Pain and Analgesia

Question 1

When would you consider giving paracetamol for pain?

Answer 1

Mild to moderate pain. Often used by anaesthetists both intra and post-operatively as part of the patient’s analgesic regime

Question 2

What is the WHO pain ladder?

Answer 2

Structured approach to pain management, starting off with non-opioads, preogressing to weak opiods, then strong opiods

Question 3

What is the definition of acute pain?

Answer 3

Pain of recent onset and probable limited duration, and is usually the result of a clearly defined cause such as an injury.

Question 4

What is the definition of chronic pain?

Answer 4

Pain that lasts for >3 months

Question 5

What are the pain conducting fibres in peripheral tissue?

Answer 5

• A-delta fibres
• C-fibres

Question 6

Which type of fibre conducts pain signals faster?

Answer 6

A-delta

• Aδ = small myelinated (5-30m/s) cold, “fast” pain, pressure
• C = unmyelinated fibres (0.5-2m/s) warmth, “slow” pain

Question 7

What tracts do pain fibres travel in in the spine?

Answer 7

Lateral spinothalamic tracts

Question 8

Where do pain fibres cross to enter the spinothalamic tracts?

Answer 8

Same level as where the fibres enter, or a few levels above point of entry

Question 9

How many nerve fibres are there in the afferent nerve fibre tracts for pain?

Answer 9

3 nerve fibres

Question 10

Which order neuron crosses at the level of entry?

Answer 10

2nd order neuron

Question 11

What types of nerve endings are nociceptors?

Answer 11

Free nerve endings in the skin whose ion channels are sensitive to a variety of chemical, mechanical and thermal stimuli

Question 12

What is the gate control theory of pain?

Answer 12

Aβ fibers carrying sensory information about mechanical stimuli help block pain transmission. These synapse on the inhibitory interneurons and enhance the interneuron’s inhibitory activity.

If simultaneous stimuli reach the inhibitory neuron from the Aβ and C fibers, the integrated response is partial inhibition of the ascending pain pathway so that pain perceived by the brain is lessened.

The gate control theory explains why rubbing a bumped elbow or shin lessens your pain: the tactile stimulus of rubbing activates Aβ fibers and helps decrease the sensation of pain

Question 13

What descending pathways are involved in pain modulation?

Answer 13

Descending pathways from the peri-aqueductal grey matter and nucleus rapheus magnus

Question 14

What is the theory behind referred pain?

Answer 14

Visceral pain is often poorly localized and may be felt in areas far removed from the site of the stimulus e.g. pain of cardiac ischemia may be felt in the neck and down the left shoulder and arm due to multiple primary sensory neurons converge on a single ascending tract.

When painful stimuli arise in visceral receptors, the brain is unable to distinguish visceral signals from the more common signals arising from somatic receptors. As a result, it interprets the pain as coming from the somatic regions rather than the viscera

Question 15

What are the different classifications of pain?

Answer 15

• Somatic
• Visceral
• Neuropathic
• Cancer pain

Question 16

When assessing pain, what are the key things to think about (and ask)?

Answer 16

1. How long has the patient has had pain? - Acute vs Chronic
2. What is the cause? - Cancer vs non-cancer
3. What is the mechanism? - nociceptive,neuropathic,visceral
4. What is the intensity of pain?

Question 17

What is somatic pain?

Answer 17

Pain is initiated by activation of nociceptors in the skin or other superficial tissue, and is sharp, well-defined and clearly located. Can also be deep, due to activation of nociceptors in ligaments and tendons

Question 18

What is visceral pain?

Answer 18

Visceral structures are highly sensitive to stretch, ischemia and inflammation, but relatively insensitive to other stimuli that normally evoke pain in other structures, such as burning and cutting.

Visceral pain is diffuse, difficult to locate and often refers to a distant, usually superficial, structure. It may be accompanied by nausea and vomiting and may be described as sickening, deep, squeezing, and dull.

Question 19

What is the function of somatic pain?

Answer 19

Protective function

Question 20

What is neuropathic pain?

Answer 20

Abnormal processing of pain signal due to nervous system damage or dysfunction. A variety of mechnisms can lead to neuropathic pain, including:

• Increased receptor numbers
• Abnormal sensitisation of nerves - Peripheral +/- Central
• Chemical changes in the dorsal horn
• Loss of normal inhibitory modulation

Question 21

What are examples of causes of neuropathic pain?

Answer 21

• Nerve trauma
• Diabetic pain
• Fibromyalgia
• Chronic tension headache

Question 22

How would someone typically describe neuropathic pain?

Answer 22

• Burning, shooting ± numbness
• Pins and needles
• Not well localised

Question 23

How would someone describe visceral pain?

Answer 23

• Cramping
• Dull
• Tightening
• Bloated

Question 24

How would someone typically describe somatic pain?

Answer 24

• Sharp
• Throbbing
• Knife-like
• Well-localised

Question 25

What are examples of simple analgesics?

Answer 25

• Paracetamol
• NSAID’s

Question 26

What are examples of mild opiod drugs?

Answer 26

• Codeine
• Dihydrocodeine
• Tramadol

Question 27

What are examples of strong opioids?

Answer 27

• Morphine
• Diamorphine
• Fentanyl
• Pethidine
• Methadone

Question 28

How would you manage neuropathic pain?

Answer 28

Offer a choice of amitriptyline, duloxetine, gabapentin or pregabalin as initial treatment for neuropathic pain

If the initial treatment is not effective or is not tolerated, offer one of the remaining 3 drugs, and consider switching again if the second and third drugs tried are also not effective or not tolerated

Question 29

Rank all analgesia in terms of strength of analgesia

Answer 29