IEC 60601-1 and accessories

These days many medical applications are a system comprising of a main unit and accessories or detachable parts.

Under medical device regulations, it is allowed for each part of a system to be treated as an individual medical device. Despite some concerns, regulations do not require any contract or agreement between the different manufacturers making up parts of the system. 

Instead, they rely on risk management, which is appropriate given wide range of situations and regulatory issues. For example, labelling, instructions, sterilisation and bio-compatibility are reasonably under the responsibility of the accessory manufacturer. Electrical isolation from mains parts, EMC emissions and immunity are normally under the responsibility of the main unit manufacturer. In some cases there are shared system specifications (such as system accuracy shared between main unit and sensor), in other cases there are assumptions based on reasonable expectations or industry norms (such as IBP sensor insulation). In the end the analysis should resolve itself into interface specifications which allocate some or all of the system requirements to either the main unit or the accessory. 

There is a valid concern that by keeping the analysis by each manufacturer independent, critical issues could fall through the cracks. Each manufacturer could assume the other will handle a particular requirement. And sometimes system requirements are difficult to separate. 

Even so, the alternative is unthinkable: a system only approach only works if there are agreements and constant exchange of information between the different manufacturers in a system.  This would create an unwieldy network of agreements between tens of thousands of manufacturers throughout the world, difficult to implement, virtually impossible to maintain. While regulators surely recognise the concern, the alternative is far worse. Thus it remains in the flexible domain of risk management to deal with practical implementation. 

IEC 60601-1 makes a mess of the situation, again highlighting the lack of hands on regulatory experience in those involved with developing the standard.

The definition of "ME equipment" in Clause 3.63 has a "Note 1" which states that accessories necessary for normal use are considered part of the ME equipment. The standard also has many requirements for accessories, such as labelling, sterilisation and mechanical tests. This implies a system only approach to testing. 

Yet the standard trips up in Clause 3.55, by defining a "manufacturer" as the "person with responsibility for ... [the] ME equipment".

Both of these definitions cannot be true, unless again we have an impossible network of agreements between all the manufacturers of the different parts of the overall system.

Clause 3.135 also defines a "Type Test" as a "test on a representative sample of the equipment with the objective of determining if the equipment, as designed and manufactured, can meet the requirements of this standard". 

Again, this definition can only be met if the manufacturer of the accessory is contractually involved, since only the accessory manufacturer can ensure that a type test is representative of regular production, including the potential for future design changes.  

What's the solution?

An intermediate approach is to first recognise that the reference to accessories in Clause 3.63 is only a "note", and as the preamble to all IEC standards indicates, "notes" written in smaller type are only "informative". In other words, the note is not a mandatory part of the standard. 

Secondly, it is possible that the writers of the standard never intended the note to mean the standard must cover accessories from other manufacturers. Rather, the intention was probably to highlight (note) that in order to run the various tests in the standard accessories would be needed to establish normal condition. The note is a clumsy way of avoiding that manufacturer insists the tests are done without any regard to the accessories.

A longer term solution would be to add a new clause in the standard (e.g. 4.12) which requires an analysis of accessories from other manufacturers to:

  • Allocate system requirements to either the main unit or accessory, either in part or in full

  • Document a rationale behind the selection of representative accessories to establish normal condition during tests on the main unit

  • Document a rationale to identify accessories in the instructions for use: either directly by manufacturer and type, or indirectly by specification

The following is an example analysis for a patient monitor with a temperature monitoring function (for illustration only):

This analysis should be included in or referenced from the risk management file.

The analysis might appear onerous, but the ability to stream line type testing will save time in the long run, and allow common sense apply. In the current approach, decisions about accessories are made on the run, and can result in both over and under testing.

Manufacturers are also reluctant to mention accessories in the operation manual, partly due to the logistics of keeping the manual up to date, and partly due to a fear of being seen to be responsible for the accessories listed. This fear often extends to the design documentation including the risk analysis, with virtually no mention accessories in the files. The above approach helps to address the fear while at the same time highlighting that accessories can't be simply ignored. A rationale for the requirements, representative selection and documentation to the user is both reasonable and practical.   

The recommendations above cover a simple system of an main unit designed by manufacturer "X" working a sensor designed by manufacturer "Y". There exists another more complicated scenario, where part of the electronics necessary to work with the accessory provided by manufacturer Y is installed inside the main unit from manufacturer X. A common example is an OEM SpO2 module installed inside a patient monitor. Technically, manufacturer X takes responsibility for this "interface module" as it falls under their device label. In such a case, a formal agreement between X and Y is unavoidable. Once this agreement is in place, the same risk analysis for the three points above should apply.

In this special case, a type test also needs some consideration. In general it is not practical for manufacturer of the main unit to support testing for the module, as it usually requires the release of a large amount of information much of which would be confidential. Instead, the laboratory should look for test reports from manufacturer B for the interface module, essentially as a "component certification" similar to an recognised power supply. Another option would be for the report to report to exclude requirements on the presumption that these will be handled by the module/accessory manufacturer, as per the inter-company agreement. The module manufacturer would then have their internal reports to cover the excluded clauses. In case of product certification and CB scheme, some exclusions may not be allowed, in which case the module is best covered by a CB certificate to allow simple acceptance by the laboratory responsible for the main device. 

Finally, there is a bigger role that standard can play to help avoid gaps in responsibility - the development of standards for well established accessories which define clearly which manufacturer should cover which requirements. Such standards already exist at the national level, for example ANSI/AAMI BP 22 for IBP sensors. A generic standard could also be developed which handles accessories not covered by a particular standard, which highlights risk analysis and declaration of assumptions made. 

It's time that the IEC 60601 series was better aligned with modern regulations and reality: accessories are a separate medical device.