CAL - sedation, premedication and induction of anaesthetics Flashcards
Name 5 alpha-2 agonists
- xylazine
- detomidine
- romifidine
- medetomidine
- dexmedetomidine
Which alpha-2 agonist has the longest effect?
Romifidine (analgesic properties questioned)
What effects does medetomidine have?
Very powerful sedative, hypnotic and analgesic. Its effect may be enhanced by combining with an opioid (butorphanol)
What can be used to revere the sedative and other actions of alpha -2 agonists?
Alpha-2-antagonists such as Atipamezole, Yohimbine, Tolazoline and Idazoxan
How do alpha-2-antagonists work?
Act at both pre- and post-junctional sites on noradrenergic nerves centrally and peripherally. Wide ranging effects.
Via which route are alpha-2agonists strong analgesics?
epidural route
What is the biphasic BP response of alpha-2 agonists?
Transient (5-15 min) hypertension, (due to vasoconstriction) followed by prolonged (but very slight) hypotension
What are the 2 main side effects of alpha -2 agonists
bradycardia and fall in CO
Why is emesis common in small animals soon after alpha-2 agonist administration?
CRTZ stimulation. Gut motility then almost totally ceases.
What skin reactions occur with alpha-2 agonists?
Sweating common in the horse. Piloerection may occur with very high doses. Occasional ‘anaphylactic’ skin plaques - most commonly with romifidine.
Where are alpha-2 agonists metabolised?
Liver
T/F animals given alpha 2 agonists may respond violently to some stimuli, especially touch
True - this effect can be reduced by combining with opioids as low doses of opioids are synergistic
What drug interactions might occur with alpha-2 agonists?
- some ABs (potentiated sulphonamides)
- NSAIDs
What should you be aware of when giving ruminants alpha-2 agonists?
severe respiratory depression possible –> hypoxia
What are the contra-indications for alpha-2 agonists?
- ABSOLUTE CI - urinary obstruction
- PARTIAL CI - myocardial disease, liver/renal failure, pulmonary disease, pregnancy, DM, hypovolaemia
What drugs are excellent for determining a colic’s response to analgesia
Alpha 2 agonists (partly because they inhibit gut motility)
List some examples of benzodiazepines
- Diazepam
- Midazolam
- Zolazepam
- CLimazolam
What is an antagonist to benzodiazepines?
Flumazenil and Sarmazenil
How do benzodiazepines work?
Agonists at several CNS sites for BZ1/, BZ2 sites on the GABA-A-R causing increased chloride conduction. No effect on peripheral receptors of this type due to no benzodiazepine binding site.
Indications for benzodiazepines
Reduce anxiety, taming effects, behavioural changes and relaxation of skeletal muscle (spinal effect), stimulate appetite (IV administration in cats).
Benzodiazepine pharmacokinetics
Highly lipid soluble, therefore rapidly cross BBB. Converted to active metabolites in liver, which may have much longer half-life than parent compounds, so that circulating concentrations of the latter may not be predictive of duration of action.
Benzodiazepine side effects
- minimal CVRS effects, even high doses
- may be synergistic with many anaesthetic agents in causing respiratory depression
What is a risk when injecting benzodiazepines?
some formulations cause thrombophlebitis and pain on injection (midazolam is water soluble and can be given IV or IM and is NOT painful on injection)
What is the main anaesthetic use of benzodiazepines?
in combination with opioids or ketamine or as part of an anaesthetic induction protocol
T/F: phenothiazine and butyrophenones have many similarities.
True - they are typical tranquilizer drugs
What is an example of a phenothiazine?
Acepromazine (ACP)
Name 3 examples of butyrophenones
- Azaperone
- Droperidol
- Fluanisone
Name an antagonist to acepromazine (ACP)
There is not antagonist - if serious hypotension occurs whilst giving ACP, treat with IV fluids.
Why shouldn’t you give adrenaline with acepromazine (ACP)?
ACP causes alpha-1 adrenergic blockage so adrenaline may stimulate an unopposed beta-2 adrenergic receptor action. This effect will increase vasodilation and so hypertension may worsen.
What effects do phenothiazine and butyrophenones have?
relieve anxiety, ‘mood altering ‘ or ‘neuroleptic’ effects, steep dose/response curve, maximal sedative effects occurring at comparatively low doses.
Pharmacodynamics - phenothiazine and butyrophenones
Antagonists for dopamine-2 (DA2) receptors in the CNS.
What is a side effect of phenothiazine and butyrophenones?
alpha-1 receptor blockade –> hypotension.
