Analgesia

Question 1

What are the cornerstones of peri-operative pain management?

Answer 1

1. Pre-emptive analgesia; ie that which is applied before the painful stimulus. This approach may help to reduce the likelihood of development of central sensitisation

2. Multi-modal analgesia; lower doses of individual drugs can be used by taking advantage of additive and synergistic effects that certain drugs show when given together with a consequent reduction in side effects. Includes use of locoregional anaesthesia

Question 2

COX 1 and 2 enzymes result in the formation of what from what?

Answer 2

Result in the formation of prostanoids (prostaglandins and prostacyclins) from arachadonic acic (AA)

NB AA is freed from cell membrane phospholipids through the action of PLA2 enzyme. This step is inhibited by corticosteroids

Question 3

Potential benefits for the use of COX-2 selective NSAIDs.

Answer 3

Preseveration of COX-1 function (which is constitutively expressed vs the inducible COX-2) should preserve COX-1 functions incl. coagulation, protection of gastric mucosa and maintenance of renal blood flow

However there is evidence to demonstrate superior analgesia with inhibition of both COX isoenzymes vs COX 2 alone

Question 4

Potential adverse effects of NSAIDs

Answer 4

Gastric ulceration, renal dysfunction (hypotensive effects may rx in causing papillary necrosis (a feature in most cases), chronic interstitial nephritis, and chronic tubular interstitial nephritis, and right dorsal colitis

Sequential monitoring of serum and urine albumin and protein respectively may be the most sensitive way of monitoring at risk horses during treatment.

Question 5

MOA, pros and cons of buprenorphine vs butorphanol

Answer 5

Buprenorphine - partial µ agonist (high affinity, low efficacy)

+ longer duration of antinociception to thermal stimuli than butorphanol

• more side effects when used as CRI w detomidin for standing procedures, incl. box-walking, muscle tremors or shivers and approx half of the horses were hypersensitive to noise vs morphine

Butorphanol - µantagonist, 𝞳 agonist. Analgesic doses may be as high as 0.1-0.2mg/kg

Question 6

Pros and cons of fentanyl patches and optimal site of application

Answer 6

Most appropriate site is on the thorax. Should clip and prep the skin first (obv not req in humans), altohugh this is often impractical and easier to maintain on a limb under a bandage

The variable lag time and systemic absorption means that the use of transdermal fentanyl patches requires close attention to the monitoring of pain scores, but may be useful for long-lasting analgesia of outpatients post-operatively

Question 7

Ketamine analgesic MOA and potential benefits

Answer 7

Used at sub-anaesthetic doses, analgesia effects are through NMDA receptor ANTAGONISM

Dose is 0.4-0.8mg/kg/hr

In chronic pain states, NMDA receptor antagonism limits the development of central sensitisation by inhibiting temporal summation and secondary mechanical hyperalgesia

Has been used in naturally occurring laminitis - 0.6 mg/kg/h ketamine for 6 h once daily for 3 days, alongside tramadol twice daily, increased forelimb loading was found both during and after treatment and this was attributed to ketamine’s effect on reducing central sensitisation