Pain and Analgesia Flashcards
Why is pain provided to an unconscious patient?
- Pain wakes you up
- Prevention of arousal
- Suppression of reflex responses to a painful stimuli eg tachycardia, hyperension
When would you consider giving paracetamol for pain?
Mild to moderate pain. Often used by anaesthetists both intra and post-operatively as part of the patient’s analgesic regime
What is the WHO pain ladder?
Structured approach to pain management, starting off with non-opioads, preogressing to weak opiods, then strong opiods
Descrine WHO pain ladder
-
Non-opiod
- Aspirin
- Paracetamol
- NSAIDs - ibuprofen
-
Weak opiod
- Codeine
- Dihydrocodeine
- Tramadol
-
Strong opiod
- Morphine
What is the definition of acute pain?
Pain of recent onset and probable limited duration, and is usually the result of a clearly defined cause such as an injury.
What is the definition of chronic pain?
Pain that lasts for >3 months
What are the pain conducting fibres in peripheral tissue?
- A-delta fibres
- C-fibres
Which type of fibre conducts pain signals faster?
A-delta
- Aδ = small myelinated (5-30m/s) cold, “fast” pain, pressure
- C = unmyelinated fibres (0.5-2m/s) warmth, “slow” pain
What tracts do pain fibres travel in in the spine?
Lateral spinothalamic tracts
Where do pain fibres cross to enter the spinothalamic tracts?
Same level as where the fibres enter, or a few levels above point of entry
How many nerve fibres are there in the afferent nerve fibre tracts for pain?
3 nerve fibres
Which order neuron crosses at the level of entry?
2nd order neuron
What types of nerve endings are nociceptors?
Free nerve endings in the skin whose ion channels are sensitive to a variety of chemical, mechanical and thermal stimuli
What is the gate control theory of pain?
Aβ fibers carrying sensory information about mechanical stimuli help block pain transmission. These synapse on the inhibitory interneurons and enhance the interneuron’s inhibitory activity.
If simultaneous stimuli reach the inhibitory neuron from the Aβ and C fibers, the integrated response is partial inhibition of the ascending pain pathway so that pain perceived by the brain is lessened.
The gate control theory explains why rubbing a bumped elbow or shin lessens your pain: the tactile stimulus of rubbing activates Aβ fibers and helps decrease the sensation of pain
What descending pathways are involved in pain modulation?
Descending pathways from the peri-aqueductal grey matter and nucleus rapheus magnus. They inhibit nociceptive neurones in spinal cord. (5-HT)
What is the theory behind referred pain?
Visceral pain is often poorly localized and may be felt in areas far removed from the site of the stimulus e.g. pain of cardiac ischemia may be felt in the neck and down the left shoulder and arm due to multiple primary sensory neurons converge on a single ascending tract.
When painful stimuli arise in visceral receptors, the brain is unable to distinguish visceral signals from the more common signals arising from somatic receptors. As a result, it interprets the pain as coming from the somatic regions rather than the viscera
How would you manage neuropathic pain?
Offer a choice of amitriptyline, duloxetine, gabapentin or pregabalin as initial treatment for neuropathic pain
If the initial treatment is not effective or is not tolerated, offer one of the remaining 3 drugs, and consider switching again if the second and third drugs tried are also not effective or not tolerated
How to rate pain
- Pain assessment
- Numerical rating scale (0-4)
- Verbal rating score
