Pain and analgesia Flashcards

Question

Pain modulation is perceived as

Answer 1

The same painful stimulus can be perceived differently (i.e., more painful or less painful) depending on the individual The signal can slo be altered – either heightened or dampened – as it passes from the periphery to the brain. This is called “Pain modulation”

Answer 2

Peripheral hyperalgesia Central hyperalgesia (aka wind up pain)

Answer 3

Aka primary hyperalgesia, local hyperalgesia Increased sensation of pain Due to inflammation at the site where pain occurred Tissue damage causes inflammation, which results in release of inflammatory mediators, including prostaglandins and substance P These chemicals act on the nociceptors at the original site and decrease their activation threshold (easier to turn on) In other words, the area becomes hypersensitive to further stimulus NSAIDS and steroids are effective at blocking this inflammatory pathway

Answer 4

Aka secondary hyperalgesia, “wind up pain” Occurs with chronic pain Can reduce by providing preemptive analgesia Constant transmission of pain signals along the spinal cord causes pain fibers to become hyper excitable These pain fibers are more readily activated by stimuli originating anywhere in the body. In other words, there is increased perception of pain originating from anywhere in the body Harder to treat and persists

Answer 5

Is a type of hyperalgesia where pain is produced by a stimulus that would not normally cause pain ex. A feather stroking the skin Vs hyperalgesia is an increased sense of pain to something that would typically cause a lower level of pain These responses are associated with what is referred to as neuropathic pain

Answer 6

Using multiple drug watch with a different mechanism of action i.e. each drug targets a different part of the pain pathway

Answer 7

Reduces dose of individual analgesic drugs When used preoperatively, can reduce dose of anaesthetic required Decreased dose means fewer risks and side effects for each individual drug

Answer 8

Pre surgery = preemptive analgesia s part of premed

Answer 9

Main method of pain control is general anaesthesia GA stops conscious perception of pain GA does not block steps 1-3 of the pain pathway Can add local anaesthetic block

Answer 10

Immediately post op (in hospital use) Medication TGH; may be required for chronic use

Answer 11

Administering analgesia before the pain occurs Ex: analgesic as part of the premed Ideally, drugs used for preemptive analgesia should also provide or enhance sedation Preemptive analgesics that do not enhance sedation include, NSAIDs and blocks with local anaesthetics Avoid steroid use pre-op as may impair healing

Answer 12

Opioids- excellent analgesia Alpha 2 agonists - block nociceptors and substance P Ketamine – moderate somatic analgesia

Answer 13

Reduces overall requirements for anesthetic drugs Less CNS depression, fewer GA related drug adverse effects, faster recovery Reduces overall requirement for post op analgesia Decreases dose and duration of postop analgesia Less pain = less stress; decreased psychological costs associated with pain Most effective method of preventing windup

Answer 14

Opioids - Injectable opioids (morphine, hydromorphone, meperidine, butorphanol, buprenorphine, methadone) - Tramadol - Fentanyl patch - Gabapentin Monoclonal antibody therapy (Solensia) Local anaesthetics Ketamine Alpha 2 agonists Anti inflammatories NSAIDS Steroids

Answer 15

Hydromorphone, fentanyl, oxymorphone, morphine, meperidine Butorphanol Buprenorphine Methadone

Answer 16

Butorphanol Buprenorphine Tramadol® Fentanyl patch

Answer 17

Already discussed as a class of premedication Drugs vary in potency, duration of action, side-effects Pure-mu agonists are the best choice for analgesia Kappa-agonist can treat mild to moderate pain Better analgesia if combined with NSAIDs

Answer 18

Sedation Respiratory depression GI stasis

Answer 19

Controlled drugs EXCEPT naloxone, naltrexone Multiple routes of administration: most common are IV (mg/kg as a bolus), CRI (mg/kg/hr), IM, SQ, transdermal, epidural

Answer 20

Comes as a 10mg/ml injectable (5ml vial) Labelled for use as a premedication and for post operative pain associated with ovariohysterectomy and castration in cats Labelled for IM injection only Labelled for use in dogs in other countries, but nor in canada

