Pre-Meds II Flashcards
Sedation/excitation occurs at what level?
Supraspinal - this is species/dose/breed dependent
What are opioids derived from and how are they metabolized?
Derived from opium or synthetic; Hepatic metabolism (except remifentanil)
Where are opioid receptors located and what are they?
CNS and peripheral NS; Mu, kappa, and delta
What are the respiratory effects of opioids?
- Respiratory depression - dose dependent
- careful in patients with intra-cranial dz or resp dz
Are opioids anti-tussive?
- Yes; allows ET tube tolerance, but may incr risk of aspiration
- Makes them useful for procedures like: tracheal stent, bronchoscopy, BAL
What are the CV effects of opioids?
- Bradycardia/AV blocks
- incr parasympathetic tone
- easily treatable w/ anticholinergics
- otherwise - MINIMAL CV effects
*opioids can be safely used in patients with CV dz/instability!! - EXCEPT those w/ life threatening bradyarrhythmias/pacemakers
What are the effects of opioids on pupillary diameter?
Miosis (mydriasis in cats)
What are the GI effects of opioids?
- Nausea/vomiting
- both anti-emetics (emetic center) AND pro-emetics (CTZ)
- the more lipophilic they are, the faster they reach the emetic center —> the LESS they vomit
- ALL are lipophilic - hydromorphone and morphine are LEAST lipophilic = MOST likely to cause vomiting
What are the effects of opioids on gastric motility?
- They cause ileus
- may initially cause incr large bowel movement (dogs + cats)
- incr signs of colic - untreated pain also causes ileus!!
What can be used to combat opioid-induced ileus?
Methylnaltrexone = opioid antagonist
- does not cross BBB, reverse ileus w/o reversing CNS effects
By acting on spinal, supraspinal, and peripheral receptors, opioids _________ pain transmission to the brain
Modulate
What are common side effects observed with opioids?
- dysphoria
- resp depression
- bradycardia
- nausea/vomiting
- aspiration pneumonia
- ileus
- urinary retention
- hyper/hypothermia
- hyperalgesia
What are the effects of opioids on urinary system, immune system, histamine releases, and thermoregulation?
- Urinary: urinary retention (can be reversed with naloxone)
- Immune system: suppression vs. stimulation
- Histamine release: morphine, meperidine +++, pruritis after neuraxial admin
-
Thermoreg:
- hypothermia - change set point in hypothalamus (dogs pant but re not hot)
- hyperthermia - cat, ferret, swine, horse, wild (capture)
What are the main reasons to use opioids as premeds?
- They are sedatives - esp if combined w/ alpha2 agonists/ace
- contribute to intra-operative analgesia
- MAC sparing effects
- Minimal CV effects
- Can contribute to smooth, pain-free recovery
Which opioids are classified as full mu agonists?
Morphine, Hydromorphone, Oxymorphone, Methadone, Fentanyl, Remifentanil, Tramadol
What is the general MOA of full mu agonists and why are they used as pre-meds?
They elicit maximal activation of mu receptors; used for moderate-severe pain, and often be used alone as a pre-med or in combo with ace or alpha2 agonists
Describe the effects of morphine
- lasts about 4 hrs
- H release: slow IV admin
- Nausea/vomit
- Can be given many routes:
- IV, IM, SQ, CRI
- Neuraxial - long duration, urinary retention, pruritus
- Intra-articular
- On cornea
What are the effects of hydromorphone?
Nausea/vomiting
More potent than morphine
What are the effects of oxymorphone?
Less nausea/vomiting/H release
More potent than morphine
What are the effects of Methadone?
- Lasts about 4 hrs
- Less nausea/vomit
- No H release
- Also NMDA antagonist
Describe fentanyl and the different routes it can be given
- IV (often give a bolus to patients w/ catheters in already)
- Epidurally - less urinary retention, lasts < morphine
- Not IM/SQ
- Short duration = CRI
- Trans-dermal patches: off label, lag time 12 h, duration 72 hr
How is Remifentanil given, and for what types of patients is it often used? Duration?
- IV only!
- used in patients with severe liver disease
- Lasts 3-5 min = CRI/IV only!
- broken down via hydrolysis by plasmatic esterases
*rarely used as a pre-med
Describe Tramadol, its MOA, and what is it’s active metabolite?
- Synthetic weak mu agonist
- MOA: NE and serotonin re-uptake inhibitor
- Active metabolite: o-desmetyltramadol
- more potent mu agonist - works better in cats
What are ultra potent opioids used for and what are two examples?
used for capture; Etorphine and carfentanil
Describe Etorphine
- 4000 times more potent than morphine
- antagonized with diprenorphine
Describe Carfentanil
- 10000 times more potent than morphine
- Antagonized by naltrexone
Describe Buprenorphine and some of its effects
- a long-lasting partial agonist (6-8hrs)
- binds tightly to mu receptor - hard to antagonize
- causes minimal sedation/resp depression
- no nausea/vomiting
- good oral/trans mucosal absorption in cats
* only use for mildly painful procedures/peri-operative management!
What is the FDA approved extended release formulation of buprenorphine?
Simbadol - one SQ dose = 24 hr analgesia
What is an example of a agonist-antagonist opioid?
butorphanol
Describe butorphanol
- MOA: agonist at k receptors, antagonist at mu receptors
- limited analgesic effect - often used in horses
- good sedative/anti-tussive
- does not cause emesis
- 2 hr duration
T or F: Butorphanol is a good choice as a pre-med if a patient needs surgery
False! Should only be used for non-painful procedures
What are three opioid antagonists?
