Batteries in Medical Devices - Technologies, Use and Maintenance
December 12, 2005
- Rechargeable Batteries and Battery Testing for Hospitals - Bruce Adams, Cadex Electronics Inc.
- Batteries & Medical Devices: A Managed Approach to Risk Reduction - Timothy J. Zakutney and Mark Cleland, University of Ottawa Heart Institute
- Can I Trust a Low-Cost Medical Battery? Improving Battery Reliability While Lowering Operational Cost - Isidor Buchmann, Cadex Electronics Inc.
- The Effects of Lead Sulfate on New Sealed Lead Acid Batteries - Mark Cleland, Maloney JP, Rowe BH, The Ottawa Hospital
- Batteries: From Alkaline to Zinc-Air - Robert Dondelinger, Biomedical Instrumentation & Technology, March/April 2004
Posted with permission from Biomedical Instrumentation & Technology, a peer-reviewed journal published by the Association for the Advancement of Medical Instrumentation (AAMI). Visit www.aami.org to learn more about AAMI or to view BI&T's current issue.
FTS-HHS FDA CDRH MedSun
Battery Technology and Medical Devices
Clinical Engineering Audioconference
December 13, 2005
1:00 p.m. EST
Coordinator: Welcome and thank you for standing by. At this time all participants are in a listen-only mode. Today’s conference is being recorded; if you have objections you may disconnect at this time. I will now turn the meeting over to Mr. Jay Crowley. Sir, you may begin.
J. Crowley: Thanks, Deb. Welcome everyone to the next in our series of Clinical Engineering Audio Conferences. The topic of this audio conference is “Battery Technology and Medical Devices,” and again, I welcome you all. The structure of the call, the way this will work today is we have three speakers and each presentation will take about 15 minutes, and at the end of those presentations we will open up the lines for questions. As Deb mentioned, you’re in a listen-only mode for now, and at the end of the presentations we’ll go ahead and open it up for questions.
The speakers will be referring to handouts and the page numbers on those handouts as they go through them. You should have received the handouts by e-mail. If you did not you can either call 1-800-859-9821 and have them e-mailed to you, or you can go to the participant Web site for this audio conference and you can download them yourselves. I will attempt to read the link for this audio conference. It is: MedSunaudioconference.s-3.net. If you go there you’ll be able to not only find the three presentations from today, but there’s also three additional references that we’ve provided on that Web site for you on batteries and medical devices.
As Deb also mentioned, this audio conference is being recorded for transcription, so I just want you to be aware of that when you’re asking questions. If you prefer, you may ask your questions anonymously.
Today’s audio conference, as I mentioned, will be on batteries, and batteries, as we all know, are ubiquitous in electronic devices today, and ,of course, a constantly growing number of medical devices are battery- powered. As a consequence, a large number of reported device problems have to do with battery failures or shortcomings. At both of our Medsun annual conferences this year speakers from the Ottawa Heart Institute described their battery evaluation and maintenance program, and this audio conference is designed to expand on that topic, presenting some information and resources to enable clinical engineers and others to better understand the various battery chemistries, their strengths and weaknesses, maintenance and requirements, and suitability in various applications.
Just as a short disclaimer, I’ll let you know that the opinions and assertions presented during this audio conference are the views of the presenters and are not to be construed as conveying either an official endorsement or criticism about the FDA. That’s an official disclaimer that I need to give.
So with that, I’m going to introduce each speaker and they’re going to present, and then we’ll move through our three speakers today. Our first speaker today is Bruce Adams, and he is Territory Sales Manager for Cadex Electronics, a manufacturer of battery test equipment and custom charges for the professional market. Bruce has worked in sales for Cadex since 1996 and he has a Bachelor of Science in Biochemistry from the University of British Columbia, and I welcome you, Bruce, to our program, and why don’t you take your presentation away?
B. Adams: Thank you very much, Jay. I appreciate that. Good afternoon, everybody. The title of my presentation is “Rechargeable Batteries and Battery Testing for Hospitals.” As you can imagine, this is a presentation based on Cadex’s perspective. You can see two great resources on slide number one in the presentation, Cadex’s Web site, which has links to other battery technology Web sites, including BatteryUniversity.com and also Bachman.ca, and you’ll see those on the last slide of the presentation.
Let’s move to slide number two and we’ll go through an overview of what I’ll be talking about today.
On slide number two I’m going to talk a little bit about Cadex Electronics, who we are and why we know about battery packs. I’m going to talk about common and rechargeable battery types and the types of rechargeable packs you see in hospitals, and which rechargeable battery types are most common. I’m going to speak a little bit on the advantages and limitations of different common chemistries, including nickel cadmium, nickel metal hydride, sealed lead acid, and lithium ion. I’m going to talk about the thorn in everybody’s side, why battery packs fail. We’re going to talk a little bit about what you know in terms of battery testing and battery maintenance and how you go about that. Part of that will be selecting the right test equipment or analyzers for your facility. Then we’ll wrap it up with what to expect from battery testing. Let’s move to slide number three, please.
Cadex Electronics is a designer and manufacturer of battery chargers and battery analyzers and testers for professional markets. Our main markets are professional ... radio, cellular and medical applications. We’ve been in business over 25 years and we’re based just outside of Vancouver, British Columbia. Currently, our products are sold in over 100 countries worldwide and our products and manufacturing and design practices comply to CSA, UL, CE, FDA, Standards for Safety, and ISO 9001 and 13485 for GMP for quality. Let’s move on to slide number four and get into the good stuff.