Answer 21

Mu agonist opioid Binds and activated the mu opioid receptors

Answer 22

Absorption: good absorption following IM injection. If accidental SQ injection, absorption is slower/unreliable Distribution: Very large volume of distribution. Drug likes to accumulate intracellularly in tissues. Metabolism: Primarily metabolized in the liver Excretion: Via the kidneys Although most of the drug is metabolized in the liver prior to excretion, a small amount is not metabolized and is excreted in its active form

Answer 23

Potent analgesic via activation of mu receptors Adverse effects are similar to all other mu agonists Respiratory depression Hyperactivity Occasional hyperthermia

Answer 24

Respiratory or cardiac failure Liver or renal dysfunction Known cases of hypersensitivity

Answer 25

Pure mu-agonist (no kappa activity) 50 – 100X morphine REALLY short acting (20 min if given systemic) Can give as an epidural Can give as CRI for sustained analgesia Can use at higher dose with benzodiazepines or alpha-2 agonists for induction and maintenance Can also SEND HOME in the form of a sustained slow-release patch Continuously releases small amounts of drug to maintain therapeutic levels Side-effects same as for all mu-agonists

Answer 26

Transdermal delivery system Perioperative analgesia for excellent pain control Patches come in set sizes/doses NEVER cut a patch; Can cover half the patch for “half-dosing”

Answer 27

Location: thorax, inguinal, base of tail (D), neck (H) Prepare application site: Close clip, 1 cm clear margins (do NOT apply to skin that is broken) Wipe skin with damp cloth (WATER ONLY) Press firmly with hand for 2-3 min. Cover patch with bandage. Label cover (drug name, dose, time + date of application) Make sure animal cannot eat patch (cover well or E-collar) – watch other pets in the house too. Remove when no longer effective Gloves optional Return to clinic to dispose; may be residual drug present

Answer 28

Dog: 12-24 h Cat: 6-12 h H: 12+h

Answer 29

Dog: 3 d Cat: 5 d H: 2d

Answer 30

NEVER cut patch. For “half dosing”, cover half of patch with a water proof membrane. Make sure animal cannot eat patch (will need to treat for an overdose depending how long after application) Make sure owners do not have opioid sensitivities Do NOT use if fever. Do NOT place heat source next to patch (water bottle). Will increase absorption and risk OD Some patients develop skin reactions where patch was applied Caution with children; bring back for taking off and disposal

Answer 31

mu-receptor agonist Also inhibits reuptake of norepinephrine and serotonin SA use Moderate pain (half the analgesia of morphine) PO only; need to wait for animal to resume eating Onset: 4 hours to reach therapeutic levels Compounded capsule or slow-release human tablet (breaking the tablet or disrupting coating takes away slow release)

Answer 32

Works well in people – not so well in dogs More info is emerging on the use of Tramadol in cats may be more useful than in dogs. However, dosing is challenging (requires compounding)

Answer 33

The opioid and serotonergic agonist analgesic drug has become very popular in veterinary medicine due to a wide therapeutic index and low potential for abuse June 26, 2018

Answer 34

Partial mu-agonist Fewer mu-related s/e than hydromorphone; little dysphoria; good in old/sick cats

Answer 35

Analgesia – mild to moderate pain only Take home opioid for cats

Answer 36

Versatile Can give IV, IM, SQ, epidural Can give sublingual in cats Owner squirts into buccal pouch or under the tongue Drug must be absorbed through the oral mucosa Will NOT work if swallowed Longer duration of analgesia than most opioids (comparable to Tramadol (~ 8h)

Answer 37

Neuropathic Pain Analgesic Also an anticonvulsant Also used for stress/anxiety reduction in cats Mechanism largely unknown Can be helpful in the treatment of chronic pain in dogs or cats Prevent hyperalgesia Good take home option as non-controlled Large range in suggested doses

Answer 38

Sedation most common Starting at a low dose and increasing gradually can diminish this effect Partially metabolized in the liver Renal excretion Caution with renal disease There is an oral liquid form, but it contains xylitol (human formulation) – avoid! Generics available/compounded into capsules

