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Medical equipment regulation and the role of the test house
9 Medical equipment regulation and the role of the test house N O R M A N H. R I C H A R D S O N
The need for ever safer electromedical equipment can be readily appreciated when one considers that in the space of 40 years development has been such that patients, instead of being connected, on rare occasions, to a simple valve-operated ECG monitor and possibly a lung ventilator, are now frequently connected to a complete life-support system with maybe a dozen items providing treatment or displaying and recording patient status information. The risk to the patient from equipment malfunction increases not just in direct proportion to the increased amount of equipment, but much more than that, because of the unfortunate interactions that can take place between various-items. HISTORICAL DEVELOPMENT OF REGULATORY PROCESSES Since the 1950s, governments in the UK have been only slightly behind technical developments in publishing safety codes or standards to which medical equipment must conform. This timing sequence has turned out to be the most realistic approach, since any attempt to predict the path of technological development and encompass those predictions in standards would lead to much wasted effect, as so often the reality turns out to be different from the prediction. In 1956 the famous 'Grey Book' was produced--the Report of a Working
Party on Anaesthetic Explosions, including Safety Code for Equipment and Installations (reprinted in 1961, published by HMSO). For the first time specific recommendations were set out to avoid the ignition of flammable anaesthetic gases in operating theatres. These explosions had occurred many times in the past, the flammable agent usually being ether vapour and the source of ignition usually, but not always, being a spark due to static electricity. (Other sources of ignition were surgical diathermy and cautery electrodes.) A significant development took place in 1963; this was the publication by HMSO of the first edition of Hospital Technical Memorandum No. 8, The Safety Code for Electromedical Apparatus (HTM8). This set out for equipment manufacturers precisely what they had to achieve in terms of equipBaillibre's ClinicalAnaesthesiology--Vol. 2, No. 2, June 1988
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ment safety; it became widely used in the UK and, although it was only intended as a British document, abroad too. HTM8 was revised in 1969 and reprinted in 1970 and, together with the support of measures shortly to be described, was probably the greatest factor in improving the safety of electromedical equipment. It was prepared by the then Scientific and Technical Branch (STB) of the Department of Health and Social Security (DHSS) based then, as now, at Russell Square, London WC1, and this organization introduced two other measures to reinforce the application of HTM8. The first was the establishment of a test laboratory at Russell Square where equipment could be thoroughly tested to check compliance with HTM8, or to establish the points of departure from it, though there was no mandate to issue certificates and equipment was advisedly never allowed to be described as being 'approved' by the DHSS. The second measure was the setting up of an equipment defect reporting procedure. Any staff members of an NHS hospital--medical, technical, nursing or any other--were requested to send a report to Russell Square of any unsatisfactory or unsafe equipment they encountered or used in their work. The reports were investigated (then as now) and the equipment to which they related was nearly always examined in the test laboratory at Russell Square. As a result of this it was often necessary to publish advice, a cautionary note or an urgent warning to the NHS; two vehicles were used for this information: advice and cautionary notes appeared in Health Equipment Information (HEI), published three or four times a year. For urgent warnings to the NHS blue Hazard Notices (HNs) were published and distributed throughout the NHS. By this latter means all hospitals could be warned of hazardous equipment within a few days of the hazard being notified to Russell Square. In the nearly 30 years that the system has been in operation little has changed. The defect reporting procedure is as much in use now as ever, with typically a thousand defects reported per year; advice and cautionary notes now appear as Safety Information Bulletins (SIBs), and urgent warnings still appear as Hazard Notices. It should be noted that manufacturers and suppliers are, and always have been, consulted before any publication concerning their equipment is issued. Other functions carried out by the Russell Square test laboratory were to assist manufacturers at the prototype stage to ensure that their equipment would meet HTM8 when in production; to look at new products, not on a routine basis but where there was particular cause for concern; to recreate hazards reported from the field in a safe and closely monitored enviror~ment; and to examine modifications to equipment resulting from defect reports. Experienced defect investigation engineers know, however, that not all hazardous situations encountered in the field can be recreated in a laboratory. The writer knows of a hospital where the operating theatre was at the end of a long mains feeder and, depending on how much equipment was in use, the mains voltage fluctuated between 170 and 250 V. In addition to the obvious problems that this can cause, the supply line impedance in such a case can produce considerable unwanted interaction between separate items of equipment.
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As medical equipment continued to evolve, a significant political development took place when Britain joined the European Economic Community, with its requirement that there shall be no non-tariff barriers to trade; in other words, equipment that is technically acceptable in one country should also be technically acceptable in the others. This called for harmonized standards for, among other things, medical equipment. A start was made in the early 1970s by experts not only from EEC countries but from many others as well, including strong representation from the UK and particularly the STB. The task of producing a safety standard for electromedical equipment, acceptable internationally, advanced enough to take into account the most recent technological developments, as unambiguous as possible in its interpretation, specific enough to be able to prescribe precise tests but not so specific as to impede future development of equipment, proved exceptionally difficult. However, in 1977 the International Standard for the General Safety Requirements of Medical Electrical Equipment was published (International Electrotechnical Commission 601-1, 1977). During the detailed and extended international discussions that took place during the creation of this standard, a new philosophy for the safety of medical electrical equipment was put forward, being that of safety in 'Single Fault Condition' (SFC). The requirement is that the patient and user shall still be safe if an item of equipment in use develops one, and only one, fault. The standard sets out quantitatively the safety levels which the equipment must meet in normal condition (NC) and additionally sets out relaxed levels to be met when the equipment has one fault. The relaxed SFC levels are still regarded as safe for patient and user. This philosophy is achievable in the design and construction of the equipment, even though the possible number of single faults may be almost infinite. What has been suggested from time to time but is n o t achievable within normal economic limits is safety in the presence of two or more faults. For the philosophy of safety in SFC to work it should be evident in some way to the user of the equipment that there is indeed a fault present; should this not be so and a second fault develops the safety of the equipment can no longer be relied on. The British Standards Institution, assisted by UK experts, made editorial amendments such that references were made to other British Standards and Codes of Practice, and the International Standard was published as a British Standard BS5724, Part 1, in 1979. This document was, as may be imagined, considerably more complex than HTM8, running to over 200 pages of detailed requirements, tests and diagrams. There are also specific requirements for equipment used in the presence of flammable anaesthetic agents, thus supplanting the recommendations of the Grey Book. A treatise on safety would not be complete without including the concept which has made an enormous contribution to electrical safety. This is the fully electrically isolated patient or 'earth-free' patient. The requirement for this was introduced with HTM8 and later refined and quantified precisely in IEC601-1. It means that the patient is not directly connected to the main part of the equipment which is monitoring or treating him, but there is
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interposed in the input stages (or output stages of therapeutic equipment) an isolating barrier past which, by suitable design, electrical signals may pass but which acts as a block to mains electricity. Thus, even if the patient were to be subjected to mains electricity due to the electrical failure of a device in his environment, such as a bedside lamp or television, or, indeed, an item of electromedical equipment connected to him, he would not be at risk as there would be no path via which a current could flow to earth. In IEC601-1 and BS5724 Part 1, the part of the equipment connected to the patient, the 'applied part', is specified in one of three ways. A 'type B' applied part has an earth connection on the patient, or the equipment has no applied part (such as a treatment lamp). A 'type BF' applied part is isolated as described above, and its safety compared to type B is greatly enhanced. A 'type CF' applied part is isolated to an even greater degree, to the extent that it is suitable for direct application to exposed heart tissue without risking ventricular fibrillation, and this represents the most stringent safety category. A final point to make on this subject is that although there are typical forms of construction associated with types B, BF and CF applied parts, the equipment type is defined not by construction but by numerical values of safety performance; this ensures that novel or future forms of construction are not disallowed.
