Transcription
Hi, I got four Justine Lee, and I'm super excited to be able to do this video with Rachel Bassett, who's a certified veterinary technician and a BTS in anesthesia. So you're probably wondering what that is: she's a veterinary technician specialist in the academy of veterinary technician anesthetist, and she's actually our lead technician and our specialty team lead here at Animal Emergency and Referral Center. And today she's going to be teaching us the difference between non-rebreathing and rebreathing circuits.
Thank you so much for doing this video today.
Thank you for inviting me to do it. I'm excited to share knowledge with you guys and get up to speed on the ICS machine. Awesome. So anesthesia machines are super scary to people who aren't familiar with them, and so what we wanted to do is just do a casual review of an anesthesia machine. And I just hope that you could just walk us through how to hook it up. If we don't feel comfortable, if you could just walk us through what to do, what the Popoff valve is, what these tubes are, and how to hook them up.
Absolutely. It is very intimidating; lots of cords, lots of tubes, everything coming off of here can be really scary to the anesthetist. The biggest tip that I can give to everybody is find a system that works for you and keep it the same. Be habitual. Find a routine and set it up the same way every time. You're going to avoid a lot of mistakes; you're going to find problems before you get started. And the best way to do that is to follow the flow of the oxygen through the machine all the way to your patient and back out. That's going to help you identify any problem areas.
In general, our oxygen supply source is going to come from either a small tank attached to your machine or a large tank of compressed oxygen in the back of your facility that's plumbed in through piping to a ceiling drop, for example. We have here that oxygen supply is going to travel down in this machine to the very back. So follow your tubing; it's going to connect up here to this little black box. We spin that around; you'll see here this is our oxygen flow meter. The oxygen flow meter is going to allow us to convert the high-pressure compressed oxygen coming out of the tank at about 2200 PSI down to about 50 PSI and then into the flow meter, the opportunity for us to control the actual amount that we're delivering to the patient. And it's helpful because because it's color-coordinated; its color-coordinated oxygen is green universally all across the world. The first step with this is checking to make sure your tank is on, checking to make sure your oxygen line is hooked up properly, and then also touching, you know, testing the flow meter valve; make sure that the knob is working properly. A good tip for everybody: when the ball returns to zero, don't overtighten this knob. They're very easily overtightened and stripped, and the next guy will have a very, very hard time trying to get this to work.
On the back of the anesthesia flow meter, you'll find another tube coming back out. If we follow that down, it's going to connect up here to the side of our vaporizer. So the vaporizer is liquid anesthetic that is being converted into a gas, and the gas needs to be carried to our patient. And so this tube that's connecting to the side of our vaporizer is providing our fresh oxygen flow through the vaporizer, picking up our inhaled gas and sending it along. Tips on the on vaporizer are to check the window before you start; make sure you have enough inhalant in there. It should be between the two guidelines, or ideally at the top. When filling your vaporizer, it's important to check the well. Some vaporizers have a well situation where you'll pour the inhalant in, and in other cases you'll have a key that situation where you'll put a little adapter, and to prevent any spills. If during this process you're noticing any kind of liquid anesthetic dropping or spilling from here, check that post in the middle; this is the post to drain the vaporizer, so you want to make sure that that's tightened and properly functional so we don't drain that. Other considerations are the vaporizer are that if they are tipped over or shaken or crashed into, it can alter the delivery of the anesthetic or change the concentration. So it's important if you suspect any kind of damage or trauma to your vaporizer that you completely drain it, either by running it with oxygen to a scavenge system until the vaporizers empty or draining it from the drain valve. But when in doubt, always give it up.
Right. Exactly. If you're transporting anything like that, you should consider emptying the vaporizer. You want to verify that your dial is working properly, turning that on or off. The other thing to consider within this system is not only is there oxygen flowing into the vaporizer, you'll see that we have another tube coming off of the oxygen flow meter around the side, and this is going right up to a common gas outlet. This little silver button many of you know is the oxygen flush valve. The oxygen flush valve is going to provide high PSI air, depending on your machine, anywhere between 30 to 50, even up to 70 liters per minute coming out of your system. The thing to know about the oxygen flush valve: because it's providing just fresh oxygen from your system, it's in fact bypassing your vaporizer. We also like to call it the wake-up valve. So we want to make sure that if you're using that to remember the high velocity of oxygen that's coming out and consider not hooking up to your patient while you're filling the system with fresh oxygen; it's it's just a high risk of barotrauma. And then also to consider that you're not actually picking up any inhalants when using that.
