Gases supplied for medicinal use are medicines. Along with their associated equipment, they are widely used for treating patients.
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Medicinal gases are classified as medicines in compliance with The Human Medicines Regulations. Medicinal gases must always be managed and controlled by an appropriately qualified healthcare professional. In a healthcare facility this will be the responsible Pharmacist. Where medicinal gases are prescribed for patients at home this will be the approved service provider. Information on managing medicinal gases by Pharmacists is provided by the Specialist Pharmacy Service.
Medicinal gases are administered by healthcare professionals in hospitals, clinics and care homes, by para-medics within the emergency services or are self-administered by the patient at home (having received appropriate training).
All medicinal gases and much of the associated equipment is regulated by UK legislation. UK and European legislation are generally aligned. The gases are classified as medicinal products for administration to a patient and the associated equipment is classified as a medical device when used to control the administration of the gas to the patient. Some gases used for medical purposes can also be classified as medical device gases where they do not have a specific therapeutic outcome for the patient.
Medicinal gases, like other medicinal products, are required to have a Marketing Authorisation (product licence) in order to be placed on the market. The Marketing Authorisation defines the quality specification, when a gas can be used (or not used) and how it should be administered to a patient. Specific guidance is provided for the information to be displayed on a medical gas cylinder package in BCGA GN 38, Medical gases. Labelling of medicinal gas cylinders.
Although medicinal gases are similar to non-medical gases, medicinal gases are not to be used for non-medical purposes. Equally, non-medical gases must not be used as a medicinal gas. The UK Regulator for medicinal gases is the Medicines and Healthcare products Regulatory Agency (MHRA), who are an Executive Agency of the Department of Health and Social Care (DHSC). The MHRA protects and promotes public health and patient safety by ensuring that medicines, healthcare products and medical equipment meet appropriate standards of safety, quality, performance and effectiveness, and are used safely.
Any organisation that manufactures medicinal gases must have a Manufacturer’s Authorisation issued by the MHRA. The organisation is required to operate a quality management system which complies with the basic principles and practices of Good Manufacturing Practice (GMP) for medicinal products and specifically for medicinal gases. Any organisation that supplies and / or distributes medical gases must have a Wholesale Dealer’s Authorisation issued by the MHRA. The organisation is required to comply with the basic principles and practices of Good Distribution Practice (GDP). BCGA GN 32 , Medical gases. Good distribution practice, was developed with the MHRA to ensure compliance with good distribution practice for medicinal gases.
Some equipment, such as medical gas regulators, demand valves and medical gas flow meters, that are associated with the administration of medicinal gases, are classified as medical devices. Medical devices must comply with the Medical Devices Regulations. Any organisation that manufactures medical devices (including medicinal gases classified as medical device gases) must be registered with the MHRA. Conformity assessment. Medical devices must undergo Conformity Assessment for compliance with the legislation where they are placed on the market. In the UK, conformity assessment is carried out by an Approved Body and compliance is indicated by the use of a certification mark, the UKCA mark. The MHRA provide guidance, including for placing medical devices on the market in Northern Ireland, here. In Europe, conformity assessment is carried out by a Notified Body and compliance is indicated by a CE mark. The MHRA provide guidance on conformity assessment and the use of the European CE mark for medical devices placed on the market in the UK here.
Every site where medicinal gases are used must have a suitable storage area with appropriate security provision. Advice on the management of security at healthcare facilities is available in BCGA TIS 50, Security of facilities where medical gases may be present.
Within larger healthcare facilities, the primary method of supply for medical oxygen is for it to be supplied as a cryogenic liquid into a storage tank(s), from where it is converted into a gas then delivered through a medical gas pipeline system (MGPS) into the facility, for administration to patients.
As well as medical oxygen, separate MGPS’s are also used for other medicinal gases, vacuum systems and anaesthetic gas scavenging systems (AGSS). These MGPS have to be compliant with various standards, including those required by the DHSC. Compliance is required, for example, with:
Health Technical Memorandum (HTM) 02 – Medical Gas Pipeline Systems
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Another method of supply is through the use of transportable medical gas cylinders. Transportable medical gas cylinders are also used as a supply source for a MGPS, where demand is lower, or as a secondary source of supply for a liquid system. Gas cylinders contain substances which are under pressure, whilst each individual gas may have its own specific hazardous properties. Gas cylinders must always be stored and handled with care. When not in immediate use all gas cylinders must be kept:
When choosing a cylinder for use, good stock management principles should be applied, for example, by selecting those with the shortest life remaining first, ‘first-expired, first-out’ (FEFO).
NOTE: Gas cylinders are attractive to thieves and are frequently stolen, both for the value of the materials they are made from and for their contents. This is particularly true of medicinal gases. Each store must incorporate appropriate security features and be included within the site security plan.
