Episode 340: Keywords Part 35: Respiratory Physiology

[SPEAKER_01]: Hello and welcome back to ACRAC. [SPEAKER_01]: I'm Jed Wolpa and I am thrilled to have back with me today the one and only Dr. Tim Kaiser Torah for another ACRAC keyword episode. [SPEAKER_01]: We're going to talk about respiratory physiology today, which is a highly tested topic. [SPEAKER_01]: And I am excited to review it.

[SPEAKER_01]: Tim, welcome back to the show. [SPEAKER_02]: Thanks so much for having me as always, and first things first, it's going to be a little bit of review time. [SPEAKER_01]: Fabulous? [SPEAKER_02]: Question 1. [SPEAKER_02]: Which of the following is the most common peripheral nerve injury associated with general anesthesia?

[SPEAKER_02]: A, owner nerve B, median nerve or C, common perennial nerve. [SPEAKER_01]: All right, well, we did talk about this in a prior episode, hence the review, and I think that the common mistake here is to say common peronial or peronial nerve because it can be injured as we talked about in stirrups, but the most common peronial injury is the owner nerve as it is unprotected in the owner groove there in the arm and so that's going to be your answer here.

[SPEAKER_02]: That's correct, and yeah, it's, I thought it was a good one to review, but it's one of those things you just have to know, no real way to reason or way into that answer. [SPEAKER_02]: Question two, a patient in the post anesthesia care unit with a normal VTE, VD, VT ratio of 30%, suffers from a pulmonary embolism with an increase of their VD, VT ratio to 60%.

[SPEAKER_02]: To maintain constant alveolar ventilation, the patient will compensate by doing which of a following. [SPEAKER_02]: A, decrease their type of volumes. [SPEAKER_02]: B, increase their respiratory rate, or C, maintain their current title line. [SPEAKER_01]: Right, so this is going back to our episode that included pulmonary embolus and you now have more dead space because of the pulmonary embolus.

[SPEAKER_01]: And so if you have more dead space, but you still want to exchange the same amount of gas. [SPEAKER_01]: You have to increase your minivanolation. [SPEAKER_01]: And so the answer that does that here is increase your respiratory rate. [SPEAKER_01]: So that's what you're going to do. [SPEAKER_02]: That is perfect and that's a great explanation of a little bit of what we'll see when we talk about that space later since we are in the respiratory physiology section of the keywords today.

[SPEAKER_00]: Nice to see you again, I like it. [SPEAKER_02]: Question 3, which of a following is least likely to be a good candidate for surgery at an ambulatory center? [SPEAKER_02]: A, an 86-year-old male with high blood pressure undergoing a cystoscopy. [SPEAKER_02]: B, a 55-year-old female status post-liver transplant one year ago under a going cataract surgery or C, a 47-year-old female with CAD status post-drug-looting statement two months ago undergoing an eventual hermene repair.

[SPEAKER_01]: All right, so they're trying to get you here with the 86 year old, making you think a old person, high blood pressure, that's scary, but assistoscopy is a very low intensity surgery, and there's not a lot going on there with just some high blood pressure. [SPEAKER_01]: But that 47 year old though, young had a drug looting stench just two months ago, and that is going to for sure, I mean, she's not a good candidate for an ambulatory center.

[SPEAKER_02]: Yep, and as a reminder, they're not in another tested thing. [SPEAKER_02]: It's just sort of how long do you wait after stint placement and for a drug-looting stint out, be six months before you would consider surgery, even if it is minor like that. [SPEAKER_00]: Absolutely, especially if it's elective.

[SPEAKER_02]: For a middle-aged male returns for the next session of ongoing outpatient electro-convulsive therapy, his home medications include Metroprole, Larazepan, and Occasional is Cinnamon FM, which he took this morning, which medication should be administered before inducing a seizure. [SPEAKER_02]: A and C-docestine, B-clucygon, or C-flumatinal.

[SPEAKER_01]: All right, so hopefully it's pretty clear that Larazapam is an benzodiazepine that is an anti-epileptic. [SPEAKER_01]: And so if you've got that on board, it's going to make it hard to induce a seizure. [SPEAKER_01]: So reversing that is going to make it more likely and that's what you want for ECT.

[SPEAKER_01]: So fullumazonella is the reversal for Larazapam and that should be the answer. [SPEAKER_01]: Perfect. [SPEAKER_02]: And now we'll happen to today's topic, which is respiratory physiology. [SPEAKER_02]: This appears in both of the basic and advanced outlines, though the coverage is much more broad in the basic outline, just a little bit in the advanced.

[SPEAKER_02]: These sessions fill out a lot of detailed sub-topics you need to know, and though I usually read the outline and so I'll only frame from reading it for a bit of a today, but in some granularity, [SPEAKER_02]: This is a section one basic outline, see organ-based clinical, the organ-based advanced clinical to respiratory system.

[SPEAKER_02]: We have a physiology, one functions in cellular processes, and this is where everything fits. [SPEAKER_02]: One is one volume, such as static and dynamic volumes in dead space. [SPEAKER_02]: Two is one mechanic, such as static and dynamic compliance, and surfactant, and the plus law. [SPEAKER_02]: in relation to profusion, that's where distribution of ventilation and west-owned sit.

[SPEAKER_02]: for its diffusion with apeningoxygenation and diffusion hypoxia. [SPEAKER_02]: Five is blood gas with O2 transport, CO2 transport, the borothect, halden effect, systemic effect of hypercarbia, hypocarbia, hyperoxia, and hypoxemia. [SPEAKER_02]: Six is control of ventilation. [SPEAKER_02]: Seven is non-reciatory functions of a lung including metabolic and immune functions, and then eight is perioperative smoking.