Following that, it's going to exit the vaporizer; we're going to follow this tube here; it's going to come up to what we call a common gas outlet, so it can either be located on the side of your machine or, depending on your system, a little bit higher up the line. This is going to follow up to what's labeled on most machines is our inhalation valve. You'll notice on our machine we're set up for a rebreathing system. In the rebreathing system or circuit, we're going to be utilizing two valves; they're called unidirectional valves: inhalation, exhalation. On inhalation, the patient is going to be breathing in fresh gas that's a combination of our oxygen and our inhalant. That fresh gas is going to flow down your breathing system to your patient, and on exhalation, the patient is going to breathe back oxygen, waste oxygen and set at gas and CO2. That is going to enter your exhalation valve, and within these unidirectional valves, we have little—they're called flutter valves—is kind of the general term for them. Important to know with the flutter valves is the the little disks inside are controlled by the patient's breath and the exertion of their breath. If condensation develops, especially in the exhalation side, these flutter valves can get stuck open, so it's really important to visually inspect those while you're setting up your machine and make sure that everything is tight. It also is a source of anesthetic leak.
Following the exhalation into this flutter valve, it's going to recycle some of this inhalant or waste anesthetic gas into our soda lime canister or CO2 absorber. The soda lime or CO2 absorbent is going to remove or neutralize acid basically and create a base from our exhaled CO2 so that it can be recycled back to the patient. Something to consider with the soda lime canister is that the soda lime won't last forever. So we need to—machines are a little bit different—but you're going to remove the lid to your soda lime canister, take the canister out, and you're going to visually inspect the granules and also manually inspect them. Reach your fingertips a few inches, grab up some granules, and try to crush them. They should crumble easily; this means that it's still able to absorb CO2. If they're really hard and don't crumble well, it's time to change it. Another guideline is manufacturers will make these last for eight hours, and so some clinics will find it helpful to have a little manual or little form on the side of their machine, and they can log the start of anesthesia, the end of anesthesia, and then dispose of this once it's been exposed for eight hours. So usually a lot of people will look for the purple coloration.
If it translated purple with semi—that's a really good question—the manufacturers are have created a setup where these will turn purple when they're exposed to CO2; that means those granules are specifically exhausted. In fact, if you watch your machine, I'm following anesthesia, the granules will turn back to white. So really, getting a manual inspection or doing a timed evaluation of the exposure is more helpful, so that can be misleading.
Correct. Correct. And even exhausted granules may turn back to white even though they are completely exhausted. So we've evaluated our soda lime or our CO2 absorbent for efficacy to remove the CO2 from our patient. You're also going to notice within this setup there's a manometer, a pressure manometer. So anytime that we're going to manually give our patient a breath, we're going to see that positive pressure inspiration. Additionally, behind the exhalation valve, you're going to see a Popoff valve, also known as an APL valve or adjustable pressure limiting valve. Everyone is very nervous about these; you know, they they can certainly cause serious damage to your patient. It's important to check the function of it before your procedure and also understand how it works. In this situation, it is is hooked up to a scavenge system. The scavenge system is going to remove waste anesthetic gas that does not go into the CO2 absorbent and become rebreathed. With the Popoff valve, it's always staying open so that way anesthetic gas can travel out our scavenge tubing, and if you'll follow, it will travel up to our scavenge in the ceiling. Scavengers come in several different systems, and we return to the Popoff valve in a minute. Our scavenge system on the back of our machine here is set up in such a way that looks really confusing. What's important to know about these systems is that there are several: we have passive scavenge or active scavenge. An example of a passive scavenge is a charcoal canister. The charcoal in this system is going to absorb waste anesthetic gas up to a certain point; it will need to be disposed of and replaced. There's no actual suction or vacuum creating a hole to this canister; it's just strictly passive. With a charcoal canister, it's important to use the the scale on the back; these should be weighed ideally weekly and replaced after they've gained 50 grams of waste anesthetic gas, if you will. The second type of scavenge is active scavenge. Most hospitals are set up with a vacuum system or a ventilation system in an active form, which we have here. They're the the exterior of the building is set up with a compressor to draw air out of our system or out of this ventilation system. The reason for this unique setup here is that the vacuum may be so strong that it may actually hurt our patient or create too much vacuum. This is set up as a what we'd like to call a yoke. What's happening here is our waste anesthetic gas is traveling into this, for lack of a better word, in this example, another reservoir bag, and as other to which needs to remain open to room air is sucking in room air and equalizing the pressure. So this is known as an atmosphere-equalizing setup, and that equalized pressure will draw in room air and push the waste anesthetic gas up to our scavenge in the ceiling and then out to the exterior of our building. It's really important to make sure that this is not being recirculated back into a ventilation system in the hospital. This is probably one of the most confusing things to folks as they're setting up their machine, but very important to leave this to open to air to equalize that. If we don't, and we don't have this option and we were just directly suctioning through our scavenge, are we would notice that our reservoir bag on our breathing system would become collapsed, and it would be difficult for our patient to maintain a good anesthetic depth.