Slide number four is an overview of revenue by year for different secondary or rechargeable battery packs. The ones that I covered there are the ones that you most typically will see in your hospitals, those being ... acid, lithium ion, nickel cadmium, and nickel metal hydride. It’s important to note from this graph that you can see that over one-half of the world’s total demand for rechargeable batteries is made up by lead acid packs. That graph’s statistics include ... lead acid batteries, which are typically found in automotives, as well as gel and ... regulated lead acids which are used in backup applications or uninterrupted power sources for medical equipment. You can also see by the trends in the graph that lithium ion is currently the sweetheart of rechargeable battery packs and you’ll continue to see that type of chemistry grow in portable applications because of some of the other advances that I’ll talk about later in the presentation.
Moving to slide number five, the next four slides I will talk about advantages and limitations of the common rechargeable chemistries, and I notice that one of the resources, written by Robert Doniger, does a great job of detailing a lot of these advantages and limitations more completely, so if you go to the Web site where the materials are kept, you can actually get that as a resource.
The first chemistry I’d like to talk about is nickel cadmium, and this is one of the oldest commercially available rechargeable chemistries. Although these days it kind of has some environmental stigma because of heavy metals, there are still some significant advantages to the chemistry, those being that it’s actually a very fast and simple chemistry to recharge and has the highest number of charge/discharge cycles of all the common rechargeable chemistries. It’s very forgiving. Some of the limitations of nickel cadmium are that it has a relatively low energy density, being surpassed in terms of power per mass by nickel metal hydride and lithium ion. Of course the one sort of popular marketing term that goes with nickel cadmium is the fact that it’s plagued by what’s called the “memory effect,” and that really is just a crisp line formation that builds up in the electrode place in the battery pack that’s not discharged completely on a regular basis, so nickel cadmium must be exercised or reconditioned periodically. Also, nickel cadmium is based with a relatively high self-discharge, so if you charge a battery pack up and you take it out of the device and stick it on the shelf for any period of time the actual energy you put into the battery pack will ... or spontaneously discharge. So it’s important to know that self-discharge in that pack is a significant factor.
Moving on to slide number six, I’m talking about a nickel metal hydride battery pack. You’ll note that, again, the energy density in nickel metal hydride is higher than in NICAD by 25-30%. Nickel metal hydride is less prone to memory than NICAD and requires fewer exercise or condition cycles. Some of the limitations are that it requires a more complex charging cycle, and that has a lot to do with temperature that’s created during the charge process or at the peak charge. So there’s more sophisticated charge algorithms and potentially charge circuit required, so that your charger price can go up with nickel metal hydride. Also, a very significant limitation with nickel metal hydride is that it has a very high self-discharge rate, in the range of 50% higher than a nickel cadmium pack, so it’s even worse if it’s charged and set on the shelf for any period of storage. Also, nickel metal hydride is not as environmentally durable as NICAD and does not perform as well at higher temperatures.
Moving to slide number seven, this is a chemistry that you see very commonly in hospitals, in fact, it’s probably the most common, and Mark and Tim will talk more about lead acid in their presentation. The style of lead acid that shows up most commonly in hospitals is referred to, typically, as ... regulated lead acid, or gel cell. Those have been commercially available since the 1970s. The advantages of lead acid are, again, it’s very inexpensive, in fact, it has the lowest cost per watt hour of all the ... rechargeable batteries; it has a very low level self-discharge; and there are low maintenance requirements. It does not require a periodic discharge, in fact, because—as you’ll see later in my presentation—of the lower number of cycles the chemistry does ... when it’s actually maintained at a full charge status. Some of the limitations of ... lead acid are low energy density, and again it’s got a poor weight to energy ratio, and that’s why you most see it commonly in backup, or ... dual power supplies or ... applications, because of the weight. Also, it cannot be stored in a discharge state, so the pack does better when it’s a flow charge situation, and again, that’s why a lot of medical applications will use lead acid as the backup power in tethered applications, where the device spends most of the time plugged into the wall, therefore, the battery pack can be maintained in a charged state.
Moving on to slide number eight, we’re going to talk a little bit about today’s rechargeable sweetheart chemistry, that’s lithium ion. Some of the things I’ll talk about today will probably be surpassed or superseded in the next five years, there’s so much development going on with this chemistry. We’re hearing about different voltages for cells that they’re coming out with in the next little while, faster charge times for lithium ion, so I think you’re going to see a lot of developments and probably lithium ion will become more common in hospitals within the next five years.
Some of the significant advantages are that it has a very high energy density, it’s the highest of all rechargeable chemistries, and you’ll see in a later slide that it’s pushing 200 watts per kilogram and it still has potential for higher capacities. It has a very low self-discharge, in fact, most energy that the battery uses while it’s in storage and not charged is the power fuel gauge or protection circuitry that’s built into the battery pack. It has, again, similar to lead acid, a very low maintenance, there’s no periodic discharge required. For chemical reasons it does require a condition cycle periodically to recalibrate the fuel gauge, but the chemistry itself does not require any discharge. Limitations are, for lithium ion, is that the battery pack does require protection circuit to maintain voltage and current within the safe limits, and that adds to your battery price. Lithium ion chemistry is subject to aging when it’s not in use, and you’ll find that it has, compared to the other chemistries, a lot weaker self-storage life than the other common chemistries. It’s still expensive to manufacture, and again, where there’s a field gauge built into it, which communicates information to the charger or the device, it’s important to recalibrate the lithium ion battery packs periodically.
Moving to slide number nine, this is a nice table overview of a lot of the advantages and limitations I’ve just talked about for the four common chemistries: NICAD, nickel metal hydride, lithium ion, and lead acid. Some things to point out: you can see, again, the energy density at the top of the table, so the four common chemistries, and you’ll see, I’ve got lithium ion listed between 110 and 160 watt hours per kilogram. In fact, we’re seeing some new data from manufacturers that shows that pushing 200 watts per kilogram, therefore, the energy density in lithium ion can be anywhere from two times or over two times the other chemistries.
