Maintenance Flashcards
Name 3 reasons Xenon offers promise as an inhalational agent?
- cardiovascularly stable
- Non-toxic
- Can be extracted out of room air.
What is a vapour?
Liquids vaporised in a carrier gas
Name 5 types of vapour?
- nitrous oxide
- Halothane
- Isolfurane
- Sevoflurane
- Desflurane
What is present in the nitrous oxygen tank compared with the oxygen tank and why?
In the nitrous oxide tank, there is both liquid and gas present. this is because nitrous oxide gas has a higher critical point therefore can be compressed into a liquid.
What is the critical temperature?
This is the point at which a gas cannot be liquified, not matter how much pressure is applied.
What happens to gas above critical temperatre?
It cannot form liquid - stays as gas.
What happens to vapour below critical temperature?
It can form liquid and gas e.g. nitrous oxide.
What is a vapour?
A vapour is a substance in gas phase below its critical temperature meaning it can be compressed into a liquid of solid by increasing the pressure without changing the temperature.
What is the critical temp of water? what does this mean?
374 degrees C - this is the highest temperature at which liquid water can exist.
What will the vapour and liquid/solid be in if the two phases can live together?
They will be in equilibrium.
What does a vapouriser do?
It liberates molecules of agent from the surface of a liquid
In the modern vaporiser, what controls how much vapour is produced?
- temperature compensated
2. flow compensated.
What happens when the temperature of the vaporiser drops?
The metal rod or bi-metalic valve moves so that there is more fresh gas allowed into the vaporiser chamber therefore increased flow rate as compensation.
What happens when the vapour is inhaled by the patient?
It crosses into the blood stream.
Name 4 things that the concentration of agent in plasma depends on?
- ventilation
- concentration of agent in carrier gas
- cardiac output (inversely)
- solubility of agent in the body (inversely)
What is the Blood:gas coefficient?
Solubility
What is the blood:gas coefficient?
This is the ratio of the amount of anaesthetic in blood and gas when the two phases are of equal pressure and volume.
Which anaesthetic is irritant?
Isoflurane
What is the rule for the blood:gas coefficient?
The lower the blood:gas coeffictient, the faster the administration of anaesthesia will be.
Why is the lower the blood:gas coefficient leading to a faster administration?
The LESS soluble agents (low coefficient) are washed away LESS quickly therefore the alveolar concentration rises FASTER.
Why do fat animals recover more slowly than a thin one?
Because redistribution of the anaesthetic into the fat therefore this acts as a depot of anaesthetic therefore a fat anaesthetic will recover slower than a fast one.
Which anaesthetic will provide the most rapid recovery?
The one with the HIGHEST blood:gas coefficient
What is one of the theories as to how inhaled agents work?
LGIC (ligand gated ion channels)
- GABA, Ach, NMDA
What is the MAC (minimum alveolar concentration)?
The alveolar concentration (at 1 atm) producing immobility in 50% of patients in response to noxious agent.
What is another term for MAC?
potency
In which patients does MAC apply?
Health, un-premedicated patients.
Name 9 things that affects MAC?
- Age
- Nitrous oxide
- hypotension
- hypoxia
- anaemia
- opioids
- sedatives
- LAs
- pregnancy
Name 6 things that MAC is unaffected by?
- sex
- species
- stimulation
- duration
- NSAIDs
- Cabon dioxide
What does a high fat solubility mean for MAC?
High fat solubiliy, Low MAC.
- slow induction and recovery.
What is typical anaesthesia in terms of MAC?
1.2-1.5 MAC
Name 9 things that make the ideal anaesthetic agent?
- stable at room temperature
- no preservatives
- Non-inflammable
- Cheap
- Ozone friendly
- Non-metabolised
- Non-toxic
- No CVS effects
- Analgesic
Name 7 physical properties of a good anaesthetic?
- Non-flammable, non-explosive at room temp
- stable in light
- liquid and vaporisable at room temp e.g. low latent heat of vaporisation
- stable at room temp with long shelf-life
- stable with soda lime, as well as plastics and metals
- environmentally friendly - no ozone depletion
- cheap and easy to manufacture
Name 6 ideal biological properties?
- pleasant to inhale, non-irritant, bronchodilation
- low blood: gas solubility e.g. fast onset
- high oil: water solubilyt e.g. high potency
- minimal effects on other systems e.g. cardiovascular, respiratory, hepatic, renal or endocrine
- no biotransformation - should be excreted by the lungs. unchanged.
- non-toxic to operating personel.
Name 3 of the negative effects of inhaled agents to the animal?
- forms carbon monoxide with soda lime
- cardiorespiratory depression
- formation of other toxic gases
What does nitrous oxide cause in the anaesthetist?
- bone marrow suppression (carcinogenic)
2. teratogenesis (abortions and birth defects)
Name 7 things that all inhalants cause?
- reduce cardiopulmonary function (except N2o)
- Reduce CO, reduce BP, reduce GFR, reduce renal blood flow
- vasodilation
- arrythmias
- respiratory depression
- halothane and hepatitis
- decrease cerebral metabolic rate of oxygen
What does COSHH mean?
