Post-operative pain: Pathophysiology and treatment

Question 1

Define pain.

Answer 1

An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage

Question 2

Which factors can influence pain?

Answer 2

Pain is always a personal experience that is influenced to varying degrees by biological (genetic), psychological, and social factors

Question 3

Describe what happens in our body for us to feel pain.

Answer 3

Pain is triggered from the periphery by surgical insult
• Release of cytokines, activation of pain fibers (C fiber, A delta)
• Local inflammation
• Activation of neurofibers –> To spinal cord –> transmitted to the cortex and brain stem where pain is perceived (cortex) but also triggers release of neurogenerative response – Release of hormones, catecholamines, modulation of afferent signals to inhibit pain

Question 4

Which part of the brain perceives pain?

Answer 4

The cortex

Question 5

What is done by our body to inhibit pain?

Answer 5

Release of hormones, catecholamines, modulation of afferent signals to inhibit pain

Question 6

Name the 3 types of pain

Answer 6

Somatic
Visceral
Neuropathic

Question 7

Describe what is somatic pain

Answer 7

o Origins from skin, muscle
o Classical pain: hit your knee, fall down. Painful area can be clearly identified (able to localize pain).
o Pain triggered by surgical skin incision in surgery
o Somatic pain increases with mobilization

Question 8

Describe what is visceral pain

Answer 8

o Origins from the viscera: Organs, pleura, peritoneum and periosteum
o Triggered by membranes that cover our organs
o This type of pain is difficult to localize. Diffuse pain.
o Visceral pain does not increase with mobilization

Question 9

Describe what is neuropathic pain

Answer 9

o Origins from nerves
o Sharp/burning sensation. Due to the inflammation, fibrosis and repair of nerves touched during surgery (either intentionally or unintentionally)

Question 10

What does pain cause in terms of complications (besides sensory experience for patients)?

Answer 10

Pain –> Immobility –> risk of thromboembolic complications (DVT, pulmonary embolism, blood clots)
Pain –> triggers sympathetic NS –> cardiac complications
Pain –> Afferent pain fibers trigger spinal cord simple reflex that inhibit respiratory function (resp muscles) –> pulmonary complications (pneumonia, atelectasis, immobilization)
Pain –> Stress response (anxiety) –> decreased appetite, sleep disturbances
Pain –> bowel dysfunction (N/V, Const, ileus)

Question 11

Describe the risk of myocardial injury with pain

Answer 11

One point increase in pain (in scale from 0-10) leads to HR of 1.12 and OR of 1.22 for myocardial injury post-op

Question 12

Describe the endocrine responses to pain

Answer 12

1. Increase in catabolic hormones (ACTH, cortisol, ADH, GH, catecholamines…)
2. Decrease in anabolic hormones (insulin, testosterone)

Question 13

Describe the metabolic responses to pain

Answer 13

1. Hyperglycemia, glucose intolerance, IR
2. Muscle protein calabolism increased synthesis of APPs
3. Increased lipolysis and oxidation

Question 14

Describe the water and electrolyte flux responses to pain.

Answer 14

Retention of water and sodium, increased excretion of K and decreased functional ECF with shifts to ICF

Question 15

Why do the endocrine and metabolic response to pain occur?

Answer 15

• Sympathetic NS increases catabolic hormones such as cortisol, catecholamines, IL-6, IL-1, aldosterone
  o And decreases availability of anabolic hormones

Question 16

Define allodynia.

Answer 16

Even stimuli that should not trigger pain response does. Can be caused by persistent nerve inflammation or injury

Question 17

Define hyperalgesia.

Answer 17

Intensity of the pain sensation is magnified, but only starting at levels perceived as painful

Question 18

What are primary and secondary hyperalgesia?

Answer 18

o Primary
 Caused by release of mediators to help healing
o Secondary
 No actual injury to the tissue

Question 19

What is central sensitization and what is it caused by?

Answer 19

 Caused by changes at the level of the spinal cord

 Causes Allodynia and/or hyperalgesia around injury site to protect us from hurting damaged area again

Question 20

What is peripheral sensitization and what is it caused by?

Answer 20

 At the site of injury, caused by release of mediators to help healing
 If you cut yourself, the cut is tender in the first few hours. Then, after few hours, areas around the wound start to feel tender as well –> central sensitization (amplifies area of pain perception; to protect ourselves)

Question 21

What is preemptive analgesia?

Answer 21

preoperative treatment is more effective than the identical treatment administered after incision or surgery. We should give those meds before surgery.

Question 22

What is preventive analgesia?

Answer 22

postoperative pain or analgesic consumption is reduced relative to another treatment, to a placebo treatment, or to no treatment, as long as the effect is observed at a point in time that exceeds the clinical duration of action of the target agent (5 ½ half-life)

Question 23

Name the risk factors for severe acute post-operative pain

Answer 23

• Gender: F > M
• Obesity
• Anxiety, catastrophizing
• Invasiveness of the surgery/Multiple injuries
• Preoperative pain (Chronic pain/ chronic use of opioids)
• Genetic predisposition
• Hx of severe postoperative acute pain

Question 24

Which type of analgesia has shown pre-emptive analgesic effect ?

