non‐noxious stimuli inhibits pain signal transmission
Nociceptive pain- Superficial somatic
– Skin
– Mucous membranes
– Subcutaneous tissues
Nociceptive pain- Deep somatic
– Muscles
– Bones
– Fascia
– Tendons
– Joints
– Ligaments
– Blood vessels
Gate control theory
- Melzack & Wall 1965
- Theorised the existence of a “gate” that could facilitate/inhibit transmission of pain signals
- Gate controlled by dynamic function of certain cells in dorsal horn
- Substantia gelantinosa within dorsal horn is anatomical location of gate
Pain experience dependent on:
- amount of information that gets “through” the gate to the brain
- Competition between large and small fibres
- Competition between pain fibres and non pain fibres
- amount of downward signaling from brain
- Endogenous chemical release
Gate control
- Descending & ascending fibres meet at the gate
- Gate open/closed depending on information received from various sources
- T cells within dorsal horn facilitates the opening & closing
- Activity such as touch can close the gate e.g. rubbing the injured site
Pain
- Necessary, protective mechanism
- Subjective experience, not necessarily consequential just from an external stimulus
- Complex interplay of multiple factors
– Biological
– Psychological/affective
– Sociological
Acute pain
- Sudden onset
- Mild to severe
- Duration dependent on “normal healing”
- Deep or superficial ‐ produce different pain
- If pain continues ‘acute pain cycle’ may occur
- e.g. migraine or angina may involve recurrent acute episodes
- Person may be fully functional in between or life may be disrupted by constant threat/become persistent pain sufferer
Classification of pain
Persistent pain (previously called chronic) Extends beyond expected healing time
* Gradual or sudden
* Mild to severe
* > 3 - 6 months (arbitrary)
* Up to 30% of population
Persistent (chronic) pain
- Usually results from chronic pathological process
- Gradual or ill defined onset
- Continues unabated – progressively more severe
- Usually no signs of sympathetic over activity (as seen with acute pain)
Issues - Not always associated with an identifiable cause
- Often unresponsive to conventional medical treatment
- Complex and pathophysiology is poorly understood
- May limit normal functioning
Nociceptive Somatic Pain
- From mechanical, thermal or chemical excitation or trauma to peripheral nerve fibres
- Mediated by widely distributed nociceptors
- Pain described as:
- dull or aching
- throbbing
- sometimes sharp
- Opioid responsive
Physiologic structures: - Cutaneous: skin and sub‐cutaneous tissues
- Deep somatic: blood, muscle, blood vessels, connective tissue
Mechanism: - Activation of nociceptors
Characteristics: - Well‐localised, constant, achy, may be initially acute
Sources of acute pain:
*Incisional pain, insertion sites of tubes and drains, wound complications, orthopaedic procedures, skeletal muscle spasms
Sources of chronic pain syndromes: - Bony metastases, osteo/rheumatoid arthritis, low‐back pain, peripheral vascular disease
Nociceptive Visceral Pain
- Dull, poorly localised deep pain
- Due to ischaemia, inflammation, obstruction
- Vague associated symptoms, may be N & V
- Referred pain
- Reflex motor & sympathetic efferent activity
- Cutaneous hyperalgesia
- May be described as sickening, deep, squeezing, dull
Nociceptor: visceral
Physiologic structures:
* Organs and linings of body cavities
Mechanism:
* Activation of nociceptors
Characteristics:
* Poorly localized, diffuse, deep, cramping or splitting
Sources of acute pain:
* Chest tubes, abdominal tube drains, bladder and intestinal distension
Sources of chronic pain syndromes:
* Pancreatitis, liver metastases, colitis
Neuropathic Pain
- Results from damage to, or pathologic changes of, the peripheral or central nervous system
- May be mediated by NMDA receptor
- Pain described as burning, tingling, shooting, electric ‐ like, lightning ‐like
- May exhibit opioid resistance or require higher doses for effect
- CNS
– Stroke
– MS
– Spinal cord trauma - PNS alteration
– Polyneuropathy
– Entrapment neuropathy
– Post herpetic (herpes/shingles) neuralgia
Neuropathic: non‐nociceptor
Physiologic structures:
*Nerve fibres, spinal cord, and central nervous system
Mechanism:
* Sources of acute and chronic pain syndromes
Characteristics:
* Poorly localized: shooting, burning, fiery, shock‐like, sharp, painful numbness
Sources of acute and chronic pain syndromes:
*Nerve tissue injury due to diabetes, HIV, chemotherapy, neuropathies, post‐herpetic neuralgia
Somatoform pain disorder
- Previously termed psychogenic pain
- Pain caused, increased, or prolonged by mental, emotional, or behavioural factors
- Diagnosis of exclusion
- Label or diagnosis? Sufferers are often stigmatised
- Headache, back pain and abdominal pain are sometimes diagnosed as SPD
Cancer pain
- Separate category
- Usually persistent
- Long‐term
- Often treated as acute pain
- Progressive nature
- Those with cancer may experience both persistent and acute pain
Breakthrough pain
- Common in cancer patients
- Sudden onset
- Short duration
- Unresponsive to normal pain management
Intractable pain
- Pain that is not relieved by ordinary medical, surgical or nursing measures.
