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MAHESWARI JAIKUMAR , profile picture
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SAFETY FEATURES OF ANAESTHESIA MACHINE

The anaesthesia machine has several safety features in its pneumatic components and gas delivery systems to prevent errors and ensure patient safety. These include color coding of gas lines and controls, pin indexing systems to prevent incorrect gas cylinder attachment, pressure regulators, and linkages or proportional valves to maintain minimum oxygen concentrations. Alarms activate if oxygen pressure or flow drops below safe levels. Unidirectional valves and pressure relief devices also protect the machine from excess pressure from the patient circuit.

Health & Medicine◦
SAFETY FEATURES IN ANAESTHESIA MACHINE DR. MAHESWARI JAIKUMAR maheswarijaikumar2103@gmail.com
SAFETY FEATURES IN ANAESTHESIA MACHINE • The anaesthesia machine is designed with safety devices as follows
SAFETY DEVICES IN ANAESTHESIA MACHINE Pneumatic components High Pressure Systems Low Pressure Systems Pin Index System Colour Coding Pressure Regulator Intermediate Pressure System
• Pipe Line Pressure Gauze • O2 Failure Safety Device • O2 Safety Valve • Gas Selector Switch • Stage Pressure Regulator • O2 Flush • Flow Control Knob • Hypoxia Prevention Device
• Mechanical Linkage • Electronic linkage • Unidirectional Check Valve • Pressure Relief Device • Common Gas Outlets • Different Tubes for different Gas
FRONT VIEW OF ANAESTHESIA MACHINE
BACK VIEW OF ANAESTHESIA MACHINE
PNEUMATIC COMPONENTS • The anaesthesia machine has pneumatic components that ensures safety foe the patients as follows: • 1) High Pressure System • 2) Intermediate Pressure System • 3) Low Pressure System.
HIGH PRESSURE SYSTEM • A) Hanger Yoke Assembly :- Gate Nipple Washer Retaining screw Yoke plug
PIN INDEX SYSTEM • Prevents wrong cylinder attachment. - Presence & Integrity of pins should be checked. • Filter :- Prevents dust & foreign particles from entering. • Unidirectional valve :- - Prevents backflow into the cylinder when cylinder pressure falls below the pressure inside the machine.
COLOUR CODING • Colour coding of cylinders used for same gas in machine. caps, hoses, flow control knobs, Pressure gauges ensures patient safety
PRESSURE REGULATOR • There are separate regulator for each gas, and cylinder output reduced to 45 psig Pipeline output reduced to 50-55 psig
INTERMEDIATE PRESSURE SYSTEM • The intermediate pressure system comprises of pipeline inlet connections, Fitted with threaded non-interchangeable DISS and colour coded for gases.
PIPE LINE PRESSURE GAUGE • Is Colour coded for each gas. • Is Present on the pipeline side of the unidirectional valve ( If present on the machine side – will show cylinder pressures) • Thus wont read 0 if pipeline supply fails. • The piping inside the machine is able to withstand 4 times the intended service pressure.
OXYGEN FAILURE SAFETY DEVICE • With respect to Oxygen Fail Safe Valve & N2O Shut off Valve ASTM Stds require that, whenever O2 supply pressure falls below manufacturer specified min pressure, the delivered O2 conc at the CGO should not fall below 19%. • If O2 pressure falls – N2O pressure falls proportionately. • If O2 supply fails – N2O is shut off.
CHECKING O2 SAFE VALVE • Switch on the flows of N2O & O2 in flow meters. • Disconnect O2 pipeline/ Close the cylinder valve. • N2O flow indicators falls to 0 even before the O2 indicator falls • O2 Failure Safety Alarm :- Alarm will set of when O2 pressures fall below specified minimum. (Usually 30 psig) Not possible to silence unless the pressure is restored
GAS SELECTOR SWITCH • Present in some machines prevents Air & N2O from being used together.
STAGE PRESSURE REGULATOR • Reduces pressures further to : O2 – 14 psi N2O – 26 psi • Provides a stable pressure to flow meters i.c.o. pipeline pressure fluctuation.
OXYGEN FLUSH • Delivers high flows (35-75 L/min) at intermediate pressures. •Can be activated even if the master switch is off. • Inappropriate & long activation – Barotrauma & Awareness to dilution is designed as “Single purpose, self closing device & recessed” • Usually recessed/ placed in a collar – to prevent accidental activation
FLOW CONTROL KNOB • There is only 1 flow control for each gas. • Is colour coded for each gas. • Appears in different size, consistency & position. eg :- O2 – larger & fluted & on the right side/ downstream.
LOW PRESSURE SYSTEM • Flow meter assembly : Stops @ full ON & OFF pos. Stop at full on pos – at top ↓ a) Prevents escape of indicator from tube to common manifold. • Prevents blockade of common manifold by the stop. • Prevents indicator from ascending to the top where it cant be seen clearly. Stop collar to flow meter knob – prevents damage to seat by pin when tightened.
DIFFERENT TUBES FOR DIFFERENT GAS • Tubes vary in diameter & calibration. • Tubes made leak proof by “O-rings” (Neoprene washers) at both the ends. • Tubes are coated with anti-static coating on both surfaces ↓ prevents indicator from sticking. • Made of glass – transparent material ↓ indicator clearly visible throughout the tube.
HYPOXIA PREVENTION DEVICE • Mandatory Min O2 Flow (MMOF) A MMOF – 50-250 ml/min – must as soon as the master switch is turned on and O2 flow – can’t be reduced below that. Some machines alarms when O2 flow falls below MMOF. • Min O2 Ratio : ASTM Stds require that; A Min O2 ratio/ Min O2 conc of 21% in the FGF at CGO. 2 types of linkages to achieve this.
MECHANICAL LINKAGE • Mechanical Linking of O2 & N2O. O2 – 14 tooth sprocket, & N2O – 29 tooth sprocket Connected by metal chain. • Both knobs turn together – to maintain min 25% O2 conc.
ELECTRONIC LINKAGE • An electronic proportionating valve ↓ maintains min 25% O2 conc in FGF. • A computer continuously calculates the N2O flow for the given O2 flow ↓ If higher N2O flow & O2 conc <25% ↓ Electronic proportionating valve automatically reduces N2O flow • Alarms is set off when O2:N2O falls below a preset value.
UNIDIRECTIONAL CHECK VALVE • Location :- Downstream to vaporisers Upstream to the point where O2 flush meets FGF. • Positive pressures generated within the ckt.s (eg – during controlled ventilation, when O2 flush is used) ↓ if transferred back to the machine ↓ dilution of volatile agents & interfere with the outflow through flow meters & vaporisers.
• Prevents +ve pressures within the ckt.s to be transferred to the machine. • Disadvantage :- Leaks upstream to the valve cant be detected.
PRESSURE RELIEF DEVICES • Location :- Downstream to the unidirectional valve Upstream to the point where O2 flush joins FGF. • To protect machine from high pressures. Opens & vents gases to atmosphere when preset pressure is exceeded. • Disadvantage :- Limits ability of the machine to provide adequate pressures ↓ Jet ventilation cant be provided
COMMON GAS OUTLETS • ASTM stds require that;- It should be difficult to accidently disconnect the delivery hose from the CGO. ↓ Thus fitted with std 15mm female slip joint fitting with 22mm coaxial male connector. • Some machines have 2 CGOs ↓ ASTM stds require that;- Only 1 CGO must be functional at a time.
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