Pain Management Flashcards
Definition of pain (3)
- an unpleasant sensory & emotional experience associated with actual or potential tissue damage
- a physiological & psychological response that vary from person to person & day to day
- pain is anything the patient tells you
Classification of pain (2)
- duration
- Acute
2. Chronic
Acute pain (2)
- associated with invasive procedures, trauma & disease
- resolves over days to weeks
Chronic pain (3)
- persists past normal tissue healing
- 4-6 weeks or 3 months
- can be malignant or non-malignant (eg headache, migraine)
Types of pain (4)
- location
- Nociceptive pain
- Neuropathic pain
- Referred pain
- Ischemic pain
- Nociceptive pain & their receptors
- arises due to tissue damage from noxious stimuli (chemical, thermal & mechanical)
- Visceral (organ)
- often refer pain to a distant cutaneous site
eg appendicitis, cholecystitis
- stretch receptors - Somatic (skin, muscles, bones)
- localised pain
- A-delta fibres & C-fibres
- Neuropathic pain (3)
& description
- Central
- Peripheral
- no area of tenderness
- no area of allydonia (decreased pain threshold)
- resistance to opioids
- Referred pain (2)
- pain located away from its point of origin
- occurs because signals from different part of the body travel along the same pathways
- Ischemic pain
- loss of blood flow
Somatic pain sensation (nociceptive) (4)
- aching
- stabbing
- throbbing
- pressure
Visceral pain sensation (nociceptive) (4)
- gnawing
- cramping
- aching
- sharp pain
Neuropathic pain sensation (4)
- burning
- tingling
- shooting
- electric / shocking pain
How to do pain assessment (4+1)
- Believe the patient’s report of pain
- Use open-ended questions
- Take history of each pain
- Any psychological distress
(( SOCRATES )) Site Onset Character Radiation Associations (any other symptoms) Time course Exacerbating / relieving factors Severity
Steps to developing pain management treatment (6)
- Characterise & quantify pain
- using scales - Identify pain syndrome
- acute or chronic
- malignant or non-malignant - Infer pathophysiology
- nociceptive, neuropathic or mixed - Evaluate physical & psychological comorbidities
- Assess degree & nature of disability
- Develop a therapeutic strategy
WHO Ladder (Pharmacological treatment for pain)
- mild
- moderate
- severe
Mild pain : non-opioids +/- adjuvants
eg paracetamol, NSAIDs
- avoid aspirin due to irreversible anti-platelet effects
Moderate pain : weak opioids +/- adjuvants
eg tramadol, codeine
Severe pain : strong opioids +/- adjuvants eg morphine (q4h), fentanyl, oxycodone (q6), methadone
WHO treatment guides for cancer pain (5)
- Oral dosage form preferred
- Regular dosing
- Detailed dosing instructions
- Initiate dose according to patient’s pain intensity/scale
- Titrate to adequate pain relief & tolerable side effects
Titration of analgesics
Mild pain : even slower titration
Moderate pain : slow titration
Severe pain : rapid titration
Dosing of Paracetamol / Acetaminophen
Dose (normal) : 0.5-1g every 6-8h (max 4g/24h)
Dose (hepatic impairment) : 1g every 12h (max 2g/24h)
Advantages of Paracetamol / Acetaminophen (3)
- low incidence of ADR
- PO/PR available
- multi-preparations & combinations
Disadvantages of Paracetamol / Acetaminophen (3)
- lack anti-inflammatory properties
- hepatotoxicity with large doses (avoid >4g/24h)
- risk of overdose as many combination preparations contains paracetamol