EQUIPMENT TESTING PROCEDURES It became clear that a professional testing organization would be needed to test and certify equipment to this new standard, as each item needed to be subjected to hundreds of tests, including tests following environmental chamber acclimatization at elevated and reduced temperatures and humidities. In the UK, following careful consideration and much discussion with various test organizations, the BSI test house at Hemel Hempstead was chosen as the one which should be developed for testing to BS5724, because of their long experience of testing other equipment and safety devices, because of their international credibility, and because of their lack of commercial allegiance. Other countries were also having to choose national test houses: in France, LCIE and LNE (in combination forming GLEM); in Germany, the VDE and TUV organizations; in Italy, IMQ in Milan; in Sweden, SEMKO, and so on. Having published a standard as all-embracing and complex as BS5724, the process of testing to it does not follow automatically. Several hundred tests are called for under varying conditions as noted above, and so to produce a workable test routine the BSI worked closely with the STB for many months. The result was a sequence of tests in the form of a series of questions. There was so much interest in this test sequence in its readily understandable presentation that it was published to assist manufacturers in carrying out preliminary checks on their products; indeed, the publication is entitled Manufacturers' Aid to Checking Medical Electrical Equipment
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(HMSO, 1982). This publication attracted international interest and was used as a basis for testing by test houses in Europe and America. All test houses, however competent, need some form of accreditation in the first instance to demonstrate their competence to a supervising authority, and then on a continuing basis to ensure that there is no deterioration in the quality of work, and, of course, to discuss problems which arise. Each country has an accreditation authority for the test houses in that country; for the electromedical test laboratory at the BSI the authority is the DHSS. Work at the International Electrotechnical Commission (IEC), with its national organizations supported by the national standards' institutions of the particular countries and the individual experts and participating professional and trade organizations, continues with vigour and will continue to do so. Reference has already been made to IEC601-1 and its British equivalent BS5724 Part 1. These are general requirements which cover the whole range of medical electrical equipment from electrically operated beds and patient hoists through defibrillators, infusion pumps and baby incubators to dental drills and ophthalmoscopes. It can be appreciated that each category of equipment presents its own particular problems and its own safety hazards. To cover these areas IEC Technical Committee (TC) 62, Electrical Equipment in Medical Practice, is divided into four Sub-Committees (SC), being (A) general safety, common aspects; (B) X-ray equipment to 400 kV; (C) high energy and nuclear medicine; (D) electromedical equipment. Each SC is then divided into Working Groups (WGs) and, broadly speaking, each one of these WGs deals with one category of equipment. WGs are created as new topics are required to be discussed and in due course are disbanded when the work on that topic is complete, so it is not possible to give a definitive list of WGs which will remain valid. However, each SC will comprise somewhere between say three and ten WGs. Some WGs with a wide remit--such as SC62D WG1 Diagnostic and Patient Monitoring Equipment, or SC62D WG2 Therapeutic and Surgical Equipment--may remain in being for ten or more years. Each Working Group is engaged in the task of producing particular safety standards for the categories of equipment for which it is responsible. Particular performance standards will also be produced but with a much lower priority. These particular safety and performance standards will be so structured that the general safety standard IEC601-1, or in the UK BS5724 Part I, will be the 'top document' (i.e. basic reference) and all the particular standards will relate to it, adding to it, deleting from it or varying it as appropriate to the particular equipment. Thus, in due course, for any of the main items of electromedical equipment there will be three applicable related standards: the general safety standard, the particular safety standard, and the particular performance standard. This may appear to be unwieldy, but a number of other standards--for example, the standard for household electrical equipment, BS3456--are structured in a similar way, and it is in fact a successful scheme following a period of familiarization by users of the standards.
