Clarifying Confusion Around Life Definitions

The main purpose of mandatory regulations is to obtain marketing authorization to enter global markets. Consequently, a manufacturer must demonstrate that all safety-related aspects, including compliance with relevant standards for basic safety, essential performance, risk management, usability, etc., have been reviewed, that all applicable requirements have been met, and that a quality system mechanism has been implemented. 

With regard to medical devices included within the field of the medical electrical equipment (MEE), it is striking to observe how the clauses describing these specific concepts vary among applicable EU Directives, guidelines, regulations, IEC, ISO standards, and other requirements applicable to design, regulatory compliance, marketing, and health professionals. 

Moreover, the concept of expected service life (ESL) for MEE comes on top of the already existing standards. Thus, due to an incomplete definition of ESL, there is a long chain of misunderstandings regarding the analysis and assessment required to determine compliance with MEE requirements. 

In this article, we’ll attempt to clarify this confusion through a discussion of the standard definition of ESL found in IEC 60601-1 and the requirements applicable to MEE at the end of their ESL. 

What Does Expected Service Life Mean?

With reference to the ESL of medical devices, applicable regulatory documents specify many life-related terms, including service life, shelf life, useful life (or practical life), lifetime (or life span), and life cycle. (Don’t confuse the use of these terms in the context of a device’s safety or performance with warranty-related issues, which is a commercial consideration.)  

An explanation of the meaning of the following life terms should help to provide a better understanding of the issues we seek to address in this article:

1. The term service life includes the time of use that a device is intended to remain functional after it has been manufactured, put into service, and maintained as specified.
2. Shelf life is the term or period during which a device or accessory remains suitable for the intended use, whether it is stored or used. The termination of shelf life is represented by the expiration date, after which the device may no longer function as intended.¹
   The EU Guidance document in the medical devices vigilance system MEDDEV 2.12/1² requires that the service life and the shelf life must be specified by the device manufacturer and included in the master record (technical file) and, where appropriate, in the instructions for use (IFU) or labeling, respectively.
   For life-sustaining equipment, the failure rate should approach zero within the labeled shelf life.
   To determine if a particular piece of equipment requires a shelf life and be assigned an expiration date, several parameters must be considered, including susceptibility to degradation that would lead to functional failure (e.g., implantable devices) and the level of risk that the failure would present.
   If parts or accessories with a specified shelf life are used in a device, their shelf life must be carefully considered in relation to the shelf life of the whole device.Examples
   1. The patient could not be defibrillated due to insufficient contact of the defibrillator pads with the patient’s chest because the labeled shelf life of the pads was exceeded. 
   2. The patient is given a blood glucose test, receives a faulty diagnosis, and is given an incorrect insulin dosage because the test strip used for the blood glucose test was beyond the expiration date specified by the manufacturer.
3. In general, the useful life is defined as an estimation of the average number of years an asset is considered usable before its value is fully depreciated. Specifically, for an electrical device, IEC 60050 defines useful life as the time interval beginning at the start of use (a given moment in time) and ending when the failure intensity becomes unacceptable or when the item is considered to be unrepairable as a result of a fault.³ Another similar definition is the time interval from first use until user requirements are no longer met due to economics of operation and maintenance or obsolescence.(Note: In this context, first use excludes testing activities prior to hand-over of the item to the end-user. For the useful life of a medical device, the accepted definition is the duration of actual use, or the number and duration of repeat uses before some change results in the device’s inability to achieve its intended function.)
4. The lifetime (life span) of a medical device refers to the time interval from design and development of the device to the decommissioning (proper disposal) of the MEE. The lifetime of the device could be how long the MEE is expected to be functional (i.e., fulfill its intended use) and remain safe (i.e., free from unacceptable risk) per IEC 60601-1 requirements.
5. The life cycle represents all phases in the life of a medical device, from the initial conception to final decommissioning and disposal.⁴
6. The expected service life is defined in the third edition of IEC 60601-1:2005 as the “maximum period of useful life as defined by the manufacturer,” but fails to provide an explanation or reference about the meaning of useful life (!). The needed clarification was achieved in IEC 60601-1, Amendment 1:2012 which clarifies the ESL definition as being the:“…time period specified by the manufacturer during which the ME equipment or ME system is expected to remain safe for use (e.g., maintain basic safety and essential performance); (Note: Maintenance may be necessary during the Expected Service Life.)”Fortunately, Rationale Annex A4 provides a further explanation of the meaning of safe for use, as follows:“The ESL is the time period during which the ME equipment or ME system is expected to remain suitable for its intended use, and all risk control measures remain effective ensuring that risks remain acceptable. The ESL needs to be determined by the manufacturer, as part of the risk management process, as a precondition for assessing compliance with many requirements of this standard, such as 4.5, 4.7, 7.1.3, 8.6.3, 9.8.2, and 11.6.6”.⁵  

