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Modern Anaesthetic machines (modern anaesthetic machines (6 basic…
Modern Anaesthetic machines
History
5 elements still present at modern machines
flowmeters
vaporizer
presure gauge and reducing valves
breathing system
high pressure supply of gases
HEG Boyles original machine 1917
modern anaesthetic machines
anti-static tyres
improve flowmeter performnce
reduce risk of ignition of flammable gas
modifications to suit the environment
compact or wall-railed models, for restricted areas
single position back bar
Pneupac 110
Frontline genius compact Anaesthesia machine (Blease)
larger- trolley or ceiling mounted
Aestiva 15 pendant version
MRI compatible version
Prima SP Anaesthetic machine (Penlon)
6 basic subsystems
vaporizer
gas delivery: breathing system and ventilator
gas flow measurement and control (flowmeters)
scavenging
gas supplies: pipelines and cylinders
monitoring
Gas supplies
Piped gas supplies
Piped medical air
a compressor with an outlet filter
cylinder manifold
Nitrous oxide
cylinder manifold
Piped oxygen is drawn from a central source
vacuum insulated evaporator
cylinder manifold
oxygen concentrator
fed into labelled, colour coded, flexible pipelines
3 components
Flexible hosepipe
Oxygen- white, nitrous oxide- french blue, medical air- black/white
Non-interchangable screw thread (NIST) connection to anaesthetic machine
Schrader probe (unique diameter)
Cylinders
As back up, when the central system fails
Safety features
safety outlet, fitted between the valve block and cylinder neck; melts at relatively low temp to allow gas leaks to prevent explosion in case of fire
Color coding for each gas and vapour
Leaks are prevented by a nylon ring around the spindle
Molybdenum alloy steel construction
Pin index system
Bodok seal (BOnded Disk)- non combustible neoprene washer; provides gas tight seal
Pressure regulators
Secondary regulators: level out gas delivery
Primary regulators: Reduced potentially dangerous high cylinder pressure to machine working pressure at 4 bar (420kPa)
Gas flow measurement and control
Features reducing inaccuracy
Features reducing inaccuracy to within 2 %
Tubes have different length and diameters
Anti-static inner and outer coating
Sight tubes for each gas individually calibrated at 20'C at 101.3kPa; non interchageable
Tubes are leak proof because of neoprene washers (o-ring) at both ends of flow meter block
Bobbin is visible and has vanes to improve its rotation
Hypoxic mixtures prevent devices
Pneumatic devices, eg MIE, use a ratio mixer valve
Electronic devices eg Penlon, use a paramagnetic oxygen analyser to continuosly sample the gas mixtures from the flowmeters; if the inspired oxygen ratio < 0.25 the nitrous oxide is temporary cut off
Mechanical, eg Ohmeda, use a chain to link flow control valves for oxygen and nitrous oxide; a stop fitted to the valve ensuring minimum flow of oxygen 175-250 ml/min even with the valve apparently closed
Flow control valves: govern transition from high- to low pressure
Vapourizer
Selectatec type (DatexOhmeda) or Interlock (Drager)
Modern vaporizers safety features
A non-spill reservoir with upto 180' allowable tilt
a keyed-filler or pour-fill system prevent filling with an incorrect volatile agent and minimize leaks
A clear indication of liquid level
an increase wig capacity
An interlock to isolate vaporizers not in use
safety features of back bar
pressure relief valve- set at 30-40kPa
Emergency oxygen flush (35-75 L/min)
spring loaded non-return valve- prevent surges in back pressure from damaging flow meters and vaporizers
oxygen failure warning device
( when oxygen supply pressure < 200kPa
Gas delivery
ventilators
electroniclly controlled, pneumatically powered
Breathing system
circle
Anmedic Q-mix- using shunt valve, adjust the proportion of exhaled gas into the absorber canister -> manipulate end tidal CO2 concentration
t-piece
APL valve (Adjustable pressure limiting)
allows excess gas to escape when a preset pressure id exceeded , thus minimizing risk of barotrauma
adjust via manual or electronic
use in both types of breathing systems
Scavenging
4 components
transfer system
wide bore tubing connecting collecting system to receiving system
receiving system
reservoir, air brake, flow indicator and filter
collecting system
APL valve of breathing circuit
disposal system