Essential pain management Flashcards
1
Q
Classification of Pain
A
- 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
2
Q
What is Nociceptive pain? (also called physiological or inflammatory pain)
A
- Obvious tissue injury or illness causing pain
- Has a protective function
- Description from the patient is:
- Sharp or dull
- Well localised
3
Q
What is Neuropathic pain?
A
- 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
4
Q
What are the 4 basic steps of pain physiology that result in the experience of pain in a patient?
A
- 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
5
Q
The periphery
A
- 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
6
Q
Spinal cord
A
- 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.
7
Q
What happens once the pain signal reaches the Thalamus?
A
- 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
8
Q
Where does pain perception occur within the brain?
A
In the cortex
9
Q
Modulation
A
- Decreases the pain signal
- Those who have a very active descending inhibition will have less pain experience
10
Q
Describe the ‘gate theory’ of pain
A
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
11
Q
What is neuropathic pain?
A
- 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)
12
Q
What are the pathalogical mechanisms that result in neuropathic pain?
A
- 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
13
Q
What are the 2 main classes of drugs used to treat pain?
A
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
14
Q
Other analgesics
A
- 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)
15
Q
How do we treat injury to the periphery to reduce pain?
A
- Non-drug treatments - rest, ice, elevation
- NSAIDs - to reduce amount of prostaglandins and inflammation
- Local anaesthetics - reduce nociceptive afferent triggering
27
Q
The WHO pain ladder is used for which type of pain?
A
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
28
Q
WHO pain ladder
A
- 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
