Anaesthesia

SPEAKER_02 1:25

It's great to have you on board. Thanks very much for joining us for DMET Ed. It's really great to have an eastern here to ask a few questions for the medical students. One of the first few questions I've asked us about is actually about preoperative assessment. What do you take on board when you go to assist a patient prior to an anesthesia?

SPEAKER_00 1:41

Well, like anything in medicine, it's done by history examination and investigation. Probably more so on the history. First thing we always ask is about previous anesthetics and have there been any problems? And the answer is no, usually no, but um it's so it's nice to know if they have had any specific issues before. Other things that are important to know are about other medical problems that the patient may have, so we take a full medical history, particularly with the cardiovascular and respiratory system, although any system is important. We like to know about what medications they're on, uh if there's any potential for interactions with the anesthesia or that might might pose problems for the surgery, and we like to know if they have any allergies that may or may not be specific to anesthesia. We also, for our examination, we do look at all systems, again, particularly the cardiovascular and respiratory system, but we do an assessment of the airway as well to see whether one, if there'd be an easy airway to manage uh and how easy they might be to put a tube into. Moving on to investigations, which, if they're fit and healthy, doesn't have to be done, but common things would be blood tests, uh, and then if they have any respiratory or cardiovascular issues, we might look for things like chest x-rays, pulmonary function tests, or echocardiograms, ECGs, those kind of things.

SPEAKER_02 3:12

What about fasting? How important is the fasting time for an anesthesia?

SPEAKER_00 3:18

Yeah, fasting is important. Um so generally we like patients to be fasted for six hours for food, uh, four hours for non-clear fluids, and two hours for clear fluids, so things like water. Uh, and the reason for this is we don't want patients to aspirate. So if they have an empty stomach, the risk of aspiration is is vastly reduced. We don't generally anesthetise patients who have a full stomach unless it's an emergency situation because there is a significant risk of aspiration.

SPEAKER_02 3:49

That's a good question for a medical student. So saying there's an emergency scenario, is there a way of giving an anesthesia safely in that situation?

SPEAKER_00 3:57

Oh yes, yes, there is. Uh so again, if if it cannot wait until the patient's fasted, uh, we would proceed with anesthesia. Um if we have to give them a general anesthetic, we would give we would provide anesthesia through a or induction through a rapid sequence induction. Um perhaps prior to that we would give an antacid, so uh something like sodium citrate to neutralize any acid that is sitting in the stomach. That doesn't make any difference to any any solid food that might be sitting there. Uh and then we'd pre-oxygenate them uh and and put on cricoid pressure and use drugs that will uh increase the speed at which anesthesia induction occurs so that we can get a tube in quickly and minimize the risk of aspiration.

SPEAKER_02 4:49

So, what does pre-oxygenation involve?

SPEAKER_00 4:51

So, preoxygenation, we do that really because uh the the body's reserves of oxygen are very small, there's very minimal oxygen stored in the blood. Most of your oxygen is stored in your lungs, so in your functional residual capacity. So when we're breathing air, as you know, air is uh mostly nitrogen, 70% nitrogen, and only 21% oxygen. Uh so uh what we want to do is wash out all the nitrogen and replace that with oxygen so that your functional residual capacity then is full of oxygen, and that that is then your reserve of oxygen while you're at NIEC or while we try and get the uh have the airway controlled. Um until we have the airway controlled, uh we've got a reserve of oxygen there so that they don't desaturate and and their oxygen sat, you know, they don't become hypoxic.

SPEAKER_02 5:49

Obviously, in a standard generator seizure, it can be broken down into different phases, I believe. I I believe it's induction, maintenance, and emergence. Are they the terms that you would use and what are the different stages involved and what medications would use involving in those stages?

