Transcript Anaesthetic Machines

Anaesthetic Machines
Sophie Young
21st February 2007
Aims and Objectives
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Components of anaesthetic machines
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Safety features of anaesthetic machine
Why do we need an anaesthetic
machine?
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Supply compressed gases
Measure flow of gases
Add vapours in known concentrations
Deliver vapours and gases to patient via a
breathing system
Scavenge waste
Monitor machine and patient
Anaesthetic Machines
“Pressurised gases are supplied by cylinders
or pipelines to the anaesthetic machine
which controls the flow of gases before
passing them through a vaporiser and
delivering the resulting mixture to the
patient via the breathing circuit”
History
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Original Continuous-flow Anaesthetic Machine
designed by Boyle in 1917
Most current anaesthetic machines derived from
Boyles Machine
Simpler anaesthetic machines – ‘draw over’ used
by Armed Forces (no need for fresh gas supply)
Boyles Anaesthetic Machine
http://www.nda.ox.ac.uk/wfsa/html/u06/u06_015.htm
Components of the Anaesthetic
Machine
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Gas supplies
Pressure gauges
Pressure reducing valves
Rotameters
Vapourisers
Common gas outlet
High flow oxygen flush
Pressure relief valve
Oxygen supply failure alarm
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Breathing
system
Ventilator
Scavenging
Suction
Monitoring
devices
Basic Components of Anaesthetic Machine
Fundamentals of Anaesthesia
Gas Supply - Pipelines
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Central supply point
O2, N2O, air, medical vacuum supplied
Pipelines throughout hospital
Outlets – colour and shape coded
Flexible colour coded pipelines run to
anaesthetic machine
Pipelines permanently fixed to machine (NonInterchangable Screw Thread – NIST)
Pressure 400kPa (4 bar)
Gas Supply - Cylinders
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Molybdenum steel
Size E
Filling pressures
Colour coded
Pin Index System
Bodok seal
Valve (open + close prior to attaching) – key
and keyless
Essentials of Anaesthetic Equipment
Pressure Gauges
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Pressure gauges to measure pipeline and
cylinder pressures
O2, N2O and air gauges on front of machine
Gas colour coded and calibrated
Bourdon Gauge
www.frca.co.uk/article.aspx?articleid=100325
Pressure Regulators
Function:
 Reduce pressure to protect machine
 Maintain constant supply to compensate for
changing cylinder pressures + demand
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Reduce pressure from 13 700kPa to ~400kPa
Compression spring
acting on diaphragm
coupled to inlet valve
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Essentials of Anaesthetic Equipment
Rotameters
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Measure flow rate of gas passing through them
Calibration (accuracy +/- 2.5%)
Components: flow control
(needle) valve, tapered tube,
bobbin (slits + dot)
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Low flow rates: flow laminar +
function of gas viscosity
(Poiseuille’s Law)
High flow rates: flow turbulent
+ function of gas density
Essentials of Anaesthetic Equipment
Problems with Rotameters
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Non-vertical tubes
Tube damage/leakage (O2 enters back bar
downstream from other rotameter outlets)
Back pressure from common gas outlet – drop in
bobbin level
Bobbin sticking:
 Static electricity
 Dirt
Back Bar
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Horizontal part of machine between rotameters
and common gas outlet
Vapourisers mounted here so volatiles can be
added to fresh gases
Pressure ranges 0-30 kPa (1 kPa at outlet end)
Non-return pressure relief valve downstream of
vapourisers set at 35 kPa – prevents barotrauma
to rotameters, vapourisers and patient
Vapourisers
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Add controlled amount inhalational agent, after
changing it from liquid to gas, to fresh gas flow
Design depends on SVP, boiling point and MAC
of volatile being used – variable bypass or
measured flow vapouriser
Accurate delivery of anaesthetic agent
regardless of time, gas flow and temperature
Antispill mechanism
Colour coded keyed filling devices
Safety interlock device
Variable Bypass Vapouriser
Essentials of Anaesthetic Equipment
Measured Flow Vapouriser
http://www.frca.co.uk/article.aspx?articleid=100151
Common Gas Outlet
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Fresh gas mixture supplied to patient or
ventilator
Often mounted on swivel
22mm male – outlet’s external diameter
15mm female – outlet’s internal diameter
Safety Features of Anaesthetic
Machines
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Non interchangable
pipeline outlets
Colour coded pipelines
and cylinders
Pin index system
Pressure gauges for
gases
Colour coded
rotameters
Oxygen rotameter on
left, protrudes, ridged
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Oxygen/nitrous oxide
interlink device
Emergency oxygen
flush
Oxygen failure warning
device
Keyed vapouriser fillers
Pressure relief valve
Anaesthetist to check
the machine
Oxygen Failure Warning Device
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Upstream of rotameters
Specifications (British Safety Standard):
 Audible alarm >60db, 1m from machine, >7
seconds
 Activated when O2 supply falls to 200kPa
 Power supply from O2 supply pressure
 Alarm can’t be switched off/reset until O2 supply
restored
 Coupled to gas cut off valve – opens machine
circuitry to air
Ritchie Whistle (1960)
Fundamentals of Anaesthesia
Emergency Oxygen Flush
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Non-locking button
Bypass rotameter block and back bar
Delivers flow > 30 l/min
Pressure ~400 kPa
Risks:
 Barotrauma
 Awareness
Summary
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Basic components of anaesthetic machine
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Safety features of anaesthetic machine
Any Questions?
References
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Al-Shaikh et al (2002) Essentials of Anaesthetic Equipment.
Churchill Livingstone
Pinnock et al (2003) Fundamentals of Anaesthesia. Cambridge
Aitkenhead et al (2001) Textbook of Anaesthesia. Churchill
Livingstone
Davis et al (2005) Basic Physics and Measurement in Anaesthesia.
Butterworth Heinemann
Milner (1996) Update in Anaesthesia
http://www.nda.ox.ac.uk/wfsa/html/u06/u06_015.htm
Anaesthesia UK (2005) Temperature Measurement
www.frca.co.uk/article.aspx?articleid=100325
Anaesthesia UK (2004) Precision Vapourisers
http://www.frca.co.uk/article.aspx?articleid=100151