Week 1 - Pain concepts and assessment Flashcards
Definition of pain
Sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
Types of pain
- Acute
- Persistent (previously chronic)
- Nociceptive
- Neuropathic
Types of pain mechanisms
Nociceptive = tissue - Somatic - Visceral Neuropathic = nerve NB: There is no pain without the brain
Nociceptive pain response (4)
- Transduction
- Transmission
- Perception
- Modulation
Afferent pathways related to sensation and perception of pain (3)
- Nociceptors (pain receptors)
- Afferent nerve fibres
- Spinal cord network
Central nervous system related to sensation and perception of pain (5)
- The limbic system
- Reticular formation
- Thalamus
- Hypothalamus
- Cortex
Efferent pathways related to sensation and perception of pain (3)
- Reticular formation
- Midbrain
- Substantia gelatinosa in dorsal horn
Where are nociceptors distributed in?
- Somatic structures (skin, muscles, connective tissue, bones, joints)
- Visceral structures (visceral organs such as liver, gastrointestinal tract)
What are nociceptors?
Sensory receptors (nerve endings) activated by noxious stimuli, transmit impulses via C fibre and A-delta fibres.
What is transduction?
- Response to tissue injury
- Release of chemical mediators
- Conversion of energy types
- Generation of action potential
What are the chemical mediators of pain?
- Prostaglandins
- Substance P
- Histamine (mast cells)
- Bradykinins
- Serotonin
- Potassium
Three phases of transmission
- Injury site to spinal cord (A-delta and C fibres)
- Spinal cord to brain stem and thalamus
- Thalamus to cortex
What are action potentials?
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 (afferent)
- Signals from brain travelling downwards
- Amplification of dampening of the pain system
- Release of chemical substances
What chemical substances are released in modulation (afferent)?
- Endogenous opioids
- Encephalins
- Endorphins
- Serotonin
- Noradrenaline (norepinephrine)
Modulation (efferent):
- 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 delta 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
Deep somatic nociceptive pain
- Muscles
- Bones
- Fascia
- Tendons
- Joints
- Ligaments
- Blood vessels
Superficial somatic nociceptive pain
- Skin
- Mucous membranes
- Subcutaneous tissues
What is the gate theory?
- Theorised the existence of a “gate” that could facilitate/inhibit the transmission of pain signals
- Gate controlled by dynamic function of certain cells in dorsal horn
- Substantia gelatinosa within dorsal horn is anatomical location of gate
Gate control theory pain experience is dependant on:
Amount of downward signaling from brain
-Endogenous chemical release
Amount of information that gets “through” the gate to the brain
- Competition between large and small fibres
-Competition between pain fibres and non pain fibre
What is acute pain?
- Sudden onset
- Mild to severe
- Duration dependent on “normal healing”
- Deep or superficial - produce different pain
What is persistent pain? (chronic)
- Extends beyond expected healing time
- Gradual or sudden
- Mild to severe
- > 3-6 months (arbitrary)
- Up to 30% population
- 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)
What is 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 and sometimes sharp
- Opioid responsive
What is nociceptive visceral pain?
- Dull, poorly localised deep pain
- Due to ischaemia, inflammation, obstruction
- Vague associated symptoms, may be N & V
- Referred pain
- Reflex motor and sympathetic efferent activity
- Cutaneous hyperalgesia
- May be described as sickening, deep, squeezing, dull
What is 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, lightening-like
- May exhibit opioid resistance or require higher doses for effect
What is 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
What is breakthrough pain?
- Common in cancer patients
- Sudden onset
- Short duration
- Unresponsive to normal pain management
What is intractable pain?
- Pain that is not relieved by ordinary medical, surgical or nursing measures
- Pain usually persistent
What is phantom pain?
- Pain felt in a body part that is missing e.g. amputation
- Sensation
- Pain
What is referred pain?
Felt at a site other than the injured/diseased organ/body part
Variables that influence pain:
- Genetic
- Developmental
- Familial
- Psychological
- Social
- Cultural
Psychological and physical aspects of pain:
- Anxiety
- Sense of helplessness
- 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
What can pain be affected by?
- Attention
- Expectations: previous experience
- Interpretation: attitudes and beliefs
- Context: what is the meaning of pain
- Emotions and mood: anxiety, depression, anger, sad
- Coping strategies: perception of control
What can cause 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
- Patients beliefs about pain, expectations and treatment preference
- Coping mechanisms
- Patients knowledge of pain management techniques and expectation of outcome
- Family expectations and beliefs about pain and the patient’s illness
Uni-dimensional pain assessment 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 pain 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
Uni-dimensional pain scales:
- Numerical
- Visual analogue scale
- Verbal rating scale
Multi-dimensional pain scales:
- PQRST
- OPQRSTUV
- Initial pain assessment tool
What does the pain assessment PQRST stand for?
P= Provocation/Palliation Q= Quality/Quantity R=Region/Radiation S= Severity scale T= Timing
What does the pain assessment OPQRTSUV stand for?
O= Onset P= Provocation/Palliation Q= Quality R= Region/Radiation S= Severity scale T= Treatment U= Understanding impact V= Values
What are the categories of a behavioural pain assessment scale?
- Restlessness
- Muscle tone
- Vocalisation
- Face
- Consolability
Functional activity score (A,B,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
Questions you can ask someone with persistent pain:
- Is there a pattern of 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 the 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
What is the brief pain inventory?
- 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)
What is the McGill Pain Questionnaire?
- 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 pain assessment scales:
- Routine questions
- Verbal scales
- Numeric scales
- Pictorial scales
Behavioural measures of pain include:
- Age related behavioural
- Motor responses
- Facial expressions
- Crying
- Behavioural responses (e.g. sleep-wake patterns)
Physiological changes due to pain include:
- Altered observations (HR, RR, BP, etc)
- Posture/tone
- Sleep pattern
- Skin colour/sweating
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
Principles of pain:
- Patients should be involved in their management plan
- Pain management should be flexible and individualised
- Pain should be managed early: established pain is more difficult to manage
- Pain should be managed to a comfortable/tolerable level
Management plan of pain - three phases:
- Assessment: History and physical examination +/‐ further investigations
- Management: discuss pain management options, providing information, assurance and advice encouraging return to normal activity
- Review: reassess and revise
What is allodynia?
Pain that occurs from a stimulus that does not normally provoke pain. For example, stroking the skin lightly with clothes or cotton wool will produce pain
What is analgesia?
Absence of sensitivity to pain/no pain
What is hyperanalgesia?
Excessive pain sensitivity, perception of a painful stimulus as more painful than normal
What is paraesthesia?
Abnormal burning, tingling, or numbing sensation, typically associated with neuropathic pain
Visceral pain origin:
Organs
Nociceptive pain origin:
Connective tissue, eg skin, muscles, blood vessels
Neuropathic pain origin:
Nerve damage
