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Hemodynamic Monitoring in the ICU
Dr. Michael Scott discusses hemodynamic monitoring in the ICU.
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Learn more about Michael Scott, MD
Michael Scott, MD
Michael Scott, MD is the Director of Critical Care Anesthesiology at Virginia Commonwealth University.Learn more about Michael Scott, MD
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This podcast is sponsored by immune express immune express offers, SEPTA site rapid a host immune response test, which can provide results in one hour to differentiate between sepsis and SIRS in patients suspected of sepsis, thus expediting and optimizing patient management decisions and appropriate therapy. For more information, visit www.septisite.com.
Dr. Michael Smith: Hello, and welcome to the I-Critical Care Podcast. Sponsored by the Society of Critical Care Medicine. I'm your host, Dr. Michael Smith. Today, we're going to talk about hemodynamic monitoring in the ICU with Dr. Michael Scott. He's an adjunct professor of anesthesiology and critical care medicine at the University of Pennsylvania. Dr. Scott, welcome to the show.
Dr. Michael Scott: Thank you very much. It's very good to be on the show, thank you.
Host: You know, Dr. Scott, you're speaking to a radiologist, right I haven't been in the ICU. And so, so many years, I do remember very specifically the importance of hemodynamic monitoring, fluid management, in critical care patients.
So, I just thought maybe for a moment, we could just back up for a sec and talk about why this is so important, you know, even given the context of COVID, today, like, what are you, what are your thoughts about this topic is.
Dr. Scott: Yeah, I think fluid therapy is one of the key interventions that we do on critical care that can make a massive difference to the patient. I think everyone's aware that the fluid therapy is key to maintaining intravascular volume. And a good cardiac output and blood flow around the body to perfuse organs and avoid organ dysfunction. And also, there's increasing recognition, but there is a threshold mean arterial pressure below which you go, gives you a signal of, of injuries, particularly AKI and my caudal injury. And so you could say, well, why not just give lots and lots of fluid to a patient and just to optimize those all the time. But we do know too that there's a downstream major complications are caused by fluid overload. And as soon as you give roundabout 40 to 50 miles per KIDO of fluid above someone's, sort of dry weight, which is about two to three kilograms in practice. You start getting a signal of all cause complications because you get pulmonary problems, you get gutta, DEMA, and, and the more fluid overload you get downstream, the more, the signal is of increasing complications. So, you've got this problem that the easiest thing to do is to give fluid. but if you don't pay particular attention to it, you get, you pay for it downstream. So, what we really need is some form of monitoring system to add to clinical ability, to enable the fact that we can keep our patients well resuscitated, but avoid that fluid overload downstream. It's been particularly person in the COVID crises because we've seen different phases of how patients get sick. They've arrived, dehydrated and very sick initially, then fluid resuscitated, and then there's been different patterns of how they've been treated. Either reef kept them breathing on oxygen or they've ended up being intubated and on a ventilator. And for both of those, our approach to fluid therapy has also been different.
Host: Yeah, it's interesting, right doctors. Cause I do remember this, right. There's a balance between, dry and wet, right? At the end of the day, we don't want to be too dry in critically care patients. As you mentioned in the COVID crisis, a lot of these people are coming in. To the hospital are ready in severe distress from what I understand. And, they are dehydrated. You give that fluid, but there, but you've got to balance that you got to, you got to know when to, when to back that off is, do you believe that's one of the greatest challenges for, critical care doctors when it comes to maintaining profusion is figuring out , like wet versus dry. Like how do I balance it? Is that one of the biggest challenges?
Dr. Scott: I think it is actually because obviously too much fluid and the first organ often to go down and see your lungs, particularly in physiological situations, such as COVID where you've got, a disease process in the lungs. And, breakdown of the alveolar membrane can be to increase its true vascular lung water and, and a R D S. And then you've also got your kidney, which, which likes, adequate intravascular volume. So really what we're seeing in medicine is, is you've got to balance the risk between organs. we did have the luxury really when continuous intravenous hemodialysis came along, that we could always, run patients on the slightly drier side. in order to protect their lungs and put them on only dialysis, but what's been fascinating in the last few months with COVID is because there's been such a strain on resource allocation. We haven't really had that luxury of being able to have this backup of a renal support that you would otherwise be able to offer every patient, because we've just had such a huge number of patients that have been so sick requiring it a lot of, facilities.
