 And our next speaker in this session is Dr. William Bourbien-Souligny. He will talk about perioperative role of ultrasound, of urinal ultrasound. I'm looking forward for your presentation. Greetings, everyone. My name is William Bourbien-Souligny. I'm a nephrologist from Montreal. And today I've been invited to speak about the perioperative role of renal ultrasound. Thank you for the invitation to participate to this symposium. Here is our my disclosures. So the objective of this talk is to describe the normal anatomy of the kidney and its appearance on 2D ultrasound and also describe the normal appearance of Doppler renal ultrasound. And then to identify abnormal findings and their significance in a perioperative setting. Why would you want to perform renal ultrasound in the perioperative settings? Well, first, if it's an urgent surgery and the patient has kidney failure, you may want to do a differential diagnosis before the surgery starts. After that, in the perioperative setting, the patient may develop oliguria and anuria. And this requires some differential diagnosis at the bedside. After there is the opportunity to optimize kidney perfusion and also anticipate acute kidney injury in the postoperative period. So let's go on and move to the assessment and the normal anatomy of the kidney. So the kidney is an intra-abdominal organs. You can see the basic anatomy here. This is a longitudinal view of the kidney. So you see that it is usually closed by the liver on the right side and the spleen on the left side. And you see that the first layer here, which is the renal cortex is usually hypo- or iso-ecogenic to the liver on the side. The second layer, the medulla, contains the renal pyramids, which are usually hypo-ecogenic compared to the cortex. And after that, in the center of the kidney, there is the renal sinus and it is more ecogenic because of the fat. But you see that usually there is, we don't see the collecting structure because they are empty in normal setting. On surface ultrasound, the best way to assess the kidney and the most simple interpretation that is lying down is to go by the side, about the mid-excelery line. And when you approach the kidney that way, make sure that sometimes you must rotate the probe a little bit to obtain the full longitudinal view of the kidney, since the kidney is often at an angle in the abdomen. Now using TEE, the result, you can also usually see the left kidney using a trans-gastric approach as shown in the screen. Success is about 60% in adults, but papers in the pediatric literature reports a higher success rate using TEE. And you obtain a view which is shown in the screen and you can identify the normal structure on to the ultrasound. Now when you turn on color Doppler, you can identify the normal vasculature of the kidney and you can usually, when the signal is good, you can usually identify both the segmental, the interlober arteries and the interlobular arteries. So the interlober arteries and veins are usually between each of the pyramids of the medulla. When you move your sample volume over this area and you activate post-wave Doppler, you will usually obtain a waveform that look like this. So on surface ultrasound on the left and on TEE on the right. And you see that the upper part of the screen, of the baseline on the left is an arterial waveform with a sharp systolic upstroke. And on the bottom of the screen, you see the venous Doppler that is usually seen in the same image because the artery and the veins are usually close by. And the best described indices to measure on the arterial waveform is the renal resistive index. And it is usually the maximal velocity minus the minimal velocity divided by the maximal velocity during the cardiac cycle. And the normal resistive index is usually lower than 0.7 in the normal population. Now let's move on to abnormal findings. So the first thing that you will want to rule out in a patient that is anuric or reduce urinary output or in kidney failure of unknown cause is to determine if there is a urinary obstruction. Of course, even if the follic catheter is inserted, it's quite possible that the obstruction is on the upper part of the urinary system. So on the screen, you see a normal kidney and you see that in the middle, in the renal sinus, it is a bright echogenic without any collecting structure C. And then as hydronephrosis develops, you see that the collecting structure become dilated. This is mild hydronephrosis, moderate hydronephrosis with the major galaxies being dilated and then severe hydronephrosis with ballooning of the minor galaxies. Now, when hydronephrosis is chronic and prolonged, you see that the collecting structures are dilated but also that the cortex is very thin. So there is atrophy of the renal parenchyma due to chronic hydronephrosis. And this is something of, you can see that as unexpected findings in patients with minimal urinary symptoms presenting with kidney failure. Now, there is some renal condition into the ultrasound that mimics hydronephrosis. So here on the left, you have an example of medullary cyst. So medullary cysts are not that common. It's cortical cysts that are most common in the kidney. But here you see that medullary cysts could mimic hydronephrosis, but you see that the main difference is that those cavities does not join together in the center of the kidney. On the right side of the screen, you see some preeminent renal pyramids. And this can be seen sometimes and can mimic hydronephrosis. But as you can see as in the case of medullary cyst, you see that these structures does not join in the middle. So on the right image, in fact, this is a condition called nefrocalcinosis where the pyramids get calcified with chronic disease. There is also settings where, especially when a kidney Doppler is difficult, that you can miss hydronephrosis. So this is a patient