Anaesthetic Machines

Equipment Friday ūüėÉ

BT_SQ 1.3 Outline the mandatory safety requirements for anaesthetic machines. Refer to College professional document T3: Minimum Safety Requirements for Anaesthetic Machines for Clinical Practice.

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TRUE/FALSE The oxygen failure alarm shall activate at pressures of less than 410 kPa.

TRUE/FALSE The anaesthetic machine must contain an automatically activated reserve oxygen supply.

TRUE/FALSE The oxygen supply failure alarm must be user cancellable.

TRUE/FALSE The oxygen supply failure alarm must shut off the supply of all other gases in the event of oxygen failure.

TRUE/FALSE The oxygen supply failure alarm must shut off the supply of all other gases in the event of oxygen failure.

TRUE/FALSE If the anaesthetic machine incorporates a gas flowmeter bank, oxygen must be the first gas to enter the common gas manifold at the top of the flowmeter tubes.


And a special bonus question:

TRUE/FALSE Equipment is rarely asked in Primary vivas.


Pin Index System

BT_SQ 1.10 Describe the supply of medical gases (bulk supply and cylinder) and features to ensure supply safety including pressure valves and regulators and connection systems

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T/F The Bodok seal shown on the right contains latex

T/F The Pin Index System can be defeated by placing two Bodok seals over the nipple

T/F The seal must not be combustible because of the high temperatures achieved when the cylinder is turned on

T/F The Pin Index for Oxygen is a single pin at the 6 o’clock position

T/F The Pin Index system is not used in the main hospital manifold

Have you ever wondered why we only use the pin index system for cylinders and not for gas hoses? The answer was in the recent A&IC History Supplement. If the connection is inserted upside-down, it is possible to fit the wrong coupling into the yoke. This is less of a problem with cylinders for obvious reasons.


BT_SQ 1.5BT_SQ 1.5 “Describe basic physics applicable to anaesthesia in particular:

· Principles of humidification and use of humidifiers


T/F A Heat and Moisture Exchanger (HME) primarily reduces heat loss by warming the inspired gas.

T/F A Heat and Moisture Exchanger (HME) warms inspired gases to a temperature of 35-37¬įC

T/F At this temperature a Heat and Moisture Exchanger (HME) achieves a humidity of 85-93%

T/F A Heat and Moisture Exchanger (HME) reduces the risk of bacterial and viral cross-infection between patients.

T/F A Heat and Moisture Exchanger (HME) is less effective when using high gas flows in a circle system.


Gas Connections & Hoses

BT_SQ 1.10 Describe the supply of medical gases (bulk supply and cylinder) and features to ensure supply safety including pressure valves and regulators and connection systems

Fabius Hoses

With reference to the above diagram:

T/F The colour coding of the nitrous oxide hose is correct

T/F The air hose is white because it uses the American colour coding system

T/F The hoses are connected to the machine using the Sleeve Index System



With reference to the above diagram:

T/F It would be possible to attach this hose to any gas connector of this type

T/F The standard does not allow hose clamps to be used to attach flexible gas hoses to non-interchangeable gas connectors.


BT_SQ 1.12 Describe the principles and safe operation of vaporizers

Q. They are heavy because they are full of liquid.  TRUE/ FALSE

Q. Must be positioned in a particular order if there are two different vaporizers on the machine.  TRUE/ FALSE

Q. All require power to operate correctly.  TRUE/ FALSE

Q. A Desflurane Tec 6 vaporizer does not require adjustment when used at altitude.  TRUE/ FALSE

Q. Should not be laid on their side.  TRUE/ FALSE

2017.1 : SAQ 2

Compare and contrast oxygen delivery via nasal cannulae (nasal prongs/specs), simple face mask (eg Hudson or CIG mask) and Venturi mask.

BT_SQ 1.14

A very practical question, understanding the physics of oxygen delivery by these different means will aid you in appropriate use.


Having an end-expiratory pause will affect the performance of the Hudson mask   TRUE/FALSE

Having a high peak inspiratory flow will affect the performance of nasal cannulae   TRUE/FALSE

Low flow rates may lead to an increased inspired pCO2 with the Hudson mask TRUE/FALSE

The Bernoulli effect is relevant for Venturi mask function   TRUE/FALSE

With nasal cannulae the nasopharynx acts as an oxygen reservoir   TRUE/FALSE



BT_GS 1.52 Explain the principles involved in the electronic monitoring of depth of sedation, including EEG analysis.

Although a unique EEG “neural correlate of consciousness” has not yet been identified, drugs that induce anaesthesia do have characteristic effects on the spontaneous EEG. However, it is important to note that these effects are not the same for different drugs, even though they may produce a similar clinical endpoint. Appreciating these differences is the key to understanding why commercial EEG monitoring devices may give misleading results when certain drugs are used.