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At the time of writing the following particular safety standards have been published: 5724.2.1 Medical electron accelerators, 1 to 50 MeV. 5724.2.2 High frequency surgical equipment. 5724.2.3 Short wave therapy equipment. 5724.2.4 Cardiac defibrillators and monitors. 5724.2.5 Safety of ultrasonic therapy equipment. 5724.2.6 Microwave therapy equipment. 5724.2.8 Specification for therapeutic X-ray generators. 5724.2.20 Nursing incubators. 5724.2.21 Transport incubators. 5724.2.23 Oxygen concentrators, hospital and domiciliary. In addition to these, a number of others will be published shortly, including those for anaesthetic machines and lung ventilators. As each particular standard approaches publication, the test houses need to become familiar with it (ideally this may have happened during the drafting process), to prepare test schedules for it, and then, after some practical experience on some sample items of appropriate equipment, to apply to the accrediting authority for recognition. The recognition process is an extended visit to the test house, examination of documentation, supervision of tests and approval of reporting format. The requirement to have medical equipment tested by an approved test house varies from country to country, and in some countries depen-'ds on the type of equipment. The UK policy is that compliance with published standards is required, but this is not supported by legislation as it is in some other countries. It has been found that the onus which falls on health authorities when a non-complying item of equipment causes an incident is a sufficient incentive for the purchase of complying equipment. Furthermore, in the UK type testing (the thorough testing of one single representative sample of a particular model as described earlier, as distinct from routine testing, sample testing or other processes of continuing verification) by a test house is not mandatory either, although compliance with the standards in effect is, unless good reason can be shown why this is not required. It is up to the manufacturer to achieve and verify compliance with standards in the manner of his choice, which may be testing in his own laboratory, testing by an unrecognized test house or even no testing at all if he is sufficiently confident that his design process took in all the requirements of the standard. The first two of these approaches are less satisfactory than testing in a recognized test house, whilst the third is definitely not to be recommended, except perhaps for very simple equipment or variants of previously tested models. The liability for injuries caused by defective or substandard equipment (not just medical, but equipment of all types) now rests with the manufacturer (or importer), according to the Consumer Protection Act 1987 which came into effect on 1st March 1988---assuming, of course, that the equipment has not been tampered with by inexperienced or unauthorized persons. The manufacturer is required to take all reasonable steps to ensure that his equipment
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is safe and, in the eyes of the law, he will have done this if his equipment complies with current safety standards. It would therefore be an ill-advised manufacturer who did not take the greatest care to ensure compliance with these standards, and this care should extend from the design process through manufacture to type testing. Attention so far in this chapter has been focused on IEC601-1 (BS5724 Part 1) and the subsequent parts of this standard. However, there are many other British and international standards relating to health care equipment and accessories; for example, there are about a hundred standards relating to all aspects of anaesthetic equipment: lung ventilators, gas cylinders, pipe-lines and fittings, oxygen concentrators, antistatic tubing, anaesthetic and respiratory connectors, tracheal tubes, and so on. The question is, do the test houses have a part to play in ensuring compliance with these other standards? In cases where the standard covers the manufacture of a disposable device produced in large numbers, or a non-disposable device produced by a continuous machining, injection moulding or extrusion process, a type test carried out by a test house would not be of use other than for that particular batch. The only satisfactory way to regulate the production of such items, and to be reasonably certain that they meet the appropriate standards, is to ensure that the manufacturer has an adequate quality assurance system. This then begs another question in relation to electromedical equipment which has been type-tested. Having had an item of equipment submitted to a test house, and it having passed, what is the likelihood that the next unit from the production line is the same, and so on, all meeting the standard? Once again, the answer is to ensure that the manufacturer has an adequate quality assurance system. It is this path which is being followed by health departments in the UK and in other countries. The UK and USA now both have manufacturer registration schemes (MRSs) in which manufacturers of various categories of medical devices are required to be registered with the DHSS in the UK or the Food and Drug Administration (FDA) in the USA. Registration requires firstly that the manufacturer has a quality system appropriate in scope and detail and complying with published requirements for the products he is making; secondly, that he makes himself known to the health departments by applying for registration and sending the appropriate fee where applicable; and thirdly that his premises are inspected by duly authorized and trained inspectors. The UK and USA schemes differ in that in the USA (the Americans being the forerunners in good manufacturing practice [GMP] schemes) a set of quality assurance requirements is laid down in the Federal Code and all manufacturers of medical devices must meet these requirements. The terms 'quality assurance' and 'good manufacturing practice' are approximately synonymous. In the UK there are several quality assurance guides which differ in detail, in specificity, and in severity according to the product categories to which they relate. The guides, identified by colour, are all based on BS5750--Quality Systems (in six parts, mostly revised 1987) with additions or deletions as mentioned, appropriate to the products. The guides are as follows:
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Blue Guide: sterile medical devices and surgical products; Red Guide: implantable cardiac pacemakers and leads; Green Guide: medical equipment; Gold Guide: orthopaedic implants; Manilla Guide: rehabilitation equipment. (All are likely to be revised.) Certain other items of medical equipment are covered either by BS5750 unamended, or by the same standard with unpublished amendments. A manufacturer's premises and processes are inspected or 'audited' at intervals of two years in the USA or about three years in the UK, and the audit is a thorough process taking two inspectors three or four days, or more if there are several production plants. In order to ensure uniformity of approach in the UK, one of the two inspectors is from the DHSS Scientific and Technical Branch, now re-named Supplies Technology Division (STD), and the other may be from the BSI Quality Assurance Inspectorate. In the USA, the registration scheme with the FDA is a mandatory process covered by legislation. In the UK it is not; the scheme is a recommended one in that those having the responsibility for making purchasing decisions for medical products and devices are strongly recommended to purchase only from registered manufacturers. In practice it is a strong scheme as it is easy to imagine the difficult situation a purchaser would be in if a device bought from an unregistered manufacturer were to cause an incident. Of course, there has to be some flexibility in cases where hospital research departments buy equipment for animal experiments, or where these departments buy industrial equipment which the manufacturers only rarely supply to hospitals, or where there is only one supplier of a particular type of equipment and he is not registered, and so on. At the time of writing a number of countries have schemes for inspecting manufacturers administered by the country's health authority. Among these are (in addition to the UK and USA) Germany, Italy, Spain and Hungary. When a potential purchaser is considering placing an order for medical equipment he will have a number of questions to ask, two important ones being whether or not the equipment meets current safety (and performance) standards, and whether the manufacturer is registered. In the UK such a potential purchaser is encouraged to send to the manufacturer a questionnaire which includes these and a number of other questions, such as: How is the equipment cleaned? What service arrangements are there? For how long will spare parts be available? This questionnaire, known as the medical and laboratory equipment questionnaire (MLQ), is stocked by hospital supplies departments for use where required. It is published by UK health departments (periodically revised) and is in three parts: MLQ1, which is the request for information; MLQ2, which is the questionnaire itself to be completed by the potential supplier; and MLQ3, explanatory/guidance notes. The potential purchaser is then able to decide on the basis of the replies to the questions on MLQ2 whether or not he wishes to proceed with the purchase. Occasionally there is some confusion about the application of the MLQ
