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Flashcards in Anaesthetic equipment Deck (28)
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What is the function of the anaesthetic machine?

To deliver oxygen along with a precisely controlled concentration of anaesthetic vapour

Volatile anaesthetic agent = Isoflurane or Sevoflurane- liquids which are volatile.

The resulting vapour has anaesthetic properties when inhaled


Name different parts of the generic anaesthetic machines

1.High-pressure side directly from the oxygen and nitrous oxide cylinders

2.Pressure gauge


4.Low pressure side

5.Needle valves and rotameters (flowmeter)


7.Oxygen flush

8.Common gas outlet to circuit

9.low oxygen alarm


Describe the oxygen supply

Black and white cylinder

Compressed gas

Sized E, F and J

Pin indexed


Describe the nitrous oxide supply

Blue cylinders

Liquid/gas equilibrium

Pin indexed


Describe piped gas

Safer- cylinders outside

Cheaper- larger cylinders used

Access more difficult when cylinder needs changing


Describe the oxygen pressure gauge

Gauge on anaesthetic machine is a reliable indicator of the amount of oxygen remaining in the cylinder

Unless using piped gas,the oxygen pressure gauge on the machine will just tell you the pressure within the pipes. There will be another gauge on top of the cylinder that will give you an indication of how much oxygen remains.


Describe the nitrous oxide pressure guage

Gauge is not a reliable indicator of remaining nitrous oxide

gauge will only show the gas pressure – will remain high until all liquid gone, then drop suddenly

To estimate how much remains, weigh cylinder


Name different methods of delivering inhalational agents

Anaesthetic chamber


Breathing system (circuit) with ET tube


What are some considerations when deciding on the method of anaesthetic delivery?

Provision of oxygen +/- volatile agent

Removal of carbon dioxide


Describe anaesthetic chambers

Tend to be used for induction of small wriggly patients

Must be airtight

Volume as small as possible for given patient to minimise anaesthetic use

Should be scavenged

Keep flow rates high to avoid rebreathing CO2

Allows small mammals (especially rats, mice) to be minimally restrained

Difficult to assess anaesthetic depth without removing patient- switch to a mask as soon as possible


Describe anaesthetic masks

Can be used for
-induction and maintenance of anaesthesia
-provision of O2 pre/post anaesthesia
-Supplementing O2

Should be close fitting


What are the advantages of anaesthetic masks?

Easy to use

Useful for short procedures

Useful for small and exotic species that are not easily intubated


What are the disadvantages of anaesthetic masks?

Mask will tend to leak

Airway not secure

IPPV difficult or impossible

Requirement to hold mask against face (?sandbags)

Surgical access to mouth and face restricted


Describe endotracheal tubes

Should use the largest tube that will pass comfortably

Cuffed tubes in dogs

Non-cuffed tubes in cats


What are the aims of breathing systems?

Delivery of oxygen and volatile agent (+/- nitrous oxide)

Removal of carbon dioxide and volatile agent

Control of ventilation in some cases (IPPV)


How do we choose which breathing system to use?

Size of patient

(economy of circuit)

Is nitrous oxide being used?

Will we need to use IPPV?


What options are available for breathing systems?

Non re-breathing
Modified T-piece


(Parallel), coaxial


Parallel, (coaxial)

Humphreys ADE

Humphreys ADE


Describe re-breathing systems

Oxygen and anaesthetic agent are continually circulated

The system is topped up to replace lost gas (closed vs semi-closed)

Carbon dioxide is removed by soda-lime

Low flow rates make them ideal for larger patients


What are the advantages of re-breathing systems?

Low gas flow rates

Low volatile agent consumption

Expired moisture and heat conserved

Less pollution


What are the disadvantages of re-breathing systems?

High resistance to breathing

Cannot use N2O safely

Expensive to purchase

Regular soda lime replacement needed

Inspired gas undetermined

De-nitrogenation required

Can be slow to change level of anaesthesia


Describe non re-breathing systems

If no soda lime is present then the system must not allow rebreathing.

Enough gas must be supplied to flush away all the carbon dioxide before the next breath is taken

Each circuit has a circuit factor which is used to calculate the fresh gas flow rate to deliver to prevent rebreathing


What are the dependants when calculating the required gas flow?

Tidal volume

Minute volume

Circuit factor


What is tidal volume?

the volume of air breathed in in a normal breath

cats + small dogs 15ml/kg

medium + large dogs 10ml/kg


How do you calculate minute volume?

tidal volume x respiratory rate


How do you calculate flow rate?

Minute volume (litres) x circuit factor


What types of gas will be within the anaesthetic system?

Fresh gas

Alveolar gas (rich in CO2)

Anatomical dead space gas

Mechanical dead space


Describe mechanical dead space

Not to be confused with anatomical dead space gas!

We cannot change dead space in the patient

We can change dead-space in the circuit

ET tubes are the most common source of increased mechanical dead space

Masks can also create a larger mechanical dead space


Describe the Humphrey ADE system

Used with the soda lime as a circle

Used without as a Lack

The APL valve is special!

In the circle system it helps to reduce resistance allowing it to be used on smaller patients than a normal circle

In the lack configuration it allows very low flow rates, as it permits re-breathing of anatomical dead space gas