The expected service life is the anticipated and planned safe for use in-service life of the device. Safe for use means that the state of the device maintains both basic safety and essential performance. Therefore, it is critical to establish the ESL of a device regardless of the method chosen to verify it.

In reading these definitions, we find clear differences among various standards and specifications. Although all refer to the life of medical devices, the term means different things. Indeed, it seems that the terms lifetime and life cycle cover the most extended period of the life of a medical device. 

But these varying terminologies and definitions are the source of many misunderstandings and much confusion, especially now when the term ESL represents a compliance requirement within IEC 60601-1. However, the ESL requirement must be regarded as a safeguard equal to those addressing intended use (function), ratings, environmental conditions of installation and use, etc. 

ESL and IEC 60601-1

The inclusion of the ESL in the 3^rd edition of IEC 60601-1 should be seen as a positive step since it is the manufacturer who has the responsibility and obligation to specify the time segment of the lifetime or of the life cycle for a medical device in which the basic safety and essential performance are maintained. 

We are reaching a very sensitive point of our analysis: unequivocally, clause 7.9.2.15 of IEC 60601-1 ed.3.1 specifies: 

“The instructions for use shall provide advice on the proper disposal of waste products, residues, etc. and of the MEE and accessories at the end of their expected service life.”

In other words, IEC 60601-1 specifies that the MEE shall be decommissioned as a waste product at the end of its ESL. According to the standard, the end of ESL represents the end of all other lives. 

However, in the real world, the situation may be different. For example, a medical device can finish its specified ESL (e.g., seven years) and, through sufficient refurbishing or re-manufacturing, start a new ESL period (e.g., three years), during which time its basic safety and essential performance requirements continue to be met. In theory, this cycle could continue until such time that a device can no longer be refurbished or re-manufactured. This is the real moment of the end of lifetime, life cycle, or useful life (or however you want to designate the whole life of the device!). 

In using terms like refurbished or re-manufactured, it is important to remember that there is no universal standard applicable to refurbished goods. Thus, the terms refurbished, re-manufactured, renovated, and reconditioned are considered to be synonymous. All can be defined as the processes of restoring a used device to an as-new condition for performance and safety so that the device can again be safely placed on the market.

Maybe due to the misunderstanding of terms or misinterpretation of them, IEC 63077⁶ defines the refurbishment as a:

“…process or combination of processes applied during the expected service life to restore used medical imaging equipment to a condition of safety and performance according to the specification of the manufacturer.” 

But in the same standard, used equipment refers to equipment that has been put into service. Mysteriously, it seems to indicate that if a problem arises with a device after just a week of use, the device must be refurbished. Perhaps the standard’s contributors considered the maintenance or repair processes, which are different from refurbishment. During the ESL, safety and performance need to be maintained (as IEC 60601-1 requires), and there is no need to perform a refurbishment. This kind of confusion can lead to difficult situations for a manufacturer and for a device user, since the necessity to replace one component or another doesn’t mean a refurbishment. 

Of course, if at some point during the life of the device, the majority of components need to be replaced to keep the device functioning or to fulfill the ESL specified by the manufacturer, this should be considered the end of the original ESL of an MEE while leaving open the potential for a refurbishment.

Estimated typical equipment lifetimes for healthcare technology can be found in published literature.^7,8,9 In general, the expected lifetime is estimated at a minimum of seven years. A few exceptions exist, such as cardiac laser units (three years), alarms oxygen depletion units (five years), ECG leads (two years), cell counters (five years), cuffs (two years), duodenoscopes (five years, aneroid sphygmomanometers (five years) and infrared thermometers (five years).  