Host: And a lot of these patients, obviously that are coming in have comorbidities, diabetes, heart disease, COPD, lung, other lung issues, et cetera, et cetera. I guess, I guess what comes to my mind then is like when someone like yourself is at the bedside. And you're, you're trying to balance that, that fluid management yet at the same time, there's some clinical interventions that may be, you need to do, to stabilize the patient, make sure that they're getting better. How do you, how do you, how do you manage that? How do you decide, okay, If I'm going to do this intervention at bedside, how does that affect the hemodynamics? A w is that a conversation you have with the other doctors? Are there, is there standardization for some of those. Interventions and how they affect profusion.
Dr. Scott: Yeah. I wouldn't say there is, there's a great standardization across the ICU community, because everyone has different skillsets and different equipment available. But one of the, the two key areas, I think, which have helped push us towards an area where we can start standardizing and, and that is the use of bedside ultrasounds. To assess fluid status and the filling of the heart and the other is use of, arterial wave form analysis, which we can now use algorithms to estimate stroke volume. And also, responsiveness to fluid. And I think that's where the community are going. It's, it's, it's the patient should be responsive to for bolus or not. And if you do give that food bonus, is it actually going to benefit them or is it going to harm them downstream? So I think that's the framework of how we approach a patient. And so really when you're faced with a patient who needs resuscitating hypotensive, initially, it’s a straightforward, problem, because you, can ultrasound them, show that they're intravascularly, dry and give them a float bolus. I think the problem comes is when you've got complex disease mechanisms that we see on ICU, you've got visa dilation of the arts are freeze, so you've got vasoplegic shock. So you can actually keep giving fluid. And it then stops actually raising the blood pressure. And what you really need is pervasive process such as something like Knorr epinephrine. And so the art of getting the balance of filling the circulation and before squeezing it with a vasopressor is actually absolutely key because if you start the vasopressin too early, then you're going to hurt your splint, Nick and renal blood supply, and, and actually create more problems. So the artist's getting the balance and I like to really break it down very simply and call it. The approach is fill flow pressure where you fill the tank, which is the heart and make sure there's adequate flow and options delivery. And after you've got enough options, delivery and flow to the organs, and really what you've got to do is set your profusion pressure. And that venue is dialing up the Knorr. Epinephrine always oppressive, which of use to get the right mean arterial pressure. And then you ended up with a balanced circulation with a minimum amount of fluid that you need to.
Host: But Dr. Scott, then that implies that we're not just doing an ultrasound at the bedside. We got it. We have to do some echoes. Right? So you have, you have two different. Technicians working at the bedside right together, making sure that the heart is maintaining that flow based on that bolus of fluid. And then they, and then the ultrasound tech, making sure that we're perfusing, like, for example, the kidneys properly with that. So do you see both of those technologies working together in this kind of scenario?
Dr. Scott: Yeah, so, and I think what we've seen in the last 10 years is most critical care physicians such as myself. Have now, taken up the skill of bedside ultrasound to look at both the venous capacitance, measuring the IVC, and also being able to do a good estimate of filling of the left ventricle, looking at different views and making sure that the heart is structurally sound and there's no other issues such as a tamper nod or valve.
It. Issues. So it's increased our bedside decision making by having this skill sets. So we can do the first two things. You said, the fill in the flow and optimize that. And then when you look at the pressure after that, and you know, you've optimized the previous two, you can safely start a visa presser and then maintain profusion.
Host: How do you, as, as a critical care physician though, like when you're giving some of these medications that can dilate versus constrict, et cetera, et cetera, how, how do you measure then some of the other key parameters when giving fluids such as like stroke volume, stroke, volume variation, like how, how do you, and I bring this up because you mentioned there really isn't a lot of standardization, within your field. So, so when giving fluids. How do you standardize the applying to some of these key parameters like stroke volume?
Dr. Scott: Yeah. And stroke volume can be measured in many different ways. you obviously you can use a Thermo dilation such as the song dance Kaphas. You can use transthoracic or transesophageal echo. You can use a software Gerald Doppler, and then you can use wave form data’s, often arterial line, the wave form data off an arterial line in a patient breathing spontaneously can give you trends and it can give you swings and it can give you the response to flu bolus. but we can have more information if you've got a ventilated patient, if you can ventilate a patient, a title of one of your ground, about eight mils per kilos, you can then look at something called the pulse pressure variation or the stroke volume variation. And that is actually using the post-concert wave analysis. You can actually measure the estimate, the stroke volume and how that's changing through the respiratory cycle. And this has been shown to be very accurately predict whether you will be responsive to a fluid bolus or not. And we're looking at figures of a stroke volume variation of, of less than 12%. You're very unlikely to need fluid. If you're ventilated at eight mils per kilo and pulse pressure variation, slightly higher around about 14%. And these markers are very useful because when you were not to align in and sedated and ventilated patient bedside, you can have these running constantly. And then obviously you can track the changes. So if you'll start voting very well, let's see you raised to say 16 or 18%. There is a very strong chance of that patient would benefit from a fluid. Bolus, and then the stroke volume variation would go back to a more normal thicker, less than 12%.
