anaesthesia 9 - perioperative pain management Flashcards
what are the 4 main pillars why we should do it?
- ethical
- professional - we agree to it as a vet.
- legal - must recognise and treat all pain as much as we can.
- clinical/practical
why do we use perioperative pain management? (4) pain = catecholamine release.
- facilitates the prep and examination of animals
- reduces risk of personal injury
- reduces induction problems
- smooths induction in horses (not so violently)
why would some people choose not to do it?
- fear of adverse drug affects
- fear of adverse drug interactions
- premature damage of place of interest if not painful = weight on it
- results in recumbency if sedation
- obfuscated diagnosis
- inconvenient
- cost?!
- attracts burglary if have eg. morphine around
what does it prevent if done correctly?
‘wind up’ - intensified pain after op. (sensitized_
nociception - dysrhytmias, hypertension, bleeding, reduced renal blood flow, reduced liver flow, ileus (colic) - pain shuts down gut if no analgesia.
reflex movement prevented.
also prevents? eg. appetite? -ve energy and protein? immunosuppressed? sleep? ventilation?
pain would impair appetite
causes negative energy and proteins which impair wound healing and cause muscle wastage.
pain causes immunosuppression
pain impairs ventilation (eg. if sore chest wall)
what are the main advantages of analgesia (effective pain management)?
improves animals activity
simplifies nursing
allows repositioning - lowers lethargy and hypostatic lung congestion.
allow wound inspection and dressing
reduces vocalisation
imporved recovery in horses - impaired if painful
prevents abortion (glucocorticoids released in pain = abortion)
2 types of sensitization?
peripheral (at the wound) and central (dorsal horn - substantia gelatinosa)
what is sensitization?
phenomema of this exerts the opposite effect to endorphins/ enkephalins. (reduce pain to help you get away)….instead it causes increased pain and memory of this! amplifies the pain experience.
peripheral sensitization?
at the wound. begins when noxious stimulus activates PLA2. which releases arachidonic acid - acted upon by lipoxygenase to produce leukotrienes and lipotoxins. these cause vasodilation and increase permeability. plus they cause COX to produce prostaglandins. these form the basis of the ‘sensitizing soup’ which has thromboxanes PG’S. LT’S, Cox, SEROTONIN, substance p, bradykinin. these all increases sensitivity of peripheral nociceptors and so amplify pain here. - less intense stimuli initiate a response and a signal is sent to the spinal relay centre.
central sensitization? how can you prevent NMDA receptors? how does it happen (4) and what does it result in?
pain impulses at dorsal horn initiates complex cell changes within grey matter.
- adrenoreceptor induction
- gene expression
- axonal sprouting
- NMDA receptor proliferation (pain). in spinal cord. - prevent by ketamine!!!!
results in enhancement of post operative pain experience - post injury pain, hyperalgesia, allondynia (even touch = painful) neuropathic pain!!! (phantom limb) may become permanent of fade.
if sensitization is prevented then?
no post-operative pain!!
what doesnt anaethesia do necessarily?
- not an analgesia
- drug and dose dependant
- if poor analgesic then allows - nocifesive responses, depression at high doses, do not prevent sensitisation, do not supress post op pain!!
4 ways to optimize peri-operative comfort?
- PEA - Pre-empitive analgesia
- PMPT - polymodal pain therapy
- PIVA - partial IV anaesthesia
- PPOPT - prolonged post operative pain therapy.
what is PEA?
pre-emptive analgesia - giving them before surgery/ any pain. giving NSAIDS prevents ‘sensitising soup’ forming and LA given between the surgical site the the neuraxis will stop pain!! not always possible to do if trauma incident.
what is PMPT - ? eg?
Polymodal pain therapy - uses more then one drug so allows minimal use of the main drug and so less side effects. provides total analgesia, synergistic drug effects, while at the same time reducing the likelyhood of side effects. eg. c-section and cattle - lidocaine, alpha 2 agonist, flunixin and clenbuterol.
