Medical Gases

BT_SQ 1.10  Describe the supply of medical gases (bulk supply and cylinder) and features to ensure supply safety.


T / F   Medical air contains about 0.04% carbon dioxide

T / F   Historically, anaesthetic machines were fitted with CO2 cylinders (the anaesthetist could administer CO2 to ‘stimulate’ breathing). Since this was banned in the early 1980’s, there is no longer any use for medical carbon dioxide cylinders.

T / F   Entonox is the only medical gas cylinder with a single pin index hole

T / F   Heliox is a mixture of 72% helium and 28% oxygen

T / F   The critical temperature of nitrous oxide is 36.5 degrees C. Below this temperature, the gas cannot be liquefied regardless of the pressure applied.


1. BOC Cylinder Data Sheet
2. Magee & Tooley

BT SQ 1.10 Describe the supply of medical gases (bulk supply and cylinder) and features to ensure supply safety.

This is a Lego anaesthetic machine made for the huge American ASA Conference quite a few years ago. Fortunately our real machines have less parts. You need to be quite familiar with all the components of your machine- you don’t necessarily have to be able to deconstruct it, though!

The pin index system means you can connect an oxygen cylinder to any manifold because it has a universal setting T/F

Oxygen cylinders may be coloured white or green or black with white shoulders T/F

A carbon dioxide cylinder contains a mixture of liquid and vapour T/F

A full oxygen cylinder contains gas at over 150 atmospheres of pressure T/F

A full  C size oxygen cylinder on the back of your machine contains about 760 litres of oxygen T/F

Medical Gas Cylinders

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


T / F   nitrous oxide cylinders have a blue body, and blue shoulders

T / F   a medical gas cylinder with a single pin index hole would contain carbon dioxide

T / F   a full C-size oxygen cylinder at 20 degrees C would contain 490 L of oxygen, at 400 kPa

T / F   an Entonox cylinder contains 50% liquid nitrous oxide and 50% gaseous oxygen

T / F   the fitting which couples to the cylinder neck is known as a Schrader valve


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?


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.