BT_SQ 1.5 Describe basic physics applicable to anaesthesia, in particular:
…. principles of humidification and use of humidifiers ….


T / F   during quiet breathing, air reaching the carina is close to 37 degrees C and 100% relative humidity

T / F   at 37 degrees C, air can hold a maximum of 44 mg/L of water vapour

T / F   during expiration, water vapour condenses onto the airway mucosa

T / F   absolute humidity depends upon both the temperature and the atmospheric pressure

T / F   a HME can warm inspired gases to about 30 degrees C, but this takes about 20 minutes

Pressure Regulators

BT_SQ 1.10

O-Series regulator with attached pressure gauge. If you have a particular interest in this regulator, it is described in detail in Russell. You are probably more familiar with the small transport oxygen cylinders with the integrated pressure regulator, flowmeter and pressure gauge.

Integrated Regulator 2

T/F Pressure regulators should be regularly lubricated with a hydrocarbon based grease to prevent sticking.

T/F Pressure regulators for oxygen may be used with air but not nitrous oxide

T/F Adiabatic gas expansion can cause moisture to freeze and jam pressure regulators

T/F Rupture of a regulator diaphragm can cause loss of gas from the anaesthetic circuit to the pipeline.

T/F Pressure regulators convert a constant upstream pressure to a variable downstream pressure


BT_SQ 1.9

Dedicated scavenging pumps. The hospital vacuum is designed to suck up fluids, and usually vents in to the plant room of the hospital. The plant room staff will not thank you for connecting the scavenging to such a system. The anaesthetic gas scavenging system should be vented away from where people will inhale the gases.







T/F A risk of using a scavenging system is excessive positive pressure in the breathing circuit

T/F Active scavenging systems should be capable of developing a high negative pressure

T/F Prolonged exposure to trace concentrations of volatile agents my be teratogenic in the second trimester of pregnancy

T/F Passive scavenging systems should have a flowmeter to measure flow

T/F A closed scavenging interface must be used with an active scavenging system

Color coding of gases

BT_SQ 1.10

For the end of January puzzle: See how many safety and standards violations you can find in this picture!


One of my friends was telling me about an incident at her hospital a while ago, where the patient became hypoxic after being given 100% oxygen. The hospital had done some work on the piping, but hadn’t tested it or notified anyone…

T/F Nitrous oxide hoses should be colour coded light blue

T/F Oxygen hoses should be colour coded green

T/F Air hoses should be colour coded yellow

T/F CO2 hoses should be colour coded gray

T/F Scavenging hoses should be colour coded black and white


Bonus questions:

1. How are the gas pipelines themselves coded so the workmen know which outlet to connect them to.

2. (Non examinable) What qualifications do you have to hold to install a medical gas pipeline in Australia?


Cleaning of Equipment

IT_SQ 1.5

Oxyvir wipesI am sure this is a subject which has you on the edge of your seats.

When I was training one of the hospitals I worked at would heat treat their PVC endotracheal tubes so they could reuse them. The trouble was that after they had been cooked, they had the structural strength of freshly cooked spaghetti. You had to unkink them several times per case. I got into the habit of tearing off the pilot balloon of cuffed tubes so that they couldn’t be re-used…



T/F Laryngoscope blades should be sterilised after use

T/F Single use items may be sterilised if the process complies with AS/NZS 4187

T/F Disinfection involves the inactivation of non-sporing organisms and spores.

T/F Bougies should be disinfected after use.

T/F The surface of the anaesthetic machine should be disinfected between patients

BT_SQ 1.13 Describe and classify breathing systems used in anaesthesia (episode 2).


I photographed this little guy in Hong Kong – he’s (or perhaps she’s??) looking bit ragged. Following yesterday’s post I did a bit of research. It tuns out that sea jellies have no breathing system at all. They meet their oxygen requirements through diffusion across their bodies….

Today we will turn our focus to the circle system. This is something most of us use every day. I asked a viva on it in the last exam and was surprised by many of the answers I was given.

The circuit is circular with unidirectional valves – does that mean that gas flows in only one direction throughout the entire system?

BT_SQ 1.13  Describe and classify breathing systems used in anaesthesia. Evaluate their clinical utility and hazards associated with their use

The circle circuit, as commonly used in current anaesthetic practice, is a closed system  TRUE/FALSE

With the standard circle arrangement, fresh gas commonly flows through the CO2 absorber   TRUE/FALSE

Placing the APL valve before the CO2 absorber (on the expiratory limb) helps to conserve the CO2 absorbent  TRUE/FALSE

When running the circle as a closed circuit, minimal gas monitoring is required, as it is a stable system        TRUE/FALSE

A safe circle system requires the fresh gas flow to be placed between the patient and the expiratory valve  TRUE/FALSE

BT_SQ 1.13 Describe and classify breathing systems used in anaesthesia.


What sort of  breathing system do those guys have? Certainly none of the ones we will be discussing today…

Today I will focus on the Mapleson classification of breathing systems. Here is an article written about them by Mapleson himself. He is still alive and in his 90s. You can read a little more about him here. Textbooks on the ANZCA primary exam reading list generally cover this topic adequately too.

BT_SQ 1.13 Describe and classify breathing systems used in anaesthesia. Evaluate their clinical utility and hazards associated with their use

The Mapleson A circuit is more efficient for a spontaneously ventilating patient compared with Mapleson D    TRUE/FALSE

A Mapleson E circuit is also referred to as classic T-piece     TRUE/FALSE

In the Mapleson D circuit the reservoir bag is located off the expiratory limb    TRUE/FALSE

The Mapleson D circuit is more efficient for controlled ventilation (CV) compared with spontaneous ventilation, due to the longer expiratory phase with CV    TRUE/FALSE

The Mapleson C circuit is the most efficient of these systems for spontaneous ventilation TRUE/FALSE


Anaesthetic Machines

Equipment Friday 😃

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.

NAD Back 4.png

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

Pin Index.png

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 1.5 “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°C

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.