The anaesthetic machine Flashcards
what are the principle functions of an anaesthetic machine..
principle function of an anaesthetic machine is to deliver FGF to a patient +/- anaesthetic gases safetly and with accurate pre-set concentrations of gases
thus it usually has
- common gas inlet - with flow meters to control these
- vapouriser
- common gas outlet with a mixture of gases usually connected to circle system or a different breathing system
PLUS…
- safety features - pressure regulators and relief valves, alarms, hypoxic gaurds.
- also usually connected to scavenging, ventilator, monitoring for inspiratory/exp gases, volume, flow, pressure.
describe the components of an anaesthetic machine (describe how gas flows through)
can be described in 2 parts
high pressure system
- gas inlets from pipelines or cylinders (137 bar)
intermediate pressure system
- pressure regulators - reduce cylinder pressure to 400kpa, maintain pipeline pressure at 400kpa. protects machine from excess pressure
- pressure relief valves incase these fail - set to 700kpa
- transfers gas to the flowmeters
- O2 flush contains high pressure gas all up to common gas outlet (400kpa)
low pressure system
- flow meters reduce pressure of the system to 1-2 bar
- back bar contains vapouriser
- one way valve after vapouriser to prevent pumping
- joins common gas outlet.
common gas outlet then attached to a breathing circuit with CO2 soda lime, ventilator, monitoring system for gas’s and a display unit
what method of gas supply are there to an anaesthetic machine?
pipelines = 400kpa / 4bar
cylinders 137bar (except N20 = 52bar)
how are the pipeline gases connected to the machine
non interchangable screw thread (NIST) - each pipeline is attached to machine by permanent attachement
each pipeline is colourcoded
attached to wall by removable connection - schrader connection - the probes are tappered to fit correct shape of socket for that pipeline gas. also colourcoded ports at the wall.
how does an oxygen flush work?
non locking button can be pushed to open path for O2 to be released.
4bar pressure
35-75L/min flow rate
100% O2
what are the dangers of the O2 flush?
dilutes anaesthetic gases
causes barotrauma
what is a pressure reducing value and how does it work?
pressure reducing valve is present on anaesthetic machine to help maintain pressures of 4bar.
work via a diaphragm and spring method
the pressure that they regulate is determined by the complaince/ stiffness of spring and diaphragm.
constant bobbing up and down of the diaphragm allows smooth constant pressure to be maintained.
what different types of pressure regulators do you know?
pressure regulators maintain constant pressure
they can be single stage e.g. that seen in anaesthetic machine - one diaphragm and one valve
or double stage e.g. that seen in an entanox cylinder - 2 diaphragms and 2 valves with a middle gas section.
what is a pressure release valve?
this is a valve that opens when the pressure reaches a certain point e.g. APL valve (adjusted pressure limiting valve)
they are also found on the high pressure part of anaesthetic machine incase pressure regulators fail (set at 7bar)
the pressure they work at is set by the compliance/ stiffness of the spring and diaphragm.
where is high pressure converted to low pressure , how does this work?
at the flow meters
via a needle valve
as the needle valve opens, flow increases and bobbin rises, pressure drops to 1-2bar.
how does a richie whistle work?
if the O2 pressure falls below 200kpa, a diaphragm drops, opening a valve that allows air to escape via a whistle.
sounds 60dB for 7 seconds
what are the safety features of an anaesthetic machine?
describe in direction of gas flow
power supply - usually have a back up battery and will alert if low power.
pipelines:
- NIST, Schrader, colour coding
- reinforced copper piping
cylinders:
* pin index system
* bodolk seal - tight seal
* pressure gauges - bourdon gauge at front of machine
pressure regulators
* protect machine
* back up releif valve - creates a hissing noise (7bar)
flow meters
* antistatic
* bobbins can sometimes rotate
* colour coded
* O2 to the left, larger and ridged.
* interlink N20 and O2
* O2 last gas to be added and separate stream
vapourisers
* selectatec system - prevents leak or incorrect attachment
* one on at a time
* anti spill
* keyed vapouriser filling system.
* liquid level indicator
* one way valve prevents pumping
oxygen flush
* non-locking
* recessed in housing to prevent accidental press
alarm and monitors for gases and pressures.
connectors are specific sizes 22cm for breathing system 30mm for scavenging.
how are anaesthetic machines protected from high pressures?
pressure regulators
flow restrictors
pressure relief valves
what are the different outputs for FGF in the anaesthetic machine
circle system
common gas outlet - for attaching a different breathing system
can use a switch to switch between circle and this.
where are vapourisers found on the anaesthetic machine and how are they attached?
back bar
attached via selectatec system
prevents being turned on if not attached properly
prevents 2 being turned on at the same time.
draw a 2 stage pressure regulator..
draw a one stage pressure regulator ..
by what mechanism is the N20 and O2 linked to prevent hypoxic mixtures?
the outlet for N20 is controlled by the pressure in O2 line
how does a flow restrictor work?
state correct pin index for the common gases…
identify this ..
entanox valve
It has a two-stage pressure demand regulator valve. The first one is a pressure-reducing valve and the second one is a demand valve which allows gas to flow when the pressure is reduced below atmospheric level.
