15 - Pain Management Flashcards
What is the definition of pain?
An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage
What is the physiology of pain?
Two aspects
- Sensory – the sensory signal transmitted from pain receptor (“it is a sharp sensation, likely a needle”)
- Affective – unpleasant emotional reaction to the pain (“it is excruciating, I can’t bear it”)
Nociceptors at the ends of nerves detect damage or potential damage to tissues. Nerve signals are transmitted along afferent nerves to the spinal cord
The signal then travels in CNS, up the spinal cord (mainly in the spinothalamic tract and spinoreticular tract) to the brain where it is interpreted as pain, mainly in the thalamus and cortex.
What are the two types of primary afferent sensory receptors that detect pain?
- C fibres (unmyelinated and small diameter) – transmit signals slowly and produce dull and diffuse pain sensations
- A-delta fibres (myelinated and larger diameter) – transmit signals fast and produce sharp and localised pain sensations
What is allodynia?
When pain is experienced with sensory inputs that do not normally cause pain (e.g light touch)
What is the definition of pain threshold and pain tolerance?
Pain threshold refers to the point at which sensory input is reported as painful.
Pain tolerance is a person’s response to pain. One person may experience pain but think little of it and carry on with their activities as usual. Another person may experience a similar pain and worry that it indicates a serious underlying illness, take time away from work, and seek medical investigations and treatment. Pain tolerance is influenced by many biological, psychological and social factors
What sensory inputs generate pain?
- Mechanical (e.g., pressure)
- Heat
- Chemical (e.g., prostaglandins)
What is referred pain and the cause of this?
Pain experienced in a location away from the site of tissue damage e.g MI pain in left arm
- Nerves may share innervation of multiple parts of the body
- Pain in one area amplifies sensitivity in spinal cord to signals coming from other areas
- Activation of sympathetic nervous system in response to pain results in pain in other areas
How can we measure pain?
Only subjective no objective way
Visual analogue scale (VAS): asking the patient to rate their pain along a horizontal line, where the left end indicates no pain and the right end indicates the worst pain imaginable. The distance along that line can be measured to get a numerical value to represent the pain
Numerical rating scale (NRS) involves asking the patient to rate their pain on a numerical scale of 0 – 10, with:
Smiley/Sad faces: for children or those with learning disabilities
What are some important questions to answer in a pain assessment of a patient with cancer?
IMPACT ON LIFE
75-90% of advanced cancer patients have pain. What is the issue with pain in advanced cancer?
Usually has multiple aetiologies and is persistent so can be hard to control
What are the three areas that can cause pain in cancer patients?
- Cancer related
- Treatment related
- Comorbidities
What are the different types of pain?
- Nocireceptive: visceral or somatic, nerves in tact
- Neuropathic: nerves not in tact
- Incident
How is nocireceptive and neuropathic pain felt?
What is incident pain in cancer?
Breakthrough pain caused by movement or a particular activity e.g defecating
What are the three categories of analgesia for analgesia and describe the WHO pain ladder?
ALL +/- ADJUVANTS
- Step 1: Non-opioids such as paracetamol and NSAIDs
- Step 2: Weak opioids such as codeine and tramadol
- Step 3: Strong opioids like morphine, oxycodone, fentanyl and buprenorphine
Use paracetamol and NSAIDs at all three steps
Start on appropriate step for pain
Give some examples of adjuvants that are used alongside opioids/non opioids in the pain ladder.
Best for neuropathic pain
- Amitriptyline – TCA
- Duloxetine – SNRI
- Gabapentin – anticonvulsant
- Pregabalin – anticonvulsant
- Capsaicin cream (topical) – from chilli peppers
- Diazepam - Benzodiazepine
Name some drugs used in each step of the WHO pain ladder.
Step 1: Paracetamol, NSAIDs (Ibuprofen, Naproxen, Celecoxib)
Step 2: Co-codamol, Tramadol, Dihydrocodeine
Step 3: Fentanyl, Diamorphine, Oxycodone, Buprenorphine, Morphine
Step 2 has a ceiling dose, if an opioid not working switch up to step 3 not another step 2
What are some side effects of analgesia (NSAIDs and opioids in particular)?
Medication overuse headache
NSAIDs
- Gastritis with dyspepsia
- Stomach ulcers
- Exacerbation of asthma
- Hypertension
- Renal impairment
- Coronary artery disease, heart failure and strokes
Opioids
- Constipation
- Pruritus
- Nausea
- Altered mental state (sedation, cognitive impairment or confusion)
- Respiratory depression
What are some contraindications to NSAIDs for analgesia?
- Asthma
- Renal impairment
- Heart disease
- Uncontrolled hypertension
- Stomach ulcers
What are some medications prescribed alongside NSAIDs and Opioids to try and tackle certain side effects?
(IMPORTANT)
PPIs: prevent stomach ulcers
Laxatives: prevent constipation
Antiemetic: for nausea
Naloxone: if respiratory depression
What are some side effects of the following drugs used for neuropathic pain and how long do they take to work?
- Amitriptylline
- Gabapentin
- Pregablin
Titrate dose up slowly and give at night to minimise side effects
SE: sedation, tremor, confusion
Takes 5 days to take effect
How well do the different categories of pain respond to opioids?
What is used for bone met pain and liver pain?
Bone Mets: Opioids, Bisphosphonates, NSAIDs, Radiotherapy, Denosumab
Liver Mets: Steroids
What NSAIDs are better for less GI side effects?
COX2 inhibitors like Celecoxib (CI in CVS disease)
Any NSAIDs can make heart failure worse
Paracetamol has a risk of hepatotoxicity at a dose of 4g/day. Which cancer patients should you take care in prescribing paracetamol to?
Body weight less than 50kg give half dose at 500mg
How do you step up from maximum dose codeine to morphine?
Codeine : morphine is 10 : 1
How is morphine prescribed in general in palliative care?
Always a slow release and instant release for breakthrough pain
Always prescribe by actual name of Morphine Sulfate IR/SR not Zomorph
How do you calculate the dose of morphine for breakthrough pain?
SIGN Guidelines
1/6th of the 24h dose of background morphine
Can increase background dose if lots of doses of IR used
How do you calculate the dose of morphine for slow release background analgesia?
Given BD so half TDD
How much is 10mg of morphine in these different forms?
How long do fentanyl patches last?
3 Days
Good as not really excreted
If a cancer patient has N+V so they are not getting effective pain relief from PO morphine, what can you do?
Switch to SC/Syringe driver
2:1 RATIO of PO:SC
What side effects persist with opioids and what are transient?
Persists: Constipation and Dry Mouth
Transient: Nausea and Confusion/Sedation
Respiratory depression rare in cancer as not opioid naive
What form of morphine is good for renal impairment patients as it is not really excreted?
Fentanyl
What are the legal requirements for writing a controlled drug prescription for an outpatient?
Name, Form, Strength
Have to write in words exactly the quantity e.g fifty six tablets
How do you write the dose interval for a controlled drug prescription?
Cannot state PRN as needed, need to say minimum time interval and indication to take it
Give 2 weeks worth of supply
If pain is not controlled by the standard opioid dosage, how should you uptitrate this?
How do you convert oral morphine to oral tramadol and oxycodone?
How do you convert the following doses?