Answer 39

Very new chronic osteoarthritis therapy approved in Canada for use in cats. Made by Zoetis Monoclonal antibody therapy Antibodies provided against Nerve Growth Factor Given as an injection that provides 1 month of pain control Broken down the same way as normal antibodies (protein degradation) so minimal involvement of the liver or kidneys

Answer 40

Drugs that “freeze” nerves Both sensory and motor neurons Analgesia comes from inactivation of nociceptors

Answer 41

Analgesia – significantly decreases GA requirements Local and regional nerve blocks

Answer 42

Inhibits Na+ channels in nerves → stops Na+ influx → neuron cannot depolarize (i.e., cannot turn on) Stops conduction of electrical impulses Requires liver metabolism

Answer 43

Local blocks, Epidurals Used alone for minor surgical procedures Used in combination with other analgesics/anesthetics for pre-emptive/perioperative/postoperative pain

Answer 44

Nerve blocks to diagnose lameness in horses Dental extractions Dehorning Skin tumour removals Sprayed into larynx to aid in intubation (particularly in cats) Regional blocks allow standing surgery such as C-section, etc

Answer 45

All names end in “-CAINE” Lidocaine Mepivicaine Bupivicaine (Marcaine®) Proparacaine (Alcaine® for ophthalmic use) Cocaine

Answer 46

The route of delivery and dose determines which nerves the drug acts on Peripheral sensory nerves → analgesia Peripheral motor nerves → paresis/paralysis Spinal cord → decreases transmission Autonomic nerves → affects autonomic nerve function Systemic delivery to cardiac cells → negative inotrope This can have severe effects ranging from vasodilation to cardiac blockade

Answer 47

Increases analgesia where needed At correct dose, few systemic (e.g., CV) effects Decreases amount of GA required

Answer 48

Tissue irritation, inflammation Temporary to permanent loss of nerve function if injected directly into nerve Intended to “bathe” the nerve Allergy, anaphylaxis Paresis, paralysis Ex. If too large a volume of drug is given in an epidural, will diffuse up the spinal chord → paresis/paralysis of diaphragm and intercostal muscles → stop breathing Systemic overdose can cause fatal heart block or sympathetic block (blocks all sympathetic activity)

Answer 49

No reversals; treatment is supportive care only All the local anesthetics have a toxic dose - Must know when in practice! The max safe dose is set at half the toxic dose The toxic dose in the literature may vary and will depend on whether toxicity is considered to be neurotoxicity or cardiotoxicity or even death. It will also depend on that individual patient and the person administering the drug The toxic dose also depends on whether the drug is being given IV, IM, SQ, epidural, spinal. And, how fast the drug is being given Epidurals and spinals have a maximum volume that prevents drug from diffusing too far up the spinal cord. Goal is to avoid nerves that control cardiac and respiratory function Fast IV has the lowest therapeutic index Any lidocaine spray used for intubation must be included as part of your toxic dose; close to 100% absorption Always err on the side of lowest toxicity. i.e., use lowest dose to get desired effect

Answer 50

There are NO REVERSALS! In the event of an overdose of a local anesthetic, provide supportive care until drug wears off.

Answer 51

Check and recheck calculations Chel the drug bottle Use with proper syringe to measure

Answer 52

Topical and injectable formulations 2 injectable formulations: - Lidocaine neat - Lidocaine with epinephrine

Answer 53

Only contains lidocaine (2%) Can give local, regional, or systemically Short-acting: 20 min – 1 h

Answer 54

Epinephrine causes vasoconstriction so drug stays in area longer Longer-acting: 1-2 h Can only use locally; NEVER GIVE IV

Answer 55

Carbocaine® Injectable Rapid onset (2-5 min); duration of 90 – 120 min Epidural in horses NEVER give more than 10 cc Excess volume will push drug cranially and paralyze diaphragm and intercostal muscles (stops breathing) Can also cause heart block

Answer 56

Marcaine® Injectable or epidural NEVER give IV because cardiotoxic 5-10 min onset; ~2 h duration Used for dental blocks and declaws

Answer 57

CRI and pain drips Epidurals & Para Vertebrals Intra-articular injections

Answer 58

IV bolus - give IV as single dose; may be slow IV (e.g., give single dose over 10 – 20 min) CRI - slow continuous administration of a drug via IV; calculated as mcg/kg/min or ,g/kg/h

