Essential pain management Flashcards
Classification of Pain
- Duration
- Acute - recent onset and probable limited duration
- Chronic (<3 months generally)
- Acute on chronic
- Cause
- Cancer - mixture of acute and chronic
- Non-cancer - many different causes, acute or chronic
- Mechanism (most useful classification)
- Nociceptive
- Neuropathic
What is Nociceptive pain? (also called physiological or inflammatory pain)
- Obvious tissue injury or illness causing pain
- Has a protective function
- Description from the patient is:
- Sharp or dull
- Well localised
What is Neuropathic pain?
- Nervous system damage or abnormality
- Tissue injury may not be obvious
- Does not have a protective function - pain that is going on long after injury if there is even an injury
- Description from the patient:
- Burning, shooting pain
- May have numbness or pins and needles
- Not well localised
What are the 4 basic steps of pain physiology that result in the experience of pain in a patient?
- An injury usually in the periphery
- Sends signals into the spinal cord through dorsal root ganglion
- From dorsal horn there is an ascending pathway up to the Brain (particularly to the thalamus). And then patient will experience pain.
- Modulation - descending pathway that works to switch off pain signal
The periphery
- A tissue injury results in the release of chemicals e.g prostaglandins, substance P etc
- This stimulates the nociceptive afferents (pain receptors) in the periphery
- They send a signal that travels through the Adelta or C fibres into the dorsal root ganglion - then transmitted to the spinal cord
Spinal cord
- In the spinal cord, the dorsal horn is the first relay station for pain.
- A delta and C nerve synapses connect with a second nerve here in the spinothalamic tract.
- That travels up on the contralateral side of the spinal cord to the thalamus.
What happens once the pain signal reaches the Thalamus?
- The Thalamus is the 2nd relay station and it has connections to many parts of the brain e.g
- Cortex
- Limbic system
- Brainstem
- The pathways go both way - the cortex can feed back to the thalamus and this enhances your pain experience
Where does pain perception occur within the brain?
In the cortex
Modulation
- Decreases the pain signal
- Those who have a very active descending inhibition will have less pain experience
Describe the ‘gate theory’ of pain
The gate control theory of pain describes how non-painful sensations can override and reduce painful sensations
- If there is a noxious (pain) stimulus i.e a hot flame, puncture, cut etc then it sends an afferent neuron along the A delta or C fibres to the dorsal horn.
- The gate theory is the idea that rubbing/massaging or application of heat stimulates the large (peripheral) A alpha and A beta fibres which in turn stimulates an inhibitory neuron that switches off this nociceptive afferent signal from going into the dorsal horn
- This modulation type pathway occurs in the periphery but also within the brain and spinal cord
What is neuropathic pain?
- It is caused by an abnormal processing of pain signal
- Usually caused from nervous system damage or dysfunction
- Examples:
- Nerve trauma
- Diabetic pain (ischaemic damage, peripheral neuropathy)
- Fibromyalgia
- Chronic tension headache (dysfunction of the N.S)
What are the pathalogical mechanisms that result in neuropathic pain?
- Increased receptor numbers - enhances the pain signal and keeps it going for longer
- Abnormal sensitisation of nerves (peripheral and central) - pain signal is exagerrated all through the pathway
- Chemical changes in the dorsal horn - also enhances pain signal
- Loss of normal inhibitory modulation from descending pathways
What are the 2 main classes of drugs used to treat pain?
Simple analgesics
- Paracetamol
- Non-steroidal Anti-inflammatory drugs (NSAIDs) - ibuprofen, diclofenac
Opioids
- Weak: Codeine, Dihydrocodeine, tramadol
- Strong: Morphine, Oxycodone, Fentanyl
- Both weak and strong opioids have the potential for addiction however
Other analgesics
- Tramadol - Mixed opiate and 5HT/NA reuptake inhibitor
- Antidepressants (e.g. amitriptyline, duloxetine)
- Anticonvulsants (e.g. gabapentin)
- Ketamine (NMDA Receptor antagonist)
- Local anaesthetics
- Topical agents (e.g. Capsaicin)
How do we treat injury to the periphery to reduce pain?