[SPEAKER_02]: Like I said, this basic section is really long. [SPEAKER_02]: The advanced section is much shorter, it sits in a very similar area, but the only thing they define within physiology is ventilation and profusion, and they have some advanced topics within that. [SPEAKER_02]: So we're going to hit on the highly tested aspects of most of that today.

[SPEAKER_02]: So one of those places in Outline where there's a ton of content, but relatively fewer things that get tested. [SPEAKER_02]: The things I get tested get tested often, but they don't test all of these things. [SPEAKER_02]: And there's some overlap with other portions of Outline. [SPEAKER_02]: For instance, we'll skip basic interpretation of our two-wheel blood gas today, since that's better covered in biochemistry.

[SPEAKER_02]: The control of ventilation, I feel like we covered well enough when we talked about central nervous and peripheral nervous system anatomy. [SPEAKER_02]: So we'll skip that. [SPEAKER_02]: And I've grouped the rest into sessions with similar themes. [SPEAKER_02]: I mean, to get started. [SPEAKER_02]: Ready, let's do it.

[SPEAKER_02]: All right, section one is going to be lung volumes, capacity, and dead space. [SPEAKER_02]: The four one volumes are Hydoin spritory reserve, expertise reserve, and residual, and they don't overlap. [SPEAKER_02]: And a capacity is just two or more of those added together. [SPEAKER_02]: Vital capacity is everything you can move from a maximal inspiration to maximal expiration.

[SPEAKER_02]: Functional residual capacity, which is your expertory reserve volume, and [SPEAKER_02]: uh... residual volume is the gas left after a normal passive exhale and serves as the oxygen reservoir during apnea residual volume and your FRC can't be measured by spirometry if they need body plethora or gas dilution and that space is ventilation that doesn't exchange gas it comes in three flavors anatomically conducting airways of the older if the [SPEAKER_02]: So that's sort of your basic foundational in the challenge that you need for those topics in a couple of key concepts.

[SPEAKER_02]: The first one about FRC and closing capacity, vital capacity is roughly 6670 ml per kilogram around five liters for a normal size human adult. [SPEAKER_02]: FRC falls with induction with supine positioning with obesity and with pregnancy. [SPEAKER_02]: And when it drops below closing capacity, small airways start to close during tidal breathing and you get shunt and hypoxia as a result of that.

[SPEAKER_02]: Aging raises the closing capacity in pregnancy lowers FRC while closing capacity stays put during pregnancy. [SPEAKER_01]: And I'll just add that that vital capacity, number, 60, 70 in most per kilo is not total body weight, because you can imagine if you've ever seen a CT scan of a patient with a BMI, let's say, a 70.

[SPEAKER_01]: There's normal looking lungs. [SPEAKER_01]: The same size is a patient with a BMI of 25. [SPEAKER_01]: And then all this soft tissue around it. [SPEAKER_01]: So the lungs don't grow when you become obese. [SPEAKER_01]: So the lungs are the same in those vital capacity. [SPEAKER_02]: thoroughly good clarification.

[SPEAKER_02]: Thank you. [SPEAKER_02]: And key concepts to about dead space and dead space fraction, which we saw a little bit of in the review questions. [SPEAKER_02]: And atomic dead space is about two annals per kilogram, or about 150 annals in a 70 kilogram adult. [SPEAKER_02]: And the dead space fraction, VTV, VDVT, comes from the bore equation.

[SPEAKER_02]: which is your PO2 minus your expired CO2 divided by that product or that difference divided by the PACO2. [SPEAKER_02]: So it's PACO2 minus PACO2 divided by PACO2. [SPEAKER_02]: And the wider the gap between our material and mixed expired CO2, the larger of it that's based. [SPEAKER_01]: And I'll just point out to that PECO2 is not something actually we're used to looking at because it is not PECO2.

[SPEAKER_01]: It's not entitled CO2. [SPEAKER_01]: It is the average Excel CO2 over the entire acceleration, which is different than entitled CO2. [SPEAKER_01]: So keep that in mind. [SPEAKER_02]: That's exactly what I wanted to clarify too. [SPEAKER_02]: All right, that means you are ready for some questions.

[SPEAKER_02]: Let's do a question one. [SPEAKER_02]: A frail 42 kilogram 170 centimeter male with a measured vital capacity of four liters lies down on an operating room bed prior to induction of anesthesia. [SPEAKER_02]: Compare to his measured baseline, his vital capacity is now most likely A, more than four liters, B, about four liters or C less than four liters.

[SPEAKER_01]: And so when you lay down, you start to have some lung collapse. [SPEAKER_01]: So you're going to have less vital capacity than you did when you were supine. [SPEAKER_01]: I'm sorry, when you were standing up. [SPEAKER_01]: So laying down is going to lower your vital capacity. [SPEAKER_01]: It's going to be less than four liters.

[SPEAKER_02]: And interesting. [SPEAKER_02]: You often see that tested in terms of FRC as well. [SPEAKER_02]: It's the same thing with FRC. [SPEAKER_02]: We talked about those changes of FRC. [SPEAKER_00]: You'll see that lower as well. [SPEAKER_02]: Question two, which of the following is most likely to remain unchanged in a pregnant patient by the end of the third trimester?

[SPEAKER_02]: A closing capacity, B functional residual capacity, or C minimum alveolar concentration of the inhalational agents. [SPEAKER_01]: And as you mentioned, that in pregnancy, you do get a decrease in FRC, but closing capacity stays the same. [SPEAKER_01]: And then also we know that Mac is decreased in pregnant patients.

[SPEAKER_01]: So we know that B and C go down, but closing capacity stays the same. [SPEAKER_01]: And that's what happens is that when you're FRC decreases, and you're closing capacity stays the same, you get more collapse. [SPEAKER_01]: So that's [SPEAKER_01]: Well, same with patients who are very obese, who start to get lower FRC and more collapse at baseline.

