Pain

Question 1

What are classifications of pain?

Answer 1

Duration= acute/chronic
Pathophysiology= neuropathic/nociceptive

Question 2

What is nociceptive pain?

Answer 2

• Regulated by opioidergic system -Acute nociceptive pain subsides when damage resolves
• Chronic pain persists may lead to neuropathic/mixed pain

Question 3

Describe the analgesic ladder

Answer 3

3. Non-opioid (NSAIDs, aspirin)
4. Opioid for mild-moderate pain & non-opioid (Codeine, tramadol)
5. Opioid for moderate-severe pain & non-opioid, freedom from cancer pain (morphine, methadone)

Question 4

What is the mechanism of action for non-opioids for acute pain?

Answer 4

• NSAIDs/COX-2 inhibitors act peripherally
• Paracetamol has central activity
• Efficacy in acute pain management & control of nociceptive pain

Question 5

What is the mechanism of action for opioids for acute pain?

Answer 5

• Activate endogenous analgesic system
• Stimulate receptors in limbic system to eliminate pain
• Affects descending pathway modulating pain perception
• Acts at 2 sites
• Presynaptically pain signal transmission is inhibited
• Postsynaptic membrane hyperpolarised, decreasing the probability of ap generation
• Main efficacy in nociceptive pain

Question 6

What is the mode of action and any side effects for NSAIDs?

Answer 6

MA= inhibition of cyclooxygenase, prostaglandin synthesis decreases
-SE= GI irritation/bleeding, renal toxicity, drug interactions, CV effects

Question 7

What is the mode of action and any side effects for paracetamol?

Answer 7

MA= Inhibition of central prostaglandin synthesis
SE= risk of toxic liver damage

Question 8

What are side effects of opioids?

Answer 8

• Nausea
• Vomiting
• Constipation
• Dizziness/vertigo
• Somnolence
• Dry skin/pruritus
• Respiratory depression & hypoxia

Question 9

What is epidural analgesia used for?

Answer 9

-Postop: thoracic, abdo, lower limb surgery, labour, chronic

Question 10

What are the benefits of epidural analgesia?

Answer 10

• High quality pain relief
• Improved pulmonary function
• Reduced sepsis & chest infection
• Reduced cardiac morbidity
• Reduced vascular graft failure
• Reduced incidence of DVT

Question 11

When is a celiac plexus block used?

Answer 11

• Pancreatic carcinoma

- Upper abdominal neoplasia

Question 12

Describe neuropathic pain

Answer 12

• Spont pain &hypersensitivity associated with damage/lesion of NS
• Intense pain accompanied b other pain phenomena
• Persistent & recurrent
• Associated with severe comorbidity & poor QOL
• post herpetic neuralgia, pain after CVA, post-op, painful diabetic neuropathy, trigeminal neuralgia

Question 13

What features suggest neuropathic pain?

Answer 13

• Pain different from everyday pain
• Pain in area of sensory loss
• Paroxysmal/spontaneous pain
• Allodynia (pain from non painful stimuli)
• Hyperalgesia (inc pain in response to painful stimuli)
• Dysaesthesias (unpleasant abnormal sensations)

Question 14

What drug therapy is there for neuropathic pain?

Answer 14

-NSAIDs
-Antidepressants
-Anticonvulsants
-Opioids
-Membrane stabilising drugs
Topical drugs

Question 15

What is the mechanism of action and side effects of antidepressants?

Answer 15

MA= Inhibition of neuronal reuptake of noradrenaline & serotonin
SE= Dry mouth, insomnia, inc appetite, constipation, abnormal heart rate/rhythm, somnolence

Question 16

What is the mechanism of action and side effects of anticonvulsants?

Answer 16

MA= Gabapentin: binds to presynaptic voltage-dependent Ca channels, pregabalin: interacts with special N-type Ca channels, Carbamazepine: blocks Na+, Ca2+ channels
SE= sedation, dizziness, ataxia, nausea, weight gain, peripheral oedema

Question 17

What are the types of nociceptors?

Answer 17

• Unmyelinated C fibres

- thinly myelinated Ad fibres

Question 18

What modalities do nociceptors respond to?

Answer 18

• Mechanical
• Thermal
• Chemical (histamine)

Question 19

What neurotransmitter is released by pain afferents?

Answer 19

Glutamate

Question 20

Neurons in the dorsal horn express what neuropeptide?

Answer 20

Substance P receptor (NK1) and project to the thalamus

Question 21

What can hyperalgesia be?

Answer 21

• Spontaneous pain
• Reduced threshold for pain
• Increased intensity of painful stimuli

Question 22

Describe first & second pain

Answer 22

1st=Fast, A-delta fibres, sharp/ pricking, rapid, easily localised, short time, mechanical/thermal
2nd=Slow, C-fibres, dull ache/ burning, poorly localised, persistent, polymodal, slow onset

Question 23

Where are nociceptors found?

Answer 23

• Periphery as free nerve endings

- Branched, unmyelinated in dermis

Question 24

How does hyperalgesia occur?

Answer 24

1) Tissue damage/inflammation
2) Release of prostaglandins, bradykinin, histamine
3) Sensitize peripheral nociceptors that express heterogenous receptors/ion channels
4) Transmission of impulses via A-delta & C sensory afferents to dorsal horn
5) Projection to brain via ascending pathways
6) Experience sensory/emotional hyperalgesia

Question 25

Give the sub modality, position and fibre type of thermoreceptive & nociceptive afferents

Answer 25

- Warm= C, deep epidermis - Cold=A-delta, deep epidermis - Nociceptive= either C or A-delt, superficial epidermis

Question 26

Where do nociceptive fibres have their cell bodies?

Answer 26

- Dorsal root ganglion - Travel up/down in zone of lissauer - Innervates substantia gelatinosa

Question 27

Describe the components of the ascending pain pathway

Answer 27

- Lateral spinothalamic tract - Spinoreticulothalamic tract - Anterior spinothalamic tract (to RF and periaqueductal grey matter) - Contralateral pathway at the level of the spinal cord

Question 28

What occurs in a unilateral spinal cord injury/lesion?

Answer 28

- Brown sequard syndrome - Dissociated sensory loss - Loss of pain on opposite side - Loss of sensory on the same side

Question 29

What does the VPM & VPL of the thalamus innervate?

Answer 29

``` VPM= face VPL= rest of body ```