Answer 24

• A strong consistent pre-emptive analgesic effect has been shown only with epidural analgesia

Question 25

Which type of analgesia has shown preventive analgesic effect ?

Answer 25

Perioperative anti NMDA antagonists –> proved preventive analgesic effect (prolonged effect)
• Ketamine
• Dextromethorphan

Question 26

Which type of factors determine pain intensity?

Answer 26

Most important determinants (63%) due to patient-related factors (> surgical factors)

Question 27

Name 4 examples of unidimensional pain assessments

Answer 27

o Visual Analog Scale (0-100)
o Verbal Rating Scale (0-10)
o Numeric Rating Scale (0-10)
o Face Pain Scale (0-10)

Question 28

Describe the relationship between NRS scores and the desire to receive additional analgesics

Answer 28

• Uni dimensional tool to assess pain is not enough to describe the experience of pain
• Intensity of pain reported on a 0-10 NRS does not correlate with the desire to receive additional analgesics
• High % of patients with moderate pain wish to receive extra analgesics while only about 50% of 10/10 on NRS!
• We cannot rely only on numerical tools to start medical treatment

Question 29

What is the issue with using NPS to assess pain in hospital?

Answer 29

• High opioid consumption (PACU) – Opioid oversedation more than doubles when using NRS
• High opioid-related side effects (they are dose-dependant)
Unidimensional Numeric Pain Assessment Pain as 5th vital sign campaign has contributed to the North America Opioid Epidemic

Question 30

How should we look at pain to prevent the issues with NRS?

Answer 30

We should aim to treat pain to achieve good functional outcomes (meaningful information)

Question 31

What are the steps in assessing the functional impact of pain?

Answer 31

DREAMS Patient centred outcomes
•	Drinking
•	Eating
•	Mobilization
•	And sleep

Question 32

What is the best unidimensional pain assessment tool?

Answer 32

• Unidimensional pain assessment: good construct validity

- No superiority between different unidimensional pain assessment tools

Question 33

What defines optimal analgesia after surgery?

Answer 33

Optimized patient comfort (optimal pain rating at rest and with movement, less impact of pain on emotions, function and sleep disruption)

Fastest functional recovery (drinking, eating solids, mobilizing, bladder/bowel function, normal cognitive function)

Fewer side effects (N/V, sedation, ileus, itching, dizziness, delirium)

Question 34

Describe the WHO ladder for pain control

Answer 34

• Mild pain: Use non-opioid medications
• Moderate pain: Mild opioid (e.g. codeine) +/- non-opioid +/- regional anesthesia
• Strong pain: Use strong opioid like morphine +/- non-opioid +/- regional anesthesia

Question 35

How should anti-inflammatories and paracetamol be administered based on the WHO ladder?

Answer 35

should be administered by the clock, oral route preferred

Question 36

Describe what are adjuvant drugs and give examples.

Answer 36

Some drugs are called “adjuvant drugs” – they do not have primarily analgesic effects but can be used for pain management (steroids, antidepressants, anticonvulsants, muscle relaxants, antispasmodics)

Question 37

Name the different treatment options for analgesia

Answer 37

•	Pharmacological interventions
o	Multimodal analgesia
•	Regional and Peripheral Analgesia
o	Neuraxial blockade
o	Peripheral nerve blockade
•	Non-pharmacological intervention (TENS..)

Question 38

What is the most common analgesic medication?

Answer 38

Acetaminophen

Question 39

What is the bioavailability of PO acetaminophen?

Answer 39

60-80%

Question 40

What are the advantages of acetaminophen?

Answer 40

• Opioid sparing effect (opioid consumption reduced by 20-30%)
• ↓ post-op N/V
• Better analgesia when used before sx and with NSAIDs

Question 41

What are the side effects of acetaminophen?

Answer 41

few, quite safe, ↓ dose in ETOH, G6PD deficiency

Question 42

What are the advantages of NSAIDs?

Answer 42

• Better analgesia when used with Acetaminophen, and PRN opioids than alone
• Opioid sparing effect (30-50%; better than acetaminophen)
• ↓ the incidence of nausea/vomiting (22-28%)
• ↓ the incidence of opioids induced sedation (30%)

Question 43

What are the side effects of NSAIDs?

Answer 43

o ↓ Renal function
o Peptic ulcer
o Asthma
o Bronchospasm (10-15% of asthmatic pt)
o Might contribute to anastomotic leakage (?)
 Not to be used in patients undergoing intestinal anastomosis
 Recent meta-analysis showed heterogeneous effect and no significant increase in anastomotic leakage with NSAIDs
o Bone-healing (?)
 Not to be used in patients with bone fractures

Question 44

What are COX-2 inhibitors?

Answer 44

• COX-2 selective inhibition (celecoxib, etoricoxib and parecoxib/valdecoxib)

Question 45

What are the advantages of COX-2 inhibitors?

Answer 45

• Opioid sparing effect
• No reduction in opioid side effects
• Less PLT dysfunction
• Less renal dysfunction
• Preemptive analgesic effect (?) – given before surgery

Question 46

What are the risks of COX-2 inhibitors?

Answer 46

• Patients taking COX-2 inhibitors for chronic conditions may have an increased CV risk when compared to NSAIDs. But this is not the case for short term (e.g. pre-op COX-2).