Going down to cycle life, you can see, as I talked about in nickel cadmium, it’s still kind of the work horse of the rechargeable chemistries and gives you the most charge/discharge cycles of all of the other common rechargeable chemistries. Charge time: NICAD typically had the greatest tolerance for rapid charging, but we’re starting to see, again, news from lithium ion manufacturers that show that they’re creating cells that can be charged in a lot less time than what’s common with them nowadays, which is in the four-hour range, we’re hearing that there are charge times that can be as short as half an hour or below.
The self-discharge for months, you can again see that lead acid is of the lowest; lithium ion is in the same range, and that, again, is some power required to power the protection circuit or fuel gauge; nickel metal hydride is the highest; and NICAD is in around 20%. Typically, the way it works with the nickel-based batteries is you see a significant self-discharge in the first 24 hours and then it kind of slows down for subsequent days, but these are the rates you would see per month.
Moving on to slide number ten, the issue that plagues clinical engineers, biomedical technologists, people in radio, all different applications is why do common rechargeable batteries fail. Well, it’s important to note that every rechargeable battery pack has a finite life cycle, and we talked about those in slide number nine, where we kind of showed the number of cycles each chemistry is capable of, so it’s important that as a rechargeable battery user that you choose hardware and a field service program that maximizes the number of charge/discharge cycles from your rechargeable packs.
The other reason batteries fail is poor charging storage or heat, and if you talk to battery manufacturers they’ll say that the common conditions that cause reductions in cell life include situations like: over-voltage charging or continuous charging, excessive charging or discharge current over-discharging, and out of temperature specification on charge, discharge and storage. So there are around five reasons that cause reduction in cell life, and they say that four or five are controlled by the charger, so it’s very important to choose a charger that matches the battery technology ..., and again, I think Mr. Doniger covers that very well in his article, which is published and is available as a resource to you today.
The third reason that battery packs fail is that nickel-based battery packs do develop memory, and that’s, again, with nickel cadmium it’s an electro-crystalline material that builds up on the plates and you need to choose a conditioning charger or professional ... product that allows you to condition or recover that lost capacity.
Moving to slide number eleven, now you know what the battery problem is, what can you do about it? This is just a bit of a graphic to kind of show you what a cell looks like at some stage in its life. You can see that there is, as the battery pack cell starts to degrade, there’s a portion of that cell that can never store energy, so the key thing to see there is that a weaker battery pack will get to the green light on a charger quicker than a brand new battery pack. So if you have no method of testing your battery packs in an emergency situation, only the battery packs that show the ... green light could be the ones that are problematic or ...
Moving to slide number12, so what can you do about it? Well, in Cadex’s perspective, if you have a battery maintenance program where you’re testing your battery packs on a regular basis, you label your battery packs and see what the measured capacity is, it allows you a means to qualify how good your fleet is, and that’s exactly what we suggest. So, for battery maintenance the first thing you do is, once your battery packs are labeled and they’re out in the fleet, is that you isolate date expired battery packs. It’s sometimes difficult to train an end user to do this, but if before use, maybe once a week or once every two weeks, they can look at the label, and if it’s expired, the battery pack is isolated so that it can be serviced.
Moving to slide number 13, step number two in battery maintenance is where you actually test for rechargeable packs, and that’s where you need a battery tester or analyzer. What you’re doing there is testing it, comparing it to its brand new capacity, and deciding whether or not it’s good to return to the field. The ... number is kind of related to what manufacturers will say is their warranty failure level, but as you’ll see in Mark and Tim’s presentation, you can also select a facility defined target which represents what you’ll accept as a suitable or acceptable run time.
Once the battery packs are tested, they’re re-labeled, and slide number 14 that shows the re-labeling process and return to the field. So now that you’ve actually tested your battery packs and qualified them and they hit your threshold or whatever target it may be, all the ... battery packs in the field are good, so you have no weak batteries.
Moving to slide number 15, so if you’re choosing a battery tester for your facility what are the things that you want to know? Well, you need to know that it actually matches the type and number of battery packs in your facility, so if you have, for example, maybe a thousand rechargeable batteries in your facility, you may want to choose a device that has more than two stations, something like a four station analyzer. If you have a smaller facility, then you want to be able to choose a device that has a smaller number of stations. You want to know how many battery packs can be tested at the same time. You want to know that the chemistries in the battery packs that you’re working with, whether they be NICAD, nickel metal hydride, lithium ion, or sealed lead acid, that all chemistries are supported. You need to know the range of battery pack voltages and are all those pack voltages supported. You want to make sure that it’s performing the right test, does it have a test which will prime new battery packs ... and also offer programs for testing field service returns? Of course like any device you purchase you want to know warranty period and ability to be upgraded. Of course, at the very end you’d like to know how much time will battery testing take.
Moving to slide number 16, some more things about selecting the right battery analyzer or tester; you want to choose a tester that allows you to collect service data and record or report results appropriately. So maybe a PC software package where you’re ID’ing every battery pack in your fleet and then storing that data from cradle to recycling bin is important. You want to make sure that you have the opportunity to label or ID your battery pack, so you can follow its capacity through that process. You want to make sure that your analyzer can be upgraded for different battery types, so is it an adapter based connection between the battery pack and the analyzers. So those are important things to consider.
Moving to slide number 17, so a summary. What do you need to know as a clinical engineering technologist, what do you need to know about battery pack? First of all, you want to know what the test time is per battery. I guess some general guidelines here, NICAD’s typically in the range for a service return could be six to ten hours; nickel metal hydride a little bit longer because of the charge algorithm takes a little longer to charge in nickel metal hydride; a similar sort of timeframe for lithium ion, in that sort of 12 to 15 hour range; and then 24 hour plus for lead acid battery packs.