- Non-drug treatments - rest, ice, elevation
- NSAIDs - to reduce amount of prostaglandins and inflammation
- Local anaesthetics - reduce nociceptive afferent triggering
What treatments can be used to target the spinal cord?
- Non-drug treatments - acupunture, massage, transcutaneous electrical nerve stimulation (TENS) - utilises gate theory
- Local anaesthetics - epidural, nerve block
- Opioids - through epidural route or intrathecal (into CSF)
- Ketamine - modulates pain signal
How to treat pain by targeting the brain?
- Non-drug treatments - psychological e.g positive association or hypnosis
- Drug treatments:
- Paracetamol
- Opioids
- Clonidine
NSAIDs
Aspirin, ibuprofen, diclofenac
Advantages:
- Cheap
- Generally safe
- Good for nociceptive pain
- Best given regularly with paracetamol (Synergism)
Disadvantages:
- GI and renal side effects plus bronchospasm in some patients with asthma
Codeine
Advantages
- Cheap, safe
- Good for mild-moderate acute nociceptive pain
- Best given regularly with paracetamol
Disadvantages
- Not good for neuropathic pain
- Constipation
Tramadol
Weak opioid effect plus inhibitor of serotonin and noradrenaline reuptake (modulation)
Advantages
- Less respiratory depression
- Can be used with opioids and simple analgesics
- Less constipating than opioids
Disadvantages
- Nausea and vomiting - poorly tolerated
- Controlled drug - prescribed drug
What type of pain is morphine good for?
- Moderate to severe nociceptive pain (e.g post-op pain)
- Cancer pain
Amitriptyline
Tricyclic antidepressant (TCA) - Increases descending inhibitory signals
Advantages
- Cheap, safe in low dose
- Good for neuropathic pain
- Also treats depression, poor sleep
Disadvantages
- Anti-cholinergic/muscarinic side effects (e.g. dry mouth, blurred vision, glaucoma, urinary retention, constipation)
- Long term use might be linked with cognitive decline and dementia
Give 3 examples of anti-convulsant/seizure drugs.
How do they work?
- Carbamazepine
- Sodium valproate
- Gabapentin
These suppress the excessive abnormal firing of neurons during seizures. Good for neuropathic pain.
Delivery routes for Local anaesthetics
- Epidural (+/- Opiates)
- Intrathecal (+/- Opiates)
- Wound Catheters
- Nerve Plexus Catheters
- Local Infiltration of wounds
- Lidocaine patches for some neuropathic pain conditions
What scales/scoring systems are used to assess pain?
- Verbal Rating Score
- Numerical Rating Score
- Visual Analogue Scale
- Smiling faces
- Abbey Pain Scale (for confused patients)
- Functional assessments
Non-drug treatment for the pain
Physical
- Rest, ice, elevation
- Positioning
- Surgery
- Acupuncture, massage, physiotherapy
Psychological
- Explanation
- Reassurance
- Counselling
The WHO pain ladder is used for which type of pain?
Acute / nociceptive pain
(Neuropathic pain does not respond to WHO pain ladder drugs)
- Mild
- Paracetamol (± NSAIDs)
- Moderate
- Paracetamol (± NSAIDs) + codeine/ alternative
- Severe
- Paracetamol (± NSAIDs) + morphine
WHO pain ladder
- Mild Pain: Start at Bottom of Pain Ladder
- Moderate Pain: Bottom of Pain Ladder plus Middle Rung
- Severe: Bottom of Pain Ladder plus Top of Ladder. Miss out the middle
It is okay to start at the top of the ladder for severe/ unbearable pain!!!!
As pain resolves…
- Move from top to middle of WHO ladder
- Continue Bottom Rung drugs at all times
- Lastly stop NSAIDs first, then Paracetamol as more adverse effects with NSAIDs
What is the RAT approach to pain management?
RAT stands for
-
Recognise - the pain
- More difficult in children or those who can’t communicate etc
- Ask the patient, look at them (frowning, moving easily), ask family/health workers too
-
Assess
- Severity - pain score, at rest and with movement, how is it affecting QOL etc
- Type of pain - nociceptive or neuropathic
- Other factors that may be contributing to pain - physical or psychological (drug use, anger, anxiety etc)
-
Treat
- Non-drug vs drug treatment
After RAT, reassess
