Pain management

Question 1

What is the maximum dose of paracetamol for an adult over 50kg?

Answer 1

4g/day

Question 2

What is the main risk with paracetamol?

Answer 2

Overdose

Fatal dose: 10g/day

Question 3

What may prompt adjustments of paracetamol dosage?

Answer 3

• body weight (if less than 50 kg)
• Liver impairment and risk factors of hepatotoxicity e.g. chronic alcohol consumption
• Renal impairment

Question 4

Which enzyme does NSAIDs inhibit?

Answer 4

Cyclooxygenase (COX) enzymes

which play a key role in the synthesis of prostaglandins.

Question 5

How do NSAIDs produce side effects?

Specifically non-specific COX-inhibitors (aspirin, diclofenac, ibuprofen, naproxen etv.) Why is this?

Answer 5

• Inhibits COX-1 and Cox-2
• Cox-1 is involved in the production of prostaglandins that are protective to the stomach lining, kidneys, and platelet function (production of thromboxane).
• Cox-2 primarily mediates pain.

Question 6

What are specific COX-2 inhibitors?

Answer 6

Celecoxib and paracoxib (can be given IV)
—Coxibs: (cog-sibs)

Reduce side effects of COX-1 inhibition

Question 7

List 4 side effects of NSAIDs that you should explain to patients.

Answer 7

1. Gastric irritation and bleeding (esp for people with history of PUD)
2. Renal impairment - damage to the kidneys
3. Platelet inhibition causing reduced aggregation and vasoconstriction: increase the risk of bleeding esp those with blood thinners
4. Chance that it may induce asthma (10-20%)
5. Risk of liver damage: caution with alcohol drinkers.

Question 8

Imagine a patient coming in with a history of hypertension and are on blood thinners. What should you tell them about NSAIDs?

Answer 8

• Gastric damage/bleeding
• Renal impairment
• Increased risk of bleeding

Question 9

Which three drugs in particular might NSAIDs increase in blood concentration?

Answer 9

Warfarin, heparin, lithium

Question 10

Which receptors do opioids work on?

Answer 10

Mu receptors (CNS), delta receptors (gut), kappa receptors

Question 11

List 6 acute side effects of opioids?

Answer 11

• Respiratory depression
• GI disturbances: N/V and constipation
• Sedation, altered mental state, euphoria, nightmares
• bradycardia
• Histamine release e.g. itching
• Miosis

Question 12

Generally, all areas of the brain is suppressed by opioids, apart from which 3? How do they correlate to specific side effects?

Answer 12

• CTZ - hence increase in N/V
• Edinger-westphal nucleus as part of CN3, which contains parasympathetic nerves to ciliar muscle - hence causes miosis
• ADH-secretion

Question 13

List 3 indications for amitriptyline with regards to pain management.

Answer 13

Chronic neuropathic pain e.g. post-herpetic pain, fibromyalgia, migraine prevention

Question 14

What class of medication is amitriptyline? What is its mechanism of action?

Answer 14

Tricyclic antidepressant.

Prevents/delays the re-uptake of multiple neurotransmitters e.g. acetylcholine, serotonin, noradrenaline in the synaptic cleft, which improves mood and pain perception.

Question 15

What are the main side effects of amitriptyline? What are they collectively modulated by (and more pronounced in elderly?)?

Answer 15

• Drowsiness,
• Dry mouth
• Constipation
• Urinary retention
• Blurred vision/raised IOP, headaches, mood changes

Anticholinergic effects

Question 16

What are some life-threatening side effects of amitriptyline?

Answer 16

• Arrythmias/SVT
• Worsening depression/suicidal thoughts

Question 17

Which classes of drugs might amitriptyline interact with and cause more side effects? Which patients should you look out for?

Answer 17

• SSRIs - increase risk of serotonin syndrome
• Anticholinergics e.g. atropine, oxybutynin, ipratropium
• MAO inhibitors e.g. selegiline - risk of hypertensive crisis

Mental health, parkinson’s, elderly

Question 18

What is the mechanism of action of gabapentinoids e.g. gabapentin and pregabalin?

Answer 18

Binds to voltage-gated calcium channels in the CNS, reducing calcium influx into excitatory neurons.

Hence inhibiting excitatory neurotransmission by decreasing glutamate, noradrenaline and substance P.

Actis like gaba - inhibitory effects

Question 19

What are two indications of gabapentinoids?

Answer 19

• Neuropathic pain
• Seizures

Question 20

List 4 common side effects of gabapentoinoids. (may affect appearance of people.)

Answer 20

• Dizziness
• Drowsiness
• Pedal oedema
• Weight gain
• Diarrhoea
• Impotence
• mood and memory changes

Question 21

Which gabapentinoid is more likely to be abused?

Answer 21

Pregabalin. and it has faster onset of action.

Question 22

How does capsaicin work?

Answer 22

It binds to TRPV1 receptor on sensory neurons, which causes heat and pain sensations. Application, though initially causing burning sensations, can deplete substance P, which is a neurotransmitter involved in pain transmission.

** It works by depleting substance P **

Question 23

How should patients safely use topical capsaicin patches or ointments?