How often do we need to service our battery packs? Well again, it depends on the chemistry and what the application is and how they’re used, but for some general guidelines, NICAD’s would be every 30-60 days; nickel metal hydride every 60-90 days; and lead acid and lithium ion every six months. Again, the discharge in this case with lead acid and lithium ion is not because the chemistry requires it, it’s just because you’re trying to qualify that it meets your facility’s pass/fail target.
How much operational time is required? Once you have your test system installed, and Mark and Tim will talk on this more, the actual amount of time required to run battery testing is probably less than 30 minutes a day. So the bottom line to know about battery testing is that it improves the reliability of medical equipment and minimizes the expense of unnecessary battery replacement, so it gives you a lower cost of operation.
Moving to slide number 18, that’s my sign-off slide. I want to thank you all again for participating today. I’ll pass this back to Jay, and look forward to the presentation from Mark and Tim. I’ve just given a few resources there for extra information related to Cadex, that’s Cadex.com, again, Battery University, which is a nice educational Web site, and the Web site from the president of the company, ... which contains information from his book called Batteries in a Portable World. Thank you very much.
J. Crowley: Great, Bruce. Thank you very much. That was very insightful and a great overview of the world of batteries. Again, if you have any questions for Bruce we’re going to take those at the end, so go ahead and jot those down, and after our next two speakers we’ll open up the lines for questions.
Now, I want to introduce our next two speakers, and I’m going to introduce them both now and then they have sort of a tag team presentation. Tim Zakutney and Mark Cleland, who are from the Biomedical Engineering group at the Ottawa Heart Institute, are going to, again, go together. Tim Zakutney is Manager of Biomedical Engineering Services for the Cardiovascular Devices Division of the University of Ottawa Heart Institute in Ottawa, Ontario, Canada. Mr. Zakutney holds a Master’s in Health Sciences and Clinical Engineering from the University of Toronto, and is also a professional engineer with a specialty in systems design from the University of Waterloo. Mr. Zakutney is a member of the American College of Clinical Engineering and holds appointments on two scientific advisory committees for Health Canada.
His co-presenter today is Mark Cleland, who is a Biomedical Technologist with the University of Ottawa Heart Institute. Mark has 17 years of experience in the biomedical field and his interests extend throughout the critical care and diagnostic settings, including anesthesia perfusion, cardiac ultrasound, and electrophysiology. Mark has been very active in research and has 19 publications within various medical journals. So with that, I will turn it over to Tim, who will start this tag team presentation. Tim.
T. Zakutney: Thank you, Jay. Some of you may have attended our presentations back in Baltimore and San Diego, and just to give people an idea of how we sort of came about participating in these, the Medsun Group crew made a trip up here to Ottawa to visit with Health Canada. Health Canada here, our equivalent of the FDA, was interested in trialing a pilot project similar to Medsun, and a lot of the clinical engineers in the Ottawa area were invited to attend. As our conversations revolved around incident reports and issues surrounding medical devices, I brought up the topic of batteries and so on and so forth, that we ended up being able to go down to Baltimore and San Diego. I’d like to thank everybody for participating. We’re going to go over a little bit what we’ve done back in Baltimore and San Diego, but also provide a little bit more detail in terms of the protocols that we use in analyzing our batteries.
So let’s go on to slide two, and really this whole presentation revolves around: what does this mean? Do these two graphs mean that your battery is good, it’s poor? But more importantly, will these devices provide you the operation that your nurses or technologists staff need, in terms of in the context of a patient transport? Will a battery that reflects these last for transport monitor, or a defibrillator? I think ultimately what we’re trying to achieve here is that there is less reliance on what these sort of indicators mean and give clinical engineering and medical engineering departments the ability to quantitatively measure the condition of their batteries.
If we go on to slide three, the agenda. I’m just going to do a little brief introduction about the Heart Institute and our group, a bit about medical batteries and a glossary. Bruce had talked significantly about different chemistries and we’ll talk about capacity analysis, a little bit more detail on the protocol we use here at the Heart Institute in analyzing and assessing our batteries, and we’re going to present a case study we did with infusion pumps, and then start talking about a philosophy of addressing medical device batteries, have a discussion of benefits, and since that will be the end, we’ll allow for questions towards the end.
If we go to slide four, the University of Ottawa Heart Institute here in Ottawa, Ontario, Canada, we’re a bilingual academic health center, which is bilingual in French and English, who deal with therapeutic, diagnostic, and prevention approaches to cardiac care. We’re a regional facility serving a population of approximately 1.8 million people, and we’re a resource to the province, the rest of Canada, and also the international communities.
On slide five, we are a 140-bed cardiac care institution with four cardiac ORs, four cath labs, one EP lab, and a comprehensive rehabilitation center. Our diagnostic modalities include echocardiography, nuclear med, cardiac imaging, ECG and Holter stress testing. We also have a significant research component in Positron Emission Tomography and also the Canadian Cardiovascular Genetics Center.
On slide six, the department itself is comprised of myself as the Clinical Engineering Manager, and we have five biomedical engineering technologists on staff. For those of you, which I would imagine most of you, are part of medical engineering departments you’ll see the list here of roles and responsibilities that we have, and the purpose of doing that is simply to relay to you that our department is no different than any other department throughout Canada and also throughout the United States, in terms of what responsibilities lie on our shoulders, what sort of workload we’re dealing with, and that it is, in fact, possible to integrate this approach that we’re going to talk about into your day-to-day operations.
On slide seven, I’m going to pass it over to Mark to talk a bit about background information on batteries.
M. Cleland: Thank you. Batteries essentially perform two functions. They are either the primary or secondary source of power and they retain critical parameters and data in the event of power disruption. We find a variety of devices used for employee battery technology, all of our portable equipment here, including infusion pumps, defibrillators, ventilators, and transport monitors, including intra-air balloon pumps and ventricular assist device ... lead acid batteries. That will be the primary focus of our discussion. These batteries range in size, while they are mostly 12-volt, they range in capacity from two amp hour right up to 36 amp hour batteries. Bruce talked a little bit about battery technology and battery chemistry in his analyzers, and we employ those analyzers here and we measure and analyze a full range of batteries. So while our talk will be primarily focused on the batteries that are employed within infusion pumps, I want to make it clear that we do test a wide arrangement of batteries.
