Anesthesia delivery system webinar

Great thank you, I really appreciate everyone attending our webinar today. I'm Andrew Clay, and with me, my partner in crime is Mike Raiche and we're coming to you from lovely Everett, Washington just north of Seattle, maybe 20 miles from the Pike Place Market and our talk today is going to be on anesthesia testing.

So, we're going to talk a little bit about the history of anesthesia and where it started. We were doing some research on this and I found out that as far back as 4,000 BC, people were using poppy and opium, and they're still using that today in some parts of the world.

However, when you start to look at inhalational anesthesia, that started around the early 19th century using carbon dioxide with Henry Hickman, and when we moved into the mid-1800s, diethyl ether or nitrogen oxide, started to be used. In the modern century we started using halothane, enflurane, isoflurane, sevoflurane and desflurane. And these are the primary agents used today.

So, one thing to note is that halothane and enflurane have somewhat fallen out of favor. Halothane can cause Halothane Hepatitis and enflurane can cause epileptic compulsions. So, those have become less popular.

The most common agents being used right now are isoflurane, sevoflurane and desflurane. So, those are the ones you're going to see in the hospital environment the most.

We talk about this inhalational anesthesia do, what we're trying to do is depress the central nervous system and there's a number of effects that we want to happen. We want a loss of pain response, we want you to lose your memory of the event, we want loss of motor reflexes, we want you to be unconscious, and we want you to be paralyzed.

If that is out of balance in some way, and we'll talk a little bit more about that later, you can get some very bad effects. And so, when we're delivering anesthesia it's important to make sure our gas mix and our percentage of anesthesia delivered is actually correct.

So the purpose of the anesthesia delivery system is two-fold. One, is respiratory support because usually with the person being under, we have to control their ventilation and make sure that they're breathing and the second is anesthetic agent administration, and we do that with a number of components on the anesthesia machine.

Mainly the fresh gas delivery system, the scavenging system, the vaporizers, flow meters, the ventilator and any monitors that may be present from either measuring physiological parameters or any of the gas characteristics.

And this truly is a system, all these things work together. So as we get a bit further in the presentation, you'll see that each one of these things needs to be tested, because it truly is kind of a symbiotic relationship, one can't really work without the other, and this is critical to ensure that the patient is safe and also getting the right mix to get all those things that we saw on the last slide.

In the clinical setting, we're looking at the patient being inline or in the circuit with the anesthesia machine through the circle rebreathing system, and we'll start in the upper left with the fresh gas supply.

This then runs past the vaporizer where agent is added, through the inspiratory one-way valve, and then inspired by the patient, where it's metabolized. And you have to watch all the various characteristics of the lungs and how much oxygen and how much anesthetic agent you're giving. And that's also usually monitored by a third-party medical device as well.

When the patient expires, whatever metabolized gases come out or unused gases come out. That goes through the expiratory one-way valve, there's a reservoir bag to relieve any pressure in the system, close to the APL valve, and then scrubbed, and then we go all the way through the circuit again. Basically scrubbing the gas, adding fresh gas and adding an anesthetic agent.

So some important things to note are these one-way valves. The inspiratory and expiratory valve, make sure the flow always happens in one direction. You don't want CO2 staying in that circuit because we know that as a patient continues to breathe in CO2, that's not good for their body and it will deplete them of oxygen.

So you want to make sure that those valves are working, so when you breathe in, you only breathe in agent and oxygen, the yellow and blue lines. And when you breathe out, you're breathing out some leftover oxygen. Leftover anesthetic agent and the CO2 that you metabolized, and you want that to go out.

As we go to the left of this diagram, you see the carbon dioxide absorber, typically these are pellets and what they'll do is they'll absorb the CO2 being expired. In most systems out there change color, so it will change to like a pink or a purple to show you how much of that's being used, so that's why you see those little purple dots there.

Once it passes through that the mix is then clean and then you see that it's just oxygen and just anesthetic agent that go back into that circle. And then the fresh gas supply starts the whole process over again.

One more thing to note here is that the ventilator can typically take over the function of the reservoir bag and the APL valve, so the ventilator will take over breathing. That's one addition to this diagram that you could think about. So when the bellows are pumping, that's kind of like the reservoir bag going up and down.

And then pressure is being controlled, sometimes through PEEP or anything like that, so if you think about that bottom section and the middle as being a ventilator, it's another way to visualize it.

So, the main component of the anesthesia delivery system is the vaporizer and here we've got kind of a detailed, generic diagram of a vaporizer. It's calibrated to release a very controlled amount of anesthetic to the patient, there's usually a mechanical dial that dictates the desired concentration.

