MISC - Pain management Flashcards
What is Pain?
“an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”.
(3) types of Classification of Pain
- Duration
- Acute
- Chronic
- Acute on chronic - Cause
- Cancer (progressive)
- Non cancer - Mechanism
- Nociceptive (physiological)
- Neuropathic (pathological)
What is a chronic pain?
– Pain persisting beyond healing of injury
– Often no identifiable cause
– (Pain lasting for more than 3 months)
Describe nociceptive pain
- Obvious tissue injury or illness
- “Physiological pain”
• Can be further classified into
– Superficial somatic
– Deep somatic
– Visceral
• Descriptions include sharp, aching, dull, throbbing, cramping and pressure
Describe neuropathic pain
- Nervous system damage or abnormality
- “Pathological pain”
- Tissue injury may not be obvious
• Description
– Burning, shooting ± numbness, pins and needles
– Not well localised
How is nociception not the same as pain?
Pain is multifactorial not only injury based.
Factors include: beliefs/concerns, psychological factors (anxiety, depression, anger), cultural issues, other illnesses, coping strategies, social factors.
What are the 4 steps of pain physiology (sequence)?
– Periphery
– Spinal cord
– Brain
– Modulation
What happens at the periphery as one of the 4 steps of pain physiology?
- Tissue injury
- Release of chemicals
- Stimulation of pain receptors (nociceptors)
- Signal travels in Aδ or C nerve to spinal cord
What happens at the spinal cord as one of the 4 steps of pain physiology?
- Dorsal horn is the “first relay station”
- Aδ or C nerve synapses (connects) with second nerve
- Second nerve travels up OPPOSITE side of spinal cord (decussate at the level of spinal cord)
What happens at the brain as one of the 4 steps of pain physiology?
• Thalamus is the “second relay station”
• Connections to many parts of the brain
– Cortex
– Limbic system
– Brainstem
• Pain perception occurs in the cortex
What happens during modulation as one of the 4 steps of pain physiology?
- Descending pathway from brain to dorsal horn
* Usually decreases pain signal
What is the “second relay station” for pain?
Thalamus
What is the “first relay station” for pain?
Dorsal horn
Compare peripheral vs. central neuropathic pain
• Peripheral
– Damaged nerves (e.g. trauma, diabetes)
– Abnormal firing of nerves
• Central
– Changes in “wiring”
– Abnormal firing
– Loss of modulation
List (6) medications used for analgesia
Paracetamol (Acetaminophen) NSAIDs Opioids Tramadol Amitriptyline Anti-epileptic drugs
Describe paracetamol as an analgesic
- mechanism of action
- indications
- SE
- drug interactions
- monitoring
• Mechanism of action
– Unclear but acts in CNS
– Inhibits peripheral prostaglandin synthesis
– Analgesic and antipyretic
• Indications
– Analgesia either alone or in combination
• Adverse effects
– Hepatic necrosis
• Drug interactions
– Effects are additive with NSAIDs
• Monitoring
– Safe dose is up to 4 g per day in adult
Describe NSAID as an analgesic
- mechanism of action
- indications
- SE
- drug interactions
- monitoring
• Mechanism of action
– Non specific inhibition of COX1 & 2 to inhibit PG synthesis
– Analgesic, antipyretic, anti-inflammatory
• Indications
– Analgesia alone or in combinations
• Adverse effects – Peptic ulceration – Renal impairment – Anti platelet action – Bronchospasm in asthmatics – Exacerbation of CCF
• Drug interactions
– Reduce opioid requirements by 20-40%
• Monitoring
– Care with renal impairment or hypvolaemia
Describe opioids as an analgesic
- mechanism of action
- indications
- SE
- drug interactions
- monitoring
• Mechanism of action
– Mu opioid receptors to produce analgesia
– Site of action is the peripheral nociceptors, dorsal horn, cerebral cortex and descending tracts
• Indications
– Severe pain
• Adverse effects
– Sedation, respiratory depression
– Nausea, euphoria, miosis, bradycardia, postural hypotension, urinary retention
• Drug interactions
– Other sedative agents
• Monitoring
– Sedation, CV and respiratory
Describe tramadol as an analgesic
- mechanism of action
- (+)
- (-)
• Weak opioid effect plus inhibitor of serotonin and noradrenaline reuptake (modulation) -> hence do NOT use with SSRI/SNRI.
• Advantages
– Less respiratory depression
– Can be used with opioids and simple analgesics
– Not a controlled drug
• Disadvantages
– Nausea and vomiting
Describe amitriptyline as an analgesic
- mechanism of action
- (+)
- (-)
• Increases descending inhibitory signals
• Advantages
– Cheap, safe in low dose
– Good for neuropathic pain
– Also treats depression, poor sleep
• Disadvantages
– Anti-cholinergic side effects (glaucoma, urinary retention)
Describe anti-epileptic drugs as an analgesic
- examples
- mechanism of action
- indications
- Carbamazepine (Tegretol)
- Sodium valproate (Epilim)
- Gabapentin/Pregabalin
• “Membrane stabilisers”
– Reduce abnormal firing of nerves
• Good for neuropathic pain
What is The RAT Approach to Pain Management?
- Recognize (does the pt have pain?)
- Assess
- Treat (non pharm & pharm)
How do you assess pain?
• Measure the severity
– What is the pain score?
• At rest
• With movement
– How is the pain affecting the patient?
• Can the patient move, cough?
• Can the patient work?
Measurement of severity: verbal (mild, moderate, severe), numerical, visual
How do you treat pain non-pharmacologically?
Non-Drug Treatments – RICE: Rest, ice, compression, elevation of injuries – Nursing care, physiotherapy – Surgery, acupuncture, massage, TENS – Psychological • Explanation and reassurance • Input from social worker / pastor • Relaxation, imagery, distraction • Coping strategies
How do you treat mild nociceptive pain pharmacologically?
• Paracetamol (± NSAID)
How do you treat moderate nociceptive pain pharmacologically?
• Paracetamol (± NSAID) + codeine/oxycodone/tramadol
How do you treat severe nociceptive pain pharmacologically?
- Paracetamol (± NSAID) + morphine/oxycodone
- Regional anaesthesia
- Adjuvants (alpha 2 agonists, NMDA antagoinists)
How do you treat neuropathic pain pharmacologically?
– Traditional drugs may not be as useful – Use other drugs early • Amitriptyline • Carbamazepine • Gabapentinoids
Don’t forget non-drug treatments
Which sites are you targeting in multimodal drug treatment?
Peripheral nociceptors
Peripheral nerves (A-delta, C)
Dorsal root ganglia
Dorsal Horn
Ascending tracts
Cortex
Descending inhibitory modulation
