Post Op Pain Relief Flashcards
Define pain
An unpleasant sensory emotional experience associated with actual or potential tissue damage or expressed in terms of such damage
What is chronic pain
Duration exceeding 6 months or persisting beyond the time for tissue healing
What are the 3 aspect to pain
Physical - damage
Emotional
Rational- makes to sense to avoid painful things
Which spinal pathway is the pain pathway
Spinothalamic
1st Order neurone - periphery to spiral cord
2nd order is spinohalamic tract to the thalamus
3rd order thalamus to the cortex
What are the somatosensory pain transmitting neurons
A delta - 12-30m/sec- mechorecptors and nociceptors C fibres (0.5-2m/sec) mechanorecptors and nociceptors B fibres sympathetic preganglionic fibres A beta (30-70m/sec) cutaneous touch and pressure
What is somatosensory pain
Cutaneous, well localised, sharp, pain from deeper structures, less well localised
What is visceral pain
Poorly localised, often referred to surface are innervated By the same spinal segment
MI radiated to arm/neck
What is sympathetically maintained pain
Difficult to mx excessive sympathetic stimulation is interpreted or augmented painful stimuli
What do A beta fibres do
Normally they are no involved in signalling noxious stimuli but can do under abnormal conditions
They are more resistant to local anaesthetic blockaded that A delta and C fibres
This explains how patient under spinal or epidural analgesia may sense touch and movement but not pain and temperature. When all fibres but A alpha motor neurones are blocked patients move toes on command but will be unaware of doing so
What do A delta fibres do
Transmit faster
Are more readily injured by pressure and ischaemia
- sciatica
What are C fibres
More easily blocked by local anaesthetics so it is possible to remove sensation of pain and temperature leaving light touch/movement intact
Chemostry of pain - acute tissue trauma causes the release of what
Tissue injury factors
Inflammation
The contents of cells injury can be extruded and other inflammatory signalling pathways activated
K+, H+, bradykinins, ATP, prostaglandins, 5-HT, histamine, cytokines IL1,6,8 and TNF alpha, NGF
Neurochemistry of sensory neurones
Neuro peptides and neurotransmitters
Substance P, excitatory amino acids, glutamate and aspartate
Na+, K+ and Ca2+ channels are of major importance
What is the gate theory of pain
Noxious stimuli sensed by C fibres these are projected to the spinothalamic tract
A alpha and A beta fibres are stimulated by non-noxious mechanoreceptors
There act as an inhibitor interneurone to the C fibre reducing transmission to the spinothalamic tract reducing nociception
Examples of gate theory of pain in clinical practise
TENS machine
What is preemptive analgesia
Theory - preventing noxious stimuli from reaching the spinal cord and CNS, central sensitisation will not occur this minimises neuronal changes, reducing post op pain
In practice LAnfiltation in to tissues prior to incision, block of peripheral nerves or nerve plexus should epidural or spinal injury LA with or without opioids
In major studies a reduction in post op pain has been seen and faster discharge etc
What are NSAIDS
They are cycloxygenase inhibitors Good in body wall and orthopedics Excellent opioid sparing effect SE Peptic ulcers Broncospasm Renal failure - block prostaglandin renal failure if you become hypotensive then the renal arteries cant respond Interstitial nephritis
Opioids what are they
Good visceral analgesics poor somatic analgesic
Analgesia by the mu receptor
All except bu[renorphine have the same effects
Toxicity manifest as slow resp rates and large tidal volume
Shift in CO2 response curve upwards
Undesirable affects of opioids
Tolerance Dependence Dysphoria N/V Smooth muscle spasm Constipation Resp depression Depress cough reflex (desirable in palliative care) Muscle rigidity