There's some kind of carrier gas going through air, oxygen, N2O, flowed through the inlet and then when you look at the inlet port at the top, we can see that the anesthetic agent is at the bottom and works its way up through the wick but there's also pressure and temperature compensation and most of this is a mechanical function today, it's almost all mechanical, created by a thousand dials and that controls the amount, very precisely, how we get to the outlet port.

Yeah, and some things to note here is that the system is, I don't know if you guys have dealt with one, but they're very, very heavy. They're not the easiest things to move around, and they're sensitive to angle. So that wicking system, you see that fluid there at the bottom, the anesthetic agent, that's typically filled through bottle that is keyed, so you shouldn't be able to fill the wrong agent in there, but you can if you try really, really hard.

We've been assured of that by some customers and if you tip this over too much you can throw off the calibration of that wicking system, so you don't want it to go past a certain angle. So these things have to sit flat, they're heavy, so they're wheeled around with carts, these are just unwieldy instruments that can be dropped but basically their function is pretty simple, but things still can go wrong with them, and again, critical that this thing is doing the right job because it is in direct contact with the patient, right?

So we're going to talk just for a minute about the gas laws and how that effects respiratory physiology. We don't expect you guys to memorize this necessarily, but you should be familiar with some basic concepts around gas.

One being, that if you're at a higher altitude there's less pressure, therefore there could be more volume and you should be thinking about that when you're doing your testing or looking at your percentages or doing any kind of airway measurement whether that's flow or volume. Have some idea about how temperature, altitude, IE pressure could be effecting your system.

Yeah, and you want these things to act as a sanity check. You're making changes and adjustments to the machines, so let these laws and let human physiology guide you on whether or not the thing that are happening and what you are seeing, make sense to you.

You should understand that before you just go and start pressing buttons because again, it's patient safety at the end of the day. But, yeah, if you understand how it performs and how the human body performs, you can do your job a little bit better and a little bit safer.

Why do we test, what kinds of things can go wrong? So, what you're essentially looking at is the mix of gas in the system and what the patient is getting but right now we're focusing really on the anesthesia, so if you under administer anesthesia in some way then you can get all kinds of other things, undesired effects happening such as awareness, or feeling pain, or movement, or some kind of psychological effect that's a byproduct of those.

So, if we're not depressing your pain or we're not forcing you to lose your memory, or we don't have a loss of motor reflexes, then there could be some very bad results happen in the operating theater. On the other side, if we over administer, we can depress the central nervous system too far and put somebody into cardiac arrest or even death.

Just to add some color to under administration, put yourself in the patient's shoes. Imagine that you're lying there on the bed and you're feeling pain and you're aware of what's going on. So you're watching cuts being made, you're feeling the pain, but you can't move and you can't speak.

Imagine what that would do to you at a psychological level, imagine the trauma that, that's going to put you through and kind of the burden you're going to bear for the rest of your life.

That's kind of one of the dangers, right? But obviously the physical dangers are cardiac arrest and death from over administration, which we don't need to explain any further but there are a lot of things that can happen to the patient if you don't get this mix right.

So aside from measuring the airway gas and the anesthetic container they're in, you can also, the anesthesiologist can also monitor other physiological parameters, you know, uptake of oxygen, such as SPO2. There're other technologies that measure your awareness like bispectrol index, the BIS system, that's been around for a while, that's one way the anesthesiologist can determine your awareness level but there are also, like I said, monitoring and looking at other physiological parameters to determine what state the patient is in as far as awareness.

When we look through some of the picture we find a case study about a vaporizer malfunction where a healthy 36-year-old woman underwent surgery on her arm and the desflurane vaporizer was set at 3.5% to maintain the anesthesia. After about five minutes, the patient became oxygen-deficient and displayed a really slow heart activity, followed soon by cardiac arrest.

So, the ECG indicated that her heart had stopped. So they delivered Epinephrine to get her going again and did a defib and she came back, and the patient was sedated and transferred to the post-anesthesia unit care. An X-ray revealed there was an accumulation of fluid in her lungs.

We're going to talk about, how did that happen? Like, this is a rather healthy person who, what? Well, she got over administered, so what they found was, was that the equipment had been broken where there was a crack internally causing the desflurane to be over administered to 23% instead of 3.5%. Had that been checked or a check had been done prior to that patient going under, they would've found that.