[SPEAKER_02]: And I explained it's the decrease the apnea time and all of those patients. [SPEAKER_02]: Question three, the anatomic dead space in a 70-kilogram male is A50 milliliters, the 150 milliliters, or C250 milliliters. [SPEAKER_01]: And as you said before, the amount is about two MLs per kilo, so about 150 is going to be the answer here as close as to 140.

[SPEAKER_01]: So 150 is the answer. [SPEAKER_02]: And as much as I'm making us do math on the air, and fortunately in respiratory physiology, a lot of these questions on the basic exam, RS, and terms of, do you know the formulas? [SPEAKER_02]: So we'll do it again in question four. [SPEAKER_02]: Calculate the VD, VT ratio, or the physiologic debt space ventilation.

[SPEAKER_02]: Based on the following data, you have a PACO2 of 45, and makes expired CO2 tension of 30. [SPEAKER_02]: is your DDVT ratio A, 0.1, B, 0.2, or C, 0.3. [SPEAKER_01]: So you got to know the equation here. [SPEAKER_01]: We already said, which is PACO2 minus PACO2 divided by PACO2. [SPEAKER_01]: So 45 minus 30 divided by 45 is 15 divided by 45 is 0.3.

[SPEAKER_02]: That's right. [SPEAKER_02]: And I will just point out as sort of a test-taking skill. [SPEAKER_02]: If you ever are calculating ratios, and you've gotten yourself confused as to how to do it, you don't remember a big exact ratio. [SPEAKER_02]: If you go with big minus small divided by big, it's probably 80% of the time you're getting the ratio correct there.

[SPEAKER_02]: And that's the way it's working in this question as well. [SPEAKER_01]: Absolutely. [SPEAKER_01]: And you know, also you can look and say, well, is there even a way to get to point one or point two, right? [SPEAKER_01]: I mean, they're not. [SPEAKER_01]: Yes. [SPEAKER_01]: So if you just quickly look and you think like, I can't even see even I don't know the equation, I can't see how these two numbers could be put together in a way that's going to get me some of these answers.

[SPEAKER_01]: You can cross out some of the answers. [SPEAKER_02]: Thank you. [SPEAKER_02]: All right, session two will be respiratory mechanics and spherometry. [SPEAKER_02]: Compliance is the volume change for a given change in trans-pulmonary pressure, distensibility, and elastance is its inverse.

[SPEAKER_02]: Perfect and lowers alveolar surface tension. [SPEAKER_02]: It keeps small alveolar from empty into large ones. [SPEAKER_02]: And remember the love of the plus in which pressure needed to keep the alveolar is open is related to tension. [SPEAKER_02]: Directly a proportional detention in inverse and proportional to radius.

[SPEAKER_02]: So the key concepts here, key concepts, three, is that airway resistance depends on flow character. [SPEAKER_02]: This is tested off, and laminar flow follows passives law, radius to the fourth power, and depends on viscosity, while turbulent flow depends on density. [SPEAKER_02]: Do you have a good way to keep those straight, Jed?

[SPEAKER_01]: No, I do not do. [SPEAKER_02]: I do not, I have re-memorized this for every single test I've taken. [SPEAKER_02]: I think it's on my list of things to look at the night before and us, action to my brain yet again. [SPEAKER_02]: If I think of something I'll certainly add it in the comments at some point.

[SPEAKER_01]: Yeah, I'm just looking and thinking, you know, turbulent, dense, you know, is there, yeah, nothing that jumps out of me, laminar, viscosity, [SPEAKER_01]: No, nothing. [SPEAKER_02]: I'm trying to make sense so many times key concepts for work with breathing is basically pressure times volume and at rest the concerns only 2% of the total body oxygen.

[SPEAKER_02]: Anything that cuts FRC, like pneumovoparitanium during laparoscopy, lowers compliance in worsens oxygenation. [SPEAKER_02]: Key concept 5, obstruction drops VEF1 disproportionately, so you get a low FV1 to FVC ratio on no more to high total lung capacity. [SPEAKER_02]: While restriction drops both FVC and FV1 together, [SPEAKER_02]: So you have a normal ratio, but a low total lung capacity.

[SPEAKER_02]: And FV1 is the best marker of severity, enough shot to diseases such as cystic fibrosis. [SPEAKER_02]: question five. [SPEAKER_02]: During a normal vital type of volume five hundred and alt breath, the trans pulmonary pressure increases from zero to five centimeters of water. [SPEAKER_02]: The product of trans pulmonary pressure in VT is twenty five hundred centimeters of water ML.

[SPEAKER_02]: This expression of the pressure volume relationship during breathing determines what parameter of respiratory mechanics. [SPEAKER_01]: And as you said, worker breathing is defined as pressure times of all, oh, I'm sorry, you didn't read the answer twice to go ahead. [SPEAKER_02]: No, as you point out, if you know the answer, you should just look for the answer and I look for work of breathing, which is answer A.

[SPEAKER_02]: Your other options are B lung compliance and C error resistant. [SPEAKER_02]: So I'll go ahead and put you on the spot. [SPEAKER_02]: You knew that the product is work of breathing. [SPEAKER_01]: Right. [SPEAKER_01]: So lung compliance is volume over a change of pressure. [SPEAKER_01]: So I think of that as for any given change in pressure, how much is the lung going to change in volume.

[SPEAKER_01]: In other words, a very compliant lung with just a little pressure, you're going to get a big change in volume. [SPEAKER_01]: So that's compliance. [SPEAKER_01]: And then resistance is the inverse of that. [SPEAKER_01]: So it's pressure divided by volume. [SPEAKER_01]: And so the opposite, right?