Host: So I want to, take this conversation now into, what's obviously, the big elephant in the room and that's, COVID. and I, and I appreciate Dr. Scott, the, the work that you've been doing, you know, critical care nurses and physicians like yourself are really on the front line and doing an amazing job. So thank you so much for that. And I know, the amount of hours and time that you're putting in is like, Nutty and crazy. And I just, just so you know, that we appreciate that what you're doing and, and taking the time to come talk to us today. So let's talk a little bit about COVID. what does COVID done to the ICU? Like, how has that changed the way maybe you approach, patients who are coming in really critically ill. Really dehydrate it. some of them maybe need to be ventilated right away, maybe some don't. How are you managing all that?
Dr. Scott: Yeah, I think going to a higher level, obviously our whole approach to COVID it's been different because we've had, all the contact precautions, PPE to protect all the staff from any contact with the virus. And I must say at the university of Pennsylvania, we've been very successful with our PP in, in. W we don't know of anyone on our units, who've actually developed, COVID-19 looking after patients. So I think that's been a real success. And I think at the start of the COVID pandemic, everyone was obviously very anxious, but now people feel quite comfortable putting on the 90 fives and the Packers and entering rooms. So it's less of an issue. What the higher-level view is though is it's meant that we haven't been in such close contact with our patients, bedside, cause we've tried to limit contact, limit nurses going into the room as well as obviously the physicians. So use of an arterial line has been extremely useful in these patients because you can then monitor them remotely and you get quite a lot of information from the arterial line. So I think, what's interesting is out of this is we've learned to probably look at one that is a little bit more careful. It's just, we can't always go in and actually examine the patient necessarily as frequently as we would have otherwise. So the use of these indices, PPV and SPV have been very useful. having a continuous or two away from analysis with continuous cardiac output monitoring, those, become much more standard, I think for looking after patients. there are other things I think too is, is we've used the passive leg raise of up, to look at fluid responsiveness, because the great thing about that is, you're lifting both legs up in the air. For at least sort of half a minute that you're effectively giving a full bolus, but as soon as you drop the blog's down, you, you haven't given that through permanently. So it gives you the chance to see if the patient's food responsive without actually giving them the fluid and then arterial lines being very useful, at, assessing that as well. The other thing, I think that's a, we have done a lot in COVID patients are ventilators. They have had central Venus, candidates in place to run low dose, a cerveza pressor and also, sedatives and things. and. Although central venous lines, don't give you fluid responsiveness. They do give you an idea of the venous capacitance and whether you're, you have a very low venous capacitance if of the sippy pier, you know, not to, to, so again, we have used that influence management, and, higher CVP, from eight to 10 suddenly makes you aware that in a patient who's got acute lung injury. You might actually, as we discussed at the beginning of this, you might actually want to squeeze the circulation rather than actually give more fluid in order to attain what you're trying to do to avoid any extra fluid going into the lungs. So it has changed our approach. Is it because you're not so in contact with the patient, but you still need to be bedside? You still need to do the ultrasound. You still need to make sure that the information you're getting is correct and interpret it accordingly.
Host: What about, are there, you know, there's been some reports from different medical centers, not just in the United States, but I think throughout the world about different techniques, different, strategies. Keeping people off ventilation. And I wanted to ask you this because sometimes when I hear that, it makes it sound like ventilation is something you don't always want, but if you're managing hemodynamics correctly, It isn't ventilation one of the best ways to help people to take a break. And he'll actually, take the pressure off the lungs to, to have to take the burden of, of gas exchange. So what your thoughts on that? I mean, do you necessarily, when somebody comes in ICU, do you look at them, Dr. Scott and you say, all right, what can I do to keep this person off ventilation? Or is that maybe sometimes the better option.