SPEAKER_00 6:03

Medications uh are quite varied, um, and everyone uses slightly different things. But generally speaking, we would do inductions with an IV general anesthetic, something such as propotol or thiopentone. Um maintenance is once the case is underway, we keep the patient asleep, and that can be done with IV anesthetic agents, uh, again, such as propofol. But uh an alternative that a lot of people use are volatile anesthetics, and that's that's by inhalation, uh and that keeps the patient under anesthesia. Uh, and then emergence is really weight is when the patient you want them, the surgery is finished, and you want them to wake up at the end of it. Uh, and again, depending on what drugs you've used, you need those to come down, so the concentrations in the plasma to come down, and and therefore the concentrations in the brain to come down, so the patient will then wake up. So, for induction, we generally use uh an opiate because uh having uh an endotracheal tube put through your vocal cords is very stimulating. Uh, some proprafol to actually anaesthetise the patient and muscle relaxant to aid with intubation to relax the vocal cords. And then maintenance, uh you can either use IV proprafol or continue with a volatile anesthetic such as sebofluorane or desflorain, which is which is an inhalational anesthetic, and then as emergence you would wait for those to wear the effects of those to wear off and their plasma concentration to reduce. So if you're using a volatile anesthetic, that's uh the offset, you offset that by breathing the volatile anesthetic out. So, and then muscle relaxation is is used at the beginning of anesthesia and induction to aid with intubation, laryngoscopy intubation to relax the vocal cords. It may be required during surgery to relax muscles depending on what the surgery is. For instance, uh abdominal surgery, laparotomies, you will need the patient relaxed. Uh, sometimes uh depending where where the actual surgery is occurring, you don't necessarily need muscle relaxation. If you have used it for emergence, you either need to wait for the effects of that to have worn off, or to help to help those effects wear uh to help wear it off or to antagonize it, you can give a reversal agent as well to aid with that.

SPEAKER_02 8:33

Excellent. And with a uh anesthesia is done with a um inhalation, so people might be scared of needles and therefore the person's put off to sleep with some gas. What's done in that scenario?

SPEAKER_00 8:44

Is that the volatile anesthesia can can be used for induction of anesthesia? Um, we we'd call that a um yeah, volatile induction, and and with that we would and it's commonly used in children um because it's probably it's a bit more pleasant than having a needle stuck in in your arm. So with that, we get them to breathe through the mask on a closed circuit, uh, usually sieva fluorane, uh perhaps adding in some nitrous oxide, which is also another anaesthetic agent, they will breathe on that and that will get them anaesthetized, and then once they're anesthetized, we can put put an IV cannular in place and give any drugs IV that we need to.

SPEAKER_02 9:27

And what about the differences nowadays between laryngeur mass and intubation itself? Uh years ago it used to be purely intubation. Now I believe laryngeal masks have come on the scene and are quite popular.

SPEAKER_00 9:38

Yeah, so laryngeal masks were invented probably about 30, 20, 30 years ago. They're a super glossic device, uh, in that they sit above the vocal cords, uh, above the glossis, and they're they're not a secure airway in the same way that an endotroendracheal tube is. So an endotracheal tube uh is a tube that will go through the vocal cords. In modern anesthesia, we usually use a cuff, so that sits below the vocal cords, and that that seals seals the airway so that we can do positive pressure ventilation and it will prevent any aspiration or uh of any regurgitated stomach contents. A superglottic device doesn't have quite the same seal. Uh it sits above above the vocal cords. Uh, while you can uh give positive pressure ventilation through this, uh most of the time we'd use it with spontaneous ventilation. So it provides the patient airway, but it's not a secure airway and it doesn't protect from uh aspiration of regurgitated contents. However, the depth of anesthesia uh doesn't have to be as deep because it's not it's nowhere near as stimulating as have uh having an endrocheal tube put through your vocal cords.

SPEAKER_02 10:55

Well that means they can have a lighter anesthetic and they're not so nauseous when they wake up, I believe. Is that correct?