Yeah, and it just shows that like what I talked about how these vaporizers are unwieldy. This was probably transported to the anesthesia machine and possibly dropped. Right? That might have cracked the dial. A lot of these things can happen without us seeing them so that's why it's really important to do a check of how it functions, right? Not just a visual inspection.

Of all these components, there's a lot of failures that could happen within this system. A failure within the ventilator, the vaporizer, the interlock system, the scavenging system, the APL valves, the flow meters or the monitors. So we really need to check each one of these systems independently.

Yeah, there was one question that came in ahead of the webinar, so I do want to address that on this slide. We talked... the question was, what are the top anesthesia machine failures? And there are a lot of sources out there that say different things but in general, our research that we did here at Fluke Biomedical, shows that there are two main categories.

Most of them fall into misuse or user error. Unfortunately, we can't prevent human interaction and the things that go wrong with that. And this is about three times more common than equipment failure, which is the second category.

And if we look at the buckets that those fall into, it's typically inadequate oxygenation, right, so checking your flow meters and making sure that oxygen levels are sufficient and as administered. The other is excessive airway pressure, so another ventilator function that we need to check out. You want to make sure that your pressure control valve is working correctly.

And then there's overdose of inhalational anesthetic, which is what we saw in the last example there. That could be a valve malfunction, a spillage of the inhalational agent into the breathing circuit. It could also be the wrong dial setting as we saw in the case study.

But the main point that I want you to take away from all these failure modes is they're mostly preventable. Right? If you do a pre-administration check, if you do your preventative maintenance you can catch these failures and prevent most of them from ever occurring. So it is really important to have an adequate QA process for the entire anesthesia delivery system.

And ASA has guidelines around that. Okay, so, how do we test. We talked about why all the different things that can happen. Now we'll talk about how and we're going to talk about what the best practices should be.

The first one is about standardized testing. You need to figure out what is the right amount of test from the OEM service manual, what does the OEM recommend that you do from a preventative maintenance standpoint. Each period, and we'll talk about periods here in a minute, whether that's once C or twice C or whatever you come up with.

But you need to test all modes of ventilation, test all points and ranges, use standardized test equipment so you get similar measurements between technicians, and also lock the test procedure. And what we mean by that is some kind of urging control that says "Everyone each year, unless there's a good reason to change it, ought to use the same test procedure so that you can assure that it's consistent period on period."

Yeah, and another thing to note is that you should start with international standards, even local standards, the OEM service manual, but you can always do more, right?

So that's what you have to meet to be compliant, but if you do more, you're lowering the risk in your hospital, you're increasing patient safety, there's nothing telling you that you shouldn't go above and beyond.

So depending on what your risk tolerance and your risk threshold is, you may want to even do more if you know that a specific component fails more often than others. Run a check on that, no one’s going to slap your risk for going above and beyond.

So when we talk about periodicity, we tend to follow the medical equipment quality assurance program developed by Tobey Clark and there's a book written about this, on medical advice QA. And what they talk about is awaiting and a score based on a number of criteria.

What's the patient contact, what's the physical risk, what's happened in your hospital as far as incidence that would drive the need for more testing or maybe even less perhaps. And then what do the manufacturers or the regulatory requirements specify and when you tally that up, you get basically a score.

When we did this in our exercise we came up with 17, which puts us in the semiannual or twice a year category. But each hospital should do this sort of independently to figure out, what's the right periodicity for testing in my hospital on this ventilator? And this is one of the ways that you can do that in a quantitative way.

Yeah, this is more of a very quantitative approach to it. I hope this opens your eyes to a different way to think of how often you should be testing, what your test frequency should be because it does take into consideration, not only the medical device, right? And how it's performing out in the market but your own hospital experience with it.

Like I said if there are some components that fail more often than others maybe you should check more often. But yeah, this is kind of a really good, overarching view of how to test frequency could be determined, rather than just following what the OEM service manual says. Sometimes it doesn't state it at all, so if you don't, if it's not stated, the test frequency, then you might as well start here and then kind of adjust going forward but this is a really good starting point.

So earlier we zoomed in on the anesthesia system and the ventilator and the vaporizer specifically, now we just want to zoom out just a little bit and depending on how your anesthesia machine is configured in your operating theater, there could be a lot more items that you need to test and that you should plan for testing both from the preventive maintenance schedule as well as what equipment you're bringing into the theater or if you're testing them outside of course too.

But you need to think about does it have a patient monitor attached, what parameters are on that patient monitor to make sure that you have the right testers for it. Is there SPO2, is there noninvasive blood pressure, is there capnography involved? You need to think about all those things that need to be tested beforehand so that you have the right equipment on hand.

