What equipment do we need for anaesthesia? Machines.

Question 1

Cylinder yolk.

Answer 1

Supports the 02/N2O cylinder.
Bodok seal provides gas-tight seal.
- Made of non-combustible neoprene washer w/ a copper ring.
Allows one-way flow from cylinder to machine.
Prevents wrong cylinder being attached to the wrong yolk.
Cylinder is attached to machine via the yolk.
Tighten into place.
Open cylinder slowly.
Avoid over tightening.
Avoid oils/moisturiser on hands when handling this (fire hazard).

Question 2

Pin index safety system.

Answer 2

All cylinders have a pin index.
Ensures only correct gas can be connected to corresponding outlet.
Yolk on GA machine has 2 protruding pins which are aligned w/ the 2 holes on the corresponding gas cylinder.

Question 3

Pressure gauge.

Answer 3

Indicate pressure in kPa.
Gas specific and often colour coded. e.g. white = O2, blue = N20.
Pressure of cylinder proportional to volume of gas contained within it. Pressure gauge drops as cylinder empties.
Use pressure gauge to determine when cylinder needs changing.
Measures pressure of both cylinders and pipelines.

Question 4

Pressure regulator.

Answer 4

Cylinder gas at v high pressure (>10,000 kPa).
Pressure needs reducing to safe level so does not damage machine (~400kPa).
Reduces cylinder pressure to suitable pressure.
Compensates as cylinder contents decreases.
Ensures safe gas deliver at manageable pressure.
Smooths any fluctuations of pressure from gas supply.

Question 5

What does the flowmeter consist of?

Answer 5

Flow control valve – reduces gas pressure from 400kPa to just about atmospheric pressure (100kPa), allowing fine adjustments of gas flow through flowmeters by manual adjustment..
A tapered transparent tube – gas enters tube when the valve is open. Can see where gas level is (usually displayed in L/min).
Lightweight rotating bobbin or ball – floats within tube as gas passes around it. Bobbin rises as flow increases. (read from top of bobbin, read from centre of ball).

Question 6

Types of vaporisers.

Answer 6

Classic vaporisers.
Newer model classic vaporisers.
DIVA (Direct Injection of Volatile Anaesthetic) vaporisers.

Question 7

1. What does TEC stand for?
2. Where on the anaesthetic machine is the vaporiser situated?
3. What is contained in the vaporiser?
4. How is the agent delivered to the patient?

Answer 7

1. Temperature Compensation Mechanism.
2. Back bar, downstream of the flowmeter.
3. Volatile liquid anaesthetic agent.
4. Gas from the flowmeter is passed through the vaporiser, picking up the VA to deliver to the patient via the breathing system.

Question 8

1. Explain gas flow through the vaporiser.
2. How is the effect of vapour cooling minimised?
3. What so the wicks do?
4. What do the baffles do?

Answer 8

1. Gas enters vaporiser and splits into 2 streams.
   - Bypass channel (avoids passing liquid anaesthetic).
   - Into chamber above liquid anaesthetic.
   – Ratio passing into each of these is adjusted by a control valve.
   –> The ratio adjustment increases or decreases the concentration of vapour picked up by the gas.
   –> Valve controlled by large dial on the front of the vaporiser.
2. Vaporiser housed in a large block of brass.
3. Increase SA for evaporation of anaesthetic liquid.
4. Direct incoming gas down to the surface of the liquid.

Question 9

1. Where is the non return pressure relief safety valve positioned?
2. What does this safety valve do?
3. When does the valve open?

Answer 9

1. Downstream of the vaporiser.
2. Prevents backflow of gas to the machine / prevents back pressure. Protects the machine, not the patient.
3. When the back bar pressure is >35kPa.

Question 10

1. What is the purpose of the O2 flush button?
2. Risk of pushing O2 flush button when attached to the patient.

Answer 10

1. Allows you to quickly remove volatile gases from the system i.e. in an emergency.
2. Supplies O2 at pressure of 400kPa and 35-75L/min and bypasses flowmeters and vaporiser which are meant to control pressure.
   Use could cause barotrauma.
   Dilutes the anaesthetic gases.