Dr. Scott: Yeah, I think that's a very good question because we know that the best physiology for your body is breathing spontaneously. And obviously we have swings in going from negative to positive intrapreneurial pressures to actually take a breath. So as soon as you ventilate someone, you're putting positive pressure continuously, especially with some peop and that has physio, physiological issues, both. Basically, putting pressure on the right heart, and also increasing into thoracic pressure and obviously AOE pressure can lead to, trauma of the lungs, which is why we go for a protective lung strategy with low tidal volume and low driving pressure. The fact that we're ventilating someone is you're taking away work of breathing. When people are very sick coming into hospital work, your breathing can be 40 to 50% of your oxygen requirement. So one of the key benefits in resuscitation of ventilating, someone is you're taking away work of breathing. And it's and if you've got less than tricolor failure too, it can help offload the heart. So in those patients, it can be truly a beneficial you're immediately increasing options delivery by the fact that you're reducing work of breathing. And then by. Ventilating someone with positive pressure, you actually drive more oxygen into the body and recruit our VOD that otherwise might not be working and participate in gas exchange. So you can often improve options, delivery quite dramatically. Despite the fact that physiologically it's not always the best option. The problem we have downstream is, we know that the lymphatic drainage of the lungs is important to maintain a clear lung fields. And one of the problems with positive pressure ventilation being authenticator is you, you get these problems with lymphatic drainage and the, clearance of the lungs and secretion. So it does predispose you to getting higher risk of pneumonia and in COVID there's also other problems, because you're can get the lung injury. backing up a bit, really with the COVID lung. we, we saw two phases of COVID lung injury. The acute phase is really a, you're getting an inflammatory response in your lung with the virus. And the most profound thing is hypoxia due to shunts. So you've got areas of the language damaged and hyperemic and don't and not taking part in gas exchange. And we saw lots of that. Patients arrive in the very, very low saturations and they responded immediately to positive pressure ventilation or bypass. we also had these special helmets, which we got from Italy, which fits it over. the patient's head and we could put positive pressure on and, and that helped immediately, and would get rid of the shunt. Some patients were too sick for that needed ventilating. And in those patients, initially, people thought you would need a traditional high peak strategy, but we didn't actually find that. and they also went on to develop a more traditional S florid lung picture, five or six days later. So we, I think we saw two clear patterns of lung injury in, in the covariate, pandemic, this acute sort of shunting, or when patients arrive early in the disease and then the really Florida RTS downstream, which. not everyone got, but probably about 25% of people with bad pulmonary injury on arrival. Seem to develop that.
Host: Dr. Scott, that's just also fascinating, with everything we just discussed, it's it really is fascinating. like how would you like. To kind of summarize all this. Like how would you like to, you know, just help other, critical care providers to understand a little bit about hemodynamics, especially in the context of COVID what would you like them to know?
Dr. Scott: Well, I think the first thing to view fluids, intravenous fluid is as a drug and how much you give is importance. It's easy to throw fluid and resuscitate people early on, but you can pay for it. Later. And that's what we saw in the COVID population is once you ended up with a significant positive for balance, it was very hard to really get those patients back down to normal ventilatory parameters. And so I think the key thing is, is to, to obviously use your bedside clinical data, to use ultrasound interpretation, looking at both the IVC and the cardiac function. And so then use once, you know, you've set your fill in your flow then to titrate your razor presses. And I think that the thing that we found very useful, especially in the more hands off approach, with COVID patients, wasn't enjoying our to align and using continuous cardiac health monitoring so that you could map the trends of cardiac output and stroke volume, and those that are breathing spontaneously. And those that are ventilated at eight mils per kilo, which does prove some problems, obviously with the, with the arts network, ventilation strategy five to seven, but eight is not far off seven. so that's what we started at least after initial resuscitation and then moved on to lower tidal volume. And then you can use the other parameters like SVB and PPV. so it keeps the basics really feel slow pressure and don't give too much fluid.
Host: Fantastic. Dr. Scott, I want to thank you for coming on the show today. Dr. Michael Scott is the adjunct professor of anesthesiology and critical care medicine at the university of Pennsylvania.
This concludes another edition of the eye critical care podcast for the eye critical care podcast. I'm Dr. Mike. Thanks for listening.
This podcast is sponsored by immune express immune express offers, SEPTA site, rapid a host immune response test, which can provide results in one hour to differentiate between sepsis and SIRS in patients suspected of sepsis, thus expediting and optimizing patient management decisions and appropriate therapy. For more information, visit www SEPTA site.com. Michael Smith MD received his medical doctorate from the university of Texas Southwestern medical center. He practiced internal medicine and radiology in Dallas, Texas in the early two thousands before transitioning to the pharmaceutical and nutraceutical industries as an educator and consultant.