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forms, typically where the device is not an item of equipment in itself but an accessory (such as a physiological pressure transducer), or where disposable items are concerned (as in the case of ECG monitoring electrodes), for which, respectively, several or most of the questions do not apply. However, in general the scheme is very successful and provides the purchaser with a valuable insight into the attitude of the supplier. In 1981 the UK Department of Health published guidelines aimed at hospital electronics and medical physics departments and explaining the course of action to be followed by these departments wishing to check equipment delivered to the hospital prior to putting it into service (DHSS, 1981). This was published to dissuade these departments from carrying out potentially damaging type tests more appropriate to a test house, but yet enabling them to make a positive contribution to the safety of equipment in service, and in doing so to note each item of equipment arriving at the hospital, for logging for future maintenance. As mentioned earlier in this chapter, in some countries type testing of medical electrical equipment is mandatory; in others, type testing of only certain categories of such equipment is mandatory. Furthermore, all manufacturing countries export a significant percentage of their output; some UK electromedical manufacturers export 80% of their production, and in Denmark the proportion is even higher. While it is understandable that each consumer country has faith in its own test house and indeed is keen to keep its test house supplied with work, a situation where each country accepts only the results of its own test house would be commercially very onerous for manufacturing industry due to time delays, costs and numbers of samples needed for submission. A manufacturer would then be required to send a sample of equipment intended for export to all the potential recipient countries for type testing in each one, with the resulting enormous penalties in cost and time delay. The BSI test house together with DHSS STD have embarked on a programme of co-operation between national test houses such that the test results obtained by one are acceptable to another, subject to certain verifications. This mutual acceptability of results is not as straightforward as may be thought, and this is not due to any failings in confidence that one test house has in another. One difficulty is that test houses may have different mandates. For example, the mandate of the BSI test house at Hemel Hempstead is normally to test equipment to BS5724 Part 1, and to any published Part 2 standards. The TUV and VDE test houses in Germany are mandated by the German Ministry of Labour to test equipment to ensure it is safe. Thus, it is perfectly acceptable for TUV to omit certain tests in IEC601-1 (BS5724 Part 1) which it regards as not having a direct bearing on the safety of a particular item, and to add certain tests which do not appear in 601-1 and which are considered to be relevant to safety; examples of such additional tests could be the operation of equipment in strong magnetic fields if this is likely in normal use, not specified in 601-1, or checking for gaps in which fingers could be caught as in articulating dental chairs, also not specified in 601-1 but which will be in the particular safety standard for dental chairs. In the agreement reached between the BSI and TUV Bavaria
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in Munich there is provision for the BSI, when testing on behalf of TUV, to carry out such additional tests, and for TUV when testing on behalf of the BSI, to carry out all the specified tests in 601-1. Other differences which have cropped up in the testing techniques of the various test houses is that some only test to published standards, whereas others will test to draft particular standards as well, provided these are late drafts. Furthermore, and quite understandably, in the absence of international standards, test houses use national standards and this adds a further dimension of difficulty when it comes to mutual recognition. Nevertheless, completely satisfactory working agreements exist between BSI Hemel Hempstead and TUV Bavaria in Munich, IMQ in Milan and SEMKO in Stockholm. It is hoped to extend these agreements. EQUIPMENT EVALUATION In this cost- and safety-conscious age, users of medical equipment and their employing authorities are anxious to purchase equipment which is safe, is straightforward to use (which also contributes to safety), and represents good value for money. Furthermore, will the equipment be reliable, and when it does fail will the supplier be able to provide an adequate level of support also at reasonable cost? Will the equipment perform well? In 1977 the DHSS and a number of Regional Health Authorities embarked on an ambitious programme of equipment evaluation. The pilot projects at that time were the evaluation of ECG recorders, ECG monitors, defibrillators and surgical diathermy in Oxford, Newcastle, Sheffield and Cardiff respectively. The work was carried out by experienced electromedical engineers with support--technical, financial, editorial and administrative--from the DHSS at Russell Square. The evaluation exercise featured a technical examination of the safety and performance of the equipment; the equipment was then put into routine clinical use in four different clinical environments for periods of up to six weeks in each. The clinicians and users were asked detailed questions about the equipment at the end of each period of clinical use. Reports were prepared on each item of equipment, the manufacturer was given the opportunity to comment, and the reports were published as comparative evaluations. Much effort was expended in ensuring that the reports were fair and unbiased by any innate equipment preference in the evaluation groups. The user trials alone accounted for some six months of the evaluation period, and to this had to be added the technical examination and testing of the equipment in the regional laboratories, and the writing, editing and submission of reports to the DHSS. The manufacturers or their agents then had to have a period to comment on the reports so that their comments could appear alongside the evaluation report, and then followed the printing and distribution processes for the reports. This evaluation programme has gone from strength to strength; there are now 14 evaluation centres covering the evaluation of 25 categories of medical equipment. In the early days of this evaluation programme all the
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actual technical testing was done in the regional evaluation centres, as well as the user trials. To reduce the overall time delay, the evaluation programme has been re-structured so that the safety testing is carried out by the BSI test house in parallel with performance testing and user trials in progress on another sample of the same model at the regional evaluation centre. The evaluation programme is under constant review for means to speed up the production of reports while maintaining their high quality. The reports are published by the DHSS as Health Equipment Information evaluation issues, and are available to the NHS and to the public.
SUMMARY
This chapter sets out the need for increased regulatory action for medical equipment brought about by a number of factors, including its complexity, its ever-increasing quantity, and the requirements for it to be able to cross frontiers in international trade by being acceptable in each country. The history of the regulatory processes is covered, as this is not only important for its understanding but will serve to show new or potential manufacturers in this field the need for such regulation. The development of international standards and the means by which equipment is tested to them is also set out in some detail, so that those users of medical equipment unacquainted with the steps taken to ensure its safety may become aware of the tremendous international effort, sustained over many years, being made to achieve very high safety levels. Two major concepts contained in the international safety standard are also described: that of safety in single fault condition, and that of the electrically isolated patient. Further measures are described in which the manufacturing processes themselves are examined to ensure continuing quality of equipment, although the inspection itself is not covered in depth. Apart from ensuring that safe and reliable equipment is available, it is also essential to see that such equipment is indeed bought and used in preference to less satisfactory products. The schemes that have been set up to this end are explained, namely, the equipment evaluation programme to publicize safe and reasonably priced products, and the manufacturer's declaration of compliance with current safety standards. Work in all these spheres will continue as medical equipment not only diagnoses and treats but carries out more and more physiological functions on a long-term basis, and is used in greater numbers.
REFERENCES DHSS (1981) Health Equipment Information, No. 95. August 1981. HMSO (1982) Manufacturers' Aid to Checking Medical Electrical Equipment. Standard Test Format--Guide to the Use of British Standard 5724 Part 1.
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International Electrotechnical Commission 601-1 (1977) Safety of Medical Electrical Equipment, Part 1: General Requirements, I st edn 1977. Title later changed to Medical Electrical Equipment, Part 1: General Requirements for Safety, 2nd edn with corrections and improvements, 1988.
