Pain and analgesia Flashcards
Why is assessing pain important
Assessing pain is part of every exam
Pain = suffering
What are the 5 freedoms
Freedom from hunger and thirst
Freedom from discomfort
Freedom from disease, injury and pain
Freedom from distress
Freedom to express normal behaviour
What are the most common causes of chronic pain
Osteoarthritis
Dental disease
Cancer
Otitis media
Cystitis
Pancreatitis
Trauma (fracture, muscle injury)
Consequences of untreated pain are
Catabolic state – cachexia
Immune suppression – increased risk of infection, longer hospital stays; longer healing times
Increased anesthetic risk – higher doses of anaesthetic required to maintain a proper plane of anesthesia
Patient suffering and stress – affects outlook, behaviour, ability to perform basic functions (mobility, eating, drinking, urination and defecation, sleep)
Client suffering and stress
What procedures/conditions are painful
Surgery
Hip rads on an arthritic animal
PE on an animal with back pain
Colic
Otoscope exam if severe otitis
Examining a patient presenting for trauma (ex.HBC)
What can pain do for GA
Pain can interfere with PE
Pre exam analgesia is indicated in some situations
Analgesia should not mask the clinical signs
Sympathetic signs of pain
Increase HR, increase RR, increase BP
Shallow/exaggerated/abdominal breathing; panting (dogs); open mouth breathing (cats)
Pale mm (peripheral vasoconstriction)
Dilated pupils
Indicators of pain
Sympathetic signs
Change in temperature, sweating
Acute abdomen, colic (rolling, weight shifting)
Arched back
Lameness, stiffness, weight shifting, exercise intolerance, refusing to sit, postural change
Change in sleep patterns
Lack of grooming
Vocalization species dependent
Decreased appetite
Weight loss
Change in behaviour
Refuse to move
Aggressive; protecting painful parts of body
Cats hide
Dogs seek attention
Horses and cattle may separate form the herd
How to monitor for pain and how often
Symptom; not a diagnosis
Surgical patients – assess every hour for pain
Acute pain needs to be monitored more frequently; chronic pain is monitored less frequent
Clients can be helpful in assessing pain–they know their pets normal behaviour
Stress can mask pain
Varies between the species and breed
Cats do not show pain well; must be very painful
Exotics and birds hide pain. Often EMERGENCY by time noted
Methods of scoring pain are
Be consistent (same person to assess pain is most accurate)
There are multiple scoring systems
Verbal rating scales and simple descriptive scales
- No pain
- Mild pain
- Moderate pain
- Severe pain
Numeric rating scales
Sliding analogue scale
- An X is placed on the ruler corresponding to the level of pain the assessor feels the animal is experiencing
- Works best if always the same person
Comprehensive pan scale
What will happen to pain if the analgesia works
If analgesia is working, clinical signs and behaviours associated with pain will decrease
HR returns to normal
RR, breathing return to normal
Body position/posture return to normal
Improve mobility
Improved mobility
Improved appetit, grooming
Interaction with people, socialising – if that is normal for the animal
Pain assessment score will decrease
Analgesia means
Relief of pain without loss of consciousness
Analgesic means
Drug that relieves pain
Nociception means
Perception of a painful stimuli by the nervous system
Nociceptor means
Pain receptor; may be specific for detection of chemical stimulus, thermal stimulus or mechanical stimulus
Physiological pain is
Protective sensation
Conscious pain with minimal to no tissue injury
Teaches us to avoid things that are potentially harmful
Example – touching a hot surface
pathological pain is
Pain due to tissue injury
Describe as follows
Acute or chronic
Mild → moderate → severe
Cause: traumatic, inflammatory, psychological
Origin: visceral versus somatic
Visceral pain is and ex
pain originating from the organs
Colic, spay, renal pain, pancreatitis
Somatic pain is
pain originating from the musculoskeletal system
Superficial somatic pain – originates from nociceptors in the skin
Deep somatic pain – originates from nociceptors in the muscle, bones, joints
4 steps of the pain pathway
Transduction
Transmission
Modulation
Conscious perception
What is transduction of pain
physical stimulus (thermal, chemical, mechanical) turns on the nociceptor. Signal is converted to an electrical signal
What is transmission of pain
Electrical signal is relayed along the peripheral nerve, to the spinal cord and the brain
What is modulation of pain
Signal is suppressed of amplified as it passes along the spinal cord or in the brain
What is the conscious perception of pain
Electrical signal is processed in the brain; individual becomes aware of the painful stimulus
Pain modulation is perceived as
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”
Most common types of pain modulation is
Peripheral hyperalgesia
Central hyperalgesia (aka wind up pain)
Peripheral hyperalgesia is and due to
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
Central hyperalgesia is and due to
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
Allodynia is
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
Multi model pain therapy is
Using multiple drug watch with a different mechanism of action i.e. each drug targets a different part of the pain pathway
Advantages of multi modal pain therapy
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
Preoperative analgesia is
Pre surgery = preemptive analgesia s part of premed
Interoperative analgesia is
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
Post op analgesia is
Immediately post op (in hospital use)
Medication TGH; may be required for chronic use
Preemptive analgesia is
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
What are some common drugs for preemptive analgesia
Opioids- excellent analgesia
Alpha 2 agonists - block nociceptors and substance P
Ketamine – moderate somatic analgesia
benefits of preemptive analgesia
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
Classes of analgesics are
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
What are common injectable opioids
Hydromorphone, fentanyl, oxymorphone, morphine, meperidine
Butorphanol
Buprenorphine
Methadone
What are common TGH used for pain
Butorphanol
Buprenorphine
Tramadol®
Fentanyl patch
Opioids work how as an analgesic
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