that had hydronephrosis, but because of the bad quality of the ultrasound exam, it could have been missed. And in fact, this was clinically significant because this patient had sepsis on a urinary infection with an obstructed kidney due to a stone. So you can also note the echogenicity of the kidney as shown in the normal image here on the left. You see that the cortex is in the parankyma in general is usually a lesser dense echogenicity than the liver. But you see that the kidney can be aperecogenic in abnormal image. So in the center, this is a case of acute kidney injury due to acute tubular necrosis. And after a few days, the kidney can become aperecogenic like shown in the screen. And on the right side, you see a case of chronic kidney disease, the patient on dialysis. And you see that in this case, the kidney is atrophic and is aperecogenic, but blends with the fat in the abdomen. So it's very difficult to see. So among abnormal fine things that you can find on the renal ultrasound, there is some, the most common are cortical cysts. So you see here on the left side of the screen, a simple cyst with an anechoic image, but it is pretty large. And on the right side of the screen, you see a mass on the upper part of the ultrasound image. And you see that compared to a simple cyst, this is a complex structure with the terminal echoes. This is in fact malignant tumor, so that you could see. Be careful when reporting your ultrasound exam. The exam that you will do will likely not be to detect any abnormal mass. So be sure when you report to exam, not to write that you didn't see any abnormal mass because you will likely not do a complete exam with a complete scanning of the kidney and some mask may go on the point of care ultrasound exam. Now let's move to abnormalities that you can see on Doppler ultrasound of the kidney. So as I've shown you before, here is a normal color Doppler of the kidney. So some authors have proposed a semi-quantitative scale to identify if the kidney is well-perfused. So as you can see here, grade three means that you can see vessels in the entire field of view when you perform kidney ultrasound. But here with decreasing grade, you see that it is more difficult to see the vessels here on grade two. You see vessels in the interlobore vessels, but not beyond. And then here, grade one, you only see vessels in the vicinity of the illum. And then grade four, you can see any vessels on color Doppler. Now it will be great if this simple measurement could predict the occurrence of acute kidney injury, but that so far is not yet too convincing. This is the biggest study and studying this semi-quantitative scale of color Doppler. This is a study made in the setting of critical care with a population that had a good proportion of patients with sepsis. And you see that the semi-quantitative scale adds some capacity to identify the occurrence of acute kidney injury. But it was a very low discrimination, a little bit better than chance, but not by much and not superior to the clinician's prediction of acute kidney injury. But it must be understood that acute kidney injury is not only due to low perfusion and the fact that a lot of patients in this cohort had sepsis may have to reduce the ability to detect AKI because some patients may have abnormal kidney blood flow, but may have developed acute kidney injury nonetheless. Now this may be different in the context of cardiac surgery, although there is no definitive study on the subject. Here is an example from Dr. André de Nault on a case obtained using TE during cardiac surgery with circulatory arrest. So you see here during circulatory arrest, there's no signs of perfusion on color Doppler. And then as the mean arterial pressure increase, there is some color Doppler returning to the kidney here. This is in a map of 60, here a map of 70, here a map of 85, and here again a map of 60. But as you can see, even if the map is lower than in the previous image, the color Doppler is greater than immediately after circulatory arrest. So this may offer insight about how the kidney is reperfused after interoperative events such as circulatory arrest. Here is the reminder of how the kidney Doppler was at the mean arterial pressure of 60 just after the exit of circulatory arrest. So moving on now to the renal resistive index. So we call it the renal resistive index, but it's in fact a misnomer because it's not only measuring a renal resistant, there is no vascular resistance, but the variety of factor can influence this marker. So if you we have here our arterial tree, you see that the renal resistive index will be measured in the medium sized artery here. Everything affecting downstream resistance or impedance can affect the renal resistive index. So this can be vascular resistant, but it can also be extrinsic compression, for example, in abdominal compartment syndromes and also high venous pressure can also affect the renal resistive index, but also all the upstream factors influencing pulse pressure can affect the Doppler waveform, the arterial Doppler waveform in the kidney. So our retic valve function, artery through volume, age, vascular compliance and also any obstruction, for example, renal artery stenosis will also modify the arterial Doppler waveform and will influence the resistive index. So here's an example of how our retic valve disease can influence the renal resistive index and the overall shape of the kidney Doppler. So you see here before our retic valve replacement, we have the systolic upstroke in the arterial waveform is of lower velocity here. The acceleration is more sluggish. And then after our retic valve replacement, you see that the systolic upstroke is not brisk. So this is just an example of how it can affect. And here in the bottom of the screen, you can also see the effect of an interaptic balloon pump on the arterial