How Does a Device Manufacturer Determine Expected Service Life?

Decisions related to device ESL can be made, in part, by controlling identified residual risks that can increase to unacceptable levels as the period of use of an MEE is extended. The ESL is just one of the inputs of the risk management file that can affect the probability of occurrence of harm. Medical device ESL may be based on technical, legal, commercial, or other considerations.

The manufacturer, who needs to specify the ESL in their risk management file, needs tools to accurately determine this time period. The best way to determine the ESL of the equipment is through reliability analysis and tests. Using reliability engineering techniques such as accelerated life testing (HASS and HALT) analysis can help with estimating the potential for initial failures or projecting the average expected functional life (with random failures) or the point of expiration (wear-out failures), etc. 

However, one needs to be careful with the use of such reliability information because safety and reliability are different product characteristics that are sometimes in conflict with each other. Reliable products are not necessarily safe, and safe products are not inherently reliable. In general, safety has a broader scope than failures, and failures may not compromise safety in all situations. 

The Practical Guide for the implementation of ISO 13485 standard (formerly ISO 14969) does list a few things that may need to be considered when defining device lives. The basis of the defined lifetime of the medical device should be documented. To assist in determining the lifetime of the medical device, the rationale for the determination should be recorded and may involve consideration of the following:

• Shelf life of the medical device
• Expiration date for medical devices or components which are subject to degradation over time
• Number of cycles or periods of use (frequency of use) of the medical device, based on life testing of the medical device
• Environmental conditions of use that can result in material degradation
• Stability of packaging material
• For implantable devices, the residual risk that results from the entire period of residence of the device inside the patient’s body
• For sterile medical devices, the ability to maintain sterility
• An organization’s ability/willingness or contractual or regulatory obligation to support service
• Spare parts cost and availability
• Legal considerations including liability

In addition, the following factors may also be considered: 

• Intended use
• Experience and knowledge of the user
• Care and attention paid to use and operator maintenance
• Existence, capability, and cost of maintenance support
• Management of scheduled and unscheduled maintenance 
• Availability and cost of replacement devices
• Business, safety risks, strategic, and political risks associated with continued or discontinued use
• Compliance with current codes and standards
• Technological or clinical redundancy
• Funding availability

Based on the above factors, a device manufacturer should have sufficient information to determine the ESL, which will be included in the risk management file and the accompanying documents. Additionally, Rationale Annex A4 of ed. 3.1 of IEC 60601-1 recommends: 

“The accompanying documents should provide information to allow the responsible organization (e.g., hospital) to assess when the equipment is approaching the end of its expected service life. This could be given in terms of years of service or number of uses, or tests as part of preventative maintenance to allow the responsible organization to make an appropriate determination of ESL”.

To summarize, once the ESL is determined, it is expected that the device remains safe for use during ESL basic safety and essential performance is maintained, and the user is informed about the signs of ESL end proximity. We will see in the next section the fate of the device after the period when ESL ends. 

Is it Necessary to Supply Decommission Information? 

During the ESL period as declared by the manufacturer to be (e.g., seven years), an MEE which has undergone the recommended periodic maintenance as specified in the accompanying documents can be considered compliant with the basic safety and essential performance as required in IEC 60601-1. However, at the end of its ESL, is a device that is still compliant with the standard’s requirements be decommissioned? The answer is a categorical no. 

As we have previously discussed, the life cycle of an MEE ends when the user is forced to decommission it when it can no longer be used safely and or fails to meet its performance specifications. This point in time can occur either before or after the endpoint of the ESL. 

For example, a device may have completed its intended service and can no longer be serviced or maintained due to obsolete procedures, a lack of spare parts, or the cost of servicing. So, instead of lasting seven years (for example), the device needs to be removed from service and decommissioned as a waste product. In other cases, a device can reach the specified end of its ESL in good condition and is able to continue to be used beyond its ESL if it is serviced or repaired as needed. 

