Anaesthesia III Week 1-4 Flashcards
What are the NZ cylinder sizes?
A-J
A is our standard size
How is oxygen stored in cylinders?
As a gas
13700kPa
How is nitrous oxide stored in a cylinder?
As liquid with vapour on top
4400kPa
It is only partially filled to reduce excessive pressure with changing temperature
What is a filling ratio?
The weight of the fluid in the cylinder divided by the weight of water required to fill the cylinder.
In warmer climates the ratio is less.
0.75 filling ratio in NZ
Why might ice form on a cylinder?
At high use when plenty of liquid is being converted to a gas and using latent heat of vaporisation leaving the cylinder extremely cold
What is required on a cylinder label?
Name Chemical symbol Form ID and batch number Hazard info Size Maximum pressure (bars) Content capacity (L) Fill date and expiry date Directions Handling instructions
What are safety features of cylinder?
Molybdenum steel Thread on neck melts at temperature to let gas escape and prevent built up pressure Label Colour code Pin index system valves Regularly checked - annual
What is the storage criteria for cylinders?
Purpose built area, fire proof, well ventilated, away from heat, grease, oil, dampness and chemicals, keep empty away from full.
What is a bodok seal?
Rubber (neoprene) with brass rim to prevent a leak between cylinder and yoke
Describe the pin index and colour system for the five main gases
Oxygen: White shoulder, white body, 2,5
Nitrous: ultramarine shoulder, white body, 3,5
Air: White/black quarters, white body, 1,5
Carbon dioxide: green shoulder, white body, 1,6
Entonox: White/ultramarine quarters, white body, 7
Describe the pipelines
400kPa
Copper (reduce microbe, degradation) and brass fittings
Colour coded
Sleeve index system prevents incorrect bollard attachment
Non-interchangeable screw thread prevents incorrect machine attachment
What is the cylinder manifold?
The nitrous, entonox and back up oxygen cylinder bank
Large cylinders in 2 groups. Connected to common pipe with non return valves
Connect to pipeline via regulator
In either group in use, all valves are opened so cylinders drain evenly and auto switch to other group when empty
Describe the components of a medical gas cylinder.
Aluminium case
Neck at top where valve attaches
Detailed label
What is a VIE?
Vacuum insulated evaporator
Stores liquid oxygen
Double walled steel tank with perlite in a vacuum space - insulation
Safety valve to release excess pressure
If more O2 needed a valve allows liquid O2 to pass over insulated copper and it evaporates
-150 to -170 degrees and 1000kPa
Latent heat allows VIE to keep cool
How is medical air stored?
Compressor plant
Room air is drawn in, filtered, compressed and stored for use.
Compare and contrast bulk gas supply and cylinder supply.
Amount which is stored: VIE huge, cylinder less
13700 cylinder: 1000 VIE
VIE expensive but cheap oxygen while cylinders are cheap but expensive oxygen
VIE very cold
Both colour coded
Both hazardous
Both pressure regulated
What is a pressure regulator reducing valve?
Changes a high pressure to a low pressure
Protects machine from surges
Allows fine gas control
Reduces consequences of gas leak
Balance between high pressure and diaphragm on spring maintains a constant pressure
Relief valves in case of failure
List the 10 features of anaesthetic machine safety.
O2 failure alarm N2O cut out Anti hypoxic mechanism Back up battery Cover over on/off Recessed O2 flush button 22mm/15mm CGO Individual P gauges visible at front Anti static wheels Pressure regulator (NIST, O2 cylinder, pin index, colour coding, oxygen analyser, ventilator alarms, auto vapour compensation)
Describe a pressure gauge.
Pressure in cylinder or pipeline display
Flexible, coiled tube connected to a pointer at one end and gas supply at other. Pressure changes causes coil/uncoil so needle moves
Colour coded
Calibrated per each gas
Draw a VIE
-
How is the pressure managed from pipeline to machine?
A regulator achieves 100-200kPa
What is a one way/back flow check valve?
Next to inlet yoke
Prevents leaks from empty yokes when cylinder not attached
What is a flow meter?
Measure flow rate of gas
Calibrated to each gas at room temp and atm pressure
+/-2.5% accuracy
Flows > 1L/min measured in L/min, less than this is on 100ml/min
Comprised of control valve, conical tube and bobbin
200ml/min oxygen always flow
Control valves colour coded, ridged
O2 sits more proud, last gas, ridges
2 gears connect O2/N2O to prevent hypoxia mix
What are the features of bobbins?
