Pain relief and peri-operative pain relief

Question 1

What are three aspects to pain?

Answer 1

Physical
Emotional
Rational

Or if you're on palliative care
Physical
Social
Psychological 
Spiritual

Question 2

What are nociceptors?

Answer 2

These are free nerve endings in the skin, muscle and viscera which detect pain

Question 3

What activates nociceptors?

Answer 3

Noxious stimuli

Question 4

What type of pain is carried by C fibres?

Answer 4

Dull, poorly localised, visceral pain.

They are unmyelinated

Question 5

What type of pain is carried by delta fibres?

Answer 5

Precise, well localized, sharp pain. This is called somatic pain, they are myelinated and signals travel fast.

Question 6

Outline the gate-theory of pain

Answer 6

Local inhibitory interneurons modulate the activity of other neurons and prevent ascending pain signals being sent unless the inhibition is overcome. The gate is opened once this inhibition is overcome.

This is tonic inhibition.

Question 7

Why does mechanoreceptor stimulation reduce pain?

Answer 7

This is the sensation where rubbing and injury causes the pain to reduce.

It is because the Abeta fibres of mechanoreceptors increase the inhibition by interneurons and reduce ascending signals

Question 8

How does transcutaneous electronic nerve stimulation work?

Answer 8

Stimulation of the Abeta mechanoreceptors which increase the inhibition of interneurons in the spinal cord. This reduces ascending pain signals.

Question 9

How many neurons are involved in pain signalling?

Answer 9

These are three neuron pathways.

Question 10

What spinal cord tract carries pain?

Answer 10

The spinothalamic tract

Question 11

Outline the route of the spinothalamic tract

Answer 11

First neurone enters the spinal cord and ascends descends within Lissauer’s fasciculus

Enters the dorsal horn and synapses with secondary neuron

Second neurone decussates and ascends to the thalamus

Synapses with third order neuron at the thalamus.

Third order neuron runs to the sensory cortex/post central gyrus

Question 12

What chemical signals between the neurons responsible for pain?

Answer 12

Substance P

Excitatory amino acids such as glutamate and aspartate

Question 13

How does the descending pathway modulate pain?

Answer 13

Descending pathway modulates the activity of first and second order neurones to reduce pain signalling

Question 14

What neurotransmitters are involved in the modulation of pain transmission at the dorsal root ganglion? (Between first and second order neuron of the spinothalamic pathway)

Answer 14

Noradrenaline

Serotonin (5-HT)

Question 15

What is hyperalgesia?

Answer 15

Sensation of pain is greater, lower thresholds

Question 16

What is allodynia?

Answer 16

Sensation of pain is felt for normally non-painful stimuli

Question 17

How does inflammation increase pain?

Answer 17

Inflammation causes release of inflammatory mediators which reduce the threshold for action potential generation of the first order neuron (these include bradykinin, IL-1, IL-6 and TNF alpha). Results in hyperalgesia and sensation of pain around the injury site.

This is also called peripheral sensitisation

Question 18

How does central sensitisation occur?

Answer 18

Second order neuron becomes more responsive after prolonged stimulation.

This is due release of glutamate that acts on the NMDA receptor and relieves the voltage dependent Mg2+ block of the receptor, this results in calcium entry which increases neurone responsiveness.

Question 19

What is the theory of preemptive analgesia?

Answer 19

Preventing noxious stimuli from reaching the spinal cord allows you to prevent sensitization processes and reduce the levels of pain experienced. - thereby reduces the levels of post-operative pain

Question 20

How is preemptive analgesia achieved?

Answer 20

Local anaesthetic infiltration into tissues before incision is made- prevents sensitisation processes.

Or nerve blocks, epidurals or spinal anesthesia may be used.

+ Opioids
+ NSAIDs to prevent inflammatory pain causing sensitisation

Question 21

What receptor do opioids act on to cause pain relief?

Answer 21

Mew (that u sign)

Question 22

What are some side effects of opioids?

Answer 22

Constipation
Respiratory depression
Good visceral analgesia but poor somatic analgesia
Dependence
Tolerance
Dysphoria

Question 23

Name some opioids

Answer 23

Morphine 
Fentanyl
Codeine
Dihydrocodeine
Tramadol

Question 24

What are some side effects of NSAIDs?

Answer 24

Peptic ulceration
Nephrotoxic
Bronchospasm- May be trigger in asthma

Question 25

Why are NSAIDs nephrotoxic?

Answer 25

Prostaglandins are involved in the renal autoregulation- NSAIDs prevent prostaglandin synthesis

Question 26

For what forms of pain are TCAs or antiepileptic drugs used?

Answer 26

For neuropathic pain

Question 27

Name two TCAs

Answer 27

Amitriptyline

Nortriptyline

Question 28

What is an ideal way to deliver analgesia to palliative care patients?

Answer 28

Continuous subcutaneous infusion

Note- Prescribe oramorph for breakthrough pain which should be 1/6th of the patients daily dose

Question 29

What are some advantages to patient controlled analgesia?

Answer 29

It is difficult to overdose and patients normally fall asleep before overdose can be give.

Beneficial to patients as they can give analgesia when they feel they need it

Note- some give a small background infusion to reduce the risk of waking up in pain.

Question 30

What is problematic with continuous infusions?

Answer 30

Risk of overdose and accumulation can occur with renal or hepatic impairement

Question 31

What are some benefits of IV bolus for pain relief?

Answer 31

Rapid action- good for trauma or acute pain.
Use with care to avoid overdose
Not suitable for long term pain relief due to fluctuating concentrations