For more information, refer to BCGA CP 44, The storage of gas cylinders.
Some healthcare facilities may utilise on-site gas generation systems. Where these systems are in use they must meet the requirements for the manufacture of medical gases, including compliance with GMP and the site quality management systems under the supervision of the healthcare facility responsible pharmacist.
All personnel required to handle, move or use medical gases must be competent to do so, having received appropriate information, instruction, training and, as required, be under supervision. The appropriately qualified health care professional / Pharmacist must provide written policies and Standard Operating Procedures for the management and safe use of all aspects of medicinal gas supply and administration.
As with all medicines, medicinal gases have a defined shelf life which is specified within the relevant Marketing Authorisation. Where the medicinal gas is supplied in a gas cylinder it will have a label that will show the expiry date as well as the batch number of the medicinal product. Medicinal gases should not be used once the shelf life has expired. Once expired the gas cylinder should be returned back to the gas supplier.
The provisioning of medical gases to hospitals, mobile health providers, and in-patient care environments requires absolute conformance to stringent industry standards. As a result, manufacturers, distributors, and facility safety managers must have complete confidence in supply quality and continuity.
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It is important to note that, while accredited governing bodies do set critical industry health and safety guidelines, they neither evaluate nor inspect medical gas equipment, facilities, pipelines, nor other infrastructure. Compliance is, therefore, the direct responsibility of the medical gas OEM, along with the individual facility into which such gases are delivered. To achieve required high-accuracy monitoring and control, design engineers typically specify pressure sensors, switches, and isolation valves within finished system designs. For larger or more complex projects, they also out- source the design of bespoke manifolds. These integrate sensors, switches, valves, and other components into a single control module.
Applications that OEMs typically confront address the often-complex instrumentation requirements of medical gas delivery systems. These include the monitoring of oxygen, helium, xenon, carbon dioxide, and nitrous oxide; medical and surgical air; and compressed air vacuum systems. Typical requirements can range anywhere from a few dozen pressure switches and valves, to the custom OEM volume manufacturing of fully degreased, oxygen compatible sensors, to the full instrumentation of medical gas distribution pipelines. This article examines, by application, several key considerations for medical gas delivery systems.
Without exception, medical gas OEMs must specify instrumentation that is in strict conformance with the maximum allowable and stability concentrations of delivered patient oxygen. Smaller and more mobile healthcare environments, such as ambulances and temporary triage centers, rely upon portable, replaceable supply cylinders for patient-inhaled oxygen delivery. (See Figure 1)
Due to the wide external temperature ranges over which portable changeover systems must operate, cylinder setups are also instrumented with safety alarms. High-pressure alarms signal higher temperatures and increased risk of gas store depletion caused by evaporation. Low-pressure alarms can signal pending cylinder changeover requirements.
Pressure monitoring ranges vary, depending upon medical gas type. Thus, careful attention to proper sensor selection criteria is essential. Specified instrumentation can accurately monitor the cylinder pressure levels of oxygen, nitrous oxide, and other medical gases. Typically installed between the cylinders and gas delivery system, they also help to determine proper cylinder supply changeover criteria and timing. One transducer is used to measure incoming delivered gas supply pressure. Another measures supply feed pressure to the distribution system. This process ensures that consistent pressure levels are maintained within a specified range.
Medical grade pressure switches are also installed on cylinder alarms to provide effective early warning of possible supply system risks, as well as leaks or blockages. They are also used to facilitate the switch of cylinders from standby to on-duty modes. Complete pressure manifolds, consisting of a pressure switch and various isolation valves, are also specified for these applications. Here, several medical gas cylinder banks are monitored simultaneously. Pressure switches used within manifold applications typically incorporate special Kapton® Polyimide diaphragms, which allow them to maintain their physical properties and performance stability over a wide operating temperature range. This also allows them to be directly compatible with a variety of medical gases.
In addition, pressure sensing instrumentation is used to monitor cylinders, alarms, and inhaled nitrous oxide supplies. Inhaled nitrous oxide has proven especially effective within neonatal intensive care units for the treatment of newborn hypoxemic respiratory failure.
Surgical and medical air are essential for safe operating theatre, patient hospital ward, and intensive care unit functionality. Compressed air helps medical professionals to deliver proper surgical anesthesia and inhaled patient oxygen concentrations. It also powers diagnostic and surgical equipment, dental drills, and other non-critical medical devices.