SPEAKER_00 11:00

Or uh possibly. I mean it it's you can perhaps run them a little bit lighter. Um you you don't need as much opiates at the beginning to to to stick it in, um and patients tolerate it uh very easily. Whereas if you have a patient with an endroche tube in place, it's very irritating, very stimulating, and they'll want it they'll want to take an active if they're too light.

SPEAKER_02 11:28

I'm always impressed by the number of uh monitoring you have on the uh anesthetic machines. There's so many different numbers appearing there, monitoring oxygen levels, there's so many different controls. What are the main things you're looking at on those monitoring devices?

SPEAKER_00 11:42

So the main thing is looking at monitoring the cardiovascular system, so that would be through ECG, pulse rate, and blood pressure, the respiratory system uh by measuring oxygen saturation, but also looking at gas analysis. So we can look at entidal carbon dioxide, which gives us an idea of the arterial carbon dioxide partial pressure. Uh, but as well as that, we can look at oxygen levels in the gases that were breathing in and out, and also the volatile anesthetic agents. We can measure again what they're breathing in and what they're breathing out. And what they're breathing out, once they've reached the steady state, gives us an approximation of the arterial concentration and therefore approximation of the brain concentration. Uh there they're the main things. Sorry, and we'd also and also with the respiratory system, we'd look at um we'd look at airway pressures and flow volume loops and those kinds of things to assess how how well we're ventilating the patient.

SPEAKER_02 12:40

Sometimes you need to um put an arterial line in as well. Is that because you want to get a slightly better level of uh oxygen oxygenation or is that uh for other reasons as well?

SPEAKER_00 12:50

Uh so the benefits of an arterial line are it gives you beat-to-beat blood pressure readings rather than if when you do a non-invasive blood pressure reading, you it's a cuff on the arm and you inflate that every three to five minutes, depending on what you want to do, and that just gives you a snapshot of what the blood pressure is at that point. The arterial line gives you a blood pressure reading on a beat-to-beat basis, and also tell you the pulse rate, and it can also give you an idea of whether the patient's adequately filled with fluid. Um, we can look at the variation in the in the blood pressure on the on the arterial line. Plus, it gives us access to arterial blood, which we can use for sampling to look at oxygenation and other gas levels and do a blood gas from.

SPEAKER_02 13:36

What about the airway maintenance? If you're um during the during the process, how do you check if something plays up on the uh laryngeal mask or the intubation? Is there anything you can you're watching for?

SPEAKER_00 13:47

So I guess with so with a laryngeal mask, there's a couple of things we can watch. You've got the circuits, and if they're breathing spontaneously, you can you can look at the bag, um that which is just a reservoir bag on the end, and that will inflate and deflate as a patient breathes in and out in inspiration and expiration. Uh, you can look at airway pressures, which is uh so as they breathe in, they'll have a negative pressure, and as they breathe out, they'll have a slightly positive pressure. If you then go on to positive pressure ventilation, the airway pressures are more probably more important. You can look at peak pressures and you can look to see whether there's um uh whether it's high press, you know, particularly high pressures, which might suggest that you haven't got a patent airway for whatever reason with a with a laryngeal mask, or you can look for a leak. Um so if you're on low flows and you're not getting enough uh new gas going into the circuit, the the bellows from the ventilator will will start to drop, and you'll have to either turn the flows up or stop the leak, ideally stop the leak. If you've got an endrocheal tube in place, um which again is a definitive airway, you can look at the airway pressures and normally they'll go up during inspiration and then they'll come back down again in expiration. If they're particularly high, again, you need to look for a problem as to why that might be.

SPEAKER_02 15:12

So, therefore, there's a number of ways of keeping an idea of how well the uh patient remains intubated or how well the laryngeal mask is uh is inflated. Uh really the um other thing is what about complications of anesthesia? Are there anything important we need the medical student needs to be aware of? I've learned about malignant hypoporexia, which I believe is relates to a lot of to family history or previous knowing that patients have previous anesthesia is a good sign. Any other factors about that and what is the importance of malignant hypoporexia, i.e., how is how common is it?

