Shock - diagnosis and treatment

- In order to diagnose and treat shock what do you have to do, like how do you go about diagnosing and discovering shock, figuring out what type of shock it is and utilizing the proper treatment for that type of shock. Well, there's really three ways that I like to break it down. So, first of all, what's going on in shock? Well, we have severely decreased tissue profusion. And what that means is decreased oxygenation to the different cells of the body. And, as we know, decreased oxygenation means decreased ability to create energy. And, without energy cells can become defunct or die. So, that just of course highlights why diagnosing shock is so important. So, I'm going to break it down into three steps, but let's think about this. First of all, shock is decreased tissue profusion and so we need to focus on the delivery of oxygen. Well, how does the body deliver oxygen? Well, the heart pumps blood throughout the body to the tissues. And so here's an oversimplified version of how the cardiovascular system works. Blood is pumped from the heart to the tissues and blood returns to the heart. And this is the cycle of oxygen delivery. So, looking at this, the first thing I think is what can get this to fail? Well, first of all, we can mess with the pump, right? Is there something wrong with the pump? Is the heart not working? Also, along those same lines, the entire cardiovascular system. Is there something wrong with the pipes, are the blood vessels not performing their task of carrying oxygen to the tissues and back to the heart? So, really the first way to measure that, the first way to look at that, is to look at blood pressure. And that's tied directly to both the pipes and the pump. Blood pressure, the equation for blood pressure is cardiac output times systemic vascular resistance. So, that's both the heart, the pump, and the vascular system, the pipes. And this is usually the way that practitioners are alerted that patients might be experiencing shock of some sort. Now, how else can we analyze the pump? Now, heart cells have an enzyme called troponin. So, when these heart cells are damaged, they release troponin into the system and it can be detected in the blood. So, getting a blood test for troponins is one way to assess the pump. Getting an echocardiogram is another great way to assess the pump, to look directly at how the heart is functioning and contracting. If it's not contracting properly, blood can't be squeezed forward to the body. So, blood pressure, troponins, echo. Next, a really good test that is sometimes used is pulmonary capillary wedge pressure, PCWP. Pulmonary capillary wedge pressure. Or also assessing CVP, central venous pressure. Now, what are these abbreviations? This is a little confusing. Well, essentially these two pressures are the different pressures in the sides of the heart. Pulmonary capillary wedge pressure is associated with the left side of the heart, specifically the left atrium. The central venous pressure is the pressure that's seen in the right atrium. And so, these two pressures give you an idea of how the left and the right side of the heart are functioning. For example, if the left side of the heart is not pumping. Let's say, all this tissue down here gets damaged because the patient has a heart attack. This heart tissue is dying, or has died. So, now this heart tissue cannot squeeze, it can't function. And this makes blood accumulate in the left ventricle. It just kind of pools there, because the heart can squeeze hard enough to push it out. And so pressures in the left side of the heart will be higher, because this volume backs up and causes pressure on the heart. But now, these are both found by getting a pulmonary artery catheter and threading that catheter into the heart, into the right side of the heart, and then up through the pulmonary artery, deep into the pulmonary vasculature. In fact, so deep you essentially get a wedge pressure. You're wedging this probe into the pulmonary capillaries. So, pulmonary capillary wedge pressure you wedge this probe all the way up to determine that pressure. And that gives you a good indication of the left heart pressures. CVP, central venous pressure, here's the central vein. So, there's actually another part of the catheter, the pulmonary artery catheter, that has a probe that senses the pressure in the right side of the heart. So, using a pulmonary artery catheter, you can get an indication of the different pressures of the heart. And as I said, this can help you figure out what's going on. And can help you distinguish the type of shock. For example, if the heart is not functioning, like in cardiogenic shock, then you're going to have high pulmonary capillary wedge pressures. The heart is no longer functioning and can't pump blood forward. However, in an example like hypovolemic shock, meaning low blood volume, the pressures won't be very high in the heart at all. There's so low blood volume, that pressure is relatively low in the heart. So, pulmonary capillary wedge pressure may be very low. And so this is just an example of how you can distinguish between types of shock. Okay, so, we've looked at the pumps and the pipes. What else is important in shock? So, the second thing I think about is oxygen. Oxygen's kind of a big thing, it's what we need to survive. So, is the patient getting oxygen? So, probably the least invasive way to assess oxygen is through pulse oximetry. Pulse oximetry, often known as pulse ox, uses different wavelengths