The eye critical care podcast is the copyrighted material of the society of critical care medicine. And all rights are reserved. Statements of fact, and opinion expressed in this podcast are those of authors and participants, and do not imply an opinion or endorsement on the part of the society of critical care medicine, it's officers, volunteers, or members, or that of the podcast commercial supporter.
This podcast is sponsored by immune express immune express offers, SEPTA site rapid a host immune response test, which can provide results in one hour to differentiate between sepsis and SIRS in patients suspected of sepsis, thus expediting and optimizing patient management decisions and appropriate therapy. For more information, visit www.septisite.com.
Dr. Michael Smith: Hello, and welcome to the I-Critical Care Podcast. Sponsored by the Society of Critical Care Medicine. I'm your host, Dr. Michael Smith. Today, we're going to talk about hemodynamic monitoring in the ICU with Dr. Michael Scott. He's an adjunct professor of anesthesiology and critical care medicine at the University of Pennsylvania. Dr. Scott, welcome to the show.
Dr. Michael Scott: Thank you very much. It's very good to be on the show, thank you.
Host: You know, Dr. Scott, you're speaking to a radiologist, right I haven't been in the ICU. And so, so many years, I do remember very specifically the importance of hemodynamic monitoring, fluid management, in critical care patients.
So, I just thought maybe for a moment, we could just back up for a sec and talk about why this is so important, you know, even given the context of COVID, today, like, what are you, what are your thoughts about this topic is.
Dr. Scott: Yeah, I think fluid therapy is one of the key interventions that we do on critical care that can make a massive difference to the patient. I think everyone's aware that the fluid therapy is key to maintaining intravascular volume. And a good cardiac output and blood flow around the body to perfuse organs and avoid organ dysfunction. And also, there's increasing recognition, but there is a threshold mean arterial pressure below which you go, gives you a signal of, of injuries, particularly AKI and my caudal injury. And so you could say, well, why not just give lots and lots of fluid to a patient and just to optimize those all the time. But we do know too that there's a downstream major complications are caused by fluid overload. And as soon as you give roundabout 40 to 50 miles per KIDO of fluid above someone's, sort of dry weight, which is about two to three kilograms in practice. You start getting a signal of all cause complications because you get pulmonary problems, you get gutta, DEMA, and, and the more fluid overload you get downstream, the more, the signal is of increasing complications. So, you've got this problem that the easiest thing to do is to give fluid. but if you don't pay particular attention to it, you get, you pay for it downstream. So, what we really need is some form of monitoring system to add to clinical ability, to enable the fact that we can keep our patients well resuscitated, but avoid that fluid overload downstream. It's been particularly person in the COVID crises because we've seen different phases of how patients get sick. They've arrived, dehydrated and very sick initially, then fluid resuscitated, and then there's been different patterns of how they've been treated. Either reef kept them breathing on oxygen or they've ended up being intubated and on a ventilator. And for both of those, our approach to fluid therapy has also been different.
Host: Yeah, it's interesting, right doctors. Cause I do remember this, right. There's a balance between, dry and wet, right? At the end of the day, we don't want to be too dry in critically care patients. As you mentioned in the COVID crisis, a lot of these people are coming in. To the hospital are ready in severe distress from what I understand. And, they are dehydrated. You give that fluid, but there, but you've got to balance that you got to, you got to know when to, when to back that off is, do you believe that's one of the greatest challenges for, critical care doctors when it comes to maintaining profusion is figuring out , like wet versus dry. Like how do I balance it? Is that one of the biggest challenges?
Dr. Scott: I think it is actually because obviously too much fluid and the first organ often to go down and see your lungs, particularly in physiological situations, such as COVID where you've got, a disease process in the lungs. And, breakdown of the alveolar membrane can be to increase its true vascular lung water and, and a R D S. And then you've also got your kidney, which, which likes, adequate intravascular volume. So really what we're seeing in medicine is, is you've got to balance the risk between organs. we did have the luxury really when continuous intravenous hemodialysis came along, that we could always, run patients on the slightly drier side. in order to protect their lungs and put them on only dialysis, but what's been fascinating in the last few months with COVID is because there's been such a strain on resource allocation. We haven't really had that luxury of being able to have this backup of a renal support that you would otherwise be able to offer every patient, because we've just had such a huge number of patients that have been so sick requiring it a lot of, facilities.