[SPEAKER_01]: You can just think of it as with a [SPEAKER_01]: change in volume, it's to have high resistance. [SPEAKER_01]: It means a small change in volume, a large change in pressure. [SPEAKER_01]: So it's going to take a lot of pressure to make a small volume change. [SPEAKER_01]: Pay for us, I just want to take a second to shout out our Rockstar Returning Sponsor True Learn Smart Banks.

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[SPEAKER_01]: We rely on Truelearn for our test prep, and I recommend you do the same www.truelearn.com and use code ACRAC. [SPEAKER_01]: All right, and now back to our keyword episode. [SPEAKER_02]: Question six, what is the most likely physiologic response to abdominal cover dioxide [SPEAKER_02]: is that A, decreased arterial oxygenation, being increased lung compliance, or C, decreased intra-pulmonary shut.

[SPEAKER_01]: So you can do a little process of elimination here. [SPEAKER_01]: If you're descending the abdomen and you're therefore increasing the pressure around the lungs in the plural space, you're definitely not increasing lung compliance. [SPEAKER_01]: The lungs are going to have a harder time opening and filling with volume.

[SPEAKER_01]: So lung compliance is going to go down, so it can't be be decreased interpominary shun. [SPEAKER_01]: Even if you're not sure, you should think, well, it's probably not going to decrease it, right? [SPEAKER_01]: If you think about increased pressure and thorax, you're going to be, if it's enough pressure, [SPEAKER_01]: some of the airways and also some of the vessels, and so that's just going to increase V2 mismatch and probably increase shunt, so you're going to definitely not decrease shunt.

[SPEAKER_01]: So you can buy the process of a loanination end up at A, but also if you think that that CO2 doesn't just sit there, it gets absorbed and it gets into the circulation, and if you have more CO2, you're going to have less oxygen. [SPEAKER_01]: So by definition, you're going to decrease arterial oxygenation.

[SPEAKER_02]: Yeah, and then we haven't even talked about that aspect of the where Harbor Day Oxide and Oxygen mix and then how they affect each other, but that's totally true. [SPEAKER_02]: This is sort of a shout back to Key Concept4, right? [SPEAKER_02]: Anything that cuts your FRC is going to lower compliance and worse in your Oxygen Nation, but for all the reasons you stated, decreased arterial Oxygen Nation is the best choice.

[SPEAKER_02]: And then question seven last one for this session. [SPEAKER_02]: A decrease in which component of pulmonary function testing is the best indicator of disease severity in patients with cystic fibrosis. [SPEAKER_02]: A, residual volume, B, force extratory flow at 25% to 75% of one volume, or C, force extratory volume in one second, FEV1.

[SPEAKER_01]: And this is a little tricky because people may know that we often talk about the FEV-25 to 75 as the least effort depended and so maybe the best predictor because people can't, it doesn't really depend on how much effort they put into it. [SPEAKER_01]: But as you said in your introduction, with cystic fibrosis, especially the FEV-1 is thought of as the best indicator of divisive air disease severity.

[SPEAKER_01]: So the right answer here is C. [SPEAKER_02]: Right, and I would love to not see these two things tested against each other, but I would go with FVV1 for abstracted diseases, absolutely versus their fibrosis if they're used to choose. [SPEAKER_01]: Great. [SPEAKER_01]: And I think the reason, by the way, is that I think they're assumption is that in a test situation, they're assuming that you get complete effort, right?

[SPEAKER_01]: They're not testing you on the patient who isn't, right? [SPEAKER_01]: Unless they said it. [SPEAKER_01]: I mean, the way they would get to 25 to 75 is if they said, you know, a patient is somewhat sedated and you're not sure that they're giving full effort, which is the best test, right?

[SPEAKER_01]: But if they don't say that, I think you should assume that you have a patient who's giving a full effort. [SPEAKER_02]: Where a session 3 is going to be ventilation profusion matching and HPV, gravity makes both ventilation and profusion greater at the dependent lung, but profusion is more susceptible to this effect.

[SPEAKER_02]: And the result is a VQ ratio ventilation to profusion ratio that is high at the apex. [SPEAKER_02]: and low at the base when you're sitting our standing, if you're supine or you're lateral, you have to think about what's actually dependent. [SPEAKER_02]: And what zones formalize this? [SPEAKER_02]: So one is the alveolar pressure being higher than our two-year-old pressure.

[SPEAKER_02]: That occurs in the apex while sitting our standing. [SPEAKER_02]: While zone three, wherever our two-year-old is greater than the Venus, greater than the alveolar, is the well-prefused base of a longer. [SPEAKER_02]: the high VQ apical units where you have a lot of ventilation not a lot of flow act a little bit like that space you have higher PAO2 and lower PACO2 as a result in the low VQ basal units act a little bit like shunt stay with us will be right back [SPEAKER_01]: All right, and we're back.

[SPEAKER_02]: Key concept six in this area, and remember that the apex is high VQ, the base is low VQ when you're sitting or standing. [SPEAKER_02]: In both ventilation and profusion are greatest at the base, but profusion more so, which is why voracious still favors the apex. [SPEAKER_02]: and key concept 7 of the older hypoxia constricts the pulmonary fascusure, that's the opposite of the systemic circulation.

[SPEAKER_02]: They've heard the blood towards better ventilated lung. [SPEAKER_02]: This happens to be one of the physiological reasons that one lung ventilation can be tolerated. [SPEAKER_02]: The other is that we tend to turn patients laterally during these cases, which helps flow blood flow get to the dependent lung.

[SPEAKER_02]: And HPV is blended by volatiles and vasodilators. [SPEAKER_02]: And pulmonary facillary resistance is lowest at FRC. [SPEAKER_02]: So the high volume, when you inhale compresses alveolar vessels and when you exhale everything, the low volume sort of keeps the extra alveolar vessels. [SPEAKER_02]: So in both of those areas, you're pulmonary, in both of those situations, the pulmonary facillary resistance is higher than right at FRC.

