MEDICAL GASES
multiple patients. These systems are very sustainable since they require no transport, and they consume only enough electricity to do their job. That is, they generate very little waste. However, they are a single point of
failure, and, in areas with unreliable energy systems, they can pose a risk to patient care. We have toured hospitals in Africa who have lost countless lives due to failures of electrical systems that rendered such concentrators unusable. Many places use bottled oxygen,
generally delivered at the point of use. These systems have an environmental footprint that include the generation and the transport of the bottles to and from the site of concentration. In many high- resourced areas, hospitals invest in large oxygen tanks that are periodically refilled by trucks. Again, these systems have an environmental footprint that includes both generation and transport of oxygen to the site. Increasingly in low-resourced regions,
onsite oxygen generation is being utilised in lieu of trucked oxygen. Onsite oxygen generation allows shipping costs and emissions to be eliminated and thus, eliminates the associated carbon footprint. Another benefit to generating oxygen onsite is increased resilience during a disaster, natural or otherwise. At present, regulations may prevent
the deployment of on-site oxygen generation in high-resourced areas, but these regulations are ripe for change. Another emerging opportunity involves the purity of the delivered oxygen. Current regulations in the US NFPA 99 (5.1.12.3.11) require oxygen to be 99% pure, to meet the minimum content requirements set by the United States Pharmacopoeia (USP) of 99.0 mole % oxygen, maximum 300 ppm carbon dioxide, and maximum 10 ppm carbon monoxide. Companies that generate liquid oxygen for delivery to hospitals provide at a higher purity than that at a minimum. However, most oxygen concentrators manufactured for home use provide 93% pure oxygen. The same is true for the larger commercial on-site oxygen generators used by industrial, veterinary medicine facilities, and remote healthcare facilities outside the United States. Many sources, including Dr James Berry, stated that ‘93% pure oxygen is fine for patient use – as long as the impurities are non-toxic.’ It takes a tremendous amount of electrical energy to produce 99% purity vs. 93% purity. This additional energy usage is expended nationwide and may not be necessary. If 93% purity is adequate for acute care patients this could also open the door for more decentralised production of oxygen. Medical instrument air: Generation of
Medical Instrument Air on-site (in lieu of having compressed nitrogen or liquid nitrogen dewars delivered) is another way
48
Bottled oxygen.
to move toward sustainable medical gas systems. In 2005, NFPA 99 was revised to codify the use of on-site air compressors for operating medical tools and powering pneumatic brakes on surgical ceiling- mounted booms. This is in lieu of facilities having high-pressure cylinders or liquid nitrogen dewars regularly delivered to the site. Medical gas suppliers extract nitrogen from air, bottle it, and deliver it to hospitals – a process that takes a significant amount of energy. Now, multiple manufacturers offer packaged equipment, producing clean, dry air that can be used for all of the functions nitrogen was used for previously. Reduced use of nitrous oxide: Nitrous
oxide is one of the six greenhouse gases targeted by the Kyoto Protocol. It is also an ozone-depleting gas covered by the Montreal Protocol. With the relative decline in other ozone-depleting substances, nitrous has emerged as the primary ozone depleting agent of concern. With its double impact of impacting
both ozone and global warming, healthcare can make a significant impact by eliminating its use. Indeed, if nitrous use can be eliminated or at least, significantly minimised, it can also result in the elimination of a piping system with all of the materials and embodied energy. Nitrous is not potent enough to use it
by itself, so it is used to reduce consumption of more potent and expensive agents. Generally, nitrous oxide is good for minor procedures (e.g. dental procedures). Doctors also use it to induce pediatric sleep before moving to halogenated ether. But, the use of nitrous is declining, as other anesthetics become more available. It has some patient- satisfaction impacts, in that it causes nausea; the number one patient complaint after surgery is nausea, and patient
outcomes can be improved by eliminating the use of nitrous. The strategy, then, is to move away
from nitrous, using alternatives instead. In general, in surgical procedures, Sevo and Des flurane are substitutes. In many instances, caregivers are able to use injected or intravenous anesthesia rather than nitrous. Another strategy might include
alternative inhaled anesthetics such as xenon. Xenon has no undesirable ecological effects since it is a naturally occurring gas in Earth’s atmosphere. Xenon anesthesia has no harmful effects on the cardiovascular system; furthermore, it has a neuroprotective effect.1
Xenon is also correlated with
maintaining a slower heart rate and a greater arterial pressure value than other anesthetics. However, due to its significant cost, xenon is not likely to be an economically feasible solution in most instances.
Distribution system strategies As designers, we need to revisit or readdress why certain requirements are included in a new hospital facilities infrastructure. The International Plumbing Code (IPC) requires nonflammable medical gas systems to be designed and installed in accordance with NFPA 99C. Currently the NFPA requires medical gas zone valve boxes (ZVB) on all oxidising gases (which typically include oxygen and nitrous oxide). The purpose of using medical zone valve boxes are to avoid potential fire and explosion hazards associated with positive pressure gas systems. It should be noted that many of the gases connected to zone valve boxes are not ‘technically’ required, and therefore, could be piped with cleaned high grade copper. This would greatly reduce the total installed construction
IFHE DIGEST 2017
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