On slide eight, I won’t go over battery chemistry, because it was covered very nicely by Bruce, but I will talk to you about capacity and how that is truly our benchmark. Capacity is a measurement established by battery manufacturers, and essentially what it tells us is, it’s expressed in amp hours, so specifically how much current can a battery deliver over a specified period of time. For example, if a battery has a two amp hour rating, we know it can deliver one amp per two hours, in theory. If we place that battery on an analyzer and get a reading of 100%, then we know we can get one amp for the two hours.
On to slide number nine, where we talk about capacity analysis. When we discuss or talk with nursing about batteries and battery technology, their primary question or concern is how long will my device operate, whether it’s a transport monitor, whether it’s a defibrillator, or intra-aortic balloon pump, and to understand what measures we require to predict run time or operational time. We have to know the rate of capacity in ... hours. We’re going to measure it so that we get a percentage. We also have to know what current training equipment demands and from there we’ll be able to tell them how long their run time, or how long they can expect the battery to operate their device. The sealed lead acid batteries, how you treat them, how you manage them will dictate their life expectancy. When we talk to nursing about the battery and care of the batteries, we use a ladder as an analogy, and the fully charged battery, at 14.4 volts, represents the top of the ladder, and the bottom of the ladder represents full discharge of a sealed lead acid at 10.5 volts. So if you travel from the top to the bottom of that ladder in a continuous fashion, you will only do that 200-300 times.
Now, if you use a battery from a fully charged to a fully discharged state on a daily requirement, the nursing staff has to understand that they will get less than one year of operation of that battery, so their dependency may be questioned on transport. So we encourage them to use only the top third of the ladder, we encourage them to charge, recharge the batteries as frequently as possible. Sealed lead acids, as Bruce mentioned, have a very good tolerance to prolonged charge times, and when we use only the top portion of the ladder we can see that we get 1,500 to 2,000 cycles out of a battery, which keeps that battery in service for two to three years, up to five years even.
Now that we know this information about batteries we can progress to slide ten. Now, what do we do to start analyzing these batteries? Well, we have to devise a protocol for testing them. As Tim mentioned, we treat every battery as a piece of medical equipment, there’s no difference; they are entered as an asset into our equipment database and they are placed on a preventative maintenance schedule, as per all other electro-medical equipment. To design our protocol we have to meet with the medical directors and the end users and ask, “What are your requirements, what are the needs of the end user?” We have to understand and we have to appreciate the run times that they require, because that will help us in designing our protocol. We have to look at the battery configuration within the device, is there one battery employed within the device or are there multiple batteries? Are those batteries connected in a series, or are they connected in parallel?
Again, we have to know what the load or draw of current the equipment demands. Then we have to look at the end use of the equipment to establish a frequency for preventative maintenance. We will consult with the recommendations of the manufacturer of both the medical device and we will take in consideration the battery spec sheets. All of this goes into designing a protocol.
On slide eleven, it will show you an assessment protocol of a typical 2 amp hour battery that are employed within our infusion pumps. So we get a battery presented to us and we connect it to the analyzer. Again, based on your analyzer, it might be a set of alligator clips that you’re attaching to the terminal, or some batteries fit right into a pre-molded slot. When we receive the battery, it is connected to the analyzer and immediately a discharge cycle is initiated. We do this because we want to know what is the condition of the battery as it presents to us, we don’t want to know that after a full charge cycle the battery was fine. We feel it’s important to know how the battery, what condition it is when it’s presented to us, hence, we’ve programmed our analyzers to initiate a discharge cycle. You’ll see that we discharge our infusion pump batteries at one amp, which is approximately three times that discharge recommended by the battery manufacturer.
Why did we select one amp? We selected one amp because it replicates the current load that a three-channel pump can reach. So if we have an infusion pump with three channels all running simultaneously, we can expect a current drain of one amp. So we established a testing protocol that simulates that. As well, we established a correlation, which Tim will review with you later, looking at battery capacity and the run time, it will be based on that one amp discharge. Once the battery reaches 1.75 volts per cell, or a terminal voltage of 10.5 volts, the analyzer automatically goes to a charge cycle. For our charge current, we selected 800 million. At the end of the charge cycle, our battery will be fully charged at 14.4 volts and we’ll initiate another discharge cycle, again, as part of the automated procedure that our analyzer uses. We will obtain a second capacity measurement. If the second capacity measurement is greater than 5% of the initial capacity measure, we will generate a charge cycle and another discharge cycle.
If the final capacity measure and the initial capacity measure is less than 5%, we record the value of the capacity measure and enter it into our database. Now, if it passes our pass/fail criteria, which is 40% capacity measure, or the 2 amp hour battery, we redeploy that battery into the device. If not, the battery is recycled and removed from the database and labeled as inactive.
On slide 12 is just a bullet point form of what the protocol is. Again, we feel it’s very important to start with a discharge cycle because that will tell you what condition the battery was in as it presented to you. That might give some insight into charge related protocol issues and/or faulty chargers. So the protocol is spelled out. We can certainly be reached, help design your protocol or continue to share on ours, but for slide 13 I’ll hand the talk back over to Tim.
