Flashcards in Anaesthetic equipment Deck (28)
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
4.Low pressure side
5.Needle valves and rotameters (flowmeter)
8.Common gas outlet to circuit
9.low oxygen alarm
Describe the oxygen supply
Black and white cylinder
Sized E, F and J
Describe the nitrous oxide supply
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
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
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?
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
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
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?
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?
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