Then there are all the different ventilator tests that need to be done and independent of all the anesthesia delivery, you have to know that the ventilator performs correctly to the manufacturer specification and then lastly, we talked about the vaporizer testing, in the yellow box, but there's also, you have to think about electrical safety and what periodicity that should be done. Electrical safety testing should not be overlooked as part of the PM.

Yeah, and electrical safety is kind of the foundation upon which all other testings should fall, right? If you don't pass electrical safety testing then you can't really trust the results you're getting on any of the other functional tests you're running. So you really want to make sure your device is electrically sound before you move onto any other testing.

Another thing to note is, in terms of ventilators those on and the flows we deal with on an anesthesia delivery system, they're a bit different than your run of the mill ventilators, so you might need specific functionality that's a bit different. So, specifically ultra-low flow and ultra-low pressure, it may be out of range of many ventilator or gas flow analyzers out there on the market so you want to make sure something reaches those ultra-low flows and ultra-low pressures. Especially when you think of how they're applied in this system. So that might be something that you should look out for. Yeah.

Okay. So when we talk about how to test vaporizer and what can go wrong in the vaporizer, you could, somehow, get the wrong agent of vaporizer. That's really tough to do that these days but it does happen.

You could have saturated wick, you could have a broke or faulty concentration control dial, or you could have the vaporizer system interlock could be broke. And again, these are very low occurrences but they're not that hard to check.

So some of the solutions that you may want to think about are can I detect agents in a mix, can I identify that agent in the gas supply without having to know which agent is in there.

Yeah and somethings to note on that, with the agent identification, sometimes depending on what device you're using you might have to tell it what to look for and you might get no results because it's not finding that agent. The vaporizer might be mix filled, right? Or nonoperational. So it might force you to go do some trouble shooting.

If you have something with automatic agent ID, it will tell you what it is seeing not what you're telling it to look for, so if it's mid filled, there's no need to power down and power it back up, it's really easy just to say, "Hey, I see now that I have one vaporizer turned on, but I'm displaying a different agent." And you immediately know something is wrong.

And another point to make on measuring two agents is, it will show you that. It will automatically tell you that two agents are being administered and if that doesn't go away over time, even with flushing the system, then you know that something's wrong.

Because there could be residual agent and that might be what you're seeing which would go away over time. But if it remains there, then you'll know it's likely an interlock failure and you'll have to dig a little bit deeper.

When you're thinking about what kind of gas flow test equipment you might want, you have to think through what is the test procedure and what testing needs to be done, like what we've been talking about.

So can I test all the parameters required by the manufacturer? How is easy is it to use and learn? Do you need to store data for retrieval or report? Is automation important to you? How portable does it need to be to work in your environment? What's your return on investment? Can it be used for all different kinds of gases?

Some equipment has been limited in what kinds of gases it can test. Can it test all the agents? Can it measure two agents in a mix and does it have automatic agent ID. These are somethings that we recommend you think about when you're thinking about your gas flow test equipment.

Yeah and if you want to think about it more general terms, how are you doing your job? Right? Are you moving between rooms at the hospital or are you moving between hospital sites, right? That's where something like portability might come into play.

Do you have a lot of new employees? Do they need something that's easy to use so they can get on the job quickly. Are you a hospital that kind of values reducing risk and increasing patient safety? Is that something that you guys really value? Confidence in your measurement results, right, metrology, how do we get around that?

And then, do your people have to carry a PC? Would it be nicer if you could get rid of that, right? One less thing to carry around and if you're traveling from hospital to hospital is it nice to be able to test all day on the go? Is it nice to have on board memory and the battery so that you can go out into the field for a full eight hours, come back at the end of the day and download all of your data. How you do your job is a huge aspect to the purchasing process here, so really let that be a guide for the tool that you need.

A little bit about the technology used to look at gases or agents in the flow. The main technology is infrared photo spectrometry, and the most common one is called non-dispersive, NDIR, which uses narrow band optical filters and that's pretty much the technology used throughout, not just test equipment but also the medical devices, so you're side stream sampling devices that are in line with the anesthesia machine are typically an NDIR technology as well.

And what we're looking for is when exposed to infrared light, what's the absorption of that infrared light and these different agents and that's how you can determine what agent you have in the mix.

Yeah, and you can see that these wavelengths are really bunched together so these sensors ar really sensitive to be able to filter out which agent is truly being administered.

So if you think about that, these are highly sensitive products that deserve highly sensitive testing, so, it's good to know how these things operate and how specific these things really are.