Host: And a lot of these patients, obviously that are coming in have comorbidities, diabetes, heart disease, COPD, lung, other lung issues, et cetera, et cetera. I guess, I guess what comes to my mind then is like when someone like yourself is at the bedside. And you're, you're trying to balance that, that fluid management yet at the same time, there's some clinical interventions that may be, you need to do, to stabilize the patient, make sure that they're getting better. How do you, how do you, how do you manage that? How do you decide, okay, If I'm going to do this intervention at bedside, how does that affect the hemodynamics? A w is that a conversation you have with the other doctors? Are there, is there standardization for some of those. Interventions and how they affect profusion.
Dr. Scott: Yeah. I wouldn't say there is, there's a great standardization across the ICU community, because everyone has different skillsets and different equipment available. But one of the, the two key areas, I think, which have helped push us towards an area where we can start standardizing and, and that is the use of bedside ultrasounds. To assess fluid status and the filling of the heart and the other is use of, arterial wave form analysis, which we can now use algorithms to estimate stroke volume. And also, responsiveness to fluid. And I think that's where the community are going. It's, it's, it's the patient should be responsive to for bolus or not. And if you do give that food bonus, is it actually going to benefit them or is it going to harm them downstream? So I think that's the framework of how we approach a patient. And so really when you're faced with a patient who needs resuscitating hypotensive, initially, it’s a straightforward, problem, because you, can ultrasound them, show that they're intravascularly, dry and give them a float bolus. I think the problem comes is when you've got complex disease mechanisms that we see on ICU, you've got visa dilation of the arts are freeze, so you've got vasoplegic shock. So you can actually keep giving fluid. And it then stops actually raising the blood pressure. And what you really need is pervasive process such as something like Knorr epinephrine. And so the art of getting the balance of filling the circulation and before squeezing it with a vasopressor is actually absolutely key because if you start the vasopressin too early, then you're going to hurt your splint, Nick and renal blood supply, and, and actually create more problems. So the artist's getting the balance and I like to really break it down very simply and call it. The approach is fill flow pressure where you fill the tank, which is the heart and make sure there's adequate flow and options delivery. And after you've got enough options, delivery and flow to the organs, and really what you've got to do is set your profusion pressure. And that venue is dialing up the Knorr. Epinephrine always oppressive, which of use to get the right mean arterial pressure. And then you ended up with a balanced circulation with a minimum amount of fluid that you need to.
Host: But Dr. Scott, then that implies that we're not just doing an ultrasound at the bedside. We got it. We have to do some echoes. Right? So you have, you have two different. Technicians working at the bedside right together, making sure that the heart is maintaining that flow based on that bolus of fluid. And then they, and then the ultrasound tech, making sure that we're perfusing, like, for example, the kidneys properly with that. So do you see both of those technologies working together in this kind of scenario?
Dr. Scott: Yeah, so, and I think what we've seen in the last 10 years is most critical care physicians such as myself. Have now, taken up the skill of bedside ultrasound to look at both the venous capacitance, measuring the IVC, and also being able to do a good estimate of filling of the left ventricle, looking at different views and making sure that the heart is structurally sound and there's no other issues such as a tamper nod or valve.
It. Issues. So it's increased our bedside decision making by having this skill sets. So we can do the first two things. You said, the fill in the flow and optimize that. And then when you look at the pressure after that, and you know, you've optimized the previous two, you can safely start a visa presser and then maintain profusion.
Host: How do you, as, as a critical care physician though, like when you're giving some of these medications that can dilate versus constrict, et cetera, et cetera, how, how do you measure then some of the other key parameters when giving fluids such as like stroke volume, stroke, volume variation, like how, how do you, and I bring this up because you mentioned there really isn't a lot of standardization, within your field. So, so when giving fluids. How do you standardize the applying to some of these key parameters like stroke volume?
Dr. Scott: Yeah. And stroke volume can be measured in many different ways. you obviously you can use a Thermo dilation such as the song dance Kaphas. You can use transthoracic or transesophageal echo. You can use a software Gerald Doppler, and then you can use wave form data’s, often arterial line, the wave form data off an arterial line in a patient breathing spontaneously can give you trends and it can give you swings and it can give you the response to flu bolus. but we can have more information if you've got a ventilated patient, if you can ventilate a patient, a title of one of your ground, about eight mils per kilos, you can then look at something called the pulse pressure variation or the stroke volume variation. And that is actually using the post-concert wave analysis. You can actually measure the estimate, the stroke volume and how that's changing through the respiratory cycle. And this has been shown to be very accurately predict whether you will be responsive to a fluid bolus or not. And we're looking at figures of a stroke volume variation of, of less than 12%. You're very unlikely to need fluid. If you're ventilated at eight mils per kilo and pulse pressure variation, slightly higher around about 14%. And these markers are very useful because when you were not to align in and sedated and ventilated patient bedside, you can have these running constantly. And then obviously you can track the changes. So if you'll start voting very well, let's see you raised to say 16 or 18%. There is a very strong chance of that patient would benefit from a fluid. Bolus, and then the stroke volume variation would go back to a more normal thicker, less than 12%.
