Essential Performance: A Short Story
Why should you care about Essential Performance?
Essential performance are equipment specifications that, if one or more fail to be achieved during intended use, the result is the risk of patient harm. If you do not define the essential performance of your product you will not be able to fully claim compliance with the underlying risk management document, ISO 14971, Medical devices—Application of risk management to medical devices.
That’s great, but I just got an email from the test lab asking what the essential performance is because they can’t start testing until they have it – and I can’t even get my internal people to agree on what essential performance is. Please just spell it out in plain English!
Absolutely. Essential performance can be a tricky concept, and, in fact, poorly defined essential performance is something that we often see in FDA deficiency letters. If you properly define the essential performance of your device early you can avoid potential problems later on.
What is it?
Let’s start at the beginning. All electromedical device essential performance identification stems from the definition found in IEC 60601-1, Medical electrical equipment – Part 1: General requirements for basic safety and essential performance:
3.27
* essential performance
performance of a clinical function, other than that related to basic safety, where loss or degradation beyond the limits specified by the manufacturer results in an unacceptable risk
NOTE Essential performance is most easily understood by considering whether the absence or degradation [of that function] would result in an unacceptable risk.
What does it all mean though? Does the device not working automatically create an unacceptable risk? What is basic safety? What is the difference? Realizing that the people who write the standards and know exactly what they meant when they wrote it, are not always the people who use the standards, it follows that a high-level overview of the IEC 60601 series and its connection to ISO 14971 would be a good idea.
The Basics
The IEC 60601 series provides basic safety and essential performance requirements for a myriad of electromedical devices. The parent document, IEC 60601-1, sets out general requirements that must be met, when applicable, during product performance and safety testing.
The collateral series, the IEC 60601-1-x documents, spell out additional requirements that address characteristics of devices that are not fully covered in IEC 60601-1. Those documents address critical issues such as: EMC testing; alarm systems; environment of use – both home care and emergency medical services; and usability testing. It should be pointed out that while not every device has, for example, an alarm system, every electromedical device will require EMC testing to establish that the device can safely and effectively operate in the intended electromagnetic environment. The FDA recently released a draft guidance regarding the electromagnetic compatibility of medical devices and manufacturers should consult that document for additional information (https://www.fda.gov/media/143716/download).
Particular standards, the IEC 60601-2-x and ISO/IEC 80601-2-x series, are device specific documents that supplement the parent document, IEC 60601-1. Particular standards must be used in conjunction with the parent and collateral documents. IEC 60601-1 clause 4.3 provides additional specifics on setting performance limits and implementing risk control measures.
Because defining essential performance is so tightly intertwined with risk management, ISO 14971 and the concepts it contains are critical. The essential performance of a medical device is determined by the hazard analysis that is completed as part of the overall risk management process. Potential hazards are those that might impact the performance of a clinical function to a point where the loss of that function is beyond the manufacturer’s acceptable limits; failure of essential performance creates an unacceptable risk to the patient. It should be noted that hazards related to the basic safety of the device are not included in this definition; it is strictly related to the performance metrics determined by the manufacturer. For additional information, basic safety is defined as “freedom from unacceptable risk directly cause by physical hazards (emphasis added) when ME equipment is used under normal condition and single fault condition” (IEC 60601-1, 3.10).
Determining what the essential performance of your device is a critical part of applying the applicable risk management requirements of ISO 14971.
The steps needed to identify essential performance:
- Identify the performance of the device’s clinical functions.
- Specify the performance limits for fully functional performance versus loss or degradation of the identified performance.
- Evaluate the risk from the loss, disruption, deviation, degradation, or over-delivery (e.g., the hazard) of the identified performance.
