Pain Management Flashcards
Why should we treat pain?
Avoid physiological effects of untreated pain
- Sympathetic response
- Reduced function
- Poor mobility
- Ineffective cough
Avoid psychological effects of untreated pain
Humane thing to do
What is acute pain?
Pain of recent onset and probable limited duration
What is chronic pain?
Pain persisting beyond healing of injury
Often no identifiable cause
Lasting for >3 months
What is nociceptive pain?
Obvious tissue injury/illness
Physiological
Protective function
What are the different types of nociceptive pain?
Superficial somatic
Deep somatic
Visceral
What is neuropathic pain?
Nervous system damage/abnormality Pathological Doesn't have protective function Tissue injury not obvious Not well localised
What are the positive features of neuropathic pain?
Allodynia
Hyperalgesia
What are the negative features of neuropathic pain?
Hypoesthesia
Numbness
What happens in the periphery to first cause pain?
Tissue injury > release of chemicals > stimulation of nociceptors > signal travels in A-delta/C fibres to spinal cord
What happens to pain information in the spinal cord?
Dorsal horn 1st synapse - site of decussation
2nd nerve travels up spinal cord
What happens to pain information in the brain?
Thalamus = 2nd synapse Connections to many parts of brain - Cortex - Limbic system - Brainstem
Where does pain perception occur?
Cortex
What does pain modulation involve?
Descending pathway from brain to dorsal horn
Usually decreases pain signal
What is the mechanism of action of paracetamol?
Unclear but acts in CNS
Inhibits peripheral prostaglandin synthesis
Analgesic and antipyretic
What are the indications for paracetamol?
Analgesia alone/in combination
What are the adverse effects of paracetamol?
Hepatic necrosis in overdose
What are the interactions of paracetamol with other analgesics?
Additive with NSAIDs
What is the mechanism of action of NSAIDs?
Non-specific inhibition of COX-1 and -2 > inhibits prostaglandin synthesis
Analgesic, antipyretic, and anti-inflammatory
What are the indications for NSAIDs?
Analgesia alone/in combination
What are the adverse effects of NSAIDs?
Peptic ulceration Renal impairment Anti-platelet action Bronchospasm in asthma Exacerbation of CCF
What are the interactions of NSAIDs with other analgesics?
Reduce opioid requirements by 20-40%
What is the mechanism of action of opioids?
Mu opioid receptors to produce analgesia Sites of action - Peripheral nociceptors - Dorsal horn - Cerebral cortex - Descending tracts
What are the indications for opioids?
Severe acute pain
Cancer pain
What are the adverse effects of opioids?
Sedation Respiratory depression Nausea Euphoria Miosis Bradycardia Postural hypotension Urinary retention
What are the interactions of opioids with other analgesics?
Caution with other sedative agents
What is the mechanism of action of tramadol?
Weak opioid effect
Inhibition of serotonin and noradrenaline reuptake
What are the indications for tramadol?
Moderate pain
What are the adverse effects of tramadol?
Hypertension
Nausea and vomiting
Ceiling effect for analgesia
Lowers seizure threshold
What are the interactions of tramadol with other analgesics?
Risk of serotonin syndrome with other serotonergic agents
What are two examples of tricyclic antidepressants?
Amitriptyline
Nortriptyline
What is the mechanism of action of tricyclic antidepressants?
Inhibit reuptake of NA and serotonin into pre-synpatic terminals
Inhibit cholinergic, histaminergic, alpha1-adrenergic, and serotonergic receptors
Increases descending inhibitory signals
What are the indications for tricyclic antidepressants?
Neuropathic pain
Depression
Poor sleep
What are the adverse effects of tricyclic antidepressants?
Anti-cholinergic side effects
Postural hypotension
Liver dysfunction
QTc prolongation and arrythmia
What other drugs do tricyclic antidepressants interact with?
Monoamine oxidase inhibitors
Selective serotonin reuptake inhibitors
Tramadol
What should you monitor when a patient is using tricyclic antidepressants?
Liver function
ECG
Nortryptiline levels
What is the mechanism of action of gabapentin/pregabalin?
Exact mechanism unknown
Binds to alpha-2 delta protein subunit of high threshold voltage-dependent Ca channels > reduces Ca influx > reduces neurotransmitter release
What are the indications for gabapentin/pregabalin?
Focal seizures
Neuropathic pain
What are the adverse effects of gabapentin/pregabalin?
Sedation
What are the drug interactions of gabapentin/pregabalin?
Other sedative drugs
What should you monitor when a patient is using gabapentin/pregabalin?
Reduce dose in renal impairment
Can cause raised bilirubin
What is the mechanism of action of ketamine?
Antagonises NMDA receptors
Descending monoaminergic pain pathways
Voltage-sensitive Ca channels and opioid receptors in brain and spinal cord
What are the indications for ketamine?
Anaesthesia
Pain
What are the adverse effects of ketamine?
Sedation Hyper-salivation Tachycardia Dysphoria - Relatively contraindicated in psychiatric patients
What are the drug interactions of ketamine?
Other sedative drugs
What should you monitor when a patient is using ketamine?
Dysphoria
What is the mechanism of action of clonidine?
Alpha-2 adrenoceptor agonist
What are the indications for clonidine?
Sedation
Analgesia
Antihypertensive
Addiction medicine for opioid withdrawal management
What are the adverse effects of clonidine?
Sedation
Hypotension
Bradycardia
What are the drug interactions with clonidine?
Other sedative agents
What should you monitor when a patient is using clonidine?
Rebound hypertension
Reduce dose in renal impairment
What is the gold standard in the measurement of pain?
Self reporting
What are the non-drug treatments for pain?
RICE - Rest - Ice - Compression - Elevation of injuries Nursing care Physiotherapy Surgery Acupuncture Massage Psychological - Explanation and reassurance - Input from social worker/pastor - Relaxation - Coping strategies
What are the drug treatments for mild nociceptive pain?
Paracetamol +/- NSAID
What are the drug treatments for moderate nociceptive pain?
Paracetamol +/- NSAID +/- opioids; eg:
- Codeine
- Oxycodone
- Tramadol
What are the drug treatments for severe nociceptive pain?
Strong opioids/regional anaesthesia + paracetamol +/- NSAID
Adjuvants
- Alpha-2 agonists
- NMDA antagonists
What are the drug treatments for neuropathic pain?
Traditional drugs may not be useful, especially NSAIDs and chronic opioids Use other drugs early - Amitriptyline - Carbamazepine - Gabapentinoids
