5. Perioperative Pain Management

Question 1

1. Identify the 5 steps of the pain pathway and types of pain

Answer 1

transduction, transmission, modulation, projection, perception
Types: somatic v. visceral; acute v. chronic(pathologic)

Question 2

2. Be aware of options for assessing pain in small animals

Answer 2

• get pre and post op pain scores
• many systems: simple descriptive, numerical, visual analog (have the same trained observer score the pain for these 3)
• Also glascow (multidimentional), CSU feline acute pain scale (non verified yet)

Question 3

3. Know common drugs and MOA used for small animal analgesia

Answer 3

1. Opioids - (modulation, dorsal horn) full mu, partial, ag/antag
2. NSAIDs - block COX (transduction and modulation)
3. local anesthetics - Na channel blockers (Transmission) (Also systemically, MOA unknown)
4. NMDA antagonists (modulation) help with chronic/neuropathic pain, and prevent windup
5. alpha 2 agonists - (modulation) alpha 2 receptor in cord, brain, and periphery, may have local anesthetic effects

Question 4

4. Define Multimodal analgesia and be able to develop an analgesic plan for perioperative patient care

Answer 4

use different MOA drugs to cover multiple parts of pain pathway
- some drugs work synergistically to decrease doses, cost, drug consumption

Question 5

side effects of full mu agonists

Answer 5

respiratory depression, bradycardia, dec. GI motility

Question 6

partial my agonists

Answer 6

buprenorphine, tramadol, has a ceiling effect

Question 7

agonist-antagonist opioids

Answer 7

not very effective

Question 8

alpha 2s in small animals v. other species

Answer 8

not good enough for primary method of pain control in small animals, adjunctive only.

Question 9

nmda antagonists

Answer 9

ketamine
amantadine - oral
methadone (nmda and full mu)

Question 10

adjunctive agents for pain control

Answer 10

1. gabapentin (modulation - CNS Ca channels) neuropathic/chronic pain
2. Acetaminophen (COX3, maybe cannabinoid receptors)
   NOT IN CATS -> MetHbemia
3. Maropitant - NK1 antag, may do some visceral analgesia

Question 11

What happens to arachadonic acid after tissue injury?

Answer 11

broken to thromboxanes, PGFs from COX

Question 12

COX1

Answer 12

constitutive enzyme, always there

produces PGE2, I2, TXA2 (prostanoids for homeostasis in kidneys, GI, platelets)

Question 13

COX2

Answer 13

Inducible Enzyme, upregulated with inflammation (though technically still constitutive)
produces PGE2, PGI2, also for homeostasis (GI ulcer healing, renal BF)

Question 14

COX constitutive enzymes?

Answer 14

Both of them!!! They’re both needed, both important for homeostasis

Question 15

Inhibitory Ratio of nsaids

Answer 15

plasma concentration needed to inhibit Cox1:cox2

Because it was thought to minimize side effects by targeting COX2

Question 16

Which drugs target Cox2?

Answer 16

the ones that end in -oxib are actually cox2 preferential
(carprofen only mildly cox2 preferential)
BUT THEY STILL BLOCK COX1 SOME

Question 17

Basic pharmacokinetics of NSAIDs

Answer 17

1. good bioavailability PO, but feeding alters (give carprofen with food, robenacoxib fasted)
2. heavily protein bound (reduce dose in hypoproteinemic)

Question 18

plasma concentration of nsaids ________ reflect analgesic property

Answer 18

do not

Question 19

GI side effects of nsaids

Answer 19

cox1 - maintains cellular integrity
cox2 - repairs GI mucosa
- inappetance, v/d, inflam, melena, ulceration, perforation
** most common reason to discontinue nsaids

Question 20

risk factors for GI injury with NSAIDs

Answer 20

• inappropriate dosing
• given with steroids
• given with pre-existing GI disease

Question 21

risk factors for GI injury with NSAIDs

Answer 21

• inappropriate dosing
• given with steroids
• given with pre-existing GI disease

Question 22

Tx for GI side effects nsaids?

Answer 22

• discontinue
• palliative (fluids, bland diet)
• give H2 blocker/Famotidine or PPI/omeprazole, pantaprozole (if signs of ulceration, like melena)
• misoprostol (PGE1 analog for GI integrity)
• use different nsaid in future
• alternative analgesia

Question 23

renal effects of nsaids

Answer 23

not directly nephrotoxic but can cause AKI. regulate BF to kidney and amount of diuresis

Question 24

use nsaid in cats with mild/mod chronic renal disease?

Answer 24

yes with oral low dose

Question 25

risk factors for causing renal injury with nsaids

Answer 25

preexisting hypovolemia, dehydration, shock
preexisting disease
inappropriate dose
steroids
general anesthesia

Question 26

hepatic effects of nsaids

Answer 26

idiosyncratic reaction (not related to dose) 
inc. enzymes, bili

Question 27

coagulation effects of nsaids

Answer 27

cox1 prod thromboxaneA2

they can affect platelet coag, but only ASPIRIN is real concern, irreversibly bind COX1, needs 7 day wash out period

Question 28

Acetaminophen

Answer 28

• central acting cox inhibitor, no GI, kidney, platelet effect
• bioavailability is poor, not good for analgesia
• NOT IN CATS, they have to use sulfonidation with causes oxidative damage (toxic dose is super high in dogs however because they can do glucaronidation)

Question 29

galliprant

Answer 29

approved in dogs only
specific for EP4 receptor, does not inhibit cox/prostaglandins
high margin of safety

Question 30

When to give?

Answer 30

if preop, synergism with opiods, pre-emptive analgesia, but more adverse effects during surgery
(pro and con to both)

Question 31

should you give if post op

Answer 31

not if uncontrolled hemorrhage, intra-op hypotension, renal/GI surgery

Question 32

long term nsaids?

Answer 32

frequently recheck bloodwork and do UA before starting. discontinue if animal is not improving

Question 33

Should you change nsaids if you have adverse reaction to first?

Answer 33

yyeeaahhh

7 day waiting period (not proven, except for aspirin)