Pain Control & Use of Analgesics in Small Animals Flashcards
It is mandatory to treat pain if an animal has…
undergone a painful procedure OR has chronic pain requiring treatment of that pain
What is the official definition of pain?
“An unpleasant sensory and emotional experience, associated with actual or potential tissue damage or described in terms of such damage”
Pain has an essential protective function to announce…
the presence of a potentially harmful stimulus
Pain that has no useful function may be caused by
disease, trauma, or surgery and can delay recovery due to stress if left untreated
Appropriate analgesia results in
- a more rapid return to normal function
- a shorter hospital stay
When you undergo Surgery, you don’t perceive pain; but when you wake up after without appropriate pain meds on board, then…
you get excruciating pain when you wake up which is more difficult to treat
We use analgesics in veterinary patients because pain…
- increases distress and suffering
- increases the stress response
- increases the metabolic & energy demands
- increases conditions associated w/ prolonged recumbency
- self-mutilation
- ethical obligation for humane care
Studies in humans demonstrate that improperly controlled acute pain can…
precipitate a chronic pain syndrome that can be very difficult to control where pain itself becomes the primary disease
Pain assessment is the keystone of
pain management
if anything is done to the thorax, there are impacts to … and pain management should be used to facilitate it.
Ventilation
For successful treatment of pain, you must…
look for & recognise it
pain is now considered the 4th
vital sign monitored alongside TPR
Treat…
predictable pain
Pain assessment should be performed how often?
every 2-4 hours for acute pain
Pain assessment is key to determining
the degree & duration of pain treatment BUT should not replace treating predictable pain
Perioperative pain extends for at least… and should be managed accordingly
24-72 hours
All invasive procedures, trauma, & medical illnesses cause pain & may leave animals
unable to demonstrate pain behaviour
the worse the tissue injury, the worse the pain EXCEPT…
neuropathic pain which can be extremely intense despite relatively small tissue injury
Very sick patients may feel pain during
routine procedures & nursing
Species, breed, age, illness, temperament, drug admin influence…
behavioural responses to pain
compare an animal’s behaviour…
before & after the onset of pain if possible…
some animals respond to pain through
withdrawal
response to appropriate treatment is the gold standard to measure
the presence and degree of pain
always use a validated
pain scale, if available
What is the least subjective pain score?
composite scales where the observer interacts w/ the animal & assesses its behaviour & physiology
What is the best validated pain scale?
Glasgow Vet School Composite Measure Pain Scale (GCMPS)
What are signs of pain in the dog?
- change in posture or body position (hunching/praying position, not resting normal)
- change in demeanour
- altered/reduced interaction w/ people (aggression)
- vocalisations (barking, growling, whining)
- attention to/guarding affected area
- reduction in appetite
- altered mobility (lameness, reluctance to move)
What are the 2 validated pain scales in cats?
Glasgow
Botucatu
What things are assessed in the pain scales in cats?
posture, demeanour, vocalisations, interactions w/ the observer
The glasgow CMPS-F also addresses
facial expression
UNESP-Botucatu MCPS in cats includes
BP measurement as an optional variable
The Glasgow CMPS-F is appropriate for assessing
medical, surgical, and trauma-associated acute pain
UNESP-Botucatu MCPS was validated for
pain following OVH
When assessing pain in rabbits, what pain score constitutes further pain investigation?
Pain score of 2 in any category
In rabbits, what categories are used to watch for pain?
- ear shape & position
- orbital tightening
- nostril shape
- cheek flattening
- whisker change & position
When should analgesics be used?
Pre-operatively, intra-operatively, and post-op
Why do we use pre-op analgesics?
to provide pre-emptive analgesia
to facilitate handling/sedate animals
Why do we use intra-op analgesics?
to reduce response to noxious stimuli
to reduce anaesthetic requirements
Why do we use post-op analgesics
to control acute pain, reduce distress & suffering, etc
to prevent the development of chronic pain
Multimodal analgesia is…
the concomitant use of analgesics from separate pharmacological drug groups to provide analgesia by differing modes of action
Multimodal analgesia allows for
- better control of intra & post-op pain
- promotes haemodynamic stability
- minimises incidence of chronic pain
- reduces dose & side effects of most drugs
How do you build a multimodal analgesic protocol for P’s undergoing surgery?
