Medical gases The “Cinderella” gases

At the mention of medical gases, the first products which usually come to mind are the oxygen used for breathing therapy and the nitrous oxide (laughing gas) used for conscious sedation. Granted, these gases are vital and are used extensively in the healthcare arena. However there is an essential group of “Cinderella” specialty medical gases which are less recognized, but no less critical. These gases are supplied less frequently and in smaller quantities, but are just as vital to patient welfare.

The tale of these specialty gases reveals that they are actually used every single day at hospitals and medical laboratories and other associated organizations servicing the medical/healthcare industry. The Cinderella specialty medical gases reviewed in this article are those which have a diversity of interesting and critical applications which harness their unique properties — and which are quality-critical.

Test gas mixtures
These gases are not used in a directly therapeutic way as with, for example, inhaled medical oxygen, but rather to understand the status of patient health. The criteria used in their manufacture also differ from that of therapeutically used medical gases. The same extremely rigorous quality standards apply, but once produced, the content of specialty gases have to be accurately measured to ensure that all components are present and remain at precisely the right levels.

Within this group are the gases used to test or calibrate some of the principal instruments used in hospitals today. The efficient calibration of medical equipment, used either directly or indirectly in patient treatment, is imperative. The technology required to produce these specialized and often mixed calibration gases – whether to 100 or 1,000 parts per million – is extremely sophisticated. Maintaining the mixtures at the required levels is just as important.

Among the most common tests carried out on patients are the pulmonary or lung function tests — a group of tests that harness sophisticated diagnostic instrumentation and mixes of the Cinderella specialty medical gases containing low levels of carbon monoxide to measure how well the lungs take in air and how well they transport gases such as oxygen from the atmosphere into the body’s circulation. The amount of carbon monoxide in the exhaled air is measured and indicates the lung functionality. Since patients’ health and condition often depend on the accuracy of these readings, highly specialized gas mixes are used to calibrate this equipment on a regular basis. The lung diffusion gases are often dispensed on prescription whether used for inhalation or for calibration of the analytical instrument, since the same gas cylinder is used for both purposes.

Blood gas analyzers are in a similar category. Blood transports oxygen around the body to the vital organs and collects carbon dioxide as a by-product. Blood gas analysis, also called arterial blood gas analysis, is a test which measures the amounts of oxygen and carbon dioxide in the blood, as well as the acidity (pH) of the blood. The equipment used to conduct this test requires frequent calibration to continue to give accurate and reliable readings. Again, the calibration gases required for this purpose are in the Cinderella group of specialty medical gases.

Although not specifically a medical application, blood alcohol testing using breathalyzer equipment is utilized by police forces all over the world to combat drunk driving, a growing concern in many countries among authorities and citizens alike. These tests are commonly conducted in the gaseous phase by testing the level of alcohol in the driver’s breath, but the test is also carried out using blood samples. Either way, the instrument used must be perfectly calibrated and tested regularly to ensure an accurate reading.

This is critical if the result is required as evidence in a prosecution — so critical that national accreditation bodies have established ethanol-in-air calibration standards for evidential breath testing. Calibration gases that have been accredited against these standards allow local traffic authorities to apply the breathalyzer test with confidence that the reading will be accurate and will hold up in a court of law.

Incubators
Specialty gases and mixtures are also essential for incubators. These medical chambers create controlled environmental conditions with elements such as temperature, humidity and oxygen concentration, for vulnerable infants’ care. Physicians also use incubators to maintain the integrity of body parts and tissue destined for transplants and for growing certain cultures to create an aerobic or anaerobic cell growth environment. This is particularly important when identifying the presence of Methicillin-resistant Staphylococcus aureus (MRSA), the bacterium responsible for several difficult-to-treat human infections.

It is very important to have a controlled atmosphere that supports the intended process. When growing aerobe organisms, the ambient atmosphere is based on oxygen or air, and when anaerobe organisms are cultivated the atmospheres are based on nitrogen or carbon dioxide. Both types usually have a carbon source for maximizing the growth. A different type of growth control occurs when sterilizing mixtures are used for the opposite purpose — to get rid of all organisms.

“While temperature control is not our business, the exceedingly precise nature of the incubator’s gaseous environment is very much so,” Harrison says. “Each specific environment lends itself to the preferential preparation of cells that identify certain types of bacteria.

In vitro fertilization eggs and embryos are also stored in IVF incubators. These incubators must have very clean and constant environment. The IVF mixtures are typically either five percent carbon dioxide in air or five percent carbon dioxide, five percent oxygen in nitrogen.