[SPEAKER_02]: So you shape curve. [SPEAKER_01]: Let's do it. [SPEAKER_02]: Question A, which of the following statements concerning the distribution of alveolar ventilation in the upright lungs is true? [SPEAKER_02]: A, alveolar at the apex of the lungs are better ventilated than knows at the base. [SPEAKER_02]: B, alveolar at the base of the lungs are better ventilated than knows at the apex.

[SPEAKER_02]: And C, for distribution of ventilation is not affected by body posture. [SPEAKER_01]: Yeah, this is really key because I think this is tricky because if you think ventilation, you may think aeration, and that's not the same thing. [SPEAKER_01]: They're talking here in terms of ventilation about the exchange of CO2 as opposed to oxygenation.

[SPEAKER_01]: So, [SPEAKER_01]: I'll be like the base of the lungs are better ventilated by which we mean there is more CO2 delivered to the alveoli by the blood and that is because they are better perfused. [SPEAKER_01]: So tricky, if it's a better perfused, you'd probably definitely get it. [SPEAKER_01]: You'd say, oh, better perfused at the base.

[SPEAKER_01]: But when it says ventilated, they're talking about perfusion because they're talking about exchange of CO2. [SPEAKER_01]: So be careful there. [SPEAKER_01]: So the answer here is B that there's more CO2 exchange at the base. [SPEAKER_02]: That's really well said. [SPEAKER_02]: That's sort of when you think about respiration or you're worried about is you're eventually, that's a change of seeer, and is your oxygenation well?

[SPEAKER_02]: Good enough. [SPEAKER_02]: Question 9. [SPEAKER_02]: Which of the following statements concerning the distribution of oxygen and carbon dioxide in the upright lungs this true? [SPEAKER_02]: A, both PAO2 and PACO2 are greater at the base than at the apex. [SPEAKER_02]: B, P, A, O, 2 is greater at the apex than at the base.

[SPEAKER_02]: And C, P, A, C, O, 2 is greater at the apex than at the base. [SPEAKER_01]: Right. [SPEAKER_01]: So this is kind of the converse of what we just said. [SPEAKER_01]: So P, A, O, 2 is greater at the apex, and that's going to be your answer here. [SPEAKER_02]: Right, that's a little bit of dead space.

[SPEAKER_02]: It's not more ventilated. [SPEAKER_02]: You have more PL2 than PCO2 at that point. [SPEAKER_02]: Good. [SPEAKER_02]: So a couple of questions that drive that idea home. [SPEAKER_02]: And we'll move on to section four. [SPEAKER_02]: Gas exchange, the A gradient, shunt and diffusion are sort of the most tested things here.

[SPEAKER_02]: And the alveolar gas equation gives the PO2 you should see in the alveolar list. [SPEAKER_02]: So, P big A02 alveolar pressure pressure of oxygen is equal to your inhaled oxygen multiplied by your atmospheric pressure minus the water pressure. [SPEAKER_02]: And you subtract from that the P little ACO2 divided by the respiratory quotient.

[SPEAKER_02]: And we'll refer you to any textbook to look at that equation in writing, but that's the best I can do on air for you guys. [SPEAKER_02]: And altitude, the barometric pressure drops, so P big AO2 falls even on at room air. [SPEAKER_02]: And comparing the calculated e big A or alveolar O2 to the measured arterial P little A O2 gives the A-A gradient, which is essential tool for sorting out hypoxemia.

[SPEAKER_02]: a couple of key concepts. [SPEAKER_02]: Key concepts 8, a normal AA gradient points to high-poventilation or low-inspired OTM. [SPEAKER_02]: A wide-open gradient points to VQ-minis match, shunt or diffusion limitation. [SPEAKER_02]: And shunt signature is high-bath semiavette does not correct, with 100% OTM.

[SPEAKER_02]: T-Consup 9, Pumper the F-Side is 20 times more diffusible than L2. [SPEAKER_02]: So diffusion impairment causes the Cypaxemia long before hypercarvier. [SPEAKER_02]: Appinic oxygenation works because the LVOI keep absorbing O2 after pre-oxygenation, and commonly tested thing is the mirror image, which is diffusion hypoxia, when you're using natus oxide, and that's why we use 100% O2 when stopping natus oxide, because all of that is still in the blood, and it'll be very rapidly absorbed and developed oxygen in the lungs.

[SPEAKER_02]: I know you muted yourself, but bless you, Jed. [SPEAKER_02]: Thank you. [SPEAKER_02]: I'm ready for some questions. [SPEAKER_01]: I'm ready. [SPEAKER_02]: Question 10. [SPEAKER_02]: What is the calculated PAO2 of a patient on room air in Denver, Colorado? [SPEAKER_02]: As soon as parametric pressure of 630 millimeters per mercury, a respiratory quotient of 0.8, an APACO2 of 34 millimeters of mercury, is it A80, B90, or C100?

[SPEAKER_01]: Yeah, and so here we have to go back to the equation that you gave us of the LVLA gas equation. [SPEAKER_01]: And so we are going to take the 630, which is the atmospheric pressure, minus the partial pressure of H2O, which you also need to know for this, which they don't give you. [SPEAKER_01]: I think they would probably give you that in a test at least I would hope, but that's 47.

[SPEAKER_01]: So, 630 minus 47 times 0.21. [SPEAKER_01]: And then minus the PACO2034 divided by the rest of the equation of 0.8. [SPEAKER_01]: And if you work all that out, it gets you 80. [SPEAKER_01]: So that is your answer here. [SPEAKER_01]: You would have to know that equation in order to be able to calculate this.

