Flashcards in CAL - pain and analgesia Deck (28)
What drugs can be used for local analgesia?
- local anaesthetics
- alpha 2 agonists
(opioids and alpha 2s are generally used in association with an local anaestheic agent)
Action - local anaesthetic
reversibly blocks sodium channels preventing the transmission of action potentials along an axon. Unionized lipid-soluble drug passes through the phospholipid membrane where, in the axoplasm it is protonated. In this ionized form it binds to the internal surface of the sodium channel, preventing it from leaving the inactive state. The degree of blockade in vitro is proportional to the rate of stimulation (‘frequency dependence’) due to the attraction of local anaesthetic to ‘open’ sodium channels
What does the intrinsic vasodilator activity influence?
- duration of action
T/F: local anaesthetics cause vasodilation at low concentrations adn vasoconstriction at higher concentrations
How does cocaine have solely vasoconstrictor actions?
by inhibiting neuroal uptake of catecholamines and inhibiting monoamine oxidase (MAO)
Which local anaesthetics may be formulated with adrenaline/epinephrine
Procaine and lidocaine (lignocaine): both cause vasodilation and adrenalise helps reduce systemic absorption and increase duration of action
What is the advantage of ropivacaine compared to bupivacaine?
Ropivacaine has less cardiac toxicity compared to bupivacaine which dissociates very slowly from sodium channels and may cause persistent myocardial depression. It can also cause ventricular arrhythmias and ventricular fibrillation. Life-threatening arrhythmias may also reflect disruption of Ca and K channels. Ropivacaine dissociates more rapidly from cardiac sodium channels and produces less myocardial depression. However, it has a slightly shorter duration of action and is slightly less potent than bupivacaine, resulting in a slightly larger dose requirement for an equivalent block.
What might you use to do a mandibular nn block?
In what circumstances would you NOT perform epidural anaesthesia/analgesia?
• Infection at site of needle insertion
• Spinal/pelvic deformities
• Raised ICP
What anatomical landmarks do you need to perform a brachial plexus block in the dog? 5
- jugular vein
- cranial border of greater tubercle
- first rib
* brachial plexus located at the ventral border of the scalenus mm
Why shouldn't you ever give pethidine IV?
causes histamine release
What is a good choice analgesic for orthopaedic sz?
Does pethidine or buprenorphine have a long duration of action?
- PETHIDINE: short duration of action
- BUPRENORPHINE - long duration of action so lasts into post-op period, however it is a partial agonist so the analgesia may not be as profound as with a full agonist
Does butorphanol provide good analgesia for sx?
No because it is a mu-opioid receptor antagonist
Is midazolam an analgesic?
Does nitrous oxide provide analgesia?
Can provide good intra-operative analgesia but remember this wears off soon after its administration is discontinued at end of anaesthesia
Should carprofen be given as a top up intra-operatively?
No - should be given every 12-24 hours so will not be required intra-operatively
If morphine is given in the epidural injection during sx, how long may this provide analgesia for?
up to 24 hours
What are the vital signs? 4
Signs a cat is in pain
Reluctant to move; growling, hissing, vocalising when touched; tachycardia, tachypnoea; dilated pupils. She may look ‘distant’ and may try to hide.
What other factors might produce similar signs to pain in cats?
Anxiety, stress, unfamiliar surrounding (cage, people, other animals etc.). Cats do not like bandages and you should try to differentiate between pain and the dislike of restrictive bandages or dressings.
Can methadone be used to control pain in cats?
- a pure mu-opioid receptor agonist and appears to be efficacious for controlling pain in cats. Unlike morphine, it rarely appears to cause vomiting. May cause dysphoria at higher doses.
Can buprenorphine be used to control pain in cats?
it is a partial mu-opioid receptor agonist - i.e. its maximal effect is less than pure mu-agonists. In clinical studies, buprenorphine has produced better analgesia than morphine and pethidine. It rarely causes vomiting or dysphoria. It can also be given by the OTM route with almost 100% bioavailability.
Can NSAIDs be used to provide pain relief in cats?
Until recently, NSAIDs were not widely used in cats because of fears about toxicity. Carprofen is effective and is licensed as a once-only dose for perioperative analgesia. Meloxicam is also licensed for perioperative use and provides analgesia of similar effect and duration to carprofen.
Why use epidural analgesia?
- A successful epidural with a local anaesthetic will block all sensory input to the spinal cord during surgery and also help to reduce the amount of volatile anaesthetic needed to maintain anaesthesia. Morphine (the preservative-free preparation) can also be incorporated and will provide postoperative analgesia for up to 24 hours.
Where to place epidural analgesia in cats versus dogs?
In cats, the meninges end further caudally (between L7-S1) than in dogs and it is therefore possible that the needle may penetrate the dura and arachnoid and enter the CSF. If this does occur, the amount of local anaesthetic injected should be reduced by at least 50%.
T/F: pain is an emotional experience
True - a cat that is cold, frightened, hungry, thirsty or unable to empty its bladder will experience greater pain. Exposing cats to the noise and smell of dogs may also be stressful. Cats should also be given a box or covered bed so that they can hide and feel safe.