Major side effects of opioids
Sedation
Respiratory depression
GI stasis
Are opioids a controlled drug and how to give it
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
Methadone as a analgesic is used for
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
Mechanism of action of methadone
Mu agonist opioid
Binds and activated the mu opioid receptors
Pharmacokinetics of methadone are
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
What are the effects and adverse affects of methadone
Potent analgesic via activation of mu receptors
Adverse effects are similar to all other mu agonists
Respiratory depression
Hyperactivity
Occasional hyperthermia
What are the contraindications of methadone
Respiratory or cardiac failure
Liver or renal dysfunction
Known cases of hypersensitivity
Fentanyl works how as an analgesic and how to give
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
Fentanyl patch works how
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”
How do you apply a fentanyl patch
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
Time to reach therapeutic levels with a fentanyl patch
Dog: 12-24 h
Cat: 6-12 h
H: 12+h
How long does a fentanyl patch last
Dog: 3 d
Cat: 5 d
H: 2d
What are some cautions when using a fentanyl patch
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
Tramadol is used for and works how
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)
Can you give human tramadol to dogs
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)
Is tramadol an effective analgesic for dogs and cats?
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
Buprenorphine works agaisnt
Partial mu-agonist
Fewer mu-related s/e than hydromorphone; little dysphoria; good in old/sick cats
What are the indications for buprenorphine
Analgesia – mild to moderate pain only
Take home opioid for cats
How do you use buprenorphine
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)
What is gabapentin used for
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
What are some common side effects of gabapentin
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
Solensia is used for what and how does it work
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
What do local anesthetics do
Drugs that “freeze” nerves
Both sensory and motor neurons
Analgesia comes from inactivation of nociceptors
What are the indications for local anesthetics
Analgesia – significantly decreases GA requirements
Local and regional nerve blocks
What is the mechanism for local anesthetics
Inhibits Na+ channels in nerves → stops Na+ influx → neuron cannot depolarize (i.e., cannot turn on)
Stops conduction of electrical impulses
Requires liver metabolism
Topical blocks are used for
Local blocks, Epidurals
Used alone for minor surgical procedures
Used in combination with other analgesics/anesthetics for pre-emptive/perioperative/postoperative pain
What are some common examples of local anesthetics
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
What are some common local anesthetics
All names end in “-CAINE”
Lidocaine
Mepivicaine
Bupivicaine (Marcaine®)
Proparacaine (Alcaine® for ophthalmic use)
Cocaine
How do you use local anesthetics
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
What are some benefits of local anesthetics
Increases analgesia where needed
At correct dose, few systemic (e.g., CV) effects
Decreases amount of GA required
What are some common adverse effects of local analgesics
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)
What happens if a toxic dose of local block is given
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
What to do if you overdose on local anesthetic
There are NO REVERSALS!
In the event of an overdose of a local anesthetic, provide supportive care until drug wears off.
How to avoid giving a toxic dose of local anesthetic
Check and recheck calculations
Chel the drug bottle
Use with proper syringe to measure
How do you administer lidocain
Topical and injectable formulations
2 injectable formulations:
- Lidocaine neat
- Lidocaine with epinephrine
What is lidocaine neat and how long does it work
Only contains lidocaine (2%)
Can give local, regional, or systemically
Short-acting: 20 min – 1 h
how long does lidocaine (2%) with epinephrine work and how long
Epinephrine causes vasoconstriction so drug stays in area longer
Longer-acting: 1-2 h
Can only use locally; NEVER GIVE IV
Mepivicaine is and used for
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
Bupivicaine is and used for
Marcaine®
Injectable or epidural
NEVER give IV because cardiotoxic
5-10 min onset; ~2 h duration
Used for dental blocks and declaws
What are some special techniques for delivery of anesthetics
CRI and pain drips
Epidurals & Para Vertebrals
Intra-articular injections
How does a CRI differentiate from an IV bolus
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
How does a CRI work
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
How do pain drips work
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
What should you as a tech do when an animal is on a pain drip
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)
How does an epidural work
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
What are common drugs used for epidurals
Opioids (morphine, fentanyl)
Local anesthetics (lidocaine NEAT, mepivicaine)
Some alpha-2 agonists (xylazine in LA)
Paravertebral blocks are
Common for flank approaches in ruminants
e.g. C-section, LDA surgery
IV regional anesthesia is used for what
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.
Intra-Articular Injection is and used for
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
What are at home analgesics important for
Post-operative/traumatic pain
Chronic pain treatment (ex. arthritis, cancer)
What are some common considerations for at home analgesia
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
What are some nonpharmacologic therapies that are used at home
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
Common types of nursing care are
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
What do NSAIDS do for as analgesia
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
Alpha2-Adrenoceptor Agonists as an Analgesic (xylazine, dexmeditomidine) work how
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
How does ketamine work as an analgesic
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