[SPEAKER_02]: And you will need to know that equation for your IT and for your basic rule. [SPEAKER_02]: At some point, be asked to calculate this. [SPEAKER_02]: Question 11, which of a following is most correct regarding apnic oxygenation, a low functional residual capacity to body weight ratio increases for time to tolerate apnea.

[SPEAKER_02]: The inesult cannula can effectively deliver oxygen during apnic oxygenation, or see that arterial partial pressure of carbon dioxide decreases during apnic oxygenation. [SPEAKER_01]: let's look at the chance or a low FRC increases the time to tolerate apnea, nope, the opposite is going to decrease it.

[SPEAKER_01]: So we can get rid of A, B, a nasal cannula can affect of the delibroction during apnea oxygenation. [SPEAKER_01]: It can, so if you know that, you know it. [SPEAKER_01]: And then see the arterial partial pressure of carbon dioxide decreases during apnea oxygenation. [SPEAKER_01]: And so hopefully that just clearly can't be right.

[SPEAKER_01]: As you are not breathing, your partial partial carbon dioxide is going to go up because you're not breathing it out. [SPEAKER_01]: So hopefully you can get rid of A and B, A and C, even if you don't know that the answer is B, but the correct answer is B. [SPEAKER_02]: Yeah, and I think I think sort of your explanation of, uh, see here is, uh, matches up with what you said earlier, just remember that decision between oxygenation and ventilation, you're oxygenating because that I'll be all I are filled enough with oxygen that will continue to diffuse over a time, uh, from the LVO live that still have some oxygen to diffuse, but that carbon dioxide is going to very quickly equilibrate and then not go anyone because you're not ventilating those.

[SPEAKER_01]: Yeah, and you're still producing it, so it'll go up because you're not getting [SPEAKER_02]: In question 12, what percentage of shunt fraction QSQT will 100% FIO2 have the least effect on PAO2? [SPEAKER_01]: You're going to give me my answer choices. [SPEAKER_02]: Oh, I if you'd like them, sure.

[SPEAKER_02]: A 10% B20% or C30%. [SPEAKER_01]: Yeah, I was, I jumped it too early before. [SPEAKER_01]: So I've got to give you that. [SPEAKER_01]: Um, yeah. [SPEAKER_01]: So the key here is knowing that Shunt, as you said, up top is going to cause 100% 502. [SPEAKER_01]: The more Shunt you have the more the less effect increasing to 100% 502 will have.

[SPEAKER_01]: And so here it's just a matter of which is the most chunted. [SPEAKER_01]: And so see 30%. [SPEAKER_01]: The more shunt you have, the less effect increasing your 502 to 100% will have. [SPEAKER_02]: Yeah, this is one of those questions that I love because you look at it. [SPEAKER_02]: You see QSQT.

[SPEAKER_02]: You see a hundred percent in the STEM. [SPEAKER_02]: You see three answers that you think you're going to have to somehow reason out mathematically. [SPEAKER_02]: And there's absolutely no math in this question. [SPEAKER_02]: It's just, do you know that Shunt does not respond to increase oxygen?

[SPEAKER_02]: And if so, if you know that, then the more shunt the less it will respond. [SPEAKER_02]: Absolutely. [SPEAKER_02]: All right, section five, oxygen carrying capacity and the oxy hemoglobin curve. [SPEAKER_02]: Acidin content is overwhelmingly hemoglobin bound. [SPEAKER_02]: Another equation that we need to know is that the O2 content is equal to 1.39 times the hemoglobin times the SAO2 plus 0.003 times the PAO2.

[SPEAKER_02]: So that dissolved term that second part is usually trivial. [SPEAKER_02]: The Aussie hemoglobin dissociation curve relates saturation to PAO to an sigmoin shape, and p50 that PAO to a 50% saturation is a number that marks where the nibble of that curve sits. [SPEAKER_02]: He concept 10, Austrian content tracks hemoglobin concentration and saturation, not PAO2.

[SPEAKER_02]: Pushing PAOO2, when the blood is already fully saturated, barely changes the content. [SPEAKER_02]: Again, that last term, the dissolved term is negligible. [SPEAKER_02]: Key concept 11, you are P50 is around 26 to 27 millimeters per mercury. [SPEAKER_02]: A right shift, which is lower affinity easier to shoot unloading, comes from Asadosis, Hyperthermia, increased 23DPG, and volatiles.

[SPEAKER_02]: And remember, those are all situations in which you would want more tissue unloading. [SPEAKER_02]: So, in the tissue, it's working a lot, creating a lot of carbon dioxide, which is making that local tissue acedatic, all of those things will favor unloading, so it's a self-balancing thing.

[SPEAKER_02]: But in a left shift comes from the opposites of what we just described, plus fetal hemoglobin, carboxy hemoglobin, and methamethymoglobin. [SPEAKER_02]: that it out there. [SPEAKER_02]: A low PAO to just move you along an existing curve, it is not a shift of the curve itself. [SPEAKER_02]: Anything to add before we do some questions?

[SPEAKER_01]: No, I think that last one is really important because it can be tricky. [SPEAKER_01]: But that's kind of what the curve is measuring. [SPEAKER_01]: So you're not changing it. [SPEAKER_01]: You're just, as you said, you're moving up back and forth on the x-axis [SPEAKER_01]: But you're not shifting the curve itself.

[SPEAKER_02]: Yeah, I think that though there are some factors in the blood, such as the hemoglobulins themselves, and then two, three DPG that do shift some things. [SPEAKER_02]: I sometimes think of this as sort of the tissue sets where the curve is, depending on how much or how little unloading it means.

