Analgesia Flashcards
Pain definition
An unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of tissue damage or both
Inadequate pain relief
Global concern for pts and practitioners
Pain not always cured and requires continuous medical management, the same as any other disease process
How many people in the UK suffer from persistent pain?
About 40%
Around 28 million people
Pain pathway - why we feel pain (injury)
Normal –> protective
–> acute –> reflexes
–>prolonged –> inflammation and repair
(acute can –> prolonged)
Congenital insensitivity to pain
SCN9A gene mutation in humans
-Nav1.7 voltage-gated sodium channel mutations in a-subunit cause loss of function
Sources of pain
Injury
Disease
Fracture types
Oblique: diagonal break across bone
Comminuted: break in three or more pieces and fragments are present at same fracture site
Spiral: break spirals around bone (common in twisting injury)
Compound: broken bone pierces skin, causing risk of infection
Sensory pathways
Transduction: conversion of a sensory stimulus from one form to another e.g. nerve endings in skin?
Transmission: thalamus, spinal cord, sensory fibres (touch, pain)
Somatosensory cortex: perception
Limbic (amygdala): perception/ learning
Pain modulation
Emotion and attention profoundly modulate nociception
Amount of pain experienced does not necessarily relate to severity of tissue damage
Anxiety > pain transmission
Complex cultural and contextual influences
Chronic
Abnormal –> non-protective –> chronic (pain as disease)
Therapeutic goal for chronic and prolonged pain
Return sensitivity to normal thresholds without loss of protective function
NSAIDS and opioids problematic
??
Dental pain
Infection - acute inflammation
Exposed nerve endings: neurogenic pain
Swelling in confined space: pressure effects
Fear and anxiety
Treatment of pain
< tissue damage -NSAIDS (non steroidal anti inflammatory drugs) -steroids -cooling Nerve block: LA Spinal cord: opioids CNS: opioids, psychological factors
WHO cancer pain relief steps
Believe the pt History of symptoms Assessment of severity Physical examination Appropriate pain management
WHO analgesic ladder
Step 1: mild to moderate pain
-non-opioids e.g. paracetamol +/- NSAID
Moderate
-weak opioids e.g. tramadol, dihydrocodeine +/- non-opioids e.g. paracetamol +/- NSAID
Step 3: severe pain
-strong opioids e.g. morphine, diamorphine, fentanyl patch +/- non-opioids e.g. paracetamol and/ or NSAID
Co-analgesics: other drugs, nerve blocks, surgery, radiotherapy, complementary therapies, addressing psychosocial issues
Analgesic ladder assumptions
Synergism
Overall philosophy assessing severity, starting at lowest level and increasing if necessary
Joint Royal Colleges Report (1988) quality of analgesia in hospital practice is inadequate
Placebo effect
Placebo is anything administered which is pharmacologically and physiologically inert
Not ineffective therapeutically
-can have measurable effect
Reassurance and confidence in one’s therapy may also have an effect
WHO analgesic ladder: paracetamol
- mechanism
- effect
- route
- dose
Mechanism of action unknown - inhibitor of the synthesis of prostaglandins
Analgesic, antipyretic, not much anti-inflammatory effect
Oral, soluble potions, IV, rectal
1g 4-6 hourly adult dose
-4g in 24hr
Paracetamol: adverse effects
Uncommon
Hepatotoxicity if overdose
-early treatment with N-acetyl-cysteine
-not absolutely contraindicated in liver disease
WHO analgesic ladder: NSAIDs
- examples
- mechanism
- effect
Aspirin, ibuprofen, naproxen, indomethacin
Irreversible inhibitor of cyclo oxygenase (COX1 and/ or COX2) enzyme
COX generates inflammatory mediators: prostaglandins and thromboxanes
COX widely distributed, different isotypes
COX inhibitors effective at < acute inflammation
NSAIDs adverse effects
Due to extension of therapeutic effects
GI tract:
-occult GI blood loss from minor breaches in mucosa (loss of PGE)
-peptic ulceration
-general GI upset, indigestion
Renal function: < in intrarenal blood flow can cause renal failure
Platelets: COX inhibition, bleeding tendency
CV: as result of altered renal function, fluid retention ca precipitate heart failure
Respiratory: some ‘aspirin sensitive’ asthmatics
COX2 inhibitiors
Newer
Parecoxib celecoxib
< bleeding as GI tract and platelets have mainly COX1
