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L8: Anaesthetic machines
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24
Veterinary Medicine
Undergraduate 3
05/31/2012

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Term
Oxygen cylinders
Definition
-pure gas under P
-volume and P related
i.e. contents of cylinder proportional gas P
~135atm
Term
Nitrous oxide (N2O) cylinders
Definition
-gas compressed to liquid
-requires E for liquid to boil to produce gas
-contents of cylinder NOT proportional to gas P
~44atm
Term
Pressure gauges
Definition
indicate P and so content of cylinders of compressed gas
NB: not N2O!
Term
Content of N2O cylinder
Definition
only way to accurate idea of contents is to turn it off and wigh the cylinder
Term
How are cylinders connected to the anaesthetic machine?
Definition
valve of cylinder yoke of anaesthetic machine
Term
Pin index system
Definition
Ensures incorrect gas cylinder can not be placed in yoke of anaesthetic machine
indents/ holes in neck of valve of cylinder
... correspond with...
pins of yolk of anaesthetic machine
Term
Bodak seal
Definition
prevents leaks between cylinder valve and yoke
Term
Oil or grease use as a seal
Definition
NEVER use oil or grease as a seal - if there is a leak between the cylinder and the yoke a fire will occur
Term
Pressure regulator
Definition
provides a constant pressure to ensure a steady flow of gas is delivered to the patient (until the cylinder P falls below the output P)
-connected to yoke of anaesthetic machine
Term
How does pressure regulator work?
Definition
-uses an internal "diaphragm"
-has a safety valve which releases gas into the environment in case the diaphragm fails (which would result in high P gas being delievered to the patient)
Term
Check valve
Definition
gas from the regulator to the patient passes over a one-way check valve
-prevents the reverse flow of gas back through the regulator
-important im preventing loss of gas when cylinders are changed on the anaesthetic machine
Term
Flow meter control valve
Definition
aka needle valve
-controls the flow of gas passing through the rotameter/flowmeter and hence to the vaporiser and patient
-gas from the cylinder passes through this after the check valve
Term
Rotameter/flowmeter
Definition
measures the flow rate of gas in a closed tube -bobbin within the tube rotates - measure flow of gas from the top of the bobbin
Term
Vaporiser
Definition
for the admin of volatile agent (e.g. isoflurane) to the gas
Term
Dial on the vaporiser
Definition
indicates the percentage of FGF that is diverted to "pick up" saturated vapour
e.g. 1% isoflurane = 1% of FGF to be delivered to the patient is saturated w. iso. vapour
Term
why must vaporisers be kept upright?
Definition
-if tipped the volatile agent may get into the mixing chamber and may result in a lethal conc. of anaesthetic agent being delieverd to the patient
Term
high pressure relief valve
Definition
gas passes through this after the vaporiser
-protects the anaesthetic machine from excess P which may occur is the flow of gas from the machine is restricted
NB: not to protect the patient!
Term
common gas outlet
Definition
the connection between the anaesthetic machine and the patient
Term
Patient safety devices
Definition
-ratio regulator
-nitrous oxide cut off
-alarm whistles
NB: not all devices are fitted to all machines
Term
ratio regulator
Definition
ensures the proportion of oxygen delivered to the patient is greater than the minimum conc. set (usually 28-35%) e.g. N2O turned on before O2 flow - O2 flow will automatically be turned on at set min. conc. -provides a hypoxic guard so patients always receive O2 at safe conc. and so prevent hypoxia
Term
Nitrous oxide cut off
Definition
stope the flow of N2O to the flow control valve in the event of lost supply of O2 to the anaes. machine
NB: does not prevent patient receiving hypoxic mixture
Term
How does the nitrous oxide cut off system work?
Definition
-normally the O2 P pushes a plunger up and out of the flow of N2O so the N2O flow can pass
-w/o O2 flow, the plunger is released and blocks the passages of N2O flow
Term
Alarm whistles
Definition
-activated when P of O2 pipes of anaes. machine reaches a certian preset P
-usually powered by a small cylinder of O2 that is charged when the main cylinder is turned on or the pipeline is connected - when activated the gas in the alarm cylinder is released through a whistle
Term
Sequence of components of anaesthetic machine
Definition
Both O2 and N20: gas cylinder -->pressure regulator --> check valve
(O2 cylinder has whistle alarm system attached)
(N2O then passes through nitrous cut off valve)
Both independently--> flow meter control valve and flowmeter
Flow lines combine -->vaporiser --> high P relief valve -->common gas outlet
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