Analgesia (3)
Appropriate treatment of pain
Knowledge of patient’s concurrent analgesic medications for chronic pain
Recognition of adverse effects and avoidance of potential reactions
Pain
Unpleasant sensory/emotional experience which we associate with tissue damage or describe in terms of tissue damage or both
Inadequate relief is a global concern
Not always cured and requires continuous medical management
Pain sequence
Normal –> protective –> EITHER acute OR prolonged
ACUTE –> REFLEX
PROLONGED –> INFLAMMATION+REPAIR
Congenital insensitivity to pain
SCN9A gene mutation in humans - loss of function due to Na channel mutations
Results in injury due to lack of pain
Sources of pain
Injury e.g fractures
Disease e.g neuromyalgia
Sensory pathway
Originates in PNS and travels to CNS (spinal cord and brain)
CNS transmits to cortex to create perception of pain
Pain modulation
Emotion and attention affect nociception
Amount of pain does not relate to severity of tissue damage
Anxiety increases pain transmission
Complex cultural influences
Dental pain results from (4)
Infection
Exposed nerve endings
Swelling in confined space
Fear
NSAIDs and opioids are used to treat
Injury pain and chronic pain
By returning sensitivity to normal thresholds
Can be problematic
Treatment of pain
Reduce tissue damage (NSAIDs, steroids, cooling)
Nerve block
Spinal cord (opioids)
CNS (opioids and psychological factors)
Paracetamol When Mechanism Type Route Dose
Mild pain N/A - inhibitor of prostaglandin synthesis Analgesis, antipyretic Oral, soluble, IV, rectal 500mg-1g 4-6 hrly - max is 4g/24hrs
Paracetamol - adverse effects
Uncommon
Hepatotoxicity - early treatment with N-acetyl-cysteine
Not contraindicated in liver disease
NSAIDs e.g ibuprofen
IR inhibitor of COX1 +/ COX2
Inhibits inflammatory mediator synthesis
Effective at reducing acute inflammation
NSAIDs side effects
GI tract - blood loss from minor mucosal breaches - peptic ulceration - indigestion
Renal function - reduction in intrarenal blood flow –> failure
Platelets - COX inhibition, bleeding tendency
Cardiovascular - fluid retention due to renal failure –> heart failure
Respiratory - some aspirin sensitive asthmatics
Newer NSAIDs
Newer COX2 inhibitors
Ibuprofen, diclofenac, naproxen
Less bleeding as side effect if only COX2 affected as GI tract and platelets mainly associated with COX1
Not nephrotoxic
COX2 and CV
Absence of anti platelet effects
Prothrombotic
Increased risk of MI and stroke
NSAIDS and elective surgery
Stop 5 days prior to surgery
Reduces risk of bleeding
Consider platelet transfusion
Weak opioids - mod -severe pain
Codeine
Dihydrocodeine
Both metabolised to morphine
Some people have minimal enzyme
Cardiovascular effect of weak opioids
Reduced simp outflow, increased vagal tone
Bradycardia
Hypotension
Respiratory effect of weak opioids
Inhibit cough reflex
Respiratory depression
GI effect of weak opioids
Reduced gastric motility
Constipation
Nausea
Vomiting
CNS opioid effects
Sedation, euphoria, dysphoria, excitation
Analgesia for CNS
Spinal cord - reduced pain fibre transmission
Brainstem - reduced pain projection to higher centres
Respiratory depression, reduced brainstem response to hypoxia and hypercarbia
Weak opioid/paracetamol combinations
Co-codamol e.g
Less popular
Adjuvant therapies
Co-analgesics - other drugs, blocks, surgery, Rtherapy, addressing psychosocial issues
Pain management (3)
Assessing severity in context of daily living and functioning
Acute pain - large variation in requirements
Amount of analgesia required is enough to stop the pain
Anaphylaxis
Severe reaction to medication
Reversal of opioid effects
Naloxone 400mcg
Opioid dependency
Chronic use
Acute withdrawal symptoms if stopped suddenly
Reduced effect as the CNS improves tolerance therefore dosage increases
Hypertension, sweating, tachycardia, diarrhoea, anxiety, hallucinations
New opioids
As effective as
Effects
Nefopam, Tramadol
Codeine, less constipation
Nausea, dizziness, sweating
Adverse effects: Tramadol
Overdose causes?
New legislation?
Increased no. fatalities due to overdose
Dependency due to long term use
Controlled drug
Paracetamol combos
Co-codamol/proxamol
Cautions in prescribing opioids
Consider hepatic metabolism and renal excretion
Prolonged effect on liver and kidneys
Respiratory disease, sleep apnoea, increased sensitivity
Severe pain
Fentanyl patch
Morphine (oral dose 3x IV dose)
Post operative analgesia
IV morphine
Patient controlled
Route of administration
Oral IV Rectal Epidural Buccal Intrathecal i.m/s.c transdermal
Chronic pain
Oral morphine syrup/tabs
Transdermal patch
S.C morphine
Alternatives x2
For?
Adverse effects?
Gabapentin Pregabalin Neurogenic pain Reduce CNS transmission Dizziness, nausea, sedation, dizziness
Antidepressants
Amitryptilline
Duloxetine
Citalopram
What are enkephalins?
Enkephalin are the bodies own produced opioids. (endogenous opioids)
How do enkephalins work?
Substance P
What chemical increases substance P release for
Enkephalins inhibit pain by stimulating the kappa opioid receptors.
Pain stimulating NT
Kappa opioid receptor inhibits substance P release.
Opioids also work on the higher centres – brainstem.
NMDA – NT that increases substance P release. N-methyl-D-aspartate is released in anxiety –> pain