In Savvy Special 3.1,  we looked at the new Health Technical Memorandum (HTM) 02-01 from NHS England (we’ll refer to it as the “EHTM”) .  

A consequence of all the post Brexit political upheaval in the UK is Scotland accelerating it’s  separation from the UK.  Thus, there is now a separate Scottish national health service and now too, a scottish version of the HTM (we’ll refer to it as the “SHTM”).  It is available at:  

https://www.nss.nhs.scot/publications/medical-gas-pipeline-systems-shtm-02-01/

As the Scottish version is not likely to be the version that becomes current in other HTM observing countries, it might seem pointless to spend much time on it.  However, as mentioned in Savvy 3.1, it is worth notice not only because the document is substantially different from the EHTM version, but because it is quite radical in some elements and represents a window to a different vision of the future of medical gas systems than any other document.

The first thing about it that one will notice is the sheer size of it.  At 351 pages, it is more like a textbook than a standard. (Which is not to say the EHTM is small at 262 pages either!)  By way of comparison, the NFPA is 266 pages, in which are covered eleven distinct subjects, only two of which are medical gases.

As with the EHTM, it is presented as a guideline, not a standard or code.  The user theroetically has the option to implement whatever sections they wish, and to ignore those sections they disagree with.  As a practical matter, the target audience (heatlhcare facilities in Scotland owned and operated by the SNHS) is likely to implement the whole. 

Like the EHTM, the document opens with a warning about the inadvisability of deviating from the guidelines (p. ii/iii).  However, it includes a very detailed description and methodology for the “Informed Design Process” and an equally detailed risk assessment procedure.  In a sense, The SHTM uniquely “puts it’s money where it’s mouth is” as regards the principle of risk assessment as the governing philosophy for design and operation of medical gas systems.  All standards talk to it, this one puts it right in your face. 

Like the EHTM the SHTM can be very prescriptive but the overall impression is that it is more flexible overall than is the EHTM and prescribes fewer things. An obvious example is the lack of the elaborate tables for pipe and source sizing  found in the EHTM. 

  It is very detailed and educational in some areas such as defining primary, secondary and reserve sources for each configuration of source (Table 2.1).  

All that said, the most interesting part of the document to an outsider looking at it for ideas of how a standard should be framed will be found at the start of the Executive Summary (p. iv).  This section actually goes rather beyond the usual intent of a strict summary and in doing so gives an insight to the authors’ worldview.  

It’s worth noting that in the actual document, many of the tenets set out here are not actually implemented.  It has to be assumed that the idea behind including this at all is to make the user think about these ideas when and if they choose to deviate from the guidance.  While very interesting as ideas, it is hard to believe that an average, relatively inexpert, client would be comfortable doing it. 

This is the section in it’s entirety:

“Since the last revision of Scottish Health Technical Memorandum (SHTM) 02-01 Part A there have been considerable changes and advances in the way in which medical gases are supplied and distributed. The key drivers for this are:

1. changes in anaesthesia clinical practice:

i. a reduction in the use of nitrous oxide and other anaesthetic agents due to their environmental impact

ii. general anaesthetic practice is now based largely around low-flow inhalation techniques and greater use of total intravenous anaesthesia (TIVA)

2. local exhaust ventilation (LEV) control measures (anaesthetic gas scavenging system (AGSS)) should be reviewed to confirm they remain functional and suitable due to reduced fresh gas flow rates (FGF) and the adoption of anaesthetic agent harvesting and capture technologies

3. net-zero requirements and embodied carbon - some services are no longer required to be provided as a central plant or piped installation, with an informed design process (IDP) now being used for their specific application to identify the most appropriate and efficient supply source, medical vacuum (MV) being an example of this

4. similarly changes in technology rendering surgical air not being required as a centrally piped system

5. ‘Never-Event’ investigations and subsequent research by the National Patient Safety Agency has determined that medical air has limited clinical applications and is now not a preferred installation requirement due to numerous sub-optimal outcomes and fatalities from rebound hypoxia when it has been administered instead of oxygen

6. the continued use from a non-anaesthetic perspective of piped nitrous oxide and oxygen for dental sedation and pain management. This will include pre-mixed nitrous oxide/oxygen (50% volume per volume (v/v)) gas mixtures such as, Entonox or Equanox

7. the lessons learned from the COVID-19 pandemic in respect of acute respiratory care, respiratory medicine and practices for oxygen supply sources and distribution systems.”

There is a lot here to consider.

First, points 1 and 6 are definitely true everywhere.  These are trends that have moved all the major standards to allow for not centrally piping nitrous oxide and even decommissioning existing systems.  This change is now finishing it’s first round in this years crop of revised standards (NFPA 99, CSA Z7396-1, ISO 7396-1 and now, the EHTM and SHTM).  

A contravailing trend toward increased use of nitrous oxide for analgesia and self administered pain control is also described here and being reported everywhere.  That notwithstanding, plans to pipe nitrous oxide to support these administration devices have not resulted.  However, waste gas extraction has proven to be a problem with them, as is indicated in point 2.  

The mention of capture and harvesting is a reference to technologies that are appearing in the marketplace but have yet to gain much acceptance because of their problematic economics and the fact that waste anaesthetic is not really low hanging fruit from a regulatory perspective.  All standards have opened the door to the use of these, but none has gone any furthur. 

Points 3 and 4 are particularly interesting, and are also reflected elsewhere in the document.  This is the elimination of centrally piped vacuum and the elimination of high pressure air (surgical air).  

The authors’ view that central vacuum is no longer needed in some areas will be very controversial.  It derives largely from the proliferation of portable disposal systems such as the Stryker Neptune which can supercede central vacuum in traditional high use areas like operating rooms.  Removing that largest demand opens up a theoretical possibility of serving other areas mostly or entirely with portable machines.  The authors implication - that portables would be more energy efficient - is itself debatable, and the cost is likely to be higher when all costs are considered.  Elsewhere, a trend toward increased use of vacuum, including the advent of incontinence catheters, argues that this concept is very unlikley to gain much traction. 

Surgical and instrument air (high pressure air) for driving surgical tools is distinctly on it’s way out everywhere, as discussed in point 4.  With the advent of more powerful and durable battery powered tools,  it is clear these systems have limited value if any at all.  

The EHTM surprisingly seems to takes no notice of this, but other standards agree with this point and have begun to downplay or eliminate this system.  

Point 5 is one which has been widely discussed.  This is the problem of air flowmeters having the same outlet connection as oxygen flowmeters.  This is done because the humidifier bottles and other downstream devices are provided with the standard oxygen fitting, and putting that fitting on the outlet of the air flowmeter allows it to use all those same devices.  Very logical from the point of view of the supplier and the facility’s inventory management, but hazardous if the nurse or respiratory therapist is not careful to ensure they connect to the right flowmeter.  ISO does the staff no favor here, because the ISO color code for oxygen and for medical air is very similar.  

The conclusion of the authors is therefore to eliminate centrally piped medical air.  Like their argument regarding vacuum this is very hard to accept.  One cannot argue there is a problem, but the prescription offered seems simply to create other problems, not least of which is the inability to provide air compliant with the pharmacopeia using portable compressors or venturis. 

These ideas and concepts are not necessarily carried into the document itself.   SHTM includes sections on medical air, on surgical air and on centrally piped vacuum.  They even discuss piping nitrous oxide, including N2O / O2 premixes (Entonox / Equanox).   

So, while implementing these ideas would require a bold and very knowledgeable client working with an equally knowledgeable and bold designer.  Nevertheless, they are an interesting view of an alternate approach to implementing medical gas systems which is well worth understanding.