Pain relief and peri-operative pain relief Flashcards
What are three aspects to pain?
Physical
Emotional
Rational
Or if you're on palliative care Physical Social Psychological Spiritual
What are nociceptors?
These are free nerve endings in the skin, muscle and viscera which detect pain
What activates nociceptors?
Noxious stimuli
What type of pain is carried by C fibres?
Dull, poorly localised, visceral pain.
They are unmyelinated
What type of pain is carried by delta fibres?
Precise, well localized, sharp pain. This is called somatic pain, they are myelinated and signals travel fast.
Outline the gate-theory of pain
Local inhibitory interneurons modulate the activity of other neurons and prevent ascending pain signals being sent unless the inhibition is overcome. The gate is opened once this inhibition is overcome.
This is tonic inhibition.
Why does mechanoreceptor stimulation reduce pain?
This is the sensation where rubbing and injury causes the pain to reduce.
It is because the Abeta fibres of mechanoreceptors increase the inhibition by interneurons and reduce ascending signals
How does transcutaneous electronic nerve stimulation work?
Stimulation of the Abeta mechanoreceptors which increase the inhibition of interneurons in the spinal cord. This reduces ascending pain signals.
How many neurons are involved in pain signalling?
These are three neuron pathways.
What spinal cord tract carries pain?
The spinothalamic tract
Outline the route of the spinothalamic tract
First neurone enters the spinal cord and ascends descends within Lissauer’s fasciculus
Enters the dorsal horn and synapses with secondary neuron
Second neurone decussates and ascends to the thalamus
Synapses with third order neuron at the thalamus.
Third order neuron runs to the sensory cortex/post central gyrus
What chemical signals between the neurons responsible for pain?
Substance P
Excitatory amino acids such as glutamate and aspartate
How does the descending pathway modulate pain?
Descending pathway modulates the activity of first and second order neurones to reduce pain signalling
What neurotransmitters are involved in the modulation of pain transmission at the dorsal root ganglion? (Between first and second order neuron of the spinothalamic pathway)
Noradrenaline
Serotonin (5-HT)
What is hyperalgesia?
Sensation of pain is greater, lower thresholds
What is allodynia?
Sensation of pain is felt for normally non-painful stimuli
How does inflammation increase pain?
Inflammation causes release of inflammatory mediators which reduce the threshold for action potential generation of the first order neuron (these include bradykinin, IL-1, IL-6 and TNF alpha). Results in hyperalgesia and sensation of pain around the injury site.
This is also called peripheral sensitisation
How does central sensitisation occur?
Second order neuron becomes more responsive after prolonged stimulation.
This is due release of glutamate that acts on the NMDA receptor and relieves the voltage dependent Mg2+ block of the receptor, this results in calcium entry which increases neurone responsiveness.
What is the theory of preemptive analgesia?
Preventing noxious stimuli from reaching the spinal cord allows you to prevent sensitization processes and reduce the levels of pain experienced. - thereby reduces the levels of post-operative pain
How is preemptive analgesia achieved?
Local anaesthetic infiltration into tissues before incision is made- prevents sensitisation processes.
Or nerve blocks, epidurals or spinal anesthesia may be used.
+ Opioids
+ NSAIDs to prevent inflammatory pain causing sensitisation
What receptor do opioids act on to cause pain relief?
Mew (that u sign)
What are some side effects of opioids?
Constipation Respiratory depression Good visceral analgesia but poor somatic analgesia Dependence Tolerance Dysphoria
Name some opioids
Morphine Fentanyl Codeine Dihydrocodeine Tramadol
What are some side effects of NSAIDs?
Peptic ulceration
Nephrotoxic
Bronchospasm- May be trigger in asthma