- Pain usually persistent
Phantom pain
- Pain felt in a body part that is missing
– Sensation
– Pain
Referred pain
Felt at a site other than the injured/ diseased organ/body part
Pain perception, expression and reaction
Influenced by variables:
* genetic
* developmental
* familial
* psychological
* social
* cultural
Psychological and physical aspects of pain
- Anxiety
- Sense of helpless ness
- Poor insight
- Lack of communication skills
- Depressive mood
- Cognitive deficits
- Elderly
Environmental aspects of pain
- Unhealthy environment
- No community access
- Poor finances
- Limited education/health literacy
- Stressful living context
- Lack of secure housing
Social and interpersonal aspects of pain
- Lack of family support
- Poor social networks
- Unemployed
- Avoidance of activities
- Being single
- Frequent hospitalisation
Pain can be affected by:
- Attention
- Expectations: previous experience
- Interpretation: attitudes and beliefs
- Context: what is the meaning of the pain
- Emotions and mood: anxiety, depression, anger, sad
- Coping strategies: perception of control
Psychosocial Aspects of Persistent Pain
- Loss of employment / income
- Depression, fear, anxiety, grief, guilt, anger
- Isolation
- Sleep disorders
- Marital and family dysfunction
- Lowered self esteem and confidence
- Catastrophising
Pain Assessment/Plan
- Initial assessment
- Assessment tools
- Goals of pain management
- Ongoing assessment
- Documentation
Factors relevant to effective treatment
- Ability to use appropriate pain measurement tools.
- Patient’s beliefs about pain, expectations and treatment preference
- Coping mechanisms
- Patient’s knowledge of pain management techniques and expectation of outcome
- Family expectations and beliefs about pain and the patient’s illness
Pain assessment tools
*Uni‐dimensional tools
* measure only one dimension of the pain experience
* accurate, simple, quick, easy to use and understand
* scales have numeric/verbal rating /verbal descriptor e.g. to describe mild, moderate, severe pain
* commonly used for acute pain assessment and postoperative pain assessment
Multi‐dimensional assessment tools
- Provide information about the qualitative and quantitative aspects of pain
- Tend to be used for persistent pain or if neuropathic pain is suspected
- Require patients to have good verbal skills and sustained concentration: take longer to complete than uni‐dimensional tools.
Assessment of Acute Pain
- Definable injury / illness
- Definite onset
- Duration limited and predictable – usually subsides as healing occurs
- Associated with clinical signs of sympathetic overactivity
Pain Scales: uni‐dimensional
- Numerical
- Visual analogue scale
- Verbal rating scale
Numeric Pain Rating Scale
- Most commonly used
- Line with 0 (no pain) at one end and 10 (worst pain possible) at the other
- The patient is asked to rate pain intensity by picking the number that most closely represents the level of pain that the patient is experiencing
Visual analogue scale
Instruct the patient to point to the position on the line between the faces to indicate how much pain they are currently feeling.
