Inhalational Anaesthetics Flashcards
How are inhaled anaesthetics transported?
in carrier gasses
Name 3 types of inhaled anaesthetics
- Halothane
- Isoflurane (MUST KNOW)
- Sevoflurane (MUST KNOW)
- Desflurane
- Enflurane
- Methoxyflurane
What are these inhaled anaesthestics known as
Volatile anaesthetic agents
How is the level of agent determined
by dial up vaporiser
What do all inhaled anaesthetics cause some degree of
- respiratory depression
- cardiovascular depression
Do inhaled anaesthetics provide analgesia?
no
What are the two most commonly used inhaled anaesthetics
Isoflurane and Sevoflurane
Name the two carrier gasses?
Oxygen, Nitrous oxide, Carbon dioxide
What cylinder is oxygen kept in?
Black cylinders with white shoulders
What are 3 uses of oxygen
- 100% given to animals with anaemia, pulmonary pathology, hypoventilation, animals recovering from N2O anaesthesia/ supplied during recovery if needed
- Used operatively routinely
- Used pre-operatively if you think intubation will be difficult e.g. brachycephalics
- Post operatively
Name a benefit of oxygen?
- Does not depress ventilation
- Does not cause toxic nervous changes
- Does not cause toxic pulmonary changes
- Can be combined with nitrous oxide
How is nitrous oxide delivered?
from compressed air tanks
What is nitrous oxide combined with
oxygen
What % of concentration will provide analgesic effects?
20%
What % is nitrous oxide usually delivered at?
66% (33% oxygen)
What is the ratio of nitrous oxide to oxygen in non-rebreathing circuits?
2:1
What is the ratio of nitrous oxide to oxygen in rebreathing circuits?
1:1
Why can the use of nitrous oxide cause the anaesthetic sparing effect
if delivered at 66% then lowers need for high volatile agent levels
With what inhaled anaesthetic does nitrous oxide have a second gas effect?
Halothane
What cylinders do N2O come in?
Blue
What must you do once N20 is switched off?
oxygenate patient
Name 3 negatives with nitrous oxide?
- not to use more than 80% (will lower oxygen below normal levels and patient will go hypoxic)
- Hypoxia
- N20 diffuses into gas-filled spaces and accumulates
- Do not use in bowel obstruction
- Do not use in middle ear disease
- Delivering nitrous oxide with pneumothorax can double the size of the pneumothorax in 10 minutes
When might hypoxia occur? And how do you avoid it
if animal is breathing room air - as room air contains high levels of nitrogen
Avoid it by giving al patients 5-10 minutes of pure oxygen once N2O is switched off
What piece of equipment should you use if concerned about hypoxia?
Pulse oximeter
What cylinder is carbon dioxide in?
grey
When is co2 used?
if patient is hypo-capnic
At what level is co2 used?
4%
Name 3 advantages of inhalational anaesthetics over injectable anaesthetics?
- depth of anaesthesia readily altered
- Concentration of anaesthetic in blood or brain may be altered rapidly by changing vaporiser setting
- Elimination of inhaled agents occurs mainly via the lungs therefore advantage of liver/kidney patient
- Allows constant delivery of oxygen alongside agent
- Most patients are intubated therefore IPPV may be performed and anaesthetic is ‘safe’
- Delivered to the lungs and then goes very quickly across the blood brain barrier to the brain and into the CNS
Name 3 disadvantages of using inhaled anaesthesia over injectable anaesthesia?
- need for anaesthetic machine and range of equipment (costly)
- Hazards, personnel risk, explosion risk
- Knowledge required of circuits and machine
- Induction and recover possibly delyaed due to lung pathology (not great induction agents)
- Only alternative is IV total anaesthesia
What is MAC
minimum alveolar concentration = measure of the anaesthetic potency
How is MAC measured
it is the quantity of anaesthetic required to immobilize 50% of patients
Are MAC’s with a lower or higher number more potent?
lower MAC numbers are stronger and more potent
What is blood gas solubility?
how soluble the gas is into the blood which then gets soaked up by blood and forms a reservoir in plasma - making it more difficult to pass through alveoli and pass the blood brain barrier
Are more soluble or less blood gas soluble agents better? And why?
Low, they tend to have a more rapid induction and recovery
Name an inhalational anaesthetic with low blood gas solubility
Sevoflurane
Name an inhalation anaesthetic with high blood gas solubility
Halothane
Which is more soluble: isoflurane or sevoflurane?
Isoflurane
Which popular inhalational anaesthetic has a pungent smell?
Isoflurane
Name 3 benefits of Isoflurane?
- relatively fast induction and recovery in comparison to Halothane
- Good muscle relaxation
- Fast recovery
- Does not sensitise the heart to arrhythmias
- Dose dependent
- Licensed for variety of species
- Greater safety margin than Halothane
Name 3 negatives with Isoflurane?
- Not as fast induction or recovery as Sevoflurane
- Transient excitability especially following painful surgery
- Hypotension can occur due to CVS depression
- Potent respiratory depressant
- Poorly tolerated for mask induction due to smell
- Not good analgesic on its own
Name 4 characteristics of Sevoflurane
- Rapid induction and recovery in comparison to Isoflurane
- Lower blood gas solubility than Iso
- Odourless / pleasant non-irritant odour
- Unstable in presence soda lime
- More expensive than Iso
- Can be used for mask induction
- Non-irritant to airways
- Can be used on exotics
What happens when Sevoflurane is in the presence of soda lime
- Unstable
- Degrades producing toxic metabolites (compound A which is proven to produce renal pathology in rats though not reported in small animals)