In such situations, based on the actual IEC 60601-1 requirements, a manufacturer can claim that they are no longer responsible for the product after the end of ESL and are not required to take steps to ensure that use of the device is discontinued. However, questions of product liability now come into sharper focus. It would be most helpful if the working group responsible for developing and updating IEC 60601-1 provided some clarification on this situation(for example, by issuing an Interpretation Sheet) or by including clarification in a 4^th edition of the standard.

For device manufacturers, another ESL-related challenge is presented by the scope of basic safety and essential performance requirements found in IEC 60601-1. Specifically, only certain clauses in the standard refer to ESL, including 4.7 – Single Fault Condition; 7.1.3 – Durability of Markings; 7.9.2.15 – Environmental Protection; 8.6.3 – Protective Earth of Moving Part; 8.8.4.1 – Mechanical Strength and Resistance to Heat; 9.8.2 – Tensile Safety Factor; 11.6.6 – Cleaning and Disinfection of ME Equipment and ME Systems; and 15.3.7 – Environmental Influences. Shouldn’t all other clauses in the standard be applicable during a device’s defined ESL? Yes would be the logical answer, but the standard is unclear on that point. 

What Evidence Should a Device Manufacturer Provide to a Notified Body Regarding Expected Service Life

Lifetime is mentioned twice in Annex I of the MDR:

• Paragraph 6: “The characteristics and performance of a device shall not be adversely affected to such a degree that the health or safety of the patient or the user and, where applicable, of other persons are compromised during the lifetime of the device, as indicated by the manufacturer, when the device is subjected to the stresses which can occur during normal conditions of use and has been properly maintained in accordance with the manufacturer’s instructions”.
• Paragraph 23.4: “The instructions for use shall contain all of the following particulars: … “(k) the information needed to verify whether the device is properly installed and is ready to perform safely and as intended by the manufacturer, together with, where relevant:
  • “Details of the nature, and frequency, of preventive and regular maintenance, and of any preparatory cleaning or disinfection,
  • “Identification of any consumable components and how to replace them,
  • “Information on any necessary calibration to ensure that the device operates properly and safely during its intended lifetime, and
  • “Methods for eliminating the risks encountered by persons involved in installing, calibrating or servicing devices.”

Compliance with the above requirements should be demonstrated with objective evidence and documented in the device Technical File. These documents, together with the information used to determine the ESL, will then serve as the basis for a thorough and objective assessment of the basic safety and essential performance of an MEE during the ESL. 

What is the Best Way to Define the Expected Service Life of a Device? 

We believe that a small addition to the actual ESL definition found in Amendment 1 of IEC 60601-1 would provide the necessary clarification and help to eliminate future confusion. As such, the updated definition of expected service life would read as follows: 

“Time period of the life cycle, specified by the Manufacturer during which the ME Equipment or ME System is expected to remain safe for use (e.g., maintain Basic Safety and Essential Performance).” 

By adding of the life cycle to the ESL definition, it becomes clear that ESL is a time part of the life cycle of an MEE in which the expectation to be safe for use is present. This time part can be extended by refurbishing or remanufacturing until the MEE becomes obsolete from a performance point of view or cannot be put back into operation due to outdated technology, lack of parts, or economic reasons. This is the point at which the MEE is decommissioned from service and recycled, destroyed, or discarded as appropriate. 

Endnotes

1. FDA, “Shelf Life of Medical Devices,” 1991.
2. MEDDEV 2.12/1 rev.8, “Guidelines on a Medical Devices Vigilance System,” 2013.
3. IEC 60050:2012, “International Electrotechnical Vocabulary,” Chapter 191: Dependability and Quality of Service, Definition IEV 191-19-06.
4. ISO/IEC Guide 63:2019, “Guide to the development and inclusion of aspects of safety in International Standards for medical devices,” definition 3.5.
5. IEC 60601-1: 2012, Ed.3.1, “Medical electrical equipment –Part 1: General requirements for basic safety and essential performance.”
6. IEC 63077: 2019 “Good refurbishment practices for medical imaging equipment.”
7. “Life span of Biomedical Devices,” Biomedical Engineering Advisory Group SA, Australia, 2004.
8. “Estimated Useful Lives of Depreciable Hospital Assets,” American Hospital Association, 1998.
9. “Personal Property Manual,” State of Nevada, Department of Taxation, 2009.