[SPEAKER_02]: And then the blood content your PAO, too, is sort of where you live on that curve. [SPEAKER_02]: Okay, questions 13. [SPEAKER_02]: Chemoglobin has been stable at 15 grams per deceler. [SPEAKER_02]: But gas analysis immediately before induction reveals a PAO to 120 millimeters of mercury in an arterial saturation of 100%.

[SPEAKER_02]: After induction, the PAO2 rises to 150 millimeters per mercury and the saturation remains the same. [SPEAKER_02]: How has the oxygen content of this patient's blood changed? [SPEAKER_02]: A, it is increased by 10%, B, it is increased by 5%, or C, it is increased by less than 1%. [SPEAKER_01]: Yeah, so tricky, just thinking about it, you may say, oh, it went from 120 to 150.

[SPEAKER_01]: That's a pretty significant increase. [SPEAKER_01]: That's an increase of 30. [SPEAKER_01]: That's 25%, which actually, interestingly, is not one of the options. [SPEAKER_01]: So maybe you can realize that can't be right. [SPEAKER_01]: But... [SPEAKER_01]: And I do think it'd be very likely they might put 25% as an option there on the real test, because that would be an obvious distractor.

[SPEAKER_01]: But the key is remembering that in the oxygen content equation that you went over, you multiply the P-A-O-2 by 0.003. [SPEAKER_01]: So that change of 30, you have to multiply by 0.003. [SPEAKER_01]: It's going to be a tiny increase percentage wise. [SPEAKER_01]: And so the answer is C, less and 1 percent.

[SPEAKER_02]: Yeah, you don't need to do the math. [SPEAKER_02]: It's negligible. [SPEAKER_02]: Question 14, that P50 for normal adult hemoglobin is approximately a 15 millimeters of mercury, B25 millimeters of mercury or C35 millimeters of mercury. [SPEAKER_01]: A vest you just have to know and the answer is 25.

[SPEAKER_02]: But it'll come up either as a standalone question less likely or you will need to know it for answering some question related to oxygen carrying capacity or the oxygen you can go and curve. [SPEAKER_02]: So we put it there. [SPEAKER_02]: In question 15, which of the following will shift the oxygen and go into association?

[SPEAKER_02]: Sorry, each of the following will shift the oxygen and go into association curve to the right accept. [SPEAKER_02]: A, volatile anesthetics, B, D3, [SPEAKER_01]: So as you went over, decrease pH and volatile will, in fact, shift it right. [SPEAKER_01]: But remember we said decrease PAO to just moves you along the curve.

[SPEAKER_01]: It doesn't shift it. [SPEAKER_01]: So the answer is B. [SPEAKER_02]: That's right. [SPEAKER_02]: decrease PAO to is not a left word shift. [SPEAKER_02]: It's just no shift. [SPEAKER_02]: Right, section six, come up to ask that transport and carbon monoxide, CO2 is carried three ways as by carbonate, that's the majority, it's generated by carbonic and hydrase in the red cell, down to hemoglobin is carbon, amino hemoglobin, and dissolved.

[SPEAKER_02]: Two effects linked to O2 and CO2 transport cycles. [SPEAKER_02]: There's the Bor effect where Asidosis and Carbon by the outside right shift to O2 curve, to favor tissue unloading. [SPEAKER_02]: This is what we've been talking about when we talk about a right shift on the oxy hemoglobin curve.

[SPEAKER_02]: And the how they know effect, where the oxygen in a hemoglobin carries more CO2, favoring pickup in the tissues and releasing along. [SPEAKER_02]: If you know one of these, you'll know that the other is the other effect. [SPEAKER_02]: So I would just memorize one by name. [SPEAKER_02]: And remember that both just help unload oxygen once needed and carry away carbon dioxide from where it's generated highly.

[SPEAKER_02]: So if you think of highly metabolic tissue, [SPEAKER_02]: the bore effect will make it more likely that O2 is dumped off and the fact that less O2 is on that hemoglobin will make it more likely that that hemoglobin can carry more CO2 away from that area of that's generating. [SPEAKER_02]: You can't sub-12.

[SPEAKER_02]: When carbon dioxide binds, hemoglobin, it binds it with 200 times that affinity of 0,2, and we'll get it. [SPEAKER_02]: Carbon monoxide, carbon monoxide, carbon monoxide, binds it with 200 times that affinity of 0,2, and it left shifts the curve. [SPEAKER_02]: So, O2 constants is dangerously low, while the PAO2 looks normal.

[SPEAKER_02]: A standard post-Saximiter also falsely reads a reassuring value because it can't distinguish between Karbachsi hemoglobin from oxy hemoglobin. [SPEAKER_02]: You'll see this tested such as in question 16. [SPEAKER_02]: A 33-year-old woman with 20% Karbachsi hemoglobin is brought to the ER for treatment of smoke inhalation, which of the following is least consistent with a diagnosis of carbon monoxide poisoning.

[SPEAKER_02]: A, 98% oxygen saturation on dual wavelength post-leximeter, the PLO2 of 105 mm per mercury, oxygen saturation, 80% on initial room air onto the blood gases, or C-cynosis. [SPEAKER_01]: Yeah, so as you said, you're going to have a false elevation of your sat so that is likely A is likely that it may read 98% even though that's reading the Carboxy hemoglobin B, P-O-2 105, but a sat of 80 on initial room air arterial blood gas.

[SPEAKER_01]: That's key. [SPEAKER_01]: That's not the sat on the pulse extender. [SPEAKER_01]: That's on the blood gas itself. [SPEAKER_01]: So that is also likely because you have [SPEAKER_01]: enough oxygen in the blood that you should have a hundred percent sad but you don't so that's because of the uh... carbon monoxide cyanosis is something you wouldn't see because you get not cyanosis but in fact that cherry red appearance so you would look quite pink or red but not cyanotic even though you are in fact uh... not you do not have enough oxygen in your blood or being delivered to your dishes [SPEAKER_02]: Okay, session 7.