T / F¬†¬†¬† The EEG during sevoflurane anaesthesia has less ‚Äúrandomness‚ÄĚ than when awake.

T / F    Propofol causes burst-suppression of the EEG at levels which have little effect on spinal reflexes.

T / F    When burst-suppression is induced by propofol, total brain oxygen consumption is reduced by up to 90%.

T / F    Nitrous oxide causes similar changes to the EEG compared to sevoflurane.

T / F    Electrocortical silence cannot be produced with ketamine.



BT_SQ 1.14 Oxygen delivery systemsÔĽŅ

Clearly oxygen is a very important element for us as humans and sometimes atmospheric levels of oxygen are insufficient for our patients’ needs.

We are unlikely to find ourselves in the situation of the Apollo 13¬†astronauts, but it’s important we know how to give supplemental O2…

BT_SQ 1.14 Describe different systems to deliver supplemental oxygen and the advantages and disadvantages of these systems

A non rebreather mask has a one way valve which prevents entrainment of atmospheric air TRUE/FALSE

Venturi oxygen delivery devices make use of the Bernoulli principle TRUE/FALSE

Delivering oxygen at 6L/min via a Hudson mask, a patient with a respiratory rate of 6 breaths per minute (bpm) will recieve a higher FiO2 than a patient with a respiratory rate of 12 bpm TRUE/FALSE

Nasal cannulae are an example of a variable oxygen delivery device TRUE/FALSE

100% oxygen can be delivered to a patient using a Venturi mask with a rating of 1.0 TRUE/FALSE

BT_RA 1.9 Nerve stimulators for nerve location

A little bit off the topic of the neuromuscular junction, but we might as well cover this LO whilst we are on the topic of nerve stimulators.

BT_RA 1.9 Describe the principles of nerve stimulation to locate nerves and the safe use of nerve stimulators

TRUE/FALSE A short stimulation pulse is an advantage in a nerve stimulator for nerve localisation for neural blockade

TRUE/FALSE A nerve stimulator for nerve localisation should have a constant voltage output

TRUE/FALSE When performing a nerve block with a nerve stimulator, the needle should be connected to the positive electrode

TRUE/FALSE When performing a nerve block with a nerve stimulator, injection of 5% dextrose increases current density at the tip of the needle

TRUE/FALSE Nerve stimulators can be used to locate nerves with no motor innervation

BT_SQ 1.12 Vaporisers

Equipment Friday again ūüôā

BT_SQ 1.12 Describe the principles and safe operation of vaporisers

TRUE/FALSE The Aladin cassette vaporiser is an example of an injection vaporiser system
TRUE/FALSE Modern vaporisers use an electrical heating coil to compensate for the cooling caused by latent heat of vaporisation
TRUE/FALSE A plenum vaporiser is designed so that the gas leaving the bypass is fully saturated under normal conditions
TRUE/FALSE Thymol in sevoflurane can cause the bimetalic strip of older vaporisers to stick
TRUE/FALSE The Quick-Fill system is used only for sevoflurane


Here is a picture of a cut open Vapor 2000. See if you can identify the features shown in the picture in Dorsch & Dorsch.



The vaporisers you are used to are out of circuit with a high internal resistance. If the internal resistance is high, what is the driving pressure to force the gas through them?

How can you use a vaporiser¬†in an area which doesn’t have a pressurised gas supply? What kind of circuit would you use?

(You should know how to answer the above questions, but the following is provided for interest rather than examination purposes)

EMO Vaporiser.

This is an example of a drawover vaporiser. The patients’ respiratory effort draws¬†the fresh gas through the device. These vaporisers must therefore have¬†a¬†low internal resistance.

If you don’t have bulk gas supply, you can’t use a circle or Mapleson style circuit. The attached circuit uses an ‘Ambu’ style non rebreathing valve. The gas is drawn in through an inlet on the other side of the vaporiser, and is vented at the valve attached to the mask.

The mask is called an Everseal, and designed for prolonged mask holding. The bottom of the mask lifts up the chin to help maintain an open airway.



What would you do if you need to ventilate them? You could always use a self inflating resuscitation bag, but then it is difficult to see if the patient is breathing spontaneously.

Below is a picture of an Oxford Inflating Bellows. It can be used to hand ventilate a patient in conjunction with a drawover vaporiser. The bellows is spring loaded to make it open to the halfway position, which lets you use it with spontaneous ventilation as well.

If you use this bellows without disabling the outlet¬†valve, the back pressure on exhalation will stop the ‘Ambu’ valve from opening. This is important because it can cause a pneumothorax. The red horseshoe magnet is used to disable the valve, which allows the bellows¬†be used with the circuit depicted above. It can be taken off if you want to use the device with a different circuit.oxford-inflating-bellows_7