Back to the top of the scavenge system, we talked briefly about the APL valve or the Popoff valve. So the APL valve nearly always stays open unless we're giving a manual breath. Certainly the process would be to close the valve, squeeze our bag, and deliver a breath to our patient. It's really important to open that when we're done because it's going to continue to increase positive pressure, and the patient will not be able to exhale, and it could result in serious trauma. Some machines are outfitted with a little easy button; you can push this in, deliver a breath, and let go. This is another safety measure to make sure that we don't accidentally leave it closed. The tip I like to give everybody is whenever you're giving a breath to your patient, close that Popoff valve, give your patient a breath, but never take your hand off of it; that way you remember to reopen it again.
Except when I went to vet school, they didn't have these, so it's nice.
It's just yeah, to press down, give a breath.
Yeah, a lot of new machines are coming out with those; they're really handy, and even some of the rebreathing systems have that function as well, so super handy. So following the scavenge system, we talked about our scavenge going up to our waste anesthetic gas and beyond. What we didn't touch on is our unilateral—are unidirectional valves and how they function with our patient. We believe that our machine is set up correctly at this point. We've checked everything; we've checked all the connections, screwed all the knobs on, make sure everything is correct. The ox—the anesthesia machine is set up in three parts: the compressed air that we talked about, the machine itself, and then thirdly the breathing circuit. Every patient will require a different breathing circuit, which we can talk about in a later video. Today we're going to be utilizing the unit—the unidirectional valve, also known as the rebreathing system. In this case, we need to choose a reservoir bag appropriate for our patient and place that on our machine. We want to make sure it's tightly fitting; make sure there's no source for any cracks or leaks. Something to note: they do, you know, take on a lot of wear and tear; it's easy for them to create holes along the sides here just from repeated removing and replacing.
How do you pick the perfect size?
Excellent question. There's a calculation; it's based on our patient's tidal volume. So tidal volume is about 10 to 20 mils per kilo, and then we multiply that by six, and whenever in doubt, round up. It's always easier—a little bit more wasteful—to have a larger bag. This bag, for example, I believe is a two-liter bag, so it'll stay right there. So literally calculate their tidal volume: 10 to 20 mils per kilo times six, and that's an exercise for you.
Yep. Our breathing system today—we can talk about these in a little bit more detail—this is an F circuit, also a rebreathing system. You'll notice that most of your systems they're going to have inspiratory or expiratory or both labeled, not only on the directional valves but also on the breathing circuit. This one, for example, is labeling inspiratory. The way you know that this is inspiratory if it's not labeled is remember when your patient's taking a breath, they need to have fresh gas and inhalants delivered to them. So if we followed up our fresh gas flow behind off of our ventilator back up to these unidirectional valves, I can determine this is my inspiration valve or inhalation valve, so I'm going to place that on there, and then usually located either near your reservoir bag or your Popoff, that's going to be your expiratory valve. If they're not labeled on your machine, you want to make sure those are placed on tightly so there isn't a source of leak. It's always good practice to go ahead and visually inspect the breathing system for any cracks or tubes. They get run over by, you know, wheels and stepped on by folks or dropped on the floor—easy source for cracks or holes.
So what happens if you hook it up the wrong way?
The way you would know very quickly because your patient would not stay asleep; you wouldn't be able to deliver fresh gas to them as efficiently or quickly, and so they probably will wake up on you.
Okay, so can you follow the gas from here through these tubes?
