Post-operative pain: Pathophysiology and treatment Flashcards
Define pain.
An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage
Which factors can influence pain?
Pain is always a personal experience that is influenced to varying degrees by biological (genetic), psychological, and social factors
Describe what happens in our body for us to feel pain.
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
Which part of the brain perceives pain?
The cortex
What is done by our body to inhibit pain?
Release of hormones, catecholamines, modulation of afferent signals to inhibit pain
Name the 3 types of pain
Somatic
Visceral
Neuropathic
Describe what is somatic pain
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
Describe what is visceral pain
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
Describe what is neuropathic pain
o Origins from nerves
o Sharp/burning sensation. Due to the inflammation, fibrosis and repair of nerves touched during surgery (either intentionally or unintentionally)
What does pain cause in terms of complications (besides sensory experience for patients)?
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)
Describe the risk of myocardial injury with pain
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
Describe the endocrine responses to pain
- Increase in catabolic hormones (ACTH, cortisol, ADH, GH, catecholamines…)
- Decrease in anabolic hormones (insulin, testosterone)
Describe the metabolic responses to pain
- Hyperglycemia, glucose intolerance, IR
- Muscle protein calabolism increased synthesis of APPs
- Increased lipolysis and oxidation
Describe the water and electrolyte flux responses to pain.
Retention of water and sodium, increased excretion of K and decreased functional ECF with shifts to ICF
Why do the endocrine and metabolic response to pain occur?
- Sympathetic NS increases catabolic hormones such as cortisol, catecholamines, IL-6, IL-1, aldosterone
o And decreases availability of anabolic hormones
Define allodynia.
Even stimuli that should not trigger pain response does. Can be caused by persistent nerve inflammation or injury
Define hyperalgesia.
Intensity of the pain sensation is magnified, but only starting at levels perceived as painful
What are primary and secondary hyperalgesia?
o Primary
Caused by release of mediators to help healing
o Secondary
No actual injury to the tissue
What is central sensitization and what is it caused by?
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
What is peripheral sensitization and what is it caused by?
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)
What is preemptive analgesia?
preoperative treatment is more effective than the identical treatment administered after incision or surgery. We should give those meds before surgery.
What is preventive analgesia?
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)
Name the risk factors for severe acute post-operative pain
- 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
Which type of analgesia has shown pre-emptive analgesic effect ?
• A strong consistent pre-emptive analgesic effect has been shown only with epidural analgesia
Which type of analgesia has shown preventive analgesic effect ?
Perioperative anti NMDA antagonists –> proved preventive analgesic effect (prolonged effect)
• Ketamine
• Dextromethorphan
Which type of factors determine pain intensity?
Most important determinants (63%) due to patient-related factors (> surgical factors)
Name 4 examples of unidimensional pain assessments
o Visual Analog Scale (0-100)
o Verbal Rating Scale (0-10)
o Numeric Rating Scale (0-10)
o Face Pain Scale (0-10)
Describe the relationship between NRS scores and the desire to receive additional analgesics
- 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
What is the issue with using NPS to assess pain in hospital?
• 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
How should we look at pain to prevent the issues with NRS?
We should aim to treat pain to achieve good functional outcomes (meaningful information)
What are the steps in assessing the functional impact of pain?
DREAMS Patient centred outcomes • Drinking • Eating • Mobilization • And sleep
What is the best unidimensional pain assessment tool?
- Unidimensional pain assessment: good construct validity
- No superiority between different unidimensional pain assessment tools
What defines optimal analgesia after surgery?
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)
Describe the WHO ladder for pain control
- 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
How should anti-inflammatories and paracetamol be administered based on the WHO ladder?
should be administered by the clock, oral route preferred
Describe what are adjuvant drugs and give examples.
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)
Name the different treatment options for analgesia
• Pharmacological interventions o Multimodal analgesia • Regional and Peripheral Analgesia o Neuraxial blockade o Peripheral nerve blockade • Non-pharmacological intervention (TENS..)
What is the most common analgesic medication?
Acetaminophen
What is the bioavailability of PO acetaminophen?
60-80%
What are the advantages of acetaminophen?
- Opioid sparing effect (opioid consumption reduced by 20-30%)
- ↓ post-op N/V
- Better analgesia when used before sx and with NSAIDs
What are the side effects of acetaminophen?
few, quite safe, ↓ dose in ETOH, G6PD deficiency
What are the advantages of NSAIDs?
- 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%)
What are the side effects of NSAIDs?
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
What are COX-2 inhibitors?
• COX-2 selective inhibition (celecoxib, etoricoxib and parecoxib/valdecoxib)
What are the advantages of COX-2 inhibitors?
- Opioid sparing effect
- No reduction in opioid side effects
- Less PLT dysfunction
- Less renal dysfunction
- Preemptive analgesic effect (?) – given before surgery
What are the risks of COX-2 inhibitors?
• 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).
