2- Maintenance of anaesthesia Flashcards
There are 3 ways that anaesthesia can be maintained:
Inhalation anaesthesia
Total intravenous anaesthesia
Partial intravenous anaesthesia- which is a mixture of the 2
What agent is anaesthesia maintained by?
Volatile agents - iso/sevo
What is the volatile anaesthetic agent combined with in the vaporiser?
Fresh gas
What does the rate of the anaesthetic in the plasma depend on?
Conc of the agent, ventilation, cardiac output & solubility of the agent in the blood
Define MAC (minimum alveolar concentration)
Concentration of vapour in the alveoli of the lungs that is needed to prevent 50% of patients moving in response to surgical stimulus
Name 2 factors that affect MAC
Drug given in pre-med - often decreases MAC
Body temperature
Age
Individual variation
What animal’s is isoflurane licensed in?
Dogs, cats and horses
What affects good and bad do volatile agents have on the patient?
Anaesthesia & dose-dependent analgesia
Profound cardiovascular & Respiratory depression (dose-dependant)
Cardiovascular depression is mediated via…
myocardial depression
What maintenance agent has an extremely high MAC thus is not usually used a sole anaesthetic agent?
Nitrous oxide
Define Total IV Anaesthesia (TIVA)
When anaesthesia is both induced & maintained by intravenous administration of drugs
In small animals what 2 drugs are licensed are licensed for TIVA use?
Alfaxalone & Propofol
T/F Alfaxalone & Propofol provide analgesia
FALSE
What is in the ‘triple drip’ used in horses?
Guaifenesin (muscle relaxant)
Ketamine (NMDA receptor antagonist)
Detomidine (alpha 2 agonist)
Define partial IV Anaesthesia (PIVA)
Combination of intravenous & inhalation aesthetic techniques
What is the aim of PIVA?
Reduce the amount of inhalation anaesthetics due to there cardiovascular and respiratory depression effects.
The idea is you can use less and thus have fewer negative effects = balanced anaesthesia
What effects do opioids have on MAC?
Mac sparing - moderate doses can result in a big reduction
What happens when you turn on the fresh gas flow but not the vaporiser on the anaesthetic machine
the gas flows along the bypass pathway to the patient, will not contain any volatile agent
What happens to the gas when you turn on the vaporiser on an anaesthetic machine
Fresh gas flow divided–> half goes into anaesthetic chamber and become saturated –> flows out mixes with the fresh of the gas and goes to patient
How is inhalation anaesthetics removed
by a anaesthetic scavenger- there are different types
Which species is sevoflurane licensed in
Dogs and cats
Which volatile agent has a slightly higher MAC and a lower blood gas solubility
Sevoflurane- means it diffuses into tissues and therefore the brain more quickly than iso- quicker change in anaesthetic depth
T/F isoflurane is more expensive than sevoflurane
False
Which inhalation agent is best to use for mask induction
Sevoflurane- n as it doesn’t smell/ taste pungent and is is quicker to effect.
T/F Nitric oxide has health and safety and environmental concerns
True- main reason it isn’t used - the impact of nitrous oxide is significantly greater than for isoflurane or sevoflurane
What rules are inhalation agents restricted by
COSHH- (Control of substances hazardous to health)
Because they are volatile and not metabolised by the patient there is potential for personnel exposure
List 2 situations when the use of TIA be appropriate
intrathoracic surgery or neuro disease in small animals
field anaesthesia in horses - when can’t give inhalation agents