[SPEAKER_02]: We won't have any questions here, but this is going to be the non-respiratory lung functions in perioperative smoking. [SPEAKER_02]: This is less tested, but because we want to round out this session of the confluent outline, there's a couple of quick hits I want you to know just in case it does come up.

[SPEAKER_02]: The lungs, not on respiratory functions, or that it filters micro thrombide, converts angiotensin one to two, and clears some catacomines and stresses in immune barrier. [SPEAKER_02]: There's not great ways to test this, so they don't. [SPEAKER_02]: And in terms of perioperative smoking, I think the things that you might want to know for the test, are that [SPEAKER_02]: Carbazzi hemoglobin clears within 12 to 24 hours, so short cessation improves oxygen delivery quickly, but meaningful reductions in pulmonary complications need several weeks of abstinence.

[SPEAKER_02]: And we've all seen that, you know, the person that quit smoking a couple days before, they may have better oxygen delivery, but they will be coughing, hacking, more prone to bronchospasm, especially early in that period that they quit. [SPEAKER_01]: Yeah, and so part of that, too, is that they have still their producing excess secretions because of the smoking, but their sillyary function is starting to come back a little and so it's coming up.

[SPEAKER_01]: So now they've got all this instead of just sitting down in their lung, they've got all these secretions that are now starting to come up into their upper airways and so they're going to be coughing and hacking more. [SPEAKER_01]: So you can actually have increased secretions and airway reactivity because of all that in the days after stopping.

[SPEAKER_02]: Perfect. [SPEAKER_02]: So like I said, no actual questions or actual keywords for that little section. [SPEAKER_02]: So that is all we've got to make fabulous. [SPEAKER_01]: Well, this was great. [SPEAKER_01]: Let's go to the part of our show where we make random recommendations, Tim. [SPEAKER_01]: What would you recommend people check out for fun?

[SPEAKER_02]: I am going to recommend a funny AS with Kevin Hart, which is a Netflix, I don't know what's called, like a game show or reality TV thing. [SPEAKER_02]: He brings on comics from multiple cities and tries to find the best comic. [SPEAKER_02]: The show is totally watchable, there's nothing about sort of a...

[SPEAKER_02]: style of the tournament that is especially appealing but the comedians are absolutely hilarious. [SPEAKER_02]: I don't often watch TV. [SPEAKER_02]: I've very rarely been shows and my wife and I got through this probably in a few days because we couldn't put it down. [SPEAKER_01]: Nice, fabulous.

[SPEAKER_01]: I've been to recommend a TV show called The Land Man. [SPEAKER_01]: And I had actually heard about this and I thought about watching it, but then I looked it up and the rotten tomato reviews were okay, but not great. [SPEAKER_01]: So I had decided not worth my time. [SPEAKER_01]: And then some of the parents on my daughter's lacrosse team were saying they were really enjoying it.

[SPEAKER_01]: So I said, okay, I'll check it out. [SPEAKER_01]: And it is worth it. [SPEAKER_01]: It is very funny. [SPEAKER_01]: I mean, I'm only a few, I'm maybe half way through the first season, [SPEAKER_01]: Billy Bob Thorden plays a dad who has a 17-year-old daughter and as a father of teenage daughters, I will tell you that they really do a nice job of poking fun at that relationship and at some of the eccentricities of the teenage daughter, so if you especially are a father of teenage daughters, I would highly recommend watching it.

[SPEAKER_01]: You will laugh pretty hard and for anyone else you'll probably be entertained as well. [SPEAKER_01]: All right, Tim. [SPEAKER_01]: Thanks so much for coming back on the show. [SPEAKER_01]: Thanks for having me again. [SPEAKER_01]: All right. [SPEAKER_01]: Hopefully you got as much out of that as I did.

[SPEAKER_01]: That was really fantastic. [SPEAKER_01]: Let us know what you thought. [SPEAKER_01]: Go to the website, acrack.com, where you can leave a comment. [SPEAKER_01]: Others can learn from what you have to say. [SPEAKER_01]: If you are a fan of the show, you can follow us. [SPEAKER_01]: We're on Twitter.

[SPEAKER_01]: We are on Facebook. [SPEAKER_01]: We are on Reddit. [SPEAKER_01]: And we are on Instagram. [SPEAKER_01]: I'm AdJ Wolpa on Twitter. [SPEAKER_01]: And we're at Acrack Podcast. [SPEAKER_01]: And you can find us on all those other platforms as well. [SPEAKER_01]: If you are a fan of the show, please consider going to Apple Podcasts or wherever you get your podcasts and leaving a comment and a rating, it really helps others find the show.

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[SPEAKER_01]: You can also make donations anytime by going to paypal.me-slashacrack, or looking up J.Wallpa on Venmo. [SPEAKER_01]: Thank you so much to those who have already made donations and become patrons, we really appreciate it. [SPEAKER_01]: Thanks as always to our fantastic acrack crew. [SPEAKER_01]: So, Nya Aminat is our tech lead, Chitama Econty, Rachel Furman, and Mohamed Selab are our production assistants and social media managers.

[SPEAKER_01]: Thanks so much for all you do. [SPEAKER_01]: Our original ACRAG music is by Dr. Dennis Quow. [SPEAKER_01]: You can check out his website at studymusicproject.com. [SPEAKER_01]: All right, that is it for today. [SPEAKER_01]: For the ACRAG podcast, I'm Jed Wolpa. [SPEAKER_01]: Thanks for listening.

[SPEAKER_01]: Remember what you're doing out there every day is really important and valued.

Episode 340: Keywords Part 35: Respiratory Physiology

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