Not less nephrotoxic
COX2 and CV disease
Absence of antiplatelet effects
Slightly pro thrombotic
> risk of MI and stroke
Contraindicated in CV disease
NSAIDs and elective surgery
Need to stop at least 5 days before elective surgery
Bleeding at operation: platelet transfusion
Consider platelets if emergency surgery
Weak opioids: moderate to severe pain
- type
- mechanism
- effect
Codeine or di-hydrocodeine Both metabolised to morphine -metabolism varies -some people have minimal enzyme and hence less effective Weak opioid effects
Weak opioids: moderate to severe pain
-adverse effects
CV: < sympathetic outflow, > vagal tone -bradycardia -hypotension -excitation Respiratory: inhibit cough reflex, respiratory depression GI tract: < gastric motility -constipation -nausea -vomiting
CNS opioid effects
Sedation, euphoria,(dysphoria), excitation
Analgesia in SC and brainstem
Spinal cord: < pain fibre transmission, kappa opioid receptors
Brainstem: < pain projection to higher centres, Mu opioid receptors
CNS opioid adverse effects
Respiratory drepression, < brainstem responseto hypoxia and hypercarbia
Reversal of opioid effects
Naloxone 400mg IV
- dramatic reversal of Mu receptor opioid effects
- far less effective on newer synthetic opioid-like substances as their effects in CNS are less well defined
Opioid dependency
Chronic opioid use: < effect as CNS becomes more tolerant
-dose increase
Opioid withdrawal
Acute withdrawal --> -hypertension -tachycardia -tachypnoea -diarrhoea -sweating -anxiety -hallucinations Any chronic opioid medication will precipitate some withdrawal reaction if stopped suddenly
Newer oral opioids
- types
- effectiveness
- effects
Tramadol and Nefopam
As effective as codeine, much less constipation hence very frequently prescribed
‘Oramorph’ - lower dose oral morphine
Usual opioid effects: sedation, dizziness, nausea
Occasional flushing/ sweating with tramadol
Tramadol adverse effects
> number of fatalities from OD causing respiratory depression
Dependency develops with long term use
-difficult to withdraw
Tramadol legislation
Controlled drug (class 3) Limit to maximum prescription Must be signed for
Weak opioids/ paracetamol combinations
Co-codamol, co proxamol, various
Now less popular than either nefopam or tramadol
Need to include paracetamol in total 24hr maximum of 4g
Check BNF if an unfamiliar oral analgesic
Group cautions prescribing opioids
Dependent on hepatic metabolism and renal excretion of metabolites
-some active metabolites
Prolonged effect in liver or renal impairment
Respiratory disease, sleep apnoea, > sensitivity
Aim for minimum duration of prescription
WHO analgesic ladder: severe pain
- types
- dose
Morphine; oral, SC, IV
Diamorphine: SC, IV
Fentanyl patch (transdermal)
Oral dose approx. 3x IV dose for same efficacy
Post-op analgesia
If required IV in recovery 2mg increments every 3min until comfortable (10 - 20mg) in recovery setting
-must be given by trained staff
Ward care: morphine 10mg SC 2 hourly usually co-prescribed antiemetic; Ondansetron or cycizine
Morphine pt controlled analgesia
Syringe driver intermittent IV bolus delivery initiated by pt (push button)
1mg minimum frequency every 5 mins
Multiple studies show approx. 1/3 dose compared to nurse administered SC morphine
Routes of opioids administration
Oral IV SC and IM Rectal Intrathecal (spinal canal --> CSF) Epidural Buccal Trans dermal
Severe pain: chronic pain
Oral morphine syrup or tablets Morphine SC infusion Diamorphine SC infusion Fentanyl transdermal patch lasts 5 days Buprenorphine patch
Gabapentin and pregablin
Effective for chronic neurogenic pain
< central transmission and pain projection
Adverse effects of gabapentin
Sedation, dizziness, nausea, occasionally hypotension
Antidepressant drugs
Amitryptiline
Duloxetine and Citalopram
Have useful adjuvant effects in neurogenic pain
-also some antidepressant effect can be useful
Antidepressant drugs adverse effects
GI and CVS
Psychological support
Pain management
Pain management
Assessment of severity in context of daily living and functioning
Acute pain; large variation in requirements complex
-amount of analgesia (i.e. correct dose) required is ‘enough to stop pain’
Synergism of different drug actions, psychological factors