- Start w/ NSAID, opioid, or both
- Add local anaesthetic
- Add CRI
- Add ancillary techniques
Why are local anaesthetics so important?
they are the most efficient way of providing analgesia to the area & stop pain stimulus from getting to the brain & will not be perceived upon waking
Locals exert action by…
blocking action potentials from being propagated along sensory neurons by blocking the sodium channels and preventing depolarisation of the membrane required to trigger an action potential
Local anaesthetics completely block
the pain pathway from ever generating a response
Locals reduce the need for…
other intra-operative analgesia
What are the main local anaesthetics used?
Lidocaine, bupivacaine, ropivacaine
What is the main difference between the different types of local anaesthetics?
onset & duration of action
The speed of onset of action of local anaesthetics depends on…
pKa
Near 7.4 = fast onset of action
Higher? = slower onset of action
Duration of action of locals depends on…
protein binding
Potency of local anaesthetics depends on…
lipid solubility
more lipid solubility in locals =
more protein binding
What is the onset & duration of effect of lidocaine?
Onset of effect: fast
Duration of effect: short
What is the onset & duration of effect of bupivicaine?
Onset of effect: slow
duration of effect: long
What is the onset & duration of effect of ropivacaine?
Onset of effect: intermediate
duration of effect: intermediate
What are signs of local anaesthetic toxicity?
CNS first affected (except bupivicaine)
then CV depression
then death
Local anaesthetics should not be given… EXCEPT…
IV
Except Lidocaine at slow rate in dogs
If using lidocaine spray for intubation, the amount of lidocaine used…
needs to be taken into consideration in total lidocaine dosing
If you give too much lidocaine during GA, you won’t see signs of toxicity… the patient may just…
have a seizure or go into coma
What techniques are used with local anaesthetics?
Splash block
Tissue infiltration
Intratesticular injection
Bier block (IVRA)
Epidural
Cat sacrococcygeal epidural
Dental blocks
Wound catheters
intra-articular block
specific nerve blocks
What is a splash block?
Direct topical application of local anaesthetic to incision/wound prior to closure OR during laparotomy
What is a tissue infiltration block?
Injection of local into SQ tissues around/directly into the incision or wound which blocks the surgery site
Targets nerves: cutaneous nerves of area
What is an intratesticular injection?
Injection of local into the testicles to desensitise spermatic cord and associated structures and provides analgesia for castration
What is a Bier block?
Block of the distal limb for a short surgical procedure (<90 mins)
What are indications for epidural?
- Sx on hind legs & perineal area
- Abd & thx procedures
What are contraindications for epidural?
- sepsis, bacteraemia
- Hypovolaemia, hypotension in large animals
- Pyoderma or neoplastic changes in injection site
- clotting disorders, thrombocytopaenia
- abnormal anatomy
When do you do a sacrococcygeal epidural in a cat?
- Sx on tail, penis, vulva, or perineal area
- Dystocia
- Urethral block
- Hindlimb & pelvic Sx
When are contraindications present with a cat sacrococcygeal epidural?
Pyoderma
Anatomical abnormalities/no tail –> Manx cats
What are some common problems associated with epidural injection?
- Hypotension
- Urinary retention
- Subarachnoid injection
- Blood in hub of needle (inj off midline)
What are rare problems associated with epidural injections?
- Cranial spread of local causing respiratory depression
- Pruritis
What are the uses for a dental block under GA?
- Dental extraction
- Mandibulectomy & maxillectomy
What drugs are used in dental blocks?
lidocaine or bupivicaine
When doing local dental blocks, what do you have to remember about injecting the medications?
you have to divide the volume btw various injection sites which may require diluting the drug
Where are dental blocks given?
- infraorbital maxillary block
- caudal maxillary block
- rostral mandibular (mental) block
- caudal mandibular block
What other analgesic techniques can be used?
CRI, Paracetamol, Gabapentin, Tramadol, Fentanyl Transdermal patches
What CRI can be used in dogs for analgesia?
morphine, lidocaine, ketamine (MLK)
fentanyl, lidocaine, ketamine (FLK)
or any alone
Medetomidine or dexmedetomidine
What CRI are used in cats for analgesia?
morphine, ketamine (MK)
fentanyl, ketamine (FK)
or any alone
Medetomidine or dexmedetomidine
Paracetamol can only be used in what species of small animals?
DOGS
what animal cannot receive lidocaine IV?
Cats!