The need for ever safer electromedical equipment can be readily appreciated when one considers that in the space of 40 years development has been such that patients, instead of being connected, on rare occasions, to a simple valve-operated ECG monitor and possibly a lung ventilator, are now frequently connected to a complete life-support system with maybe a dozen items providing treatment or displaying and recording patient status information. The risk to the patient from equipment malfunction increases not just in direct proportion to the increased amount of equipment, but much more than that, because of the unfortunate interactions that can take place between various-items. HISTORICAL DEVELOPMENT OF REGULATORY PROCESSES Since the 1950s, governments in the UK have been only slightly behind technical developments in publishing safety codes or standards to which medical equipment must conform. This timing sequence has turned out to be the most realistic approach, since any attempt to predict the path of technological development and encompass those predictions in standards would lead to much wasted effect, as so often the reality turns out to be different from the prediction. In 1956 the famous 'Grey Book' was produced--the Report of a Working
Party on Anaesthetic Explosions, including Safety Code for Equipment and Installations (reprinted in 1961, published by HMSO). For the first time specific recommendations were set out to avoid the ignition of flammable anaesthetic gases in operating theatres. These explosions had occurred many times in the past, the flammable agent usually being ether vapour and the source of ignition usually, but not always, being a spark due to static electricity. (Other sources of ignition were surgical diathermy and cautery electrodes.) A significant development took place in 1963; this was the publication by HMSO of the first edition of Hospital Technical Memorandum No. 8, The Safety Code for Electromedical Apparatus (HTM8). This set out for equipment manufacturers precisely what they had to achieve in terms of equipBaillibre's ClinicalAnaesthesiology--Vol. 2, No. 2, June 1988
367
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ment safety; it became widely used in the UK and, although it was only intended as a British document, abroad too. HTM8 was revised in 1969 and reprinted in 1970 and, together with the support of measures shortly to be described, was probably the greatest factor in improving the safety of electromedical equipment. It was prepared by the then Scientific and Technical Branch (STB) of the Department of Health and Social Security (DHSS) based then, as now, at Russell Square, London WC1, and this organization introduced two other measures to reinforce the application of HTM8. The first was the establishment of a test laboratory at Russell Square where equipment could be thoroughly tested to check compliance with HTM8, or to establish the points of departure from it, though there was no mandate to issue certificates and equipment was advisedly never allowed to be described as being 'approved' by the DHSS. The second measure was the setting up of an equipment defect reporting procedure. Any staff members of an NHS hospital--medical, technical, nursing or any other--were requested to send a report to Russell Square of any unsatisfactory or unsafe equipment they encountered or used in their work. The reports were investigated (then as now) and the equipment to which they related was nearly always examined in the test laboratory at Russell Square. As a result of this it was often necessary to publish advice, a cautionary note or an urgent warning to the NHS; two vehicles were used for this information: advice and cautionary notes appeared in Health Equipment Information (HEI), published three or four times a year. For urgent warnings to the NHS blue Hazard Notices (HNs) were published and distributed throughout the NHS. By this latter means all hospitals could be warned of hazardous equipment within a few days of the hazard being notified to Russell Square. In the nearly 30 years that the system has been in operation little has changed. The defect reporting procedure is as much in use now as ever, with typically a thousand defects reported per year; advice and cautionary notes now appear as Safety Information Bulletins (SIBs), and urgent warnings still appear as Hazard Notices. It should be noted that manufacturers and suppliers are, and always have been, consulted before any publication concerning their equipment is issued. Other functions carried out by the Russell Square test laboratory were to assist manufacturers at the prototype stage to ensure that their equipment would meet HTM8 when in production; to look at new products, not on a routine basis but where there was particular cause for concern; to recreate hazards reported from the field in a safe and closely monitored enviror~ment; and to examine modifications to equipment resulting from defect reports. Experienced defect investigation engineers know, however, that not all hazardous situations encountered in the field can be recreated in a laboratory. The writer knows of a hospital where the operating theatre was at the end of a long mains feeder and, depending on how much equipment was in use, the mains voltage fluctuated between 170 and 250 V. In addition to the obvious problems that this can cause, the supply line impedance in such a case can produce considerable unwanted interaction between separate items of equipment.
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As medical equipment continued to evolve, a significant political development took place when Britain joined the European Economic Community, with its requirement that there shall be no non-tariff barriers to trade; in other words, equipment that is technically acceptable in one country should also be technically acceptable in the others. This called for harmonized standards for, among other things, medical equipment. A start was made in the early 1970s by experts not only from EEC countries but from many others as well, including strong representation from the UK and particularly the STB. The task of producing a safety standard for electromedical equipment, acceptable internationally, advanced enough to take into account the most recent technological developments, as unambiguous as possible in its interpretation, specific enough to be able to prescribe precise tests but not so specific as to impede future development of equipment, proved exceptionally difficult. However, in 1977 the International Standard for the General Safety Requirements of Medical Electrical Equipment was published (International Electrotechnical Commission 601-1, 1977). During the detailed and extended international discussions that took place during the creation of this standard, a new philosophy for the safety of medical electrical equipment was put forward, being that of safety in 'Single Fault Condition' (SFC). The requirement is that the patient and user shall still be safe if an item of equipment in use develops one, and only one, fault. The standard sets out quantitatively the safety levels which the equipment must meet in normal condition (NC) and additionally sets out relaxed levels to be met when the equipment has one fault. The relaxed SFC levels are still regarded as safe for patient and user. This philosophy is achievable in the design and construction of the equipment, even though the possible number of single faults may be almost infinite. What has been suggested from time to time but is n o t achievable within normal economic limits is safety in the presence of two or more faults. For the philosophy of safety in SFC to work it should be evident in some way to the user of the equipment that there is indeed a fault present; should this not be so and a second fault develops the safety of the equipment can no longer be relied on. The British Standards Institution, assisted by UK experts, made editorial amendments such that references were made to other British Standards and Codes of Practice, and the International Standard was published as a British Standard BS5724, Part 1, in 1979. This document was, as may be imagined, considerably more complex than HTM8, running to over 200 pages of detailed requirements, tests and diagrams. There are also specific requirements for equipment used in the presence of flammable anaesthetic agents, thus supplanting the recommendations of the Grey Book. A treatise on safety would not be complete without including the concept which has made an enormous contribution to electrical safety. This is the fully electrically isolated patient or 'earth-free' patient. The requirement for this was introduced with HTM8 and later refined and quantified precisely in IEC601-1. It means that the patient is not directly connected to the main part of the equipment which is monitoring or treating him, but there is
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interposed in the input stages (or output stages of therapeutic equipment) an isolating barrier past which, by suitable design, electrical signals may pass but which acts as a block to mains electricity. Thus, even if the patient were to be subjected to mains electricity due to the electrical failure of a device in his environment, such as a bedside lamp or television, or, indeed, an item of electromedical equipment connected to him, he would not be at risk as there would be no path via which a current could flow to earth. In IEC601-1 and BS5724 Part 1, the part of the equipment connected to the patient, the 'applied part', is specified in one of three ways. A 'type B' applied part has an earth connection on the patient, or the equipment has no applied part (such as a treatment lamp). A 'type BF' applied part is isolated as described above, and its safety compared to type B is greatly enhanced. A 'type CF' applied part is isolated to an even greater degree, to the extent that it is suitable for direct application to exposed heart tissue without risking ventricular fibrillation, and this represents the most stringent safety category. A final point to make on this subject is that although there are typical forms of construction associated with types B, BF and CF applied parts, the equipment type is defined not by construction but by numerical values of safety performance; this ensures that novel or future forms of construction are not disallowed.