J. Crowley: Hello?
T. Zakutney: Sorry about that. I had my mute on.
J. Crowley: Okay.
T. Zakutney: Thank you, Mark. Slide 13, you’ll see, is just a photo of what we call our battery workstation. As you can see, we’ve got three battery systems, conditioning systems, and they’re hooked up to that laser printer and also a computer workstation. The computer workstation is where all of the assets are recorded, and also all of the protocols are programmed into this station. In reality, the amount of work and effort required to analyze a particular value, that Mark was just speaking of, and the different charge and discharge cycles, really what it entails, from a practical point of view, is taking a battery, hooking it up to a bay—and as you can see on the left hand side of this photo you’ll see one of the larger batteries there—attaching the alligator clips and walking away. In several hours, depending on how many discharge/charge cycles have to happen, we’ll come back, and when that process is finished a report is automatically printed off on a printer that tells us all of our recordings or initial capacities and our repeated measure capacities after that. So from a practical point of view it really is a matter of minutes after your system has all been programmed and set up.
We go to slide 14. I’m just going to present a little bit of a case study that we did with infusion pumps, and I’m just going to take a step back and give an explanation as to one of the reasons why we went about looking at infusion pumps and looking at batteries. We had an event in our ORs where we had an infusion pump that was used on an ..., consistently plugged in, not moved around, but in this one instance they removed this IV, this infusion pump, to transport the patient over to our recovery area. Within a matter of seconds the pump indicated a low battery and then the pump shut off. This caused us quite a bit of concern because this pump has always been plugged in. So that prompted our chief of anesthesia to start asking questions as to what was the problem. We fell into investigation mode and as it turns out the battery was in very poor condition. So really that prompted us to say to ourselves, what can we do, as biomedical engineers in our department, to try and avoid these sorts of things? What sort of condition are we putting—what batteries are we putting into these devices? This particular device was always plugged in, so it created a lot of the questions that we wanted to address.
What we decided to do is let’s try and get a relationship between battery capacity with run time, and we assessed 100 infusion pump batteries, not new batteries, just random batteries that came up from the floor. Our measurements were based on an infusion rate of 100 mils per hour, which was as per the service manual of our particular infusion pump provider. We measured the battery capacity. We also determined what the time to alarm is and determined the total run time of these batteries, as they presented themselves.
If we move on to slide 15, you’ll see the raw data that we collected. The solid blue line, actually let’s start with the solid dashed line, this is the time to alarm. So we’ve run these pumps on these particular batteries for a period of time, and this is the relationship between the time to alarm and battery capacity. The solid blue line indicates a linear representation of the data for total run time, and you’ll see, when you start getting into low battery capacity measurements, you’re treading into very dangerous waters, which is something that we had encountered, where the time difference between total run time and time to alarm is very negligible. This is something that needs to be addressed by the algorithms of the devices, to help make these two lines essentially more parallel and to give you a better consistent approach to allow you time to resolve low battery alarms.
If we go on to slide 16, we collected all this data and the next step we did was to approach our medical directors and our nursing units downstairs and said, “What are your expectations, what are your needs when it comes to these particular batteries?” From the discussion, it was that they required three hours of run time. The reason why they chose three hours was in order to get a CT scan patients had to be transported to a neighboring hospital on the same campus, and to allow for the patient transport to the CT scan, have the scan, come back and also allow for a safety merge, and it was a run time of three hours.
When we looked at our data and grouped them with what we would call “very low,” “low” and “acceptable,” as it turns out the minimum for batteries with a capacity range of 40% or greater was 182. So at that point we said, for our criteria for these particular batteries, for this particular device, we said that 40% would be acceptable in our assessment of criteria. That is a process that can be placed for any device, any battery, and really we’re focusing them on the different modalities. You would have a different set of criteria for defibrillators, for balloon pumps, ventilators, and in particular ..., where you can have patients going home. And you can imagine how important it is for an infusion pump in hospital, but this sort of approach is very important when you have a patient going home on an artificial heart or artificial device.
On slide 17, I’m going to start talking about philosophy. Really, Mark alluded to it, it’s really about treating batteries as you would medical devices, and this is a picture of some of our batteries that are on our shop and our part storage, and you’ll notice that they all have individual tag numbers, they have ... due date numbers on it, you know, in a lot of cases these particular ... due date stickers, for example, aren’t going to be seen by the nursing staff, but they’ll certainly be seen by us. So if a pump presents itself at the shop to be repaired, at first glance we’ll know if they’re due for their assessment or not.
If we move on to slide 18, just as you would any other medical device, we log all procurement information, purchase date, P.O. number, cost and supplier. We use the date of the battery to serve as a serial number in our particular asset management system. We also monitor parent/child relationships; our system allows us to keep track of what batteries are in what devices. On all new batteries we perform initial assessments, and as Mark described our protocol, we measure both initial and final capacity, because you have to keep in mind that many battery providers and battery vendors may not perform this exercise prior to selling you the batteries.
We log all inspection and assessment data, and we will isolate trends, in the sense that if we receive some batteries from a particular vendor that fail our criteria, that’s one way that we can identify that.
Last but not least, it’s part of our equipment management program, so it’s given an inspection frequently and a PM procedure is produced for each of the batteries. The important thing is to include this in the day-to-day operation of the department, so that it just becomes a natural habit for the technologists and the biomedical engineering group to go through this process with each of the batteries ... In our particular case, we tend to keep our batteries with the device that it came up in, mind you, as we all know, the sealed lead acids, from what was discussed today, have a very low self-discharge rate, so I think it was in the tune of 5% per month, so there’s no reason why, if an infusion pump, for example, was to come up for repair, a brand new battery, or at least, I should say, a newly conditioned battery can be installed right away. Typical biomedical engineering groups would not want a return of infusion pump unless it has been charged for a prolonged period of time, so in fact what you may experience is that you’re able to return infusion pumps immediately after the repair happens, as opposed to, say, having them plugged in overnight and then redeploying them back the next morning.
