Maintenance Flashcards
Define Vapour
Vapours = A substance in the gas phase at a temp lower than its critical point so this means that the vapour can be condensed to a liquid or a solid by increasing its pressure without reducing the temperature.
How does a vaporiser work?
Molecules of agent liberated from the surface of a liquid by a carrier gas
Switching on the vaporizer diverts the carrier gas into the chamber and there is an increased carrying of the anaesthetic agent into the lungs of the patient.
What factors affect the rate that an anaesthetic vapour is taken up into the blood?
Ventilation – will be affected by speed of breathing
Concentration of agent in carrier gas
Cardiac output (inversely) - increased cardiac output reduces time taken to induce
Solubility of agent in the body (inversely) – highly soluble takes longer to reach equilibrium so therefore requires more time to reach anaesthesia
Describe the blood gas partition coefficient
The LESS soluble agents (low coefficient) are washed away less quickly therefore the alveolar concentration rises FASTER
Describe the effect of obesity on recovery from anaesthesia
Recovery is the reverse of induction, so dependant on blood solubility, redistribution will have occurred into the fat, which then acts as a depot of anaesthetic so (depending on fat solubility) a fat animal will recover slower than a thin one
Define minimum alveolar concentration (MAC) and what factors define it?
The alveolar concentration (at 1 atm) producing immobility in 50% of patients in response to a noxious stimulus
Age, N2O, hypotension, hypoxia, anaemia, opioids, sedatives, LAs, pregnancy
How is fat solubility linked to MAC?
High fat solubility LOW MAC, slow induction and recovery
Low fat solubility HIGHER MAC, faster induction and recovery
Why cant you induce animals using Nitrous Oxide?
Cannot induce animals with nitrous oxide due to its extremely high MAC which would mean that you may end up killing it in the induction process due to hypoxia
Describe the properties of the perfect anaesthetic vapour
Stable No preservatives Non-inflammable Cheap Ozone friendly Non metabolised Non-toxic No CVS effects Analgesic
What are the negative effects of inhaled agents? (on the animal and anaesthetist)
To the animal:
Cardiorespiratory depression – always balancing this between unconsciousness and immobility
Formation of carbon monoxide with soda lime
(Formation of other toxic gases)
To the anaesthetist:
Little or no evidence on consistent exposure apart from nitrous oxide
Bone marrow suppression
Teratogenesis
Why is halothane rarely used anymore?
Toxicity problems Oxidative – forms a hapten Hepatic hypoxia – reversible Guinea Pigs - metabolite hepatic toxicity Not licensed any more
What is the MAC of Isofluorane?
Isoflurane 1.28 (dog) 1.63 (cat) 1.3 %(horse, 0.9% foal)
What is the benefit of sevo in relation to other anaesthetic vapours?
Anaesthetic induction, recovery, and intraoperative modulation of anesthetic depths to be notably faster than halothane and isoflurane
(However more expensive)
What is the MAC for sevo?
MAC 2.2%(dog) 2.58% (cat) 2.3% (horse)
What are the roles of PIVA?
Reduce MAC Reduce cardiopulmonary depression Provide additional analgesia Improve plane of anaesthesia Less pollution