EQUIPMENT TESTING PROCEDURES It became clear that a professional testing organization would be needed to test and certify equipment to this new standard, as each item needed to be subjected to hundreds of tests, including tests following environmental chamber acclimatization at elevated and reduced temperatures and humidities. In the UK, following careful consideration and much discussion with various test organizations, the BSI test house at Hemel Hempstead was chosen as the one which should be developed for testing to BS5724, because of their long experience of testing other equipment and safety devices, because of their international credibility, and because of their lack of commercial allegiance. Other countries were also having to choose national test houses: in France, LCIE and LNE (in combination forming GLEM); in Germany, the VDE and TUV organizations; in Italy, IMQ in Milan; in Sweden, SEMKO, and so on. Having published a standard as all-embracing and complex as BS5724, the process of testing to it does not follow automatically. Several hundred tests are called for under varying conditions as noted above, and so to produce a workable test routine the BSI worked closely with the STB for many months. The result was a sequence of tests in the form of a series of questions. There was so much interest in this test sequence in its readily understandable presentation that it was published to assist manufacturers in carrying out preliminary checks on their products; indeed, the publication is entitled Manufacturers' Aid to Checking Medical Electrical Equipment
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(HMSO, 1982). This publication attracted international interest and was used as a basis for testing by test houses in Europe and America. All test houses, however competent, need some form of accreditation in the first instance to demonstrate their competence to a supervising authority, and then on a continuing basis to ensure that there is no deterioration in the quality of work, and, of course, to discuss problems which arise. Each country has an accreditation authority for the test houses in that country; for the electromedical test laboratory at the BSI the authority is the DHSS. Work at the International Electrotechnical Commission (IEC), with its national organizations supported by the national standards' institutions of the particular countries and the individual experts and participating professional and trade organizations, continues with vigour and will continue to do so. Reference has already been made to IEC601-1 and its British equivalent BS5724 Part 1. These are general requirements which cover the whole range of medical electrical equipment from electrically operated beds and patient hoists through defibrillators, infusion pumps and baby incubators to dental drills and ophthalmoscopes. It can be appreciated that each category of equipment presents its own particular problems and its own safety hazards. To cover these areas IEC Technical Committee (TC) 62, Electrical Equipment in Medical Practice, is divided into four Sub-Committees (SC), being (A) general safety, common aspects; (B) X-ray equipment to 400 kV; (C) high energy and nuclear medicine; (D) electromedical equipment. Each SC is then divided into Working Groups (WGs) and, broadly speaking, each one of these WGs deals with one category of equipment. WGs are created as new topics are required to be discussed and in due course are disbanded when the work on that topic is complete, so it is not possible to give a definitive list of WGs which will remain valid. However, each SC will comprise somewhere between say three and ten WGs. Some WGs with a wide remit--such as SC62D WG1 Diagnostic and Patient Monitoring Equipment, or SC62D WG2 Therapeutic and Surgical Equipment--may remain in being for ten or more years. Each Working Group is engaged in the task of producing particular safety standards for the categories of equipment for which it is responsible. Particular performance standards will also be produced but with a much lower priority. These particular safety and performance standards will be so structured that the general safety standard IEC601-1, or in the UK BS5724 Part I, will be the 'top document' (i.e. basic reference) and all the particular standards will relate to it, adding to it, deleting from it or varying it as appropriate to the particular equipment. Thus, in due course, for any of the main items of electromedical equipment there will be three applicable related standards: the general safety standard, the particular safety standard, and the particular performance standard. This may appear to be unwieldy, but a number of other standards--for example, the standard for household electrical equipment, BS3456--are structured in a similar way, and it is in fact a successful scheme following a period of familiarization by users of the standards.
