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