Verbal Rating Scale
Uses
* verbal descriptors, e.g. mild, moderate, severe
or
* quality descriptors, e.g. ache, agonizing, or discomfort
Multidimensional Pain Tools
Acute
– PQRST
–OPQRTSUV
– Initial pain assessment tool
PQRST
P = Provocation/Palliation
Q = Quality/Quantity
R = Region/Radiation
S = Severity Scale
T = Timing
OPQRSTUV
O = Onset
P = Provocation/Palliation
Q = Quality
R = Region/Radiation
S = Severity Scale
T = Treatment
U = Understanding impact
V = Values
Functional activity score
- Ask the patient to perform an activity related to their painful area, e.g.
– deep breathe and cough for thoracic injury
– move affected leg for lower limb pain - Observe during the chosen activity and score: A, B or C.
A – No limitation: the activity is unrestricted by pain
B – Mild limitation: the activity is mild to moderately restricted by pain
C ‐ Severe limitation: the ability to perform the activity is severely limited by pain - NB Relative to baseline: refers to any restriction above any pre‐existing condition the patient may already have.
Asst. functional and medical problems
- Associated symptoms
- Effect of pain on activities
- Family history / Medical and drug history
- Medications/treatments and their effect on pain
- Physical examination
- Evaluation of disability associated with the pain
- Psychosocial
Location and description of pain
- Identify factors that exacerbate or relieve pain.
- Describe the character of pain using quality/sensory descriptors, e.g. sharp, throbbing, burning.
- Observe for signs of neuropathic pain including descriptions: e.g. shooting, burning, stabbing, allodynia
- How long does the pain last, e.g. continuous, intermittent
Assessment of persistent Pain
- May not have
– definable injury / illness
– definite onset - Duration
– not limited: persistent beyond normal healing time
– unpredictable - No clinical signs of sympathetic overactivity
Additional questions: persistent pain
- Is there a pattern to pain when you get up in the morning?
- Does pain increase as day goes on/with activity?
- What effect do analgesic medicines have on the pain?
- Does pain wake you?
- If you have severe pain, do you have any of the following effects: e.g. lethargy, nausea, changes in mood?
- Is there any numbness or loss of muscle strength associated with the pain?
- Do normal stimuli make pain worse, e.g. light touch, shower?
- Is pain tolerable for most of day?
- What relieves pain?
- Is there any weather that makes the pain worse?
Multidimensional Pain Tools
Persistent
* Brief pain Inventory: long and short forms
* McGill Pain Questionnaire: long and short forms
Brief Pain Inventory (BPI)
- Assesses pain severity and the degree of interference with function, using 0‐10 NRS.
- Validated screening and monitoring tool
- When to use
– Initial assessment
– Patient reviews and monitoring
– Useful tool with children, elderly or CALD
McGill Pain questionnaire
- McGill Pain Questionnaire (MPQ)
- Short‐form MPQ (SF‐MPQ)
- Evaluate sensory, affective‐emotional, evaluative, and temporal aspects of the patient’s pain condition.
- Three pain scores are calculated: the sensory, the affective, and the total pain index.
Paediatric Assessment
Self‐reported measures of pain include :
* routine questions
* verbal scales
* numeric scales
* pictorial scales
Behavioural measures of pain include:
* age related behavioural changes
* motor responses
* facial expressions
* crying
* behavioural responses (e.g. sleep‐wake patterns)
Physiological: RCH
Physiological changes include:
* altered observations (HR, RR, BP, etc.)
* posture/tone
* sleep pattern
* skin colour/sweating
These are not good indicators to use in isolation
Paediatric QUESTT
Q: Question the child
U: Use a pain rating scale
E: Evaluate behavior & physiological change
S: Secure parents involvement
T: Take cause of pain into account
T: Take action and evaluate results
Pain rating scales for children
- Faces
- Numeric
- Behavioural
- Behavioural/physiological
FACES pain rating scale: RCH
The patient is asked to pick the face that best represents the pain that he or she is experiencing
* These faces show how much something can hurt.
* “Point to the face that shows how much you hurt [right now]”.
* Do not use words like ‘happy’ and ‘sad’.
* This scale is intended to measure how children feel inside, not how their face looks.
Acute pain effects: Developmental
- ↑behavioural/physiologic responses to pain
- Altered temperament
- ↑vulnerability to stress disorders
- Addictive behaviours
- Anxiety states
- Infant distress behaviour
- Future pain: persistent pain syndromes