We're going to talk about best practices and how to test. I know some folks tend to use one of the medical devices to test the anesthesia machine and we really caution to think that through.

You can use a calibrated gas that has some X percent of accuracy. Then there's the accuracy of the medical device and then, there's the accuracy of the vaporizer and when you add that up and think about the metrology of that, you have really not a good flow path to knowing whether it's really good or whether it's really in spec.

So the better method is to go... if you just want to test the medical device, your side stream sample device, it's fine to use the calibrated gas but if you're going to test your vaporizer we recommend using an actual calibrated test instrument rather than the medical device to do that testing.

Yeah, and the reason why separating those out is so important is because those tolerances are additive, right? So, if you look at the diagram on the left, if you were to measure that vaporizer, your test accuracy is going to be X percent plus Y percent or in the other direction, minus X percent, minus Y percent.

So if you think of X being 1% and Y being 5%, that means that your tolerance is really plus or minus 6% there. So you really have to take all of those things into consideration and figure out, is that within spec? Is that within what my service manual truly wants me to measure?

And better way is to do it a bit more directly because any link you take out of this kind of uncertainty chain, we call it an uncertainty budget here, it reduces the tolerance of the entire system. So if you just do calibrated gas on the respiratory gas monitor, you have about 1% inaccuracy versus that plus or minus six in the other example.

So we'll spend just a moment talking about our equipment in particular and what we've done. We've release a couple of products in the last year and a half to test ventilation and anesthesia testing. And we really went out and talked to a lot of you and your compatriots and figuring out, how do you do the work and what's the best way to do the work in coordination with a lot of the OEMs. And we really looked through the different problems and how we can address, so if... I'll just highlight a few of them.

Our VT series has a single flow channel that will measure a very wide range of pressures and volumes. On our vaporizer tester, we've got auto agent ID and we can test in the mix and I'll show you some pictures of our equipment here in a moment.

Yeah, and a lot of this is just thinking about what jobs you're trying to do. So in general, yeah, you're testing each one of those functions but there are a lot of issues that we know you guys are having along the way.

So having that single high low flow channel that Andrew pointed out, helps get rid of some modules, right? Or the need to disconnect and reconnect as in our old product the VT plus. Being able to store your results and have that battery life allows you to have that on the go testing that I touched on a few slides ago.

Your work time, is always an issue, right? You want to be able to get to testing as quickly as you can so you do want to be cautious about how long that takes. And zeroing, right? How long do those sensors stay in spec, because you don't want to be changing things.

These are all issues that we heard from customers and we used to drive our product development process so we were cognizant of how much space we had when we went into developing a vaporizer tester.

So we wanted to make sure everything could fit on the bench, right? Or on the little service that pulls out. So we were cognizant of how big our vaporizer tester could be and we knew about all the things that could go wrong, so again, we're trying to solve all of these... make you, allow you to do all the jobs and allow you to have as few pain points as possible with products.

And that's kind of how we went through our product development process.

So very quickly, our auto line up of ventilator testers is the VT650 and the VT900A. VT900A works in conjunction with vapor and also adds ultra-low flow and ultra-low pressure over and above the VT650.

Yeah, so, again, if we touch on some of the features having that one, single flow channel is good. Efficiency, right? Testing quickly, right? There are a few of... you have a number of machines you have to test on a daily or yearly basis however you look at it and being able to reduce test set up by a significant amount of time is helpful.

So all of our analyzers have that and onboard memory, battery, and portability allow you to do that on the go testing. But for the anesthesia delivery system, we want to focus on the VT900A, one, it's compatible with our vaporizer tester, VAPOR, at the bottom. But it adds that ultra-low flow and ultra-low pressure to meet the needs of the anesthesia delivery system.

You can truly test everything because ranges, resolution and accuracy are all very important so that's going to give you that. On top of that it gives you an external trigger and some oxygen accuracy, so it's 1% instead of 2%, so again, it's just a better product that you're going to have increased confidence with and the ability to test the entire system.

VAPOR is the other part, so it's going to measure all five anesthetic agents, as well as CO2 and N2O concentration. Now, in the anesthesia delivery system used to say, carrier gasses are used and they are over administrable, so you need to make sure that you're not giving the patient too much of that because you can cause some unintended effects there as well. So you're truly testing everything in the system, if you use our VT900A and VAPOR.

Okay, so we'll start wrapping up by first say, thanks for joining us we really appreciate your time. You can find out more information on our website www.flukebiomedical.com, we also have free training through our Advantage Training Center on our website if you register, and you can connect with us on social media.