4th Edition Medical Equipment Standards Impact Power Supply Selection and More

The IEC 60601-1 technical standards for medical electrical equipment have changed, as new usage modes and expectations place more stringent demands on safety and effectiveness. The first territories to adopt the latest version of the standard – known as the 4^th Edition – are North America and the EU. Products entering these markets must now be in compliance as of January 1, 2019, and other territories are expected to follow their lead.

For producers of medical equipment, the best response to this move is to understand the new standards straight away, and design new products accordingly. The 4^th Edition introduces several changes, including stricter limits on electromagnetic compatibility (EMC), made necessary by generally increasing use of wireless equipment such as smartphones and wearables, and new contexts for the use of medical equipment – such as in the home. Overall, the amendments affect the product design process and documentation, as well as features and performance.

Background to IEC 60601-1

IEC 60601-1 is a suite of standards that comprise the core standard, 60601-1-1, and several collateral standards (60601-1-x) that cover specific aspects such as EMC (60601-1-2). Other collateral standards include 60601-1-11, which has been introduced recently for home healthcare equipment.

There is also a set of “particular standards” (60601-2-x) that define requirements for certain types of products. An example is 60601-2-16, covering blood dialysis and filtration equipment.

Currently, the 3^rd Edition of 60601-1 is referenced in many territories worldwide, including Japan, Brazil and South Korea, in addition to the USA, Canada, and EU. The 3^rd Edition itself has been subject to a recent update, from 3.0 to 3.1 (which includes more than 500 changes and clarifications), and some territories have yet to adopt this. Moreover, China and Taiwan continue to apply the 2^nd Edition.

The latest amendment to 60601-1 has become known as the 4^th Edition. By delving more deeply into EMC issues covered by the collateral standard 60601-1-2, the amendments have extended to cover a significant number of aspects of the 60601-1 standard as a whole.

Changing approaches to safety and functionality

Moving forward from the traditional standards-setting approach, which has typically favored prescribing equipment features and performance, the 2^nd and subsequent editions of 60601-1 display an increasing focus on risk analysis and hazard-based design principles. Ultimately, this has the potential to encourage the design of safer systems that are more robust and better suited to their operating environment. To certify a product successfully, documentation must be submitted to prove that adequate analysis has been done and the results taken into account when designing the equipment.

The 2^nd Edition established three product categories, on a scale of increasing risk severity from the point of view of the patient:

• Type B (Body): equipment used in the same room and within a 6-foot radius of the patient
• Type BF (Body Floating): equipment that comes into contact with a patient’s skin, such as a blood-pressure monitor
• Type CF (Cardiac Floating): equipment that comes into contact with the patient’s heart, such as a pacemaker or defibrillator

The 3^rd Edition recognized that operators and patients are vulnerable to electric-shock hazards in different ways. Accordingly, it introduced the concept of Means of Protection (MOP) as a replacement for insulation and isolation, which has allowed Means of Patient Protection (MOPP) and Means of Operator Protection (MOOP) to be considered separately. Different isolation, creepage, and insulation specifications apply for each MOP category, as shown in Table 1.

Table 1: 3^rd Edition isolation and creepage specifications for operator (MOOP) and patient (MOPP) protection.

The 4^th Edition builds on these principles and extends the risk-analysis approach. Recognizing modern ways of delivering healthcare – such as tele-health and self-monitoring – and the new classes of equipment emerging to support these, it replaces the previous classes that distinguished only between life-support and non-life-support equipment with three intended-use categories:

Figure 1: Intended-use categories of healthcare equipment. (Image source: CUI, Inc.)

Whereas the 3^rd Edition immunity specifications anticipated professional users’ ability to enforce a “quiet” electromagnetic environment in the vicinity of medical equipment, the new 4^th Edition classes acknowledge that this is no longer feasible given the sheer ubiquity of wireless equipment, including consumer smartphones, wearables, and other devices, acting in any environment at any given time. The more stringent test specifications defined in the 4^th Edition aim to ensure immunity to the sources of interference these environments may produce. Tables 2, 3 and 4 compare the 3^rd and 4^th Edition specifications for immunity to radiated RF, fast transients, and power instability.

Table 2: Radiated RF immunity specifications.

Table 3: Immunity to electrical fast transients.

Table 4: Immunity to power fluctuation.

As the 60601-1 standards have moved away from the traditional prescriptive approach, there is greater onus on manufacturers to submit new products for certification accompanied by high-quality documentation that describes in detail the design analysis, design process and rationale, with explanations for why certain elements have been included or omitted.

Despite this philosophical shift, the standards retain their focus on ensuring Basic Safety and Essential Performance. Basic Safety requires freedom from unacceptable risk directly caused by physical hazards when the equipment is in use. It is worth noting that Essential Performance has become more clearly defined in later editions, and now refers specifically to features or functions that would give rise to unacceptable risk if not available or degraded beyond limits specified by the manufacturer.

Power supply selection and safety

It is clear from the 2^nd Edition distinctions between Type B, BF, and CF equipment, and the 3^rd Edition Means of Protection rationale, that the power supply properties have an important influence over whether the equipment will meet safety requirements. The isolation requirements described in Table 1 call for power supplies designed specifically for medical applications. Moreover, Type CF equipment would require not only a special medical power supply but also a further isolation barrier between the supply and the point of contact with the patient.

With the arrival of the 4^th Edition bringing more stringent immunity requirements, power supply EMC performance also now comes under scrutiny. Hence, to ease the compliance process, it is recommended to select medical-grade power supplies that comply with the most recent amendments to 60601-1 3^rd Edition (3.1) and the EMC standards set out in the 4^th Edition. CUI offers a range of internal and external power supplies through DigiKey that comply with IEC 60601-1 Edition 3.1 and the 4^th Edition EMC standards, to help product manufacturers take advantage of this approach to simplify certification and accelerate time to market.

Figure 2: CUI offers a variety of internal and external power supplies that meet or exceed the 4^th Edition of the IEC 60601-1 technical standards. (Image source: CUI, Inc.)

Time to act

The US and EU harmonized the timeframe for mandatory compliance with the 4^th Edition 60601-1 standard. After December 31, 2018, all new products submitted to the US Food & Drug Administration (FDA) must comply with the new standard, and the EU set the same Date of Withdrawal (DoW) for its current 3.1-based EN 60601-1-2:2007 standard. However, while the US continues to allow legacy equipment to be marketed in the US, the EU is making no such concession: all medical devices imported after the DoW must be compliant with the 4^th Edition. Therefore, the time to act is now.