of hemoglobin to assess the oxygen status. So, really what you should know is that you put a little device on the finger of a patient. It shines light through the ateries and has a way to calculate how many hemoglobin molecules are oxygenated versus deoxygenated. So, it's a quick way to assess oxygen. Now, a little more invasive, and probably one of the most important tests to get in a patient with shock, is an ABG. This is an arterial blood gas. Arterial blood gasses assess several different parameters. Of course, it'll assess the oxygen in the body. But it'll also assess blood gasses such as carbon dioxide and bicarbonate. An arterial blood gas also gives you the pH, or how acidic the patient's blood is. These are very critical readings that are important to diagnose shock. So, assessing oxygen, we have pulse ox and ABG, getting that blood test. And, also, your pulmonary artery catheter can get something called the central venous oxygen saturation, SCVO2. So, this CV is central venous. Oxygen saturation of the central vein. Now, we talked about the central vein before, that was the superior vena cava and the inferior vena cava, which dump blood into the right side of the heart. So, look at this device here, the pulmonary artery catheter would actually sit inside the heart. So, there can be another part of this probe that assesses the oxygen content. Now, why is that important? Well, in different types of shock, the central venous oxygen saturation can be either increased or decreased. If the issue is cardiogenic shock, just as an example, when blood is pumped to the cells, it's pumped very slowly. And the cells, they require the same amount of oxygen that they had before. But now oxygen is getting there more slowly. And so the tissues furiously try to pick up more oxygen. And not as much oxygen returns to the heart. And that's assessed by the pulmonary artery catheter. So, less oxygen content means that tissues were pulling out more oxygen. And, in the same token, if there is less oxygen extraction, so, for example, if the tissues are flooded with fluid and there's a lot of edema, oxygen cannot get to the tissues. And so maybe more oxygen is carried back to the heart. And so that leads to an increased central venous oxygen saturation. So, first look at the pump and the pipes. Second, is the body getting oxygen? And, last of all, if the body isn't getting oxygen, is it getting damaged? Are the cells of the body and the organs getting damaged because they don't have oxygen. They need oxygen to create energy. And without energy, cells can't function. So, without oxygen cells can't function. Well, I should say they can't function in the long term without oxygen. In the absence of oxygen, cells of the body kick up what's known as anaerobic metabolism. Metabolism without oxygen. Creating energy without oxygen. And the body can't sustain this for very long. Now, the reason I mention this is a byproduct is lactic acid. This is not the most efficient process. So, in assessing if a patient has shock, is there any lactic acid that is accumulating in the body. Because this should not be present in high amounts under normal circumstances. That's a sign of shock, and that's probably between the ABG and this, these are probably the most important tests to get. So, what else, organ's can be damaged. What if the liver's damaged? If liver cells are damaged they release enzymes, just like the heart did when the heart was damaged. They have a specific name but this is test you perform to assess the liver's function. So, liver function tests are important. Now, how about the kidneys? The kidneys can also be damaged and if they're damaged, there's two things you can really look at. The first, if you do a blood test, you can get an elevated creatinine. Now, creatinine itself, unlike LFTs and triponins are not produced by the kidney. But, the kidney's job is to filter out fluid, right? If the kidney's are no longer producing fluid, then creatinine accumulates in the body. So, that's actually, creatinine comes from the muscles. So, it's a good marker to use if the kidneys stop working. And, similarly, if you see decreased urine output, that means the kidneys aren't producing urine. So, that's a sign that the kidneys have also started to get damaged or shut down. And there's lot of other ways you can assess how the organs are functioning. For example, the brain, if a patient has confusion, then that could be a sign that their brain is starting to lose its oxygen supply. And, last of all, treatment focuses on two things. And I like to say the first thing is you want to prime the pump. By priming the pump I mean we want to get the pump going. We need to put fluid into the heart to allow fluid to be pumped through. Now, this is exactly what happens in a water pump. Water needs to be in the pump to allow a pressure within the pump to push fluid forward. That's exactly how our heart works. There needs to be fluid in the heart to push forward. So, giving fluids may be a way to treat that. And, number two, tightening the blood vessels, increasing the resistance, right? We go back up here and we see systemic vascular resistance is a part of blood pressure. And the blood vessels are tightened by medications such as pressors. Medications that help improve resistance and improve blood pressure. And so by giving fluid you're trying to establish pre-load, trying to fill the heart up so it can pump. And pressors are trying to improve the vascular resistance, systemic vascular resistance.