NSAIDs (3)
- use any NSAIDs effective for the patient, otherwise use ibuprofen
- failure to improve even after trial of 2 NSAIDs require another approach to analgesia (weak opioids)
- COX-2 selective NSAIDs have lower GI side effects & anti-platelet activities
eg diclofenac, celecoxib, etoricoxib
NSAIDs precautions (7)
- Elderly >65y/o
- Bleeding disorder
- Anti-coagulants
- GI disease (ulcer, bleeding, perforation)
- Cardiovascular disease
- Asthma & bronchospasm
- Renal/hepatic disease
Types of Adjuvants (5)
- Gabapentin, pregabalin, antidepressants, anti-epileptics & topical lidocaine
- Corticosteroids
- Muscle relaxants
- Hyoscine
- NSAIDs & bisphosphonates
Classifications of opioids by pain intensity (2,1,5)
Weak opioids (2)
- codeine
- tramadol
Moderate opioids (1) - tapentadol (between tramadol & morphine)
Strong opioids (5)
- morphine
- fentanyl
- methadone
- oxycodone
- pethidine (not used)
Codeine metabolism (2)
- CYP2D6 metabolism to active morphine metabolite
- hence CYP2D6 inhibitors/hepatic insufficiency decrease efficacy of codeine
- use tramadol
Dosing of codeine
Normal dose
- 15-60mg up to 6 times daily
- max 400mg/day
Renal impairment
- CrCl 10-50mL (75%)
- CrCl <10mL/min (50%)
Hepatic impairment
- necessary if hepatic insufficiency
- use tramadol
Tramadol (5)
- onset 1h
- duration 9h
- also SSRI (good for neuropathic pain)
- CYP2D6 metabolism to active metabolites BUT extensively glucuronidation, demethylation & sulfation
Hence preferred > codeine if hepatic disease - high doses lowers seizure threshold
Dosing of tramadol
Normal dose
- 50-100mg every 4-6h (max 400mg/24h)
Renal impairment
- CrCl <30mL/min (50-100mg every 12h) (max 200mg/day)
- do not use ER if CrCl <30mL/min
Hepatic impairment
- Cirrhosis (25-50mg every 12h)
- do not use ER if severe hepatic dysfunction
Dosing of morphine
Normal dose
- if previously on weak opioid : 10mg every 4h OR MR 20-30mg every 12h
- if opioid-naive : 5mg every 4h
- if elderly & frail & renal impairment : 5mg every 4h
Renal impairment
- CrCl 10-30mL/min (75%)
- CrCl <10mL/min (50%)
Hepatic impairment
- mild (unchanged)
- severe (excessive sedation)
Fentanyl (2)
- 100x more potent than morphine
Hence dose is in mcg NOT mg - CYP3A4 metabolism
Dosing of fentanyl
Normal dose
- 50-100mcg/kg
- MICROgrams
No dose adjustments for renal/hepatic impairment
- monitor
Indications for fentanyl (4)
- Intolerable side effects from morphine
- Renal failure
- Dysphagia
- “tablet phobia” or poor oral compliance
- cos transdermal patch
Methadone (3)
- metabolism
- MOA
- hepatic metabolism by CYP3A4
- complex dosing hence only for experienced physicians
- MOA :
1. Opioid receptor antagonists
2. NMDA antagonists
3. Serotonin re-uptake inhibitor
Dosing of methadone (renal & hepatic)
Renal impairment
- CrCl <10mL/min (50-75%)
Hepatic impairment
- avoid in severe hepatic disease
Oxycodone metabolism (2)
- CYP2D6 (inhibitors decrease oxycodone efficacy)
- CYP3A4
Dosing of oxycodone
Normal dose
- immediate release (5mg every 6h)
- controlled release (10mg every 12h for opioid naive)
No dose adjustment for renal impairment
Hepatic impairment
- reduce dose if severe hepatic disease
Tapentadol (2)
- only for acute pain
- between tramadol & morphine
Pethidine (1)
- for acute pain only, not for chronic pain due to fast onset & short acting
Can use pethidine for palliative care?