Going to slide 19, what are some of the benefits? Certainly, staff awareness; Mark spoke a bit about talking with the nurse managers, talking with the medical directors. We’ve had some articles presented in our critical care newsletter to really elevate the profile of batteries, that they are important, that it is important to keep these pumps plugged in, and in fact, I present at orientation sessions for nurses down in our critical care area, and essentially I say, “When in doubt, plug it in.” It’s a good rule of thumb to go by with respect to the devices down there. What we also noticed was huge confidence in equipment operation, whereas before there was a lot of sort of rumor mill comments being made that, “Oh, this transport monitor won’t last,” and so on and so forth, and those have been essentially eliminated by applying this sort of protocol.
There is a potential cost savings, in the sense that you can have prolonged use of previously considered poor batteries. Environmental protection: we recycle all of our used batteries that don’t meet our criteria, and in some cases you can actually generate some funds through battery recycling programs. One of the big things we’ve found is it normalizes suppliers, so we really have the ability to pick and choose where we want to purchase our batteries based on cost. Because we do assessments on all the batteries that we purchase, we know exactly what we’re getting and from whom we’re getting them. We can choose, if in fact a company is less expensive, we can be comfortable that if we do want to purchase batteries from them, that the condition of the batteries that we’re getting are going to meet our demand.
I’m going to pass it over to Mark a bit and talk about extending beyond what ... about normalizing suppliers and new batteries.
M. Cleland: Thanks, Tim. We’re going to step away from the infusion pump work that we’ve done and go to an older study, where we looked at batteries for a pre-hospital defibrillation program that we have here in Ottawa. We looked at batteries from a supplier, and they were brand new, they were 14 months past their date of manufacture, so they’re a little dated, and I would suggest that that’s not too uncommon if you are purchasing your batteries locally. So we looked at the batteries and we found that they were presented to us, some of them had some very low capacities, and for the defibrillation program we again established a correlation and ... count, where our incoming inspection pass/fail criteria was 65%, and this graph, on slide 20, shows you that 46 of 126 batteries failed to meet our incoming inspection criteria.
I talked with the battery distributor, as well as the battery manufacturer, and the distributor did not want to take the batteries back initially, and wanted us to work with the battery manufacturer and find out if our testing protocol was legitimate. They verified all of our test procedures and they said that the batteries, again, sealed lead acid batteries, probably had reduced capacity due to a lead sulfation effect and that since they were only 14 months past the date of manufacture, that if we employed an over-discharge protocol we would probably be able to remove the lead sulfate from the plate, allowing that portion of the plate to now accept a charge and hold a charge. So they illustrated what the protocol had to be for over-discharging a sealed lead acid battery, and as radical as it may seem, what the protocol did was brought the terminal voltage down to approximately 50-100 millivolts, so you’re taking a 12-volt battery, you’re placing it over a power resistor and allowing it to sit overnight. So you fully discharge the battery, fully removing all lead sulfate from the plate, converting the chemistry inside the battery, and the next morning you come in and you remove the battery from the power resistor, allow time for the battery to settle, and you recharge it for 24 hours, you place the battery back on the analyzer and see how it did.
Well, now it was quite astounding that all of the batteries with very low capacity bounced straight up to where the manufacturer of the batteries thought they would come out, based on our testing criteria. So what we came up with was a new method of treating poorly conditioned batteries. The point is, if you do not look at batteries when they come into your door, whether they are brand new, whether you got them from Distributor A or Distributor B, if you do not look at them you do not know what their ability is to perform. Here, we saw that 46 of the batteries would not have performed well in our pre-hospital defibrillation program. After the over-discharge protocol, all 126 batteries came well above the 70% level that you see on that graph. The real message is: do not assume that just because you’re purchasing a new battery, whether you got it at a high price or a low price, that battery has to be able to perform, and the only measure of performance is by analyzing the battery’s capacity.
So to support what Tim was saying, what benefit does this provide us? Well, it gives us confidence in a battery’s ability to perform. It gives us predictability of the battery and the end product. We can now safely determine when is the end of life for this battery, and we have measures in our protocol of pass/fail criteria, and we certainly now use that as the standard as opposed to a date stamp. So do we keep our batteries longer than one year? Yes, we do. However, if the battery is unable to perform, it might be removed at ten months of use or six months of use. We keep a battery in service as long as it can meet the needs of our user. So I’ll pass on to slide 22 and pass it back over to Tim.
T. Zakutney: When we looked at how many batteries we were actually replacing—and we had data back from 2002, which is when we really started diligently collecting this information—you’ll see two of these graphs here, these are for single channel and also multi-channel infusion pumps, and as you can see, this particular vendor suggests that we replace these batteries on a yearly basis, but as you can tell by the quantities that we’re dealing with, we’re having batteries that are lasting longer. But just as Mark was saying, there are occasions where batteries are less than a year old but they do not meet our criteria, so they will certainly be disposed of and isolated out from the system, so there is certainly the ability to have batteries last a lot longer than what vendors may suggest that you do. Alongside of that, there could be potentially a cost savings in that regard.
Finally, off slide 23, the ultimate benefit at the end of the day is improved patient care. If you can minimize the number of pumps, for example, that are coming up to the shop due to battery failures, or any device, for that matter, you’re improving patient care, you’re decreasing down time, there is certainly a potential that if you incorporate this assessment protocol in this process, or at minimum this philosophy in your department, you’ll have less down time of pumps sitting in your shop waiting to be re-deployed because they’re plugged in.