If there is no probability of harm from a performance feature failing, that function is not considered essential performance. If there is a probability of harm, consult Annex C of ISO 14971 and Annex A of IEC 60601-1 for guidance on determining the probability of a potential hazard leading to harm. A hazard can only cause harm after a sequence of events or other circumstances lead to the hazardous situation. Take, for example, an alarm system that has been installed on a large volume infusion pump as a risk mitigation against under or over infusion. Alarm systems can be an excellent source of information as to the status of other potential hazards. When over infusion is detected, the alarm system sends out an alarm signal through the notification system, alerting a clinician that their patient requires immediate attention and avoiding potential harm. But what happens if the alarm system itself fails? The over infusion may be detected by the infusion pump, but the alarm signal is never transmitted and can result in serious harm or death to the patient! The risk acceptability can be evaluated by estimating the probability of harm and the severity of that harm. Any device function that fails and results in harm due to a hazardous situation can be considered an essential performance of that device. The device specific standards in the IEC 60601 and ISO/IEC 80601 series are also a good resource for determining essential performance.
In addition to the documents already mentioned, other guidance documents exist to assist manufacturers with the concepts of essential performance and device characteristics.
- Electromagnetic Compatibility (EMC) of Medical Devices: Draft Guidance for Industry and Food and Drug Administration Staff. https://www.fda.gov/media/143716/download
- AAMI CR500:2019, Basic Introduction to the IEC 60601 Series
- ISO TR 24971, Medical devices—Guidance on the application of ISO 14971
Still Confused?
If the case outlined above for defining essential performance is still sounding muddled, here is a practical example that might help.
For this example, consider a basic patient monitoring system. The patient monitor is considered a stand-alone device that integrates add-on components that measure patient physiologic parameters such as heart rate, blood pressure, and blood oxygen saturation level. Typically, patient monitors transmit that information to display on a central monitoring system in a hospital and have alarm systems to notify clinicians of changes in the patient’s condition.
As previously noted, the first step is for the manufacturer to start by listing all aspects of the monitors clinical performance functions so they may be assessed through a risk analysis as potential sources of harm. What might they be? The data display is one example. The alarm system is another example.
Next, for each of those functions, you must determine if operation over or under the specified performance level will result in harm to the patient or operator. What does that mean? Using the examples above, failure to either transmit or display data correctly on the monitoring system might result in an important physiologic change in the patient going unnoticed. If there is a failure of the alarm system, important audible and visual alarms may not be triggered which could also result in patient harm.
As noted above, if the variation in performance doesn’t result in harm, that function is not considered essential performance. If the variation does result in harm, the range of operation where harm does not occur constitutes essential performance. To keep risk at an acceptable level, a manufacturer is obligated to implement risk control measures to reduce the risk to patients or operators if a function is lost. For example, if a power loss will cause the alarm system on the device to fail which results in harm to a patient, the manufacturer could install a back-up battery to reduce the risk of device function interruption during the power loss.
Fortunately, in this instance, there is a particular standard that can provide additional information on essential performance: ANSI/AAMI MP80601-2-49, Medical electrical equipment—Part 2-49: Particular requirements for the basic safety and essential performance of multifunction patient monitors. Note that this document does not cover the separate units that are integrated into the monitoring unit. Clause 201.4.3 of ANSI/AAMI MP80601-2-49, augments the requirements found in clause 4.3 of IEC 60601-1. That clause in 2-49 specifies in Table 201.101 (below) exactly what patient monitor essential performance requirements are.
Requirement Subclause
Displaying data according to primary operating functions 206.101 c)
Determination of alarm conditions and assignment of priority 208.6.1.2
Indication of validity of measured values 208.6.3.2.101
Generating a technical alarm condition 208.6.1.2
Failure that is readily defined by the operator
You’ll see that each item in the table has a corresponding clause number within that document that provides specific details on that requirement. The requirements contained in the particular standard (ANSI/AAMI MP80601-2-49) augment the requirements found in the parent standard (IEC 60601-1) so it is critical that both are used in the determination and testing of essential performance. Keep in mind that EMC testing will also be required once essential performance is defined.