Control of substances hazardous to health
What is passive scavenging?
This is when the gases enter the environment
What is active scavenging?
This is when there is a pump which pumps the anaesthetic into the environment.
What should be monitored regularly?
PPM of anaesthetic
What does fluosorber absorb?
Absorbs the inhalants, not the nitrous oxide.
Which staff tend to be exposed to the most anaesthetic?
Recovery staff rather than the staff in the theatre.
What is one of the negatives of using inhalants?
The need for scavenging
What is a down-side of nitrous oxide?
Expensive
Is nitrous oxide an analgesia?
YES
What is the MAC of nitrous oxide?
V high (100%)
What are the effects on respiratory and CVS with nitrous oxide?
minimal effects.
Why is halothane not licensed any more?
- toxicity problems
- oxidative - forms haptens
- hepatic hypoxaemia - reversible
- guinea pigs - metabolite hepatic toxicity
Is halothane seen any more?
Not over here, but might be seen in different countries.
Does isoflurane of halothane have a lower solubility?
Isoflurane
Which is safer: isoflurane of halothane?
isoflurane
In what species is isoflurane licensed?
Cats, dogs and horses
What is the most common agent used?
Isoflurane
What is the MAC of isoflurane in dogs?
1.28
MAC of isoflurance in cats?
1.63
MAC of isoflurance in horses
1.3% (0.9% foals)
What species is sevoflurane licensed in?
Dogs, cats
What is the difference between isoflurane and halothane with sevoflurane?
Sevoflurane causes quicker onset of action as well as recovery and modulation of anaesthetic depths.
What is the downside of sevoflurane?
It is more expensive
Is the MAC higher or lower for isoflurane or sevoflurane?
Sevoflurane
What about the CVS depression of sevoflurance?
Similar to isoflurane
What has less of a pungent odour- iso or sevo?
Sevo
What do all inhaled anaesthetics cause?
dose-dependent cardiac depression
When is recovery faster?
With a less soluble agent such as sevoflurane, however MAC is higher
All inhalants are what?
CV depressants
What does evidence support?
Isoflurance use over halothane
When do 60^ GA fatalities occur?
Within the recovery period, half within 3 hours of disconnection
What is the risk of GA in horses?
0.99%
What reduces the risk of GA in horses and why?
TIVA - these procedures tend to be shorter than inhalants e.g. castration, field procedures and shorter.
When would you use TIVA for horses?
In field procedures.
Name three reasons why anaesthesia might be riskier in horses than other animals?
- size, flighty animals
- cardiopulmonary depression
3 .experience
What is the main GA cause of death?
Cardiac arrest
What is the death rate inhalational vs TIVA in horses respectively?
0.99% vs 0.31%
What did most horses in CEPEF recieve as maintenance agent?
halothane
Why is TIVA safer?
Does not cause CV depression
What happens in horses which use inhalant induction agents?
They suffer hypotention
What might the triple drip include and what is it an example of?
Triple Drip is an example of TIVA. It might contain an alpha 2 agonist e.g. xylazine, guaifenesein and ketamine
What is the triple drip limited to?
<120 minutes.
What is often encountered in horses during anaesthetic and what can monitor this?
Hypoxaemia, hypoxia
-pulse oximeter and gas analyser
What causes this hypoxia and hypoxaemia?
the inhalants inhibit pulmonary vasoconstriction which might worsen V/Q mismatch and increase shunting in the lungs.
what other physiological status is encountered during equine anaesthesia?
Hypercapnia
- > 45mm/hg
- permissive hypercapnia is tolerated by many (60mmHg)
How can hypercapnia be noticed?
Capnography or a blood gas analyser
What is hypercapnia most commonly caused by?
Respiratory depression
Which causes less respiratory depression, inhalants or TIVA?
TIVA
Which leads to a calmer recovery in horses? TIVA (IV agent) or inhalation?
TIVA
What is administered to many horses now during recovery?
sedation
Name 8 factors that influence the recovery of horses?
- pain and type of surgery
- temperament
- breed
- pre-op sedation
- inhalant used (TIVA vs inhalant)
- drugs
- duration
- comfort
What can be worse in recovery following TIVA rather than inhalants?
Ataxia
What is another option apart from volatile drugs or TIVA?
PIVA (partial IV anaesthesia)
What are the 6 goals of PIVA?
- reduce MAC
- reduce cardiopulmonary depression
- provide analgesia
- improve plane of anaesthesia
- less pollution
- better outcome?
Name 4 recipies for PIVA?
- Lidocaine (Constant rate infusion)
- Ketamine (CRI or top-ups)
- Alpha 2 agonist
- opioids
A combination of what have been shown to improve cardiovascular stability in horses during isoflurane?
Ketamine and lidocaine
What does Lidocaine offer?
Analgesia and MAC reduction
What do opioids do to MAC in horses?
They don’t usually reduce it, sometimes they increase it