Host: So I want to, take this conversation now into, what's obviously, the big elephant in the room and that's, COVID. and I, and I appreciate Dr. Scott, the, the work that you've been doing, you know, critical care nurses and physicians like yourself are really on the front line and doing an amazing job. So thank you so much for that. And I know, the amount of hours and time that you're putting in is like, Nutty and crazy. And I just, just so you know, that we appreciate that what you're doing and, and taking the time to come talk to us today. So let's talk a little bit about COVID. what does COVID done to the ICU? Like, how has that changed the way maybe you approach, patients who are coming in really critically ill. Really dehydrate it. some of them maybe need to be ventilated right away, maybe some don't. How are you managing all that?
Dr. Scott: Yeah, I think going to a higher level, obviously our whole approach to COVID it's been different because we've had, all the contact precautions, PPE to protect all the staff from any contact with the virus. And I must say at the university of Pennsylvania, we've been very successful with our PP in, in. W we don't know of anyone on our units, who've actually developed, COVID-19 looking after patients. So I think that's been a real success. And I think at the start of the COVID pandemic, everyone was obviously very anxious, but now people feel quite comfortable putting on the 90 fives and the Packers and entering rooms. So it's less of an issue. What the higher-level view is though is it's meant that we haven't been in such close contact with our patients, bedside, cause we've tried to limit contact, limit nurses going into the room as well as obviously the physicians. So use of an arterial line has been extremely useful in these patients because you can then monitor them remotely and you get quite a lot of information from the arterial line. So I think, what's interesting is out of this is we've learned to probably look at one that is a little bit more careful. It's just, we can't always go in and actually examine the patient necessarily as frequently as we would have otherwise. So the use of these indices, PPV and SPV have been very useful. having a continuous or two away from analysis with continuous cardiac output monitoring, those, become much more standard, I think for looking after patients. there are other things I think too is, is we've used the passive leg raise of up, to look at fluid responsiveness, because the great thing about that is, you're lifting both legs up in the air. For at least sort of half a minute that you're effectively giving a full bolus, but as soon as you drop the blog's down, you, you haven't given that through permanently. So it gives you the chance to see if the patient's food responsive without actually giving them the fluid and then arterial lines being very useful, at, assessing that as well. The other thing, I think that's a, we have done a lot in COVID patients are ventilators. They have had central Venus, candidates in place to run low dose, a cerveza pressor and also, sedatives and things. and. Although central venous lines, don't give you fluid responsiveness. They do give you an idea of the venous capacitance and whether you're, you have a very low venous capacitance if of the sippy pier, you know, not to, to, so again, we have used that influence management, and, higher CVP, from eight to 10 suddenly makes you aware that in a patient who's got acute lung injury. You might actually, as we discussed at the beginning of this, you might actually want to squeeze the circulation rather than actually give more fluid in order to attain what you're trying to do to avoid any extra fluid going into the lungs. So it has changed our approach. Is it because you're not so in contact with the patient, but you still need to be bedside? You still need to do the ultrasound. You still need to make sure that the information you're getting is correct and interpret it accordingly.
Host: What about, are there, you know, there's been some reports from different medical centers, not just in the United States, but I think throughout the world about different techniques, different, strategies. Keeping people off ventilation. And I wanted to ask you this because sometimes when I hear that, it makes it sound like ventilation is something you don't always want, but if you're managing hemodynamics correctly, It isn't ventilation one of the best ways to help people to take a break. And he'll actually, take the pressure off the lungs to, to have to take the burden of, of gas exchange. So what your thoughts on that? I mean, do you necessarily, when somebody comes in ICU, do you look at them, Dr. Scott and you say, all right, what can I do to keep this person off ventilation? Or is that maybe sometimes the better option.