SPEAKER_00 15:41

So mal malignant hypoporexia is is a serious complication of anesthesia. It's it's pretty rare though. Um it is a it's a pharmacogenetic disorder of calcium homeostasis of skeletal muscle. Uh so it is it is inherited, and these days it's quite common that you'll get some sort of history. You'll you should be able to pick it up in the history, um, either from a family member having had a problem or the patient themselves having had a problem. But generally, they're all if if a patient's had a test, the rest of the family will get tested to see if they have it as well. It's what it's triggered by certain anesthetic agents, uh, suxmaphonium, which is a muscle relaxant, which isn't as commonly used as it used to be, uh, and volatile anesthetics. So any of those can trigger it and it can come on quite quickly, but it can also have a very slow onset, and I've I've heard it can even you know come on a day or two after anesthesia. However, uh it would usually come on over a period of about 30 to 60 minutes, and what we would see with that is a high tech it's a hypermetabolic state, and you would see high temperatures, uh high CO2 production, acidosis, and you may get some it's a disorder of muscle, so you may get massive spasm, which is where the the muscle um at the jaw can can get can can go spastic, um, and if left untreated, muscle starts to break down and the patient gets a metabolic acidosis and gets very sick and it is life-threatening. Sorry, it is very rare and it can be treated, so uh the uh the main thing is to remove the trigger, so a move to a volatile-free anesthesia, so that would be a propriet. Um, it this is if it occurs, and the treatment is dantropyline, which is a drug that um will reverse the effects of the MH. Uh and the patient will need to go to IS remain intubated and go to ICU, they may need to be actively cooled and and all supportive measures to um until until the dantrolene has its effect and the the process is turned off.

SPEAKER_02 17:59

So it's true, it's prevent it's treatable, it's also preventable if you're aware of it.

SPEAKER_00 18:03

Um so if you're aware of it, or if the patient is at risk of it, either they've had it before their confirmed case, or there's a suspicion you would give a an an MH free anesthesia. So you just don't give volatile anesthetics and you don't use succinatonium. All other drugs are safe.

SPEAKER_02 18:21

Other questions the medical students have put in put towards you about how do you about actually the process of intubation? They're obviously wary of how they learn it. It's one of those processes they're always uh keen to learn, but it's obviously it's a quite a good technical exercise. What are the different steps you take take in the process of putting a lunch or mask in or intubation? What are the actual uh step-by-step processes you do?

SPEAKER_00 18:43

Okay, well, look, we'll we'll talk about intubation. So, first you do it you do it as safe as you possibly can, and you plan all these steps beforehand. So I was you always have an anastomic nurse assisting you. Um, you have all your equipment ready and you have all your drugs ready, and then it's uh and it's something that we're familiar with and we do over and over again, and we would use the same steps each time. So it would start off by getting IV access in the patients, uh, ideally unless unless it's a child, but we'll assume it's an adult and we've got IV access. Put all our monitoring on uh and then we would preoxygenate the patient. As we said, the preoxygenating provides a reserve of oxygen in the body, uh in the lungs. So once it adequately preoxygenated, uh, which is which is generally either three large tidal volume breaths or um uh a number of doing it for a couple of preoxygenating for a couple of minutes or waiting until the FIO2, expired FIO2, um sorry, expired oxygen is about 70%. Once that's happened, we would then give the drugs, which normally I'd use a combination. So I would give some adazalam, some fentanyl, some propofol, followed by a muscle relaxant such as rock uranium. That depending on what dose you give, that will take about 90 seconds to work. So that point, just you'll ventilate the patient with the just a handheld bag with a bag, a mask, and turn the valve so you can generate some pressure with the bag. So you're ventilating the patient, may or may not turn on some volatile anesthetic at this time to keep them asleep. Um, and then once the muscle relaxants had its effect, we'll get the maringoscope out, which will be prepared at the side. The anesthetic nurse will hand it to you, and you'll visualize hopefully visualise the vocal cords, and then you'll take your endotrachyl tube and pass that through the vocal cords, inflate the cuff, and then connect the patient back up to the circuit and confirm that the tube is in the right place. And to do that, there's a number you can look for fogging of the tube, which is the water vapor coming out of the lungs. You can feel the compliance of the lungs with the bag as you hand ventilate. But the definitive thing is looking for carbon dioxide on your gas analyzer. If it's in this if it's in the esophagus, you won't get carbon dioxide. But if it's in the trachea, you will get carbon dioxide. The other thing you can do is oscultate both lungs to make sure that you haven't gone down the right main bronchus. Um, and once you've done all that, you'll tie in the tube and then you can um pop them on the ventilator and give them volatile anesthesia, oxygen, some air, and proceed with surgery.