Doppler. So as I previously said, any obstruction in the renal artery can affect, also affect the arterial Doppler waveform. So this is a case where a retic prosthesis was being installed for type two retic dissection. And as you can see on the left side of the screen, this is the right renal artery waveform here with the high resistive index, probably because of the baseline characteristics of the patients. But on the right side of the screen, there is the kidney Doppler waveform for the left renal artery. And this artery in this case was being partially obstructed by the retic prosthesis. And that's why the renal artery waveform was being blunted. And that's why the renal resistive index was actually lower than on the contralateral side. Intral operative monitoring may also have some other applications. For example, here is a case where at the start of the surgery, the renal resistive index was almost normal at 0.7 here. But during the case, there was multiple air emboli that were detected on transcranial Doppler, but also on the Doppler of the kidney here, some upper intensity signals. And then after the case, after the CBP, there was, as you can see, an increase in the renal resistive index compared to the preoperative one at 0.85. And this patient went on to develop acute kidney injury in the postoperative period. So overall, even if the renal resistive index is a marker that is influenced by many factors, in general, the high resistive index is predictive of acute kidney injury in the postoperative period. This has been shown in multiple studies, especially in cardiac surgery. In patients with, for example, sepsis, it is less well-recognized for reasons I previously mentioned. And this is our local data that come from 145 cardiac surgery patient. You see that it has a moderate discrimination in predicting the occurrence of acute kidney injury. This is when assessed right at the admission to the ICU after cardiac surgery. So in Terry, if you assess the renal resistive index and do an intervention, for example, the passive leg raise or a change in vasopressor, the change in the renal resistive index may be proportional to the kidney blood flow. Although, as I said, many factors can influence it, including postpressure, so that may change with the vasopressor support. We did a small study in after cardiac surgery, where we performed passive leg raise in cardiac surgery patients that were also at the pulmonary artery catheter, where we can measure cardiac output. And in fact, the change in renal resistive index during the passive leg raise was quite predictive of the change in cardiac output resulting from the passive leg raise. So pretty many results, but are interesting because repeated assessment of the renal resistive index could in Terry be used to determine the change in renal blood flow, especially in cardiac surgery patients. Now let's switch to venous Doppler. So what are the principle of venous Doppler? Well, the venous circulation is usually pretty compliant. So as we go backward in the venous circulation, usually the variation in the pressure in the right atria are not transmitted deep in the venous circulation. So for example, the portal vein would be monophasic with all much variation during the cardiac cycle and the same thing for the venous flow in the kidney. So as venous compliance drop, if the venous system gets distended, those variation in pressure in the right atria gets transmitted in the periphery. And then renal, there is venous posterity that can be detected in the kidney and elsewhere in the body. So in the kidney, you see the normal Doppler waveform in the bottom of the screen. So you see during the cardiac cycle, it is continuous during the cardiac cycle, but as the venous compliance drop, it will become positile with short interruptions and it can become positile with prolonged interruption and the flow restricted to diastole as the severity of venous congestion increase. So this is a case took during cardiac surgery. You see that in the beginning of the case, it is monophasic. And then during off-pump cardiac surgery, there was a red ventricular failure developed and it become positile. And then with interventions such as nail vasodilators, you see that there is resolving of the positility here. So we studied the phenomenon in cardiac surgery patients. And as you can see, it is very rare to see abnormal kidney venous Doppler in the preoperative period, but a significant proportion of patients will develop some alterations in intravenous flow in the postoperative period. And on the right side of the screen, you see that if it is detected on admission to the ICU, there is an increased risk of acute kidney injury in the patient that have alteration in intravenous Doppler. So as conclusion of this presentation, you see that there is, there can be several application of periperative kidney ultrasound. Some are more at the research stage. Some are well-established, but I think it is worthwhile in certain settings to do kidney ultrasound if you can. So kidney ultrasound can be used to identify obstruction in the pre or postoperative setting. It also can be used to moderately anticipate the development of acute kidney injury, but especially it can be used to gain insight into the immunodynamic factor affecting kidney function and kidney perfusion and could be used to individualize management and the periperative period. So thank you so much for your attention. I want to thank all the people that are funding my research activities. And I want to thank the organizers of the symposium for inviting me. If you have any questions, please reach out to my email address on screen. Thank you very much. Thank you for fascinating lectures from Dr. Bobien Solini. I understand that Dr. Bobien Solini won't be able to answer all questions, but I believe Andrea will be able to answer some of them.