Dr. Scott: Yeah, I think that's a very good question because we know that the best physiology for your body is breathing spontaneously. And obviously we have swings in going from negative to positive intrapreneurial pressures to actually take a breath. So as soon as you ventilate someone, you're putting positive pressure continuously, especially with some peop and that has physio, physiological issues, both. Basically, putting pressure on the right heart, and also increasing into thoracic pressure and obviously AOE pressure can lead to, trauma of the lungs, which is why we go for a protective lung strategy with low tidal volume and low driving pressure. The fact that we're ventilating someone is you're taking away work of breathing. When people are very sick coming into hospital work, your breathing can be 40 to 50% of your oxygen requirement. So one of the key benefits in resuscitation of ventilating, someone is you're taking away work of breathing. And it's and if you've got less than tricolor failure too, it can help offload the heart. So in those patients, it can be truly a beneficial you're immediately increasing options delivery by the fact that you're reducing work of breathing. And then by. Ventilating someone with positive pressure, you actually drive more oxygen into the body and recruit our VOD that otherwise might not be working and participate in gas exchange. So you can often improve options, delivery quite dramatically. Despite the fact that physiologically it's not always the best option. The problem we have downstream is, we know that the lymphatic drainage of the lungs is important to maintain a clear lung fields. And one of the problems with positive pressure ventilation being authenticator is you, you get these problems with lymphatic drainage and the, clearance of the lungs and secretion. So it does predispose you to getting higher risk of pneumonia and in COVID there's also other problems, because you're can get the lung injury. backing up a bit, really with the COVID lung. we, we saw two phases of COVID lung injury. The acute phase is really a, you're getting an inflammatory response in your lung with the virus. And the most profound thing is hypoxia due to shunts. So you've got areas of the language damaged and hyperemic and don't and not taking part in gas exchange. And we saw lots of that. Patients arrive in the very, very low saturations and they responded immediately to positive pressure ventilation or bypass. we also had these special helmets, which we got from Italy, which fits it over. the patient's head and we could put positive pressure on and, and that helped immediately, and would get rid of the shunt. Some patients were too sick for that needed ventilating. And in those patients, initially, people thought you would need a traditional high peak strategy, but we didn't actually find that. and they also went on to develop a more traditional S florid lung picture, five or six days later. So we, I think we saw two clear patterns of lung injury in, in the covariate, pandemic, this acute sort of shunting, or when patients arrive early in the disease and then the really Florida RTS downstream, which. not everyone got, but probably about 25% of people with bad pulmonary injury on arrival. Seem to develop that.
Host: Dr. Scott, that's just also fascinating, with everything we just discussed, it's it really is fascinating. like how would you like. To kind of summarize all this. Like how would you like to, you know, just help other, critical care providers to understand a little bit about hemodynamics, especially in the context of COVID what would you like them to know?
Dr. Scott: Well, I think the first thing to view fluids, intravenous fluid is as a drug and how much you give is importance. It's easy to throw fluid and resuscitate people early on, but you can pay for it. Later. And that's what we saw in the COVID population is once you ended up with a significant positive for balance, it was very hard to really get those patients back down to normal ventilatory parameters. And so I think the key thing is, is to, to obviously use your bedside clinical data, to use ultrasound interpretation, looking at both the IVC and the cardiac function. And so then use once, you know, you've set your fill in your flow then to titrate your razor presses. And I think that the thing that we found very useful, especially in the more hands off approach, with COVID patients, wasn't enjoying our to align and using continuous cardiac health monitoring so that you could map the trends of cardiac output and stroke volume, and those that are breathing spontaneously. And those that are ventilated at eight mils per kilo, which does prove some problems, obviously with the, with the arts network, ventilation strategy five to seven, but eight is not far off seven. so that's what we started at least after initial resuscitation and then moved on to lower tidal volume. And then you can use the other parameters like SVB and PPV. so it keeps the basics really feel slow pressure and don't give too much fluid.
Host: Fantastic. Dr. Scott, I want to thank you for coming on the show today. Dr. Michael Scott is the adjunct professor of anesthesiology and critical care medicine at the university of Pennsylvania.
This concludes another edition of the eye critical care podcast for the eye critical care podcast. I'm Dr. Mike. Thanks for listening.
This podcast is sponsored by immune express immune express offers, SEPTA site, rapid a host immune response test, which can provide results in one hour to differentiate between sepsis and SIRS in patients suspected of sepsis, thus expediting and optimizing patient management decisions and appropriate therapy. For more information, visit www SEPTA site.com. Michael Smith MD received his medical doctorate from the university of Texas Southwestern medical center. He practiced internal medicine and radiology in Dallas, Texas in the early two thousands before transitioning to the pharmaceutical and nutraceutical industries as an educator and consultant.
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