Absolutely. So we talked about it coming off of our vaporizer after it's picked up oxygen and now created gas inhaling, so fresh gas coming up the back of the line into our inhalation flutter valve, it's traveling down this center tube. So in an F circuit, it's basically a still a circle system, but there's two tubes around each other, and we'll talk about the purpose of that in a minute, but the the middle tube is providing the fresh gas flow to our patient and exiting the end of the breathing system. The patient takes a breath; they exhale, and the waste anesthetic or exhaled gases are going to exit around the green inner tube in this example, around the outside. This is going to run through the back of this outside tube and down into our expiratory valve, and when the patient exhales, it's going to draw that flutter open and allow that wasted anesthetic gas to either come down into our soda lime canister to have the CO2 absorbed and rebreathed back into the system, or some of that will go out the scavenge. All right, a small portion of that is also going to—the inhaled gases are going to go in your reservoir bag so that when you need to, you can close your Popoff valve, deliver a breath to your patient, and release. Right. The purpose of this system, having the tube inside the tube, is that the exhaled gases, the warm air, the humidity is going to warm the compressed cold oxygen and inhalant being delivered to your patient, so it keeps them warmer.
To perform the leak check before we get started is to occlude the end of our breathing system. We've ensured everything is correctly hooked up; we're going to close our Popoff valve. In a rebreathing system, we can utilize the flush valve to fill our system. Something to note: when you follow the tubing back here behind our oxygen flush valve is that it will bypass a rebreathing system as well. So on flush valves will work to fill your system for rebreathing but not rebreathing are not non-rebreather. In a non-rebreathing system, we'll turn on our oxygen to fill the system. So I've covered my system; we're going to help—go ahead and push our oxygen flush out, and look—some—able of it. Looks like one of our connections wasn't on tight. We want to make sure that connection to our inhalant is proper—very quick fix, hopefully. We'll try this again. So oxygen flush valve, we're going to take some small bursts; we're going to inflate our reservoir bag. Ideally we shouldn't be giving a patient a breath over 20 centimeters of water, so it's always good to fill beyond that. I usually recommend going up to 30, or beyond.
Yep. On your manometer—I'm going to continue pressure on this—my oxygen is off, so I have nothing continuing to fill this system; it's just pressurized to this—in this example, 40 centimeters of water. I'm going to hold this for just a few minutes or a few seconds and watch my manometer; I want to make sure that nothing—the needle isn't dropping, which could signal a source of a leak somewhere. And you're again you're doing this just with your finger, not with the patient on the correct.
Yeah, this is just our setup. Once I've confirmed that manometer is not changing, it doesn't appear to be a leak; I'm going to continue to hold the pressure on my rebreathing system and open my Popoff valve. The reason for this: there's always anesthetic gas in this system; I don't want to puff it in my face or my co-workers' face. In addition, there's now waste anesthetic gas in this reservoir bag. He's good practice before you release your finger to just squeeze all that out your scavenge; that's what it's there for. Another important reason to not take your finger off of this breathing system until you relieve the pressure—and I've seen this happen—is in rare cases the seal of the exhalation valve, if you release that pressure quickly, can open it with such a force that soda lime can be sucked up into the valve and cause an occlusion. I have seen that before, and it can be really dangerous to your patient.
So it should use a Popoff?
Correct. Correct. So we've now concluded that this rebreathing system is all set up and ready to use for our patient. All right, so if you've performed your leak test and you are finding a leak—near manometer is not holding pressure—we need to identify where the leak might be. The simplest way that I've been trained is to close your Popoff valve, increase pressure in your system again, so use your oxygen flush valve in this case to inflate back up to 30, 40, even higher pressure if that's helpful to you, and then find a soapy solution in your clinic. We use UltraCare disinfectant. I'm going to shake this bottle, make it real foamy; I'm going to spray it over areas of my machine that I think could be a source of a leak while I continue to hold pressure in the system. This will help show me bubbles or sources of air that is escaping from the system. Special areas to consider are around the attachment of your reservoir bag, the reservoir bag itself, the flutter valves, the attachment for your inspiration and exhalation on your unidirectional system, around your soda lime canister. These O-rings can become cracked or old or be misplaced or malaligned; those are probably the largest sources of a leak in your system, and hopefully that will help you identify and quickly correct any leak in your system and also give you some time to clean it up.
Thank you so much, Rachel; that was super helpful. So again, if you're nervous about doing anesthesia, great review pointed out—go to our YouTube channel for neck girl and get some more educational video content there. Thank you again.
You're welcome.