SPEAKER_02 21:33

You've covered a lot a lot of ground so far. I've got one more final question for you, and we really appreciate the excellent uh information. The final question is actually the the reverse of all this. What about the process of exturbation? What are the steps you do to prevent a um an aspiration or reduce the chance of that?

SPEAKER_00 21:50

Again, it depend in elective surgery, you would hope that the patient is well well, the patient wouldn't have proceeded unless the patient was well fasted, so they should be relatively low. Aspiration risk. However, if it's emergency surgery and you're assuming a full stomach, they are still at risk of regurgitation and aspiration. So for exturbation to occur safely, you need the drugs that you've given to warn off so that the patient starts to wake up. You need them to be breathing spontaneously and they need to be and they need to be capable of maintaining their own airway. So we can aid that by turning off, if we're using volatile anesthesia, we turn off the volatile, turn up the flows, and the idea is they then breathe out the volatile anesthesia that's on board. And it's a slow process that will hang around for probably a few hours afterwards in very low levels, but they blow it off quite quickly. If they've got muscle relaxation on board, we either have to wait for that to wear off or give a drug that will aid in reversing that. So commonly we would use something like neostigmine combined with either atropine or glycopylate. That that increases the level of acetylcholine at the neuromuscular junction. Or if we've used a muscle relaxant such as rock uranium or vecuronium, we can use a drug called Segamodex, which specifically targets those drugs and sort of mops them out of the circulation and therefore added uh neuromuscular junction and and reverses their action. Uh there's the patient will need to have a patient capable of having a patient airway. So once once they're breathing spontaneously on the tube, open their eyes and showing some signs that they're a bit more awake, we'll take the tube out. But I guess at all those times and we'll also suction before we take the tube out, we'll suction their airway, and that's mainly to get rid of risk secretions, things like saliva that um they can also aspirate on. Um and but if we're if we're very concerned that they're sort of a full stomach, we can sit them up a little bit or turn them on their side, um, so that if anything does come out, it it will fall out of their mouth um onto the onto the pillow um rather than going down into their lungs. But if we're very concerned, you could just keep the patient asleep and send them to the intensive care unit. Um, but obviously at some point you're gonna have to take the tube out.

SPEAKER_02 24:27

Well, look, you've uh you've covered so much ground. I hope this the medical students find this brilliant and uh as I have today. It's been well w I appreciated a lot. And uh thanks again, Nick, for coming on the show.

SPEAKER_01 24:42

Um hopefully they can uh say something from this.

SPEAKER_02 24:46

The information provided to you today is designed to complement the information provided to you in your local region and to supplement your readings and teachings in that area. Please don't take it as the only way of creating this condition or setting it condition. Please be aware that medical device designed to be a core medical condition. Thank you very much for listening to our podcast at Medical Education or Media. Feel free to give me this information and I'd like any further feedback or questions directed towards me or towards gavin at medhearted.com.au. Any questions on a particular area of medicine will be directed towards a special summer area or make it as a part of our podcast for next time. Look forward to hearing from you. And once again, we look forward to the next time you might listen. Thank you once again.