Question 11

1. What is the common gas outlet?
2. What does the common gas outlet do?

Answer 11

1. Place for attachment of breathing system to the GA machine. Exit point for gases from the machine – Should be an exit only! Not an entry point.
2. Delivers gas(es) and anaesthetic agents to the patient.

Question 12

1. At what point should the oxygen supply failure alarm sound?
2. What happens when this pressure is reached?
3. What could occur if O2 drops and alarm does not sound?

Answer 12

1. When the oxygen falls below 200kPa.
2. Either alarm sounds or warning message displays on the display screen.
3. Staff not aware and O2 could run out and patient may become hypoxic.

Question 13

1. What are the 2 main types of O2.
2. Other methods (not as common).

Answer 13

1. • Cylinder attached to the machine.
     - Piped O2.
2. • Liquid O2.
     - Oxygen generators.

Question 14

Piped O2…
1. What does NIST stand for and what is this?
2. What material are the pipes made of that carry the oxygen from the cylinders to the machines?
3. How is the risk of O2 becoming too low addressed?

Answer 14

1. Non-interchangeable Screw Thread.
   It is attached to the back of the GA machine that attaches a pipe which leads to the wall and attaches to the wall via a Shrader probe which inserts into the Shrader socket. The NIST is a nut and probe w/ a unique profile for each type of gas – safety feature. Incl. one-way unidirectional valve.
2. Copper.
3. An alarm sounds to notify that the O2 is low and there is a reserve bank of 02 ready to be switched on and a new cylinder can be started and be ready for reserve when the next cylinder runs out.

Question 15

1. Purpose of the Schrader probe?
2. Advantages of Piped O2.
3. What are O2 cylinders made of?
4. What helpful feature informs as to which type of gas is contained in the cylinder?

Answer 15

1. Prevents misconnection as it has a unique diameter index collar which matches its corresponding Schrader socket.
2. The cylinders are large so do not run out as quickly.
3. Molybdenum Steel.
4. Colour coding.

Question 16

O2 cylinder safe storage.

Answer 16

• Under cover, kept dry and clean, usually locked away w/ key access.
• Room should be well ventilated and fire-proof, and away from flammable / combustible materials.
• O2 cylinders should be chained to a wall or secured well.
• Full and empty cylinders should be stored separately.
• Large cylinders usually stored vertically.
• Smaller cylinders usually stored horizontally.

Question 17

Safe handling of cylinders.

Answer 17

• Do not hold w/ one hand.
• Do not carry over your head.
• Care not to drop on your feet or anyone else’s feet.
• Care not to drop onto the floor as they can break and contain pressurised gas which can do a lot of harm.
• Large cylinders will require 2+ people to manoeuvre.
• Should transport small cylinders w/ a trolley.

Question 18

1. At what temperature does O2 liquefy?
2. What is liquid O2 contained in?
3. Where would the liquid O2 container be located?
4. How is liquid O2 delivered to the patient?
5. How do we ensure adequate supply when any primary supply system fails?
6. What are the risks of liquid O2.

Answer 18

1. -183C.
2. Vacuum Insulated Evaporator.
3. Outside.
4. Drawn off as required, passed through a vaporiser and turned into a gas before it is piped into the hospital. A control panel regulates flow of gas from the container before it enters the pipework system.
5. Backup cylinder manifolds.
6. Burns, frostbite and hypothermia.

Question 19

1. What do O2 concentrators do?
2. Where would we see these systems used.
3. Why are these systems advantageous?

Answer 19

1. Takes in air and purifies it w/ molecular sieve containing Zeolite that removes nitrogen from the air, leaving the remaining 87-95% O2.
2. By people requiring O2 at home, in ICU units and for anaesthesia.
3. Economical.

Question 20

1. What is the purpose of scavenging?
2. What are the 2 types of scavemging?

Answer 20

1. The removal of environmental contaminants such as anaesthetic VAs and gases, which are subject to the Control of Substances Hazardous to Health (COSHH) and the Health and Safety at Work Act, as they can have a negative impact of personnel safety.
2. Active and passive.

