the concept of an expiration date was created to help consumers realize when a product should be discarded. the concept has taken hold and has become an expected and regular part of daily decision-making for people around the world. though the concept can be misused, it has merit because the manufacturer knows best when it comes to the shelf life or useful life of a product!
shelf life is supposed to be assessed by the manufacturers using a scientific analysis of the product to determine when the key chemical(s) within the product lose effectiveness and/or the compound changes composition and becomes something else.
we know that electronics and technology also have expiration dates. in the world of software, manufacturers, including microsoft, stop supporting a product after it has reached its useful life. even though i was content with using windows xp, microsoft forced me to convert and upgrade. regardless of how much a consumer likes a product, manufacturers determine they cannot continue to support it and make it as safe and productive as their new platform in light of the changing world of software that now includes more sophisticated challenges, including hackers and terminal viruses.
however, in the world of hardware, we seem to take risks. our solution for aging hardware is to back it up and run it at risk. we all know that the hard disk, cpu, power supply, and the electronics have a failing point, but we insist on letting it run out its life and hope that when the device goes off the cliff and fails, it does not take us with it. this is simply not wise. in almost all cases, when a hardware device fails, it causes some sort of harm to its owner. if you are aware and proactive, the harm is not catastrophic. but if you are careless or uninformed, then the harm can be devastating. you either lose everything, if you do not have a backup, or lose the information added since the last backup. it is always a risk/benefit analysis. how much more can i get out of the machine and how much am i willing to lose, versus how proactive do i want to be in replacing the old device and how much do i want to spend?
companies whose businesses depend on computers have a systematic process for replacing old hardware before it fails. they know the mean time between failures (mtbf) measure and consciously decide to replace their machines before the prediction of the manufacturer comes true. how much earlier than the predicted mtbf you decide to replace your systems depends on the impact of failure to your business and your business's ability to recover from it.
i can't comprehend why the concept of expiration date has not reached the medical device world. although fda has addressed the idea of shelf life for a medical device, they have covered the time from manufacturing to when the device is put to use. what is missing is the expiration time from when the device is put to use, until it is no longer fit for its intended purpose.
my medical device experience is mainly in the implantable world, where we put highly sophisticated electronics inside people to help them with an ailment that could not be addressed without surgery—devices like cardiac pacemakers, implantable cardioverter defibrillators (icds), neuromodulation devices, and drug pumps. these products are basically a small computer with no redundancy system, running on batteries, and controlling vital aspects of a human body. we have experienced situations where a component failure has caused harm, and in some cases death, to patients.
companies spend millions of dollars designing a reliable machine, given the limitations of no redundancy and no failure management system that they have imposed on themselves. but regardless of how much you spend and how much you engineer, you cannot control all aspects of development and manufacturing. therefore, devices are subject to unpredictable failures that could come from any component used in the device—a resistor, transistor, capacitor, wire, antenna, battery, etc. these components have different characteristics and a different mtbf. unanticipated failure of a component due to unexpected failure could cause unpredictable behavior. an unexpected failure could occur when the device lives past its predicted life and continues to be operated. it's clear that the device will fail at some point, that the failure may not be graceful, and that it may cause severe harm. this concept might be acceptable for consumer electronics, but not when the product is implanted inside patients and its failure could have a devastating effect.
as i come from the cardiac world, i will focus more on cardiac devices, in particular, icds. but the concept applies to any product that is implanted inside the body and uses electronics to control its function for therapeutic applications.
not too long ago, icds were larger than a hockey puck, used a complex electronic system filled with discrete components, was powered by a large battery that lasted only two years at most, and had just three parameters to program. the battery life forced replacement before the device's electronics reached the limits of its useful and safe life. over the last two decades, manufacturers have managed to add much more functionality to these devices. there are more than 600 parameters to program inside any cardiac device, battery life has been tripled by using denser battery chemistry and low-power integrated circuitry, all while shrinking the device to one-third of its initial size. icds are specified to run for more than six years. as the market demands longer lasting products, the companies will continue to push the envelope and bring to market products that last close to the 10-year life target. if this continuous improvement in efficiency allows a longer life for the device, battery depletion will no longer indicate the end of life for the device—other components will.
when an icd battery runs its normal life, the device alarms the physician that the device is reaching the end of its useable life. this is called an end-of-life (for the device) warning. in normal situations when the battery depletes faster or even as predicted, the device will die down gracefully as the electronics will shut down when the battery reaches a point where normal operation is no longer feasible. how long a device will last depends on the programming, time, and application of therapy. in my experience, in most cases an icd's life is calculated based on 15% pacing and one shock per quarter. on the other hand, if the device does not deliver that shock or is programmed to pace less, or does not use pacing therapy, then the device could last much longer. is it possible for an icd to live past its mtbf? yes. as product improvements continue and battery life improves, this becomes more likely. what happens when a device outlives its mtbf? that is mostly unknown and unpredictable. engineers can tell you what will happen when each component fails, but they cannot tell you what would happen when an unpredictable group of components fail. my fear is that when that failure happens in an icd, the device could release a charge inside the body that is not needed and that could cause fatal harm to the patient.
the same thing could happen with a drug delivery device that is supposed to deliver a drug in a titrated fashion. if the decision and delivery system goes haywire, then it could release more of the drug than it should, or not release it at all. in both cases, the results could be devastating.
when a device is operating normally and reaches the end of its battery life, the physician has a choice to make. he or she either will allow the device to run its course and gracefully shut down, or replace it before that happens. the decision for the physician is a risk/benefit analysis that considers the experience of the patient with the device, the actual vs. perceived benefit that the device brings to the patient, and the risk of surgery involved in the replacement. today, physicians likely do not consider the possibility of device failure in their decision-making process, as it has not been an issue. but as devices are packed with additional functionality, more components, and longer lasting batteries, the possibility of an unpredictable failure will have to be considered.
currently, if a device fails due to electronic failure, it becomes the fault of the manufacturer. follow-on analysis would be needed to decide if it was an isolated case or a systematic situation. in the first case, it would be detrimental to the reputation of the company. the second case would spur an fda-mandated recall that would cause havoc to the business and the reliability of the manufacturer in the market. but regardless of business impact, the harm to the patient is done and cannot be taken back. this doesn't need to be the case if appropriate action is taken.
this is where an expiration date comes in to the picture. unlike the end-of-life warning which is based on the life of the battery, the expiration date would be based on the life of the electronics. all medical device manufacturers go through a rigorous engineering process to assess the reliability of their product family. this is done based on the design of the product, components used in manufacturing them, sourcing of the components, combined operation of these components, and the cumulative effect. the manufacturers can then use this information and calculate the expiration date of the product that would give the user a good margin of safety within which to operate.
having an expiration date available to consumers and physicians might affect their decision on how to continue using the device. though physicians may be comfortable allowing the device to reach end-of-life based on its battery life, they would not want to allow the device to operate past its expiration date. under no circumstances does a device shut down gracefully after a failure. we need to make sure a hardware failure does not happen while the device is inside a patient.
a side benefit to the market is the transparency of reliability information. given that the expiration date would be based on the reliability calculations of the manufacturer, it gives the users additional information that could be used in purchasing decisions. this transparency gives physicians yet another factor to consider in their purchasing decisions and gives manufacturers a useful parameter on which to compete. in any case, expiration dates would be a win for the patients that end up using these devices, since they are the ones that would suffer the consequences of a device failure.