Do alpha-2 agonists or phenothiazine and butyrophenones have a greater sedative effect?
Alpha-2 agonists have the greatest sedative effects.
Which animals sedate well with phenothiazine and butyrophenones?
the anxiolytic effect removes fear so nervous animals sedate well, but not vicious ones
What are phenothiazine and butyrophenones CVS effects?
vasodilatation and fall in arterial BP (alpha-1 block). Minimal effects on cardiac contractility. Effects on respiration are minimal.
Pharmacokinetics - phenothiazine and butyrophenones
Various formulations with various routes of administration. Some drugs are highly bound to plasma proteins (ACP = 99% bound). Relatively long half-lives.
What can phenothiazine and butyrophenones be combined with?
Opioids and anaesthetics
What do you get if you combine phenothiazine and butyrophenones with opioids?
This is the basis of neuroleptanalgesia and neuroleptanaesthesia (depending on the potency and dose of opioid).
What do you get if you combine phenothiazine and butyrophenones with anaesthetics?
Reduced anaesthetic dose needed - since it increases the duration of action of IV anaesthetics (but not to the extent that alpha-2 agonists reduce anaesthetic dose).
What increases with dose of phenothiazine and butyrophenone?
Duration (but not intensity) of effect increases with dose.
T/F the use of phenothiazine or butyrophenone as a premed reduces the anaesthetic risk.
TRUE.
It partially protects the heart from adrenaline-induced dysrhythmias. In horses it reduces the anaesthetic risk by half. In cats and dogs and cats it decreases the anaesthetic risk but not by a clinically significant amount.
Common side effects of phenothiazine and butyrophenones
Hypotension, penile prolapse, hypothermia (from peripheral vasodilation), extrapyramidal side-effects e.g. tremor, rigidity (overusage)
What are occasional side effects of phenothiazine and butyrophenones
sudden collapse following rapid IV injection, priapism in male horses (persistent and painful erection of male horses).
Contraindications for acepromazine, ACP (phenothiazine and butyrophenones)
- ABSOLUTE CI - liver disease
- PARTIAL CI 0 hypovolaemia (–> hypotension), epilepsy (high doses of phenothiazines decrease threshold at which fits occur), Boxers (likely to faint) and brachycephalics (low dosese only), breeding stallions (priapism)
What dose of ACP should you use in brachycephalics?
low doses
What dose of ACP should you use in Giant breeds?
very low doses
What is the near anaesthetic state that is achieved when high doses of potent opioids are used in combination with sedatives?
‘neuroleptanalgesia/ neuroleptanaesthesia. Examples are: Hypnorm. Fenytanyl plus fluanisone (a butyrophenone).
Should you give medetomidine IV or IM to a vicious dog?
IM (effects in 15-20 minutes)
What are post-op analgesia options?
- Carprofen tablets
- Metacam (Meloxicam)
If you have an animal that has lost a lot of blood what should you avoid giving?
Acepromazine (ACP)
Which drug should you avoid in standing horses?
Medetomidine (in standing horses can cause marked ataxia and the horse may fall). Also avoid Midazolam (benzodiazepine) as it causes mm relaxation and weakness which may cause the horse to panic).
Which class of drugs is probably best for status epilepticus?
Benzodiazepines
How should propfol be administered to induce anaesthesia?
IV slowly to effect (rapid onset of action)
If you suspect CV signs before induction, what should you pre-med the dog with?
Methadone - minimal CVS effects.
How do you anaesthetise a patient with CVS disease? 3
- Use premed
- Use a co-induction technique
- Administer the induction agent slowly to effect
What is the safest option for inducing anaesthesia in a vicious cat?
Triple combination IM with ketamine, medetomidine and butorphanol. Alternatively you could use box induction.
T/F: ketamine preserves CNS reflexes to a greater extent than other pre-meds
True. The cat may swallow, salivate and may have an active palpebral reflex. Jaw tone is likely to be greater than after propofol or isoflurane. Ketamine also stimulates the SNS so the HR and BP may be higher than you might expect in an animal anaesthetised with propofol or isoflurane.
Which drug is highly irritant extravascularly and will cause skin and SC necrosis?
thiopentone (flush area with sterile saline (to dilute the thiopentone) with lidocaine added (to cause local vasodilation to increase drug uptake out of the SC tissues)).
Which anaesthetics are not suitable to be administered to cats on several consecutive days?
Propofol - cats have difficulty metabolising both the phenol and the lipids in propofol. Repeated doses in a short period of time can lead to drug accumulation which may lead to slower recoveries and toxic effects (anorexia, diarrhoea, anaemia).