Answer 59

Requires patient be on IV fluids Requires a micro-infusion pump Can administer a minute volume of drug at a minute or hourly rate Is used for analgesia and can also be used for injectable general anesthesia

Answer 60

Similar to CRI; Slow continuous administration of drug(s) via IV Does not require a micro-infusion pump Drugs are added directly to an IV bag Amount of drug added is based on the patient’s fluid rate As patient receives fluid, will also receive drugs mixed in with fluids

Answer 61

NEVER leave patient unobserved; there is a lot of drug in the bag, if the rate were to suddenly change patient could receive too much drug too fast and overdose CLEARLY label IV bags with name of all drugs added and how much added ALWAYS use a fluid infusion pump (more accurate)

Answer 62

Drug is injected into the epidural space Blocks the spinal nerves to a particular region Location along spinal cord depends on procedure and spp Provides analgesia (excellent pain control, good duration) hind limbs, pelvis and tail (orthopedic surgery) abdomen (C-sections) caudal thorax Most epidural drugs have a MAXIMUM volume that can be given

Answer 63

Opioids (morphine, fentanyl) Local anesthetics (lidocaine NEAT, mepivicaine) Some alpha-2 agonists (xylazine in LA)

Answer 64

Common for flank approaches in ruminants e.g. C-section, LDA surgery

Answer 65

lower limb in cattle e.g claw amputation anesthetic injected IV below tourniquet which keeps anesthetic at site to diffuse into SC tissue -blocks area below tourniquet.

Answer 66

Injection of opioids and/or local anesthetics into the joint space Indications: - elbow and/or stifle surgery - Equine lameness exams Ex. Morphine + bupivicaine diluted in saline is instilled into a joint via a catheter Immediately after joint closure Provides 8-10 hours postoperative analgesia

Answer 67

Post-operative/traumatic pain Chronic pain treatment (ex. arthritis, cancer)

Answer 68

Route of delivery (fentanyl patch, oral drugs) Side-effects (esp. if chronic use) Addictive potential (opioids are narcotics; patient and client) Disposal and removal of Fentanyl patches Most common: NSAIDs > > gabapentin> buprenorphine, butorphanol, Fentanyl patches, codeine

Answer 69

Used in conjunction with or as an adjunct to pharmacological therapy Acupuncture Transcutaneous electric nerve stimulation (TENS) Massage therapy Apply cold (acute injuries) or heat (chronic injuries) Physiotherapy Chiropractic treatment Laser or magnetic therapy Chondroprotective agents Nutraceuticals / natural health products

Answer 70

Relieving patient discomfort will help pain control Keep patient and cage or stall clean and dry Comfortable bedding/quiet surroundings Opportunity to urinate and defecate Comfortable position May have to turn every 2-3 hours Reduce anxiety with toy or blanket from home Ophthalmic ointment in unconscious patients to prevent corneal drying Comforting reassurance through touch and talking Human contact

Answer 71

SAIDs and to some degree steroids will act as analgesics and anti-inflammatories. **Covered in Pharmacology – not covered/tested in this course** Opioids provide the best analgesia Opioids and NSAIDs are the most commonly used analgesics Local analgesics provide local/regional pain control Steroids provide good analgesia but are seldom used due to the numerous side effects Analgesia is an added bonus when using steroid as anti- inflammatories and immunosuppressants

Answer 72

Potentiates analgesia when used with opioids as pre-meds or as neuroleptanalgesia Can also give as a CRI Same side-effects and contraindications as for sedation If given as an epidural, will see less sedation than if given IM or IV Analgesia is longer lasting if given as epidural Reversing with atipamezole, tolazoline, yohimbine removes sedation and analgesia

Answer 73

Doesn’t produce analgesia on own Adjunctive only Used at a lower dose than for induction Improves somatic analgesia Blocks NMDA at the level of the spinal cord to prevent windup Add-on with more potent analgesics (opioids, local anesthetics, alpha2-agonists) Ex. MLK as a CRI = morphine + lidocaine + ketamine

Pain and analgesia Flashcards

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