Medical and surgical air is typically produced via specialty water- or air-cooled compressor systems. In order to remain effective, a compressor must be clean and dry, as well as remain dust-, mold-, and oil-free throughout its operation. It also must reliably perform to varying set pressure levels. To ensure this, compressors are instrumented with both an automatic manifold panel and a manifold reserve, each programmed to a predefined set buffer pressure range. In the event that an automatic manifold is exhausted, a secondary emergency reserve manifold engages, ensuring uninterrupted airflow. Both manifolds require accurate, continuous pressure level monitoring.
Rugged stainless steel pressure sensors are often specified within these generator systems. The sensors form part of a control circuit that activates and deactivates the compressor, allowing it to automatically monitor supply pressure. In doing so, they helps to ensure that buffer pressure remains within its predefined set range. These sensors can reliably operate over a variety of pressure settings, with low thermal errors and a wide temperature compensation range. Sensors may also be customized with application-specific pressure ranges, ports, connectors, cables, and electrical outputs. In addition, the sensors can act as an alarm, providing early warning should levels fall below acceptable values. Data from these sensors also provide important overall compressor health assessments.
Medical vacuum systems, like compressed air, operate from a centrally controlled source. The systems are essential for surgical suction, as well as for generating negative pressure conditions within environmental chambers. Here, pressure transducers are used for critical level monitoring, alarm activation, and support of the central vacuum generator control circuit. (See Figure 2)
Medical gas pipeline systems (MGPS) are used to transport a variety of often-combustible medical gases, including oxygen, medical air, and anesthesia from central and secondary stores into designated areas. In North America, medical gas pipelines are also designed for conformance to National Fire Protection Association guidelines. Typically constructed of copper, MGPS support high- and low-pressure medical gas delivery within hospitals, laboratories, and other clinical environments.
Basic medical gas pipeline infrastructure consists of a main line connecting the gas media supply to the risers; risers, which connect the main line to lateral pipelines; and lateral pipelines, which feed into a branch room, or set of rooms, within the medical care environment. These pipes are installed within the care setting in plain view, versus behind walls.
All MGPS must be extensively tested prior to use. This is to ensure adequate gas delivery pressure, supply regulation, and control. Particularly, gas supplies to anesthesia ventilators are most critical, as those rely upon sufficiently high pressure levels for proper functionality. To ensure such functionality, MGPS must also be continuously monitored for pressure and temperature variations and extremes. Sensors implemented within these environments are used to provide critical early warning of impending pressure drops or overpressure conditions.
The highly corrosive nature of certain gas media makes MGPS prone to corrosion, moisture, mold, pressure stresses, and other mechanical damages. Over time, these factors can contribute to pipe leakages. Within an oxygen delivery environment, such leaks can pose an especially high risk of fire or combustion, as well as patient health damage caused by depleted oxygen stores. Any cross-leakage of medical gases can further increase patient hypoxia risks.
Main MGPS supplies are controlled via manifolds. The manifolds allow for the manual or automatic switching of primary and secondary supplies between alternating stores. Gas is then transported through the main line. These systems also include a manual shutoff function, in the event of an emergency.
Instrumentation requirements call for the monitoring of individual pipelines, with their specifications based upon the type of measured gas media and untapped emergency stores. Vacuum air pressures are also monitored. Pressure switches and transducers are the key safety components to alarm for any leaks or overpressures, as well as to monitor general pressure levels. The main trunk system from the source often operates at 400 bar or 200 bar, with typical step-down distribution channels to 25 bar and 16 bar at a room level (sometimes as low as 10 bar). Pressure transducers and switches are placed strategically within the system to monitor pressure levels and alarm for any unusual conditions. Selected instrumentation must be able to withstand higher-than-typical pressure levels. Pressure sensors typically would operate at 12V or 24V, with 4 to 20 mA or 0.5 to 4.5V output. An IP67 rating ensures continued sensor reliability within possible splash environments. (See Figure 3)
Sensors specified within these applications feature high-accuracy and reliability with low thermal errors and a wide temperature compensation. Specification of sensors with compact size facilitates their ease of installation within the space constraints of a typical MGPS environment. Sensors degreased prior to shipment ensure their compatibility with specialty monitored gases.
The specialty nature of medical gas delivery systems, along with their critical end use, creates often-complex requirements. As the burdens of stringent regulatory compliance are left to the OEMs and health care facilities themselves, effective system monitoring is essential. Specified sensors and switches must be fully gas media compatible, as well as highly robust, accurate, and compact. Instrumentation must be free of contamination risks. It must also have the option for rapid customization.
This article was written by Vincent Ellis, Key Account and Marketing Manager, Gems Sensors & Controls, Basingstoke, Hampshire, England, and Molly Bakewell Chamberlin, President, Embassy Global, LLC, Hamburg, NY. For more information, Click Here " target="_blank" rel="noopener noreferrer">http://info.hotims.com/-162.
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