One of the big litmus tests, after several years of doing this, is we had an event, fairly recently, down in our critical care area where we had a severe power outage, due to some unfortunate circumstances, where there, in fact, was no generator backup power available to our critical care area. And in that sense we had no power whatsoever, but at the end of the day in our postmortem we did not have one piece of battery operated equipment that failed during the course of an hour or whatever it took to have some alternative source of power brought into the area. That was a real litmus test and made us realize, and in fact really made the whole hospital realize that there’s a huge benefit to being diligent in this respect. At the end of the day, it’s really not a huge significant amount of time to incorporate this into the day-to-day operations. One of the other benefits is that we were able to predict, because we document all of our capacities that we’re measuring, we’re able to predict how long is a battery typically going to last us. We’ve done trending on ventilator batteries and what sort of discharges that we’ll see over a course of six months, and so we can certainly predict what we should expect and whether or not they should be removed from service as they’re approaching our criteria level.
I think we’ll just move on to the last slide. I’ve put on our e-mail addresses and phone numbers, if anybody has any questions or would like to know a little bit more information about our assessment protocol and however we can be of service. I want to thank everybody for participating in this audio conference. We really strongly believe that medical batteries are used in times when patients need them most, and that’s during very critical situations during patient transport, and so there’s no reason why we should not be extremely diligent when we’re dealing with our medical batteries. It’s not the flashiest, it’s not the most glamorous part of the job, but when you think about it, when devices are on battery power are typically when the patients need that device the most. Thanks again. I’ll pass it back to Jay.
J. Crowley: All right, Tim and Mark. Thank you very much. That was a great presentation, a great tag team presentation. Obviously the little incident that you had recently was a great testament to the work that you all have done. Deb, we’re going to go ahead and open up the phone lines for questions.
Coordinator: To ask a question, go ahead and press star one.
J. Crowley: All right, so go ahead and get all those questions that you’ve been saving up in for both Bruce and Tim and Mark. We’ve got about 20 minutes left for questions.
Coordinator: We have no questions in the queue, sir.
J. Crowley: Oh, well I guess the presentations were so complete that everyone knows exactly what they need to do now and ...
Coordinator: Excuse me. I do have a question from Jim Griffin.
Question 1. We have some lithium ion batteries used in some Philips portable monitors and the manufacturer recommends that they be reconditioned after 50 cycles, and in some departments that’s about every month and a half to two months, and your literature seems to indicate that the lithium ion batteries didn’t need to be conditioned but every six months.
J. Crowley: I guess that’s a question for Bruce.
B. Adams: Yes. I think that’s a great question. Probably what they’re suggesting there has a lot to do with what I talked about in fuel gauge recalibration. It’s not a specific requirement of the chemistry to be conditioned that periodically, but probably what they’ve found in what they believe to be their normal user model is that the battery packs are short cycled frequently, or don’t hit the end of discharge voltage, and therefore aren’t recalibrating the fuel gauge. So what happens with the smart battery pack, in that case, is that the fuel gauge starts to report less than accurate information about the cell capacity, so that’s why they put a recommendation there for every 50 cycles, is because the fuel gauge is falling out of sync with the true state of health of the battery cell. So it has less to do with the lithium ion chemistry and more to do with the fuel gauge, and in that case I would definitely follow the manufacturer’s recommendations.
J. Crowley: Great. Thanks, Bruce. Tim or Mark, did you want to comment at all?
T. Zakutney: This is a good example of a vendor providing some guidance on something when taking the approach that we have, specifically for these particular batteries, and we have the same monitors, we just got them maybe about a month ago, but approaching it from the sense of what are your expectations? What are the clinician’s expectations in terms of this equipment and trying to build up a criteria as to what is the relationship between capacity and run time of this transport monitor?
This falls in line exactly to what our approach has been, and that is let’s get a real quantitative assessment between what capacity is going to be, what run time is going to be, and what are the expectations of the clinician. You’re absolutely right, doing those sorts of assessments that often, if in fact you can even track how many full cycles are going to happen on a transport monitor, is very difficult. But if you’ll take it from the approach that we have that we’ve done, you might be surprised that it might not be every 50 cycles, it might be every six months, which is somewhat more reasonable, and it might even be every year.
J. Crowley: Thank you. Great question. Deb, any more questions?
Coordinator: No, sir. That’s all.
J. Crowley: That’s all. Well, if there are no more questions, then I thank our speakers very much; Bruce Adams from Cadex, and Tim Zakutney and Mark Cleland from the Ottawa Heart Institute. Thank you very much for your presentations today. Thank all of the listeners for tuning in. With that, we will sign off and wish everyone a great holiday. Take care and bye.
Cleland MJ, Maloney JP, Rowe BH.
Biomedical Engineering, The Ottawa Hospital, Ottawa, Ontario, Canada.
Emergency Medical Services (EMS) rely on batteries to power external cardiac defibrillators. While maintenance protocols should be followed to ensure that batteries possess adequate capacity to power their defibrillator, they are not often applied to new batteries. This study examines the effects of prolonged storage on sealed lead acid (SLA) batteries, the number of batteries that are affected by lead sulfate, and the ability of a protocol to restore the capacity in SLA batteries. A prospective cohort of new batteries was subjected to testing and discharge protocols. Initial battery capacities were measured using a battery analyzer. An "over-discharge" protocol fully discharged the battery over a 24-h period, and batteries were recharged and reanalyzed. Capacity measurements were repeated twice. Sulfate buildup was defined a priori as final capacity measurements greater than predischarge measurements. There were 126 batteries studied, a mean of 14 months after manufacture. Overall, 47 batteries (36.5%) had measured capacity that was insufficient (< 65% capacity). Batteries possessing very low initial capacities (< 55%) responded with a significant improvement on average of 54.7% compared with batteries within a normal capacity range (> 65%) whose average improvement was 9.3%. After discharge, there was an average of 17% improvement in the measured capacity, with no differences in the final capacity readings in each battery type. In conclusion, sealed lead acid batteries are affected by prolonged storage. The loss of capacity created by accumulation of lead sulfate can be reversed if battery maintenance protocols are used as part of EMS quality assurance programs.
PMID: 10729667 [PubMed - indexed for MEDLINE]