Bobbin rises with gas
Fluted sides causing spin which can be seen by a dot
Measure from top of bobbin or middle of round bobbin
What are the components of the suction system?
Pump/power source continuously generate -500mmHg Suction controlled with filter Collection vessel Tubing Yankeur
What are the ideal features of suction?
-53kPa should be maintained
Should withstand 40L/min flow
Take less than 10s to generate
Reservoir large to hold but not too big to slow start up
Tubing must resist collapse, be clear, sufficient diameter and length
Yankeur should b tapered, clear, smooth and multi holes to prevent blockage
How is suction created?
Electric motor and pneumatic pumps generate negative pressure by Venturi principle
Amount of vacuum can be manually adjusted
Describe the oxygen flush and draw it.
Non locking recessed button Self close valve Delivers pure oxygen by bypassing vaporisers and flow meters 35-75L/min and 400kPa Risk of barotrauma and diluting agent
What are the 10 features of oxygen failure alarm?
Depend on O2 pressure Require no battery/mains Specific audible signal for sufficient duration and volume Warn of impending failure and actual failure Interrupt flow of other gases Prevent cancel/use until fixed Located on reduced pressure side Tamper proof Not affected by back pressures Cuts other gases (fail safe)
What is the anti hypoxic mechanism?
Mechanical: chain links O2 with N2O control valves so that an increase in N2O results in a proportional increase in O2
Paramagnetic O2 analyser: continuously measures O2 and the nitrous is auto switched off when O2 is less than 25%
Pneumatic: pressure sensitive diaphragm
Describe the common gas outlet.
Where all gas exits
22mm male and 15mm female connection
What happens at the neck of the cylinder when it gets too hot?
The neck melts to reduce explosion risk
What is a vaporiser?
Changes liquid agent to a vapour
This gets expresses as a percent of saturated vapour added to gas flow
Adds a controlled amount of agent to the fresh gas flow
What are the ideal characteristics of vaporisers?
Performance not affected by changes in FGF, volume of agent, temperature or pressure Low resistance to flow Light weight Economic and safe Corrosion and solvent resistant
What does the interlock system do? (I.e select-a-tec)
Locks vaporiser to back bar Ensure correctly mounted (Compromised agent delivery) Cannot dial on unless correctly engaged Cannot use more than one at a time FGF only enters when correctly engaged and on Trace vapour when off is minimal
Define vapour
Gaseous phase of a substance which is usually a liquid or solid. It is at a temperature less than critical point so is easily condensed.
What is the saturated vapour pressure of the main agents?
Sevo: 157mmHg
Des: 669mmHg
Iso: 238mmHg
At 20 degrees
How does the plenum vaporiser work?
Calibrated to agent spec
FGF is split as it enters: bypass and vapour chamber
Chamber fully saturates gas with vapour
Concentration adjusted by dial which alters amount of gas flowing through the chamber and bypass
Cooling occurs due to latent heat
Bimetallic strip automatically adjusts splitting ratio to compensate for this so when temperature is low more gas flows to the chamber
How does saturation of the FGF get achieved in the plenum?
High surface area on contact between the FGF and agent
Done with wicks saturated with liquid agent or a series of baffles
Define SVP?
Pressure of the vapour in equilibrium with its liquid phase. ie there is an equal amount of molecules condensing as there are evaporating. The maximum amount of evaporation has been reached
What are the safety features of the plenum 5/7?
Anti spill means agent can't enter bypass when tipped - up to 180• Interlock safety features Pressure relief valve downstream Keyes fillers Low filling port Colour and label Dial always increases anti-clockwise Release button at rear to turn dial Vaporiser ID Agent specific Liquid level indicator Anti-overfill Temperature compensatory mechs 0 on dial most obvious, extra markings for less than 1%
What are the hazards of the plenum 5/7?
Interlock uses o-ring increases leak risk
Pumping effect
Preservatives may interfere with wicks or bimetallic strip
Over tip
Simultaneous inhaled agent
Electronic failure
Incorrect agent
Describe the filling devices.
Agent specific
Geometric and colour coded
Cannot overfill
Anti pollution cap stays on bottle to prevent vaporisation
What is Mac?
Minimum alveolar concentration The concentration of vapour in lungs needed to prevent response in 50% of subjects in response to surgical stimulus Compares strength of agents Values assume no other hypnotics used Some gases are additive eg N2O