Of course, a patient monitor would not be able to actually monitor patients without the measurement components. For example, if the manufacturer wants to include an add-on component to measure pulse oximetry (Sp02) the same exercise is done to determine essential performance. They must identify the clinical functions, specify the performance limits, and evaluate the potential hazard. In this case, there is also a particular standard that provides essential performance requirements, ISO 80601-2-61, Medical electrical equipment – Part 2-61: Particular requirements for basic safety and essential performance of pulse oximeter equipment. This standard also has a clause that augments clause 4.3 of IEC 60601-1. Clause 201.4.3.101 provides a table similar to that in ANSI/AAMI MP80601-2-49. That section also adds a statement that all of the acceptance criteria for performance aspects listed in the document are required to be met. That is a key piece of information for manufacturers because it lets them know what the minimum acceptable levels are for essential performance. And where is that information listed? Check Table 201.101 in subclause 201.4.102 of 2-61 (extracted below):
Requirement Subclause
For pulse oximeter equipment provided with an alarm 201.12.1.101
system that includes the capability to detect a physiological 201.12.1.104
alarm condition:
________________________________ 208.6.1.2.101
SpO2 accuracy, pulse rate accuracy and limit alarm
conditions a
or generation of a technical alarm condition 201.11.8.101.1
__________________________ 201.12.4
______________________________ 201.13.101
For pulse oximeter equipment not provided with an alarm 201.12.1.101
system that includes the capability to detect a physiological 201.12.1.104
alarm condition:
SpO2 accuracy and pulse rate accuracy a
or indication of abnormal operation 201.12.4
__________________ 201.13.101
a Subclause 202.8.2 indicates methods of evaluating SpO2 accuracy and pulse rate accuracy as acceptance criteria following specific tests required by this document.
Once this testing is done and proper risk control measures are in place to ensure that essential performance is maintained, the manufacturer should have reasonable assurance of the safety of the device.
Wrap Up
Hopefully, this explanation has helped you to see that defining essential performance really is a critical part of the device risk management process.
If you find that you are still have questions regarding essential performance, Biologics Consulting could be a solution. Our consultants can provide services such as additional guidance and feedback on work you’ve done to date, feedback you have received from test houses, the FDA, or walk you through the entire process.
Food and Drug Administration (FDA). (December 17, 2020). Electromagnetic Compatibility (EMC) of Medical Devices: Draft Guidance for Industry and Food and Drug Administration Staff. Retrieved from: https://www.fda.gov/media/143716/download
Association for the Advancement of Medical Instrumentation (AAMI). (2019). AAMI CR500:2019, Basic Introduction to the IEC 60601 Series. Available from: https://store.aami.org/s/store#/store/browse/detail/a152E000006j678QAA
International Organization for Standardization (ISO). (2020). ISO TR 24971, Medical devices—Guidance on the application of ISO 14971. Available from: https://webstore.ansi.org/Standards/ISO/ISOTR249712020
International Organization for Standardization (ISO). (2019). ISO 14971, Medical devices—Application of risk management to medical devices. Available from: https://webstore.ansi.org/Standards/ISO/ISO149712019
International Organization for Standardization (ISO). (2017). ISO 80601-2-61, Medical electrical equipment – Part 2-61: Particular requirements for basic safety and essential performance of pulse oximeter equipment. Available from: https://webstore.ansi.org/Standards/ISO/ISO80601612017
International Electrotechnical Commission (IEC). (2020). IEC 60601-1:2005+A1:2012+A2:2020, Medical electrical equipment – Part 1: General requirements for basic safety and essential performance. Available from: https://webstore.ansi.org/Standards/IEC/IEC60601Eden2020-2421195
Association for the Advancement of Medical Instrumentation (AAMI).(2020). ANSI/AAMI MP80601-2-49, Medical electrical equipment—Part 2-49: Particular requirements for the basic safety and essential performance of multifunction patient monitors. Available from: https://store.aami.org/s/store#/store/browse/detail/a152E000006j66sQAA