Question 21

1. What is active scavenging? – What is required for patient safety?
2. What is passive scavenging? – How is passive scavenging advantageous?

Answer 21

1. Waste gases and anaesthetic agents are drawn outside of the building by a fan and vent system. – Requires an air break to prevent negative pressure being applied to the patient’s breathing system.
2. Where gas is pushed by the patient’s respiratory effort into the tubing either:
   - into tubing leading to the outside of the building. This makes it more difficult for the patient to exhale due to increased resistance.
   - into a canister container activated charcoal. Does not absorb nitrous oxide. Needs to be weighed regularly.
   – Versatile as can use on a mobile GA machine.

Question 22

How do we reduce our exposure to anaesthetic gases and volatile agents?

Answer 22

• Well-ventilated theatre / recovery area (15-20 air changes per hr).
• Use IV induction agents when possible.
• Cuff ET tubes.
• Connect animal to breathing system before turning on the gas.
• Use low flows.
• Check for leaks.
• Flush breathing system w/ O2 before disconnecting the animal.
• Use key fill vaporisers.
• Fill vaporisers at the end of the day where possible.
• Monitor personnel exposure to anaesthetic gases.

Question 23

Patient safety features of anaesthetic machines.

Answer 23

• Pin-index system and NIST for pipelines.
• Non return pressure relief safety valve.
• Colour coded pressure gauges and flowmeters.
• Colour coded gas cylinders.
• Alarm whistle.
• Reserve O2 cylinders.
• Vaporiser / volatile agent key filling device (gas specific).

Question 24

Describe how to complete a full GA machine check.

Answer 24

1. Check that there is an air break and that it is connected to the scavenging system if active scavenging.
   - Ensure scavenging system is attached to an outlet e.g. Fluosorber or wall socket. NEVER use Nitrous Oxide w/ a Fluosorber.
   - Attach scavenging hose to the common gas outlet.
2. • Check O2 supply.
     - Check cylinder firmly attached. If no cylinder, connect the pipeline.
     - Using valve spindle key w/ the “ON” side upwards, open cylinder – slowly w/ 2 twists of the key. Make sure no hissing.
     - Check contents gauge to ensure O2 cylinder not empty / nearly empty.
     - Switch machine on.
     - Turn the O2 flowmeter on and check that the bobbin moves all the way to the top, then set to 4L/min.

Question 25

…

Answer 25

3. Check N2O supply.
   - Turn N2O cylinder on in the same way as O2.
   - Check N2O cylinder gauge.
   - Turn on N2O flowmeter and check it turns smoothy and then set to 4L/min.
4. Check the O2 fail-safes.
   - Turn O2 cylinder off by using key in off position. If using pipeline only machine, turn off pipeline.
   - O2 gauge will drop to zero and O2 alarm should sound.
   - Both O2 flow and N2O flow should drop to zero as seen on the flowmeters, so N2O is not delivered when O2 has stopped flowing.
   - If pipeline, plug O2 pipeline into wall socket – makes alarm sound briefly. If not pipeline, turn O2 cylinder back on.
   -Hold the wall socket w/ one hand and tug gently on the O2 pipeline to ensure it is firmly attached.
   - Check pipeline O2 gauge and both O2 and N2O flow have been restored.
   - Turn N2O flow off.
   - Check pipeline N2O gauge now reading zero w/ O2 flow unaffected.
   - Plug N2O pipeline into wall and tug again in the same way as the O2 pipeline.
   - Check pipeline pressure gauge is reading and flow has been restored, then switch off the nitrous oxide flow meter.

Question 26

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Answer 26

5. Check the vaporiser.
   - Check vaporiser locked into position and seated properly on the back bar, straight and in place.
   - Check vaporiser turns properly and is not stuck, leave it in the ‘off’ position.
   - Check level of anaesthetic agent in the vaporiser.
6. Check for leaks in the system.
   - Check the machine for leaks by covering the common gas outlet w/ thumb. Don’t maintain pressure for long (can cause damage).
   - O2 flow will drop from 4L/min and should be audible hiss from high pressure relief valve. If there is a leak, O2 flow will not fall and hiss may not be heard.