Anaesthesia - drugs Flashcards
What anaesthetic agents can be used in food animals?
ketamine
thiopental
isoflurane
Injectable anaesthetic agents
propofol alfaxalone ketamine thiopental etomidate
what injectable agents can you use for long term maintainance?
propofol
alflaxalone
what inhalational agents are available today?
isoflurane
sevoflurane
desflurane
N2O
what are some considerations with isoflurane and sevoflurane?
very vasodilatory
secoflurane may be nephrotoxic
considerations with desflurane
expensive
irritant
considerations of nitrous oxide
- cant reach anaesthesia with it alone
- very insoluble
- switch it off before end of procedure and put on 100% O2 as can get diffusion hypoxia as it rapidly diffuses into lungs (as insoluble in blood) as end of anaesthesia and decreases oxygen pressure
what anaesthetic agent doesnt cause dose-dependant CVs and resp depression?
ketamine as causes catecholamine release which counteracts it
what is TIVA and PIVA?
total / partial IV anaesthetic
advantages and disadvantages of intermittent IV maintenance
- simple, less equipment
- swinging plane of anaesthesia, side effects when really deep
advantages and disadvantages of continuous IV maintenance?
- need a syringe driver
- can control with a computer
- need to know minimum infusion rate (MRI) where 50% dont respond to stimuli
How is inhalational agent concentration affected by vessel richness of tissues?
Vessel rich tissues will reach higher concentrations and be removed faster than vessel poor tissues
what is MAC?
minimum alveolar concentration - needed to prevent movement to a painful sitmuli in 50% of animals
what MAC is aimed for?
1.25 - 1.5 xMAC
what can decrease MAC?
hypothermia young / old hypoxia hypotension CVs depressants pregnancy
what can increase MAC?
hyperthermia
healthy and young ish
excitation
What do neuromuscular blocking agents do? What considerations do you need?
inhibit ACH binding at NMJ so the AP isnt propogated to the muscle
- cause relaxation of all skeletal muscles
- must be able to IPPV as cant breathe
- hard to monitor as cant asses reflexes
- use nerve stimulator to measure effect of block
- antagonise with ACHe and anticholinergic agent to prevent bradycardia from high ACH at muscarinic receptors
How is potency related to MAC?
potency = 1/MAC
What are the 4 classes of premed?
phenothiazines
butyrphenones
benzodiazepine
a2 agonists
what is the main phenothiazine?
acepromazine (ACP)
what does ACP do?
- sedative via dopamine antagonism
- anti-emetic
- a1 antagonism = vasodilation and anti-arrhytmic
- anti-histamine
- penile priapism
how long does ACP take to work and how long does it last?
20-30 mins to work
4-6 hours duration
IM or IV
when is ACP contradicted?
- brachycephalic
- hypotensive
- boxers
- breeding stallions
- intradermal skin testing
- organophosphates (be careful is poisoned)
what does ACP potentiate?
- opioids
- local A
- GA
how much does ACP affect the respiratory system?
not much unless very sick
what is Azaperone?
butyrphenones
-pig sedative
what are the pharmokinetics of azaperone?
- deep IM
- dose related sedation
- 30 mins of quietness to effect
- 2-3 hr duration
what are some examples of benzodiazepines?
- diazepam / valium
- midazolam / hypnovel
- diazemuls
what do benzodiazepines do?
- potentiate GABA
- muscle relaxation
- anti convulsant
- variable sedative effect
- appetite stimulant in cats
- minimal CVS / resp depression
what is the pharmacokinetics of benzodiazepines?
- good in very old/young/sick
- irritant
- absorbed onto plastic so dont draw up early
- rapid onset and short duration
- IV
what benzodiazepine can be given IM?
midazolam and diazemuls
what benzodiazepine is inhibited by erythromycin?
miadazolam / hypnovel
when are benzodiazepines contraindicated?
- long term in cats as can cause hepatic failure
- hepatic encephalopathy
- very excited / aggressive patient
what are some a2 agonists?
xylazine
detomidine / domosedan
romifidine / sedivet
medetomidine (domitor)and dexmetomidine
what do a2 agonists do?
- muscle relaxation
- initial hypertension from a1 effects post synaptically then get normo/hypo tension
- bradycardia from herpertension
- resp depression
- vomiting
- inhibit ADH and insulin
- uterine contraction
which a2 can be used in horses?
romifidine / sedivet
detomidine / domosedan
xylazine
how long do a2 agonists work for?
about 2 hrs
why do we pre-med?
- help and potentiate anaesthetics
- relieve anxiety
- analgesia
- less anaesthetic dose so less anaesthesia side effects
- smoother induction and recovery
what is a tranquiliser?
reduce anxiety but no dullness
what is a sedative?
reduce anxiety and cause drowsiness
what is a hypnotic?
anaesthesia inducing
what is a benzodiazepine antagonist?
flumazanil / sarmazenil
what is a a2 antagonist?
atipamezole
yolimbine
tolazoine
what do anti-chollinergic drugs do?
increase HR decrease salivation decrease gut motility dilate pupil relax bronchi
atropine, glycopyrollate, hyoscine
how do we estimate the brain concentration of inhaled agents?
alveoli conc = brain conc
what happens with more soluble agents?
- more in the blood so less in lungs / brain
- longer induction and recovery as takes time to saturate blood first before pressure builds up in brain and lungs
- more soluble = higher gas partition coefficient
what are 5 induction agents?
propofol propofol plus alfaxalone ketamine thiopentone / thiopental
what class is propofol?
phenol
what can propofol be used for?
induction, maintenance, TIVA
what induction agent has less cardiopulmonary depression?
alfaxalone
what induction agent cause CV stimulation?
ketamine - hypertension and tachycardia
what is an advantage of propofol plus over normal propofol?
28d shelf life compared to 1 d shelf life
which induction agent causes reflexes to remain?
ketamine
how is propofol given?
IV slowly to effect
what cant you use propofol plus for that you can use propfol for?
TIVA
what is the difference in propofol plus?
benzyl alcohol preservative (may cause toxicity)
what can alfaxalone be used for?
induction and maintenance
-rapid onset and short duration
what is a consideration of alfaxalone?
difficult recovery
what is ketamine used for?
induction and maintenance
has analgesic effects
*dont give alone as will be excitatory
what is an issue with thiopentone/thiopental?
no longer licensed
irritant if extravascular
cumulative in body fat so be careful
slow metabolism
what is the issue with propofol in cats?
cats cant conjugate glucuronides and have problems metabolising triglycerides so have a very slow recovery and toxic if dose repeated
what is the triple combination used in aggressive cats?
ketamine + medetomidine + opioid
IM lasts 15 m
what is etomidate?
minimal CVS and RESP depression so good if very sick
-depresses adrenal function (low cortisol)
what combination is used for very sick patients?
opioid and benzodiazepine