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At the time of writing the following particular safety standards have been published: 5724.2.1 Medical electron accelerators, 1 to 50 MeV. 5724.2.2 High frequency surgical equipment. 5724.2.3 Short wave therapy equipment. 5724.2.4 Cardiac defibrillators and monitors. 5724.2.5 Safety of ultrasonic therapy equipment. 5724.2.6 Microwave therapy equipment. 5724.2.8 Specification for therapeutic X-ray generators. 5724.2.20 Nursing incubators. 5724.2.21 Transport incubators. 5724.2.23 Oxygen concentrators, hospital and domiciliary. In addition to these, a number of others will be published shortly, including those for anaesthetic machines and lung ventilators. As each particular standard approaches publication, the test houses need to become familiar with it (ideally this may have happened during the drafting process), to prepare test schedules for it, and then, after some practical experience on some sample items of appropriate equipment, to apply to the accrediting authority for recognition. The recognition process is an extended visit to the test house, examination of documentation, supervision of tests and approval of reporting format. The requirement to have medical equipment tested by an approved test house varies from country to country, and in some countries depen-'ds on the type of equipment. The UK policy is that compliance with published standards is required, but this is not supported by legislation as it is in some other countries. It has been found that the onus which falls on health authorities when a non-complying item of equipment causes an incident is a sufficient incentive for the purchase of complying equipment. Furthermore, in the UK type testing (the thorough testing of one single representative sample of a particular model as described earlier, as distinct from routine testing, sample testing or other processes of continuing verification) by a test house is not mandatory either, although compliance with the standards in effect is, unless good reason can be shown why this is not required. It is up to the manufacturer to achieve and verify compliance with standards in the manner of his choice, which may be testing in his own laboratory, testing by an unrecognized test house or even no testing at all if he is sufficiently confident that his design process took in all the requirements of the standard. The first two of these approaches are less satisfactory than testing in a recognized test house, whilst the third is definitely not to be recommended, except perhaps for very simple equipment or variants of previously tested models. The liability for injuries caused by defective or substandard equipment (not just medical, but equipment of all types) now rests with the manufacturer (or importer), according to the Consumer Protection Act 1987 which came into effect on 1st March 1988---assuming, of course, that the equipment has not been tampered with by inexperienced or unauthorized persons. The manufacturer is required to take all reasonable steps to ensure that his equipment
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is safe and, in the eyes of the law, he will have done this if his equipment complies with current safety standards. It would therefore be an ill-advised manufacturer who did not take the greatest care to ensure compliance with these standards, and this care should extend from the design process through manufacture to type testing. Attention so far in this chapter has been focused on IEC601-1 (BS5724 Part 1) and the subsequent parts of this standard. However, there are many other British and international standards relating to health care equipment and accessories; for example, there are about a hundred standards relating to all aspects of anaesthetic equipment: lung ventilators, gas cylinders, pipe-lines and fittings, oxygen concentrators, antistatic tubing, anaesthetic and respiratory connectors, tracheal tubes, and so on. The question is, do the test houses have a part to play in ensuring compliance with these other standards? In cases where the standard covers the manufacture of a disposable device produced in large numbers, or a non-disposable device produced by a continuous machining, injection moulding or extrusion process, a type test carried out by a test house would not be of use other than for that particular batch. The only satisfactory way to regulate the production of such items, and to be reasonably certain that they meet the appropriate standards, is to ensure that the manufacturer has an adequate quality assurance system. This then begs another question in relation to electromedical equipment which has been type-tested. Having had an item of equipment submitted to a test house, and it having passed, what is the likelihood that the next unit from the production line is the same, and so on, all meeting the standard? Once again, the answer is to ensure that the manufacturer has an adequate quality assurance system. It is this path which is being followed by health departments in the UK and in other countries. The UK and USA now both have manufacturer registration schemes (MRSs) in which manufacturers of various categories of medical devices are required to be registered with the DHSS in the UK or the Food and Drug Administration (FDA) in the USA. Registration requires firstly that the manufacturer has a quality system appropriate in scope and detail and complying with published requirements for the products he is making; secondly, that he makes himself known to the health departments by applying for registration and sending the appropriate fee where applicable; and thirdly that his premises are inspected by duly authorized and trained inspectors. The UK and USA schemes differ in that in the USA (the Americans being the forerunners in good manufacturing practice [GMP] schemes) a set of quality assurance requirements is laid down in the Federal Code and all manufacturers of medical devices must meet these requirements. The terms 'quality assurance' and 'good manufacturing practice' are approximately synonymous. In the UK there are several quality assurance guides which differ in detail, in specificity, and in severity according to the product categories to which they relate. The guides, identified by colour, are all based on BS5750--Quality Systems (in six parts, mostly revised 1987) with additions or deletions as mentioned, appropriate to the products. The guides are as follows:
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Blue Guide: sterile medical devices and surgical products; Red Guide: implantable cardiac pacemakers and leads; Green Guide: medical equipment; Gold Guide: orthopaedic implants; Manilla Guide: rehabilitation equipment. (All are likely to be revised.) Certain other items of medical equipment are covered either by BS5750 unamended, or by the same standard with unpublished amendments. A manufacturer's premises and processes are inspected or 'audited' at intervals of two years in the USA or about three years in the UK, and the audit is a thorough process taking two inspectors three or four days, or more if there are several production plants. In order to ensure uniformity of approach in the UK, one of the two inspectors is from the DHSS Scientific and Technical Branch, now re-named Supplies Technology Division (STD), and the other may be from the BSI Quality Assurance Inspectorate. In the USA, the registration scheme with the FDA is a mandatory process covered by legislation. In the UK it is not; the scheme is a recommended one in that those having the responsibility for making purchasing decisions for medical products and devices are strongly recommended to purchase only from registered manufacturers. In practice it is a strong scheme as it is easy to imagine the difficult situation a purchaser would be in if a device bought from an unregistered manufacturer were to cause an incident. Of course, there has to be some flexibility in cases where hospital research departments buy equipment for animal experiments, or where these departments buy industrial equipment which the manufacturers only rarely supply to hospitals, or where there is only one supplier of a particular type of equipment and he is not registered, and so on. At the time of writing a number of countries have schemes for inspecting manufacturers administered by the country's health authority. Among these are (in addition to the UK and USA) Germany, Italy, Spain and Hungary. When a potential purchaser is considering placing an order for medical equipment he will have a number of questions to ask, two important ones being whether or not the equipment meets current safety (and performance) standards, and whether the manufacturer is registered. In the UK such a potential purchaser is encouraged to send to the manufacturer a questionnaire which includes these and a number of other questions, such as: How is the equipment cleaned? What service arrangements are there? For how long will spare parts be available? This questionnaire, known as the medical and laboratory equipment questionnaire (MLQ), is stocked by hospital supplies departments for use where required. It is published by UK health departments (periodically revised) and is in three parts: MLQ1, which is the request for information; MLQ2, which is the questionnaire itself to be completed by the potential supplier; and MLQ3, explanatory/guidance notes. The potential purchaser is then able to decide on the basis of the replies to the questions on MLQ2 whether or not he wishes to proceed with the purchase. Occasionally there is some confusion about the application of the MLQ