Why do we avoid pethidine in palliative care? (4)
No
- Quick onset but short duration of action
- increased risk of dependence - Norpethidine is a toxic metabolite
- Norpethidine decreases seizure threshold
- More emetogenic than morphine
PO Morphine : IM/IV Morphine
3 : 1
PO Codeine : PO Morphine
PO Tramadol : PO Morphine
PO Codeine : PO Morphine = 10 : 1
PO Tramadol : PO Morphine = 5 : 1 OR 10 : 1
PO Oxycodone : PO Morphine
1:2
Morphine : Fentanyl patch
30mg/24h : 12mcg/h
Morphine : Methadone
- complicated conversion
- stepwise over 3 days
New breakthrough dose
1/6 of new total daily dose
Stimuli for :
- A-delta fibres
- C-fibres
A-delta fibres
- mechanical & thermal stimuli
C fibres
- mechanical, thermal & chemical stimuli
Steps of Nociception (4)
- Transduction
- Transmission
- Modulation
- in spinal cord - Perception
Tools to assess pain scale if :
- <3y/o
- unable to communicate pain
FLACC
Face Legs Activity Cry Consolability
What kind of pain to use
- gabapentin
- pregabalin
- antidepressants
- anti-epileptics
- topical lidocaine for what kind of pain?
(1)
Neuropathic pain
What kind of pain to use Corticosteroids? (4)
- neuropathic pain
- bone pain
- raised intracranial pressure (reduce edema)
- liver capsule stretch pain
What kind of pain to use muscle relaxants? (2)
eg baclofen, benzodiazepines
- cramps
- muscle spasms
What kind of pain to use Hyoscine? (1)
- intestinal colic
What kind of pain to use NSAIDs & bisphosphonates? (1)
- bone pain
First line opioid for severe pain
Morphine
CYP2D6 inhibitors (3)
- chlorpromazine
- fluoxetine / paroxetine
- quinidine & quinine
Tramadol DDI (4)
Increase risk of seizures
- SSRI
- TCA
- neuroleptic drugs
- naloxone
Fentanyl patch (3)
- transdermal patch duration 48-72h
- after patch removal, still got drug depot in body
- reserve for patients (cannot morphine, renal failure, dysphagia or poor oral compliance)
CYP2D6 inhibitors decrease efficacy of __ (2)
- Codeine
2. Oxycodone
Situations to consider 25-50% dose reduction when converting between opioids (3)
- elderly & frail
- conversion to methadone
- organ dysfunction (renal & hepatic impairment)
Situations to NOT consider 25-50% dose reduction when converting between opioids (2)
- severe pain (up titration of dose)
- conversion to fentanyl patch (maintain dose)
When to up titrate total daily maintenance dose
> 4 breakthrough doses in a day
Treatment for opioid overdose if :
- Respiratory rate >= 8bpm
- Arousable
- Not cyanosed
(2)
- wait & see only, do not use naloxone
- reduce or omit next dose of morphine
Treatment for opioid overdose if :
- Respiratory rate < 8bpm
- barely arousable/unconscious
- cyanosed
(1)
- IV 20mcg Naloxone (=0.5mL) every 2min until patient RR is satisfactory
ADR of opioids (common) (3)
- N/V
- Somnolence & mental clouding
- Constipation
- req chronic use of laxatives
1-2 weeks tolerance development for 1&2
ADR of opioids (less common) (5)
- Myoclonus / seizures
- clonazepam - Respiratory depression
- Postural hypotension
- Rash / itch
- due to histamine release
- antihistamine - Urinary retention
Management of opioids ADR (3)
- Change to another opioids
- Symptomatic treatment
- Dose reduction + adjuvants
Monitoring outcomes for opioid therapy (4)
- Pain relief
- Side effects
- Recovery of function/activity
- Drug-related behaviours
- addiction
- but risk of addiction in cancer pain & acute pain unlikely
PO Morphine : PO Codeine : PO Tramadol : PO Oxycodone
2 : 20 : 10/20 : 1