“A steady and rigidly controlled stream of gases flows through an incubator’s chamber continuously, so the quality of the gas mixture must be of the highest order and must be repeatable in order not to compromise the Fourth Quarter 2011 • Speciality Gas Report 25

incubator’s function,” says Harrison. “Linde is able to provide our medical customers with certificates that guarantee the composition of these mixes and are able to prove accuracy of a given mixing tolerance.” The company’s HiQ® specialty gases range supports this field with its high purity gases, accurate gas mixtures, precision engineered gas supply systems and specialist support services.

Anesthetics
Anesthetic delivery devices also rely heavily on the Cinderella specialty medical gases. During operations carried out under gaseous anesthesia, anesthetists must achieve and sustain the right gas mixture for the patient to breathe. Although pure oxygen is generally used, this is often coupled with nitrous oxide for its pain relieving properties and to lower the amount of actual anesthetic used. In addition to nitrous oxide, among the most widely used gases in general anesthesia are desflurane, sevoflurane and isoflurane.

Anesthesiologists depend on the integrity of these highly sophisticated anesthetic delivery devices and to be sure of this, these devices require testing and calibration with accurate calibration gas mixtures.

Several of the most sensitive medical devices are found right here in the operating theater. These devices are tested and calibrated using specialty gases which are supplied in small quantities, in small cylinders, much like aerosol cans. Most people rarely see them or hear of them, yet they are completely critical for the safe conduct of today’s sophisticated surgery.

Another example, the rare gas Xenon, is an excellent anesthetic medium, because it induces quick and stable anesthesia and favors neuroprotection.

Pure gases
Pure gases, as opposed to gas mixtures, play a significant role in the health care industry. Within the arena of medical gases and their applications, the diagnostic work conducted using these gases for preventive and diagnostic medicine is an important category.

On-site clinical laboratories or stand-alone contract laboratories contracted to conduct analysis for the hospital carry out sophisticated tests on patient blood and urine samples. These tests could use plate microbiology requiring anaerobic or aerobic gas mixtures for cultivation. Also high-tech instrumentation such as liquid chromatography-mass spectrometry (LC-MS) and high-performance liquid chromatography (HPLC) are often used for diagnostic testing.

LC-MS is a powerful analytical technique used in industries requiring very low detection limits of sometimes unknown samples. The efficient physical separation of chemical substances dissolved in a mobile phase, performed by liquid chromatography, is combined with the mass spectrometer’s ability to sort and identify the components (gaseous ions) in electric and magnetic fields according to their mass-to-charge ratios. The samples analysed by LC-MS are often complex mixtures.

LC-MS requires high purity nitrogen to remove the solvent from the sample before introducing in the mass spectrometer. Pure helium could also be necessary for degassing in liquid chromatography

HPLC is a form of column chromatography that pumps a sample mixture or analyte in a solvent (known as the mobile phase) at high pressure through a column with chromatographic packing material (stationary phase). HPLC has the ability to separate and identify compounds that are present in any sample that can be dissolved in a liquid in trace concentrations as low as parts per trillion. This equipment also needs high purity gases such as nitrogen or helium to operate accurately.

Sample storage
In the liquid phase, nitrogen is used by the health care sector for its properties of extreme cold and consequent ability to store biological samples indefinitely, without risk of degradation, at temperatures as low as -321°F (-196°C).

This capability also has important implications in the realm of human fertility, where semen and eggs are stored for future use.

There is however a less cheerful application for liquid nitrogen in the medical world - evidence in medical litigations. If treatment goes wrong, the patient or the family can hold the medical professional or the facility responsible and seek damages. A duplicate sample that has been preserved using liquid nitrogen and stored for this very purpose, means the tissue can be tested again — even years later — to verify the original result.

Harrison says Linde’s role is not only to provide liquid nitrogen to customers, but also to actually operate “cryopreservation” facilities where such samples are stored cryogenically in the UK and the Netherlands.

Linde’s BOC Cryobank in the UK is a state-of-the-art facility dedicated to cryogenic bio-storage of irreplaceable samples.

Liquid nitrogen can be a hazardous substance to handle, so it makes sense to hand over this requirement to a gas company.

“Although we’ve been supplying liquid nitrogen to customers for the past 50 years and supporting customers with training in safe practices, protective clothing and gas detection equipment to identify breathable or unsafe atmospheres, the establishment of proprietary cryobanks is a sign of a definitive shift in the medical industry,” Harrison concludes. “It’s part of a global outsourcing trend that is seeing business opting to focus on their core competencies and outsourcing other requirements to appropriate service providers.”