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forms, typically where the device is not an item of equipment in itself but an accessory (such as a physiological pressure transducer), or where disposable items are concerned (as in the case of ECG monitoring electrodes), for which, respectively, several or most of the questions do not apply. However, in general the scheme is very successful and provides the purchaser with a valuable insight into the attitude of the supplier. In 1981 the UK Department of Health published guidelines aimed at hospital electronics and medical physics departments and explaining the course of action to be followed by these departments wishing to check equipment delivered to the hospital prior to putting it into service (DHSS, 1981). This was published to dissuade these departments from carrying out potentially damaging type tests more appropriate to a test house, but yet enabling them to make a positive contribution to the safety of equipment in service, and in doing so to note each item of equipment arriving at the hospital, for logging for future maintenance. As mentioned earlier in this chapter, in some countries type testing of medical electrical equipment is mandatory; in others, type testing of only certain categories of such equipment is mandatory. Furthermore, all manufacturing countries export a significant percentage of their output; some UK electromedical manufacturers export 80% of their production, and in Denmark the proportion is even higher. While it is understandable that each consumer country has faith in its own test house and indeed is keen to keep its test house supplied with work, a situation where each country accepts only the results of its own test house would be commercially very onerous for manufacturing industry due to time delays, costs and numbers of samples needed for submission. A manufacturer would then be required to send a sample of equipment intended for export to all the potential recipient countries for type testing in each one, with the resulting enormous penalties in cost and time delay. The BSI test house together with DHSS STD have embarked on a programme of co-operation between national test houses such that the test results obtained by one are acceptable to another, subject to certain verifications. This mutual acceptability of results is not as straightforward as may be thought, and this is not due to any failings in confidence that one test house has in another. One difficulty is that test houses may have different mandates. For example, the mandate of the BSI test house at Hemel Hempstead is normally to test equipment to BS5724 Part 1, and to any published Part 2 standards. The TUV and VDE test houses in Germany are mandated by the German Ministry of Labour to test equipment to ensure it is safe. Thus, it is perfectly acceptable for TUV to omit certain tests in IEC601-1 (BS5724 Part 1) which it regards as not having a direct bearing on the safety of a particular item, and to add certain tests which do not appear in 601-1 and which are considered to be relevant to safety; examples of such additional tests could be the operation of equipment in strong magnetic fields if this is likely in normal use, not specified in 601-1, or checking for gaps in which fingers could be caught as in articulating dental chairs, also not specified in 601-1 but which will be in the particular safety standard for dental chairs. In the agreement reached between the BSI and TUV Bavaria
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in Munich there is provision for the BSI, when testing on behalf of TUV, to carry out such additional tests, and for TUV when testing on behalf of the BSI, to carry out all the specified tests in 601-1. Other differences which have cropped up in the testing techniques of the various test houses is that some only test to published standards, whereas others will test to draft particular standards as well, provided these are late drafts. Furthermore, and quite understandably, in the absence of international standards, test houses use national standards and this adds a further dimension of difficulty when it comes to mutual recognition. Nevertheless, completely satisfactory working agreements exist between BSI Hemel Hempstead and TUV Bavaria in Munich, IMQ in Milan and SEMKO in Stockholm. It is hoped to extend these agreements. EQUIPMENT EVALUATION In this cost- and safety-conscious age, users of medical equipment and their employing authorities are anxious to purchase equipment which is safe, is straightforward to use (which also contributes to safety), and represents good value for money. Furthermore, will the equipment be reliable, and when it does fail will the supplier be able to provide an adequate level of support also at reasonable cost? Will the equipment perform well? In 1977 the DHSS and a number of Regional Health Authorities embarked on an ambitious programme of equipment evaluation. The pilot projects at that time were the evaluation of ECG recorders, ECG monitors, defibrillators and surgical diathermy in Oxford, Newcastle, Sheffield and Cardiff respectively. The work was carried out by experienced electromedical engineers with support--technical, financial, editorial and administrative--from the DHSS at Russell Square. The evaluation exercise featured a technical examination of the safety and performance of the equipment; the equipment was then put into routine clinical use in four different clinical environments for periods of up to six weeks in each. The clinicians and users were asked detailed questions about the equipment at the end of each period of clinical use. Reports were prepared on each item of equipment, the manufacturer was given the opportunity to comment, and the reports were published as comparative evaluations. Much effort was expended in ensuring that the reports were fair and unbiased by any innate equipment preference in the evaluation groups. The user trials alone accounted for some six months of the evaluation period, and to this had to be added the technical examination and testing of the equipment in the regional laboratories, and the writing, editing and submission of reports to the DHSS. The manufacturers or their agents then had to have a period to comment on the reports so that their comments could appear alongside the evaluation report, and then followed the printing and distribution processes for the reports. This evaluation programme has gone from strength to strength; there are now 14 evaluation centres covering the evaluation of 25 categories of medical equipment. In the early days of this evaluation programme all the
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actual technical testing was done in the regional evaluation centres, as well as the user trials. To reduce the overall time delay, the evaluation programme has been re-structured so that the safety testing is carried out by the BSI test house in parallel with performance testing and user trials in progress on another sample of the same model at the regional evaluation centre. The evaluation programme is under constant review for means to speed up the production of reports while maintaining their high quality. The reports are published by the DHSS as Health Equipment Information evaluation issues, and are available to the NHS and to the public.
SUMMARY
This chapter sets out the need for increased regulatory action for medical equipment brought about by a number of factors, including its complexity, its ever-increasing quantity, and the requirements for it to be able to cross frontiers in international trade by being acceptable in each country. The history of the regulatory processes is covered, as this is not only important for its understanding but will serve to show new or potential manufacturers in this field the need for such regulation. The development of international standards and the means by which equipment is tested to them is also set out in some detail, so that those users of medical equipment unacquainted with the steps taken to ensure its safety may become aware of the tremendous international effort, sustained over many years, being made to achieve very high safety levels. Two major concepts contained in the international safety standard are also described: that of safety in single fault condition, and that of the electrically isolated patient. Further measures are described in which the manufacturing processes themselves are examined to ensure continuing quality of equipment, although the inspection itself is not covered in depth. Apart from ensuring that safe and reliable equipment is available, it is also essential to see that such equipment is indeed bought and used in preference to less satisfactory products. The schemes that have been set up to this end are explained, namely, the equipment evaluation programme to publicize safe and reasonably priced products, and the manufacturer's declaration of compliance with current safety standards. Work in all these spheres will continue as medical equipment not only diagnoses and treats but carries out more and more physiological functions on a long-term basis, and is used in greater numbers.
REFERENCES DHSS (1981) Health Equipment Information, No. 95. August 1981. HMSO (1982) Manufacturers' Aid to Checking Medical Electrical Equipment. Standard Test Format--Guide to the Use of British Standard 5724 Part 1.
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International Electrotechnical Commission 601-1 (1977) Safety of Medical Electrical Equipment, Part 1: General Requirements, I st edn 1977. Title later changed to Medical Electrical Equipment, Part 1: General Requirements for Safety, 2nd edn with corrections and improvements, 1988.