Answer 23

Repeat application, and avoid sensitive areas e.g. mucous membranes, eyes.

Question 24

Explain 4 pieces advice for patients if you prescribe them NSAIDs.

About side effects and avoiding them.

Answer 24

Mention side effects and measures to reduce them, such as:
1. Take with food or an antacid/PPI to protect lining
2. Limiting your alcohol intake to protect gastric irritation
3. Stay hydrated to protect your kidneys.
4. Monitor for side effects e.g. heartburn, stomach pain, bleeding/black stools and contact doctor.

Question 25

Which analgesic is the safest option during pregnancy?

Answer 25

Paracetamol is the safest. e.g. for minor headaches, fever, aches and pains.

Question 26

Is NSAID safe during pregnancy? When is it advised against - and why?

Answer 26

BNF: Advised against from week 20/3rd trimester due to risk of premature closing of the ductus arteriosus. Some risk of oligohydramnios resulting from foetal renal dysfunction. ## Footnote The ductus arteriosus is vital in fetal circulation. It connects the pulmonary artery to the aorta, allowing blood to bypass the lungs, which are not yet in use before birth.

Question 27

What is the usual first dose of ibuprofen in adults?

Answer 27

300-400 mg 4 times a day

Question 28

Which opiod analgesic is also a good cough medicine? E.g. a patient under severe throat pain.

Answer 28

Methadone

Question 29

List 2 most important cautions for opioid prescription.

Answer 29

* Renal impaiment * Age

Question 30

How is buprenorphine given?

Answer 30

As a patch (72-168 hours duration of action)

Question 31

What is a quick sign to check for with opioid overdose? E.g. when a patient is unresponsive or unable to vocalise its side effects.

Answer 31

Pupils. Pinpoint

Question 32

How is fentanyl often given?

Answer 32

IV

Question 33

Why is fentanyl a good option for children?

Answer 33

Can be given intranasally (not IV, PO, IM)

Question 34

# Neurophysiology: Acute, nociceptive pain is often caused by?

Answer 34

Tissue damage e.g. trauma | Others: cancer-related, neuropathic

Question 35

# Neurophysiology: Chronic pain lasts for more than ? months

Answer 35

3 months

Question 36

What is considered successful pain management? Why is this relevant e.g. in pain managed using opioids?

Answer 36

**Pain reduction of 50%** based on objective scales. **Opioids can caused dependency** — being completely pain-free can cause more harm long-term, such as withdrawals and risks of overdose. Aim for tolerable pain.

Question 37

# Neurophysiology: Key difference between the development of pain in acute tissue damage vs cancer?

Answer 37

For tissue damage: pain is worst in the beginning, as it starts to heal. Cancer: pain gradually increased as cancer develops e.g. obstruction, stretching, nerve involvement ## Footnote Acute pain - start with adequate relief, may not be according to WHO ladder.

Question 38

How do glucocorticoids relieve pain?

Answer 38

**Inhibiting conversion of phospholipids to arachidonic acid** (then with COX-1/2 and LKT converts into prostaglandins etc.)

Question 39

How is IV morphine usually given?

Answer 39

**Using PCA (patient controlled analgesia).** **Programmable infusion pumps**. Button is connected to a syrienge driver and gives a bolus dose. ## Footnote Stable therapeutic effect.

Question 40

What is usually a single bolus dose of morphine in a PCA?

Answer 40

1mg, with lockout period of 5 minutes.

Question 41

What is the antidote and dose for opioid overdose?

Answer 41

Naloxone, 400 mcg (0.4mg) IV/IM

Question 42

Preparations for morphine

Answer 42

PO - oramorph IV

Question 43

How do local anaesthetics produce life-threatening toxicity? | More common in theatre, such as epidurals

Answer 43

Na+ channel blockage in heart and CNS (X action potential) Causing symptoms e.g. bradycardia, asystole, seizures etc. | Stop local anaesthetic immediately.

Question 44

What medication can reduce systemic toxicity of local anaesthetics and local bleeding? ## Footnote Esp when larger amounts of local anaesthetic is need

Answer 44

Vasoconstrictors. Good for prolonged surgeries that require local anaesthetics, such as dental procedures, minor surgical procedures and regional anaesthetic.

Question 45

Antidote for local anaesthetic toxicity

Answer 45

Intralipids (IV lipid emulsions) | Follow local trust guidelines

Question 46

List 2 most common complications of spinal anaesthesia e.g. epidurals.

Answer 46

1. Haematoma 2. Abscess/infection

Question 47

What may increase a patient's risk of developing a spinal haematoma from an epidural procedure? Which common medication needs to be adjusted?

Answer 47

**Anything that increases bleeding risk, e.g. anticoagulants.** Discontinue DOACs for 3 days, may use heparin as interim and discontinue 4-6 hours prior. May verify with normal aPTT.

Question 48

A 76-year-old man with esophageal cancer underwent an esophagectomy under **general anesthesia and a thoracic epidural block**. Postoperatively, he experienced back pain and lower limb weakness on the third day. What are you worried about and what is your next step?

Answer 48

* Urgent MRI * referral to neurosurgeons --> emergency laminectomy may be needed to decompress; preventing permanent damage.