Naloxone, Naltrexone, Diprenorphine
Descrbie naloxone
- most commonly used opioid antagonist
- works well on full mu agonists
- will also revere analgesia!! (use low doses to maintain during recovery)
Describe naltrexone
long acting opioid antagonist for Carfentanil
Diprenorphine is an antagonist for what opioid?
Etorphine
What two opioid can be used to reverse side effects of full mu agonists while retaining analgesia?
butorphanol and buprenorphine
I have a dog presenting for acute onset of incoercible vomiting. I suspect a GI obstruction and need to sedate the dog for rads. If the obstruction is confirmed, I will then send the dog to surgery. What opioid should I use for sedation?
A. Butorphanol
B. Buprenorphine
C. Morphine
D. Methadone
D; morphine makes you vomit, butorphanol is a poor analgesic, buprenorphine is not a great analgesic either
What is the main MOA of NSAIDs?
MOA: inhibit eicosanoid production by inhibiting COX
T or F: COX-2 inhibition does not completely eliminate the side effects associated with classical NSAIDs
T - only measure of safety of COX2 selective NSAIDs over COX1 refers to their GI effects
What are the GI side effects of NSAIDs?
- GI injury - most common SE
- due to prostaglandin inhibition–> direct mucosal irritation
- Signs: V/D, inappetence, melena, hematochezia
- Risk factors: concomitant admin of 2 diff NSAIDs or NSAID + corticosteriod; high doses
What are the kidney side effects of NSAIDs?
- kidney injury
- role of prostaglandin - regulation of GF/RBF
- Most likely - severe/persistent hypotension, low flow states
What are the hepatic effects of NSAIDs?
- hepatotoxicity
- idiosyncratic, unpredictable
- Intrinsic - predictable, dose-related
- most commonly reported with carprofen
What are the effects of NSAIDs on coagulation?
- Inhibition of COX1 = decreased TXA = platelet dysfunction
- aspirin - most selective COX1 inhibitor (plt take 9 days to reform)
- COX2 inhibitors are actually pro-coagulants
- AA metabolism produces TXA = incr plt fxn and vasoconstriction
What are the contraindications of using NSAIDs for pre-meds?
- Pre-existing:
- GI dz, kidney dz, hepatic insufficiency
- Decr effective circulating volume
- Recent/concurrent steroid/other NSAID tx/nephrotoxic drug
- MCT
- Coagulopathies
- Pediatric patients (Carprofen)
What are some things to consider when giving NSAIDs perioperatively?
- they treat pain/inflammation
- when giving to patient already on NSAIDs as a pre-med–> higher risk of PONV and normal BP must be maintained
- commonly given peri-operatively to horses
My patient has OA and is receiving carprofen. I am about to anesthetize it for a TPLO. What considerations should I keep in mind for this dog during anesthesia?
A. Carprofen will contribute to perioperative analgesia
B. I need to monitor BP thoroughly and be proactive in treating hypotension
C. I will administer IVF to this patient
D. It may be beneficial to give this patient a gastroprotectant
E. All the above
E
Which NSAIDs are approved for cats and dogs?
- Carprofen (dogs > 6 wks)
- meloxicam (chronic use in cats may cause AKF)
- Rovenacoxib
Which NSAID is for use in dogs only?
Deracoxib
Which NSAIDs can be used in large animals?
- Carprofen (horses and cattle in Europe/Asia)
- Meloxicam
- Firocoxib
- Flunixin meglumine (only FDA approved NSAID for cattle)
- Phenylbutazone (illegal in dairy cattle >20 mo; fine in horses)
In healthy small animals, ___ sedation is used to facilitate IV catheter placement
IM
Healthy (ASA I or II) Protocol in Dogs
you need something to sedate them IM so you can place an IVC
- Pick a sedative (alpha2 agonist) or tranq (ace)
- Add an opioid
- If aggressive consider adding hypnotic
ASA > III (neonatal, geriatric) Protocol in Dogs and Cats
- will likely be able to place an IVC w/o any sedation
- pick a combo w/ minimal CV effects
- opioid + benzos
Healthy (ASA I or II) Protocol in a Cat
- typically need higher dose of sedatives vs dogs to accept IVC
- pick a sedative (alpha2 agonist) - ace only in well behaved cats
- add an opioid
- if aggressive, consider adding hypnotic
Practical tips for sedating horses
- most tolerate IVC w/o no sedation
- aggressive horses:
- IV injection of alpha2 agonist +/- butorphanol
- detomidine gel (PO)
- tiletamine/zolazepam + alpha2 agonist for very aggressive (need padded box)
- need to be very well sedated prior to indution of gen anesthesia
What are signs of adequate sedation in horses?
- head is below shoulder
- not interestd in surroundings
- ptosis
- glazed eyes
- don’t chew or pull tongue back in
Tips for sedating small ruminants
- typically tolerate jugular cath placements w/o sedation
- a combo of opioid + benzo works well
- alpha2 agonists may cause pulm edema
Tips for sedating cattle
- well tolerate IVC placement w/o sedation when restrained appropriately
- calves will sedate w/ combo of opioid and a benzo
- adult cows sedate w/ combo of xylazine and opioid (go down with xylazine)
Tips for sedating swine
- need to be heavily sedated to accept IVC
- Hypnotics often useful for pre-med
- ketamine
- alfaxalone
- Sedate with benzos
- dexmedetomidine
- ketamine
- midazolam
