Part 3 in the series – The Veterinary Anaesthetic Machine Made Simple – thanks to Dr Gas Vet
Originally published on the Vet Anaesthesia Tips blog: Pipeline Gas Supply, published 18 August 2016. Scroll down for links to the entire series
In my last blog post, I started off talking about the anaesthetic machine with a description of gas cylinders. But what if you use pipeline gases? And how do you get the gas from the cylinder to the anaesthetic machine?
What is pipeline gas?
A pipeline gas supply means that your gas is stored either in a cylinder manifold (a bank of large cylinders, usually located in a store or cage external to the clinic) or as liquid oxygen. The gas then travels along a pipeline system at a high pressure (400kPa) to reach the areas of your clinic where it might be required.
The pipeline system should be labelled and colour-coded according to what gas each pipe carries (e.g. in Australia – white for oxygen, blue for nitrous oxide and black/white for medical air).
Each pipe terminates either in the wall of a particular room in the clinic or in a ceiling-mounted unit, as a self-sealing socket:
A piece of flexible pipeline, or “hose”, (of colour corresponding to the particular gas) attaches to the terminal by a specific connector on one end. The connector and socket for each different gas is a slightly different shapes so that a hose cannot accidentally be connected to the wrong type of gas terminal (e.g. you cannot attach a white oxygen hose to a nitrous oxide terminal):
The other end of the flexible pipeline or hose also has a gas-specific screw thread which means it can only be attached to the corresponding gas port on the anaesthetic machine (called a non-interchangeable screw thread, NIST).
Different countries, and clinics, might use different non-interchangeable systems (e.g. Schrader, Diameter Index Safety System DISS, Ohio quick connect system). My photos here show a DISS system:
These same flexible hoses and connectors are usually used to connect the regulator of a gas cylinder to the anaesthetic machine:
So, what does this mean for you practically?
Be familiar with the colour coding for your country and always check you are connecting the appropriate hose to the wall terminal and anaesthetic machine
Only use flexible pipelines and sockets specifically designed for the type of gas supply you are using
When connecting the hose to the terminal unit or anaesthetic machine:
- Always ensure the flowmeters on the anaesthetic machine are closed before attaching a pipeline, otherwise, there may be a large release of high-pressure gas.
- When you attach the hose to the wall or anaesthetic machine you will hear (and feel) a small hiss of gas, but then should not hear any more leaking once fully attached.
- The sockets on the pipeline hoses contain valves to ensure uni-directional flow (e.g. flow towards the anaesthetic machine rather than back to the wall). If you continue to hear gas leaking, you may not have correctly attached the hose, or there may be damage to these valves and the hose should not be used.
When detaching a hose from a cylinder, first turn the cylinder valve fully off. Then make sure the flowmeters on the anaesthetic machine are switched off. Then, press the oxygen flush valve until you cannot hear any more gas escaping. This means you have purged the anaesthetic machine of any gas, and it will be easier to detach and re-attach the pipeline hosing without a large escape of gas.
The next stage…
We have now got to the stage where we have a supply of gas (usually oxygen) to our anaesthetic machine. However, this gas is being delivered at very high pressure. So high that it would damage the more delicate structures of the anaesthetic machine (like vaporisers for instance), not to mention the lungs of any animal to which it was delivered!
In the next blog post, we will talk about pressure gauges (to assess the pipeline or cylinder pressure), and pressure-reducing valves (that reduce this high pressure to a more appropriate pressure).
Any questions for Jen? Ask them in the Comments section below…