Arterial Diseases – Hypotension and Shock

by Joseph Alpert, MD

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    00:01 Hello. This is vascular medicine: the advanced components. And this section we'll discuss hypotension—that is, decreased blood pressure—and shock.

    00:14 So let's start with the definition, as we've done in each of the other cases. Hypotension, or decreased blood pressure, is a blood pressure less than 100 mmHg systolic blood pressure, where the normal is generally, in the population, about 120/80. There are common symptoms associated with decreased blood pressure: fatigue; dizziness or lightheadedness; and occasionally, even fainting. Patients may have a fast heart rate; they may have a slow heart rate.

    00:50 But their blood pressure is low. The skin can be warm and not very sweaty in some patients, where they're markedly vasodilated in the skin. Or they may have cool, sweaty skin when the skin is very vasoconstricted. And hypotension is very commonly related to dehydration or blood loss. Shock is more severe than hypotension. Shock is not only low blood pressure, but it is an associated decrease in blood flow to critical organs. For example, it's a life-threatening condition. It's not only low blood pressure, but the brain and the heart and the kidneys are not getting enough blood flow, and they start to malfunction. This shock usually occurs in the setting of a very serious medical illness—for example, a large heart attack (large myocardial infarction), or an overwhelming bacterial infection where the bacteria are in the bloodstream, or a serious hemorrhage.

    02:01 The diagnosis is usually pretty straightforward. It consists of noticing that the blood pressure is low with a blood pressure cuff. And the patients show a number of signs when they have very low blood pressure. They're often confused. In many patients, they will have cool and sweaty skin and be pale. They have low urine output, because the kidney's not getting enough blood flow. And they often have a rapid heartbeat. However, there are exceptions. There are periods... states where the shock state is associated with warm, dry skin and with a slow heart rate, although there is almost always low urine output and confusion. The causes are many, but as I said in the first sentence in this unit, it is always—almost always —a very serious medical condition.

    02:55 For example: • A myocardial infarct or a heart attack • Bacteria in the bloodstream • A hemorrhage from some injury • Severe dehydration: We see this very commonly where I work, in Tucson, Arizona, in the desert.

    03:11 In the summertime, when the temperatures are well... can be well over 40°C, and the humidity can be 5%, dehydration is very common. • And finally, patients with severe heart failure, where the heart is functioning very poorly Each of these can result in the shock state. A number of factors can lead to this, as I've already said. The body has defense mechanisms. Remember, we talked about that in the last lecture: all the ways that the body defends a good blood pressure. But what happens in shock is that these defense mechanisms are overwhelmed, and the blood pressure decreases despite all of the attempts of the renin–angiotensin system, the antidiuretic hormone, the sympathetic nervous system—everything working to try and keep the blood pressure up, and yet they fail. For example, let's take one, a very common one: an infection in which the bacteria get into the bloodstream. What happens here is that when these bacteria get into the bloodstream, a whole lot of hormones and various chemicals are released, some of which are attempting to hold the blood pressure up. But others actually work against the system because of the invading germs, the invading bacteria in the bloodstream, and they actually depress the blood pressure. And they depress heart contraction, so that the cardiac output goes down and the peripheral resistance goes down and blood pressure falls catastrophically. So this is one of the major factors for causing shock, and this is often called bacterial shock or sepsis.

    04:55 In the normal blood pressure, as we've talked about, the arterioles constrict or dilate according to activity from the sympathetic nervous system and the various hormones in the blood that control the blood pressure, and they maintain the blood pressure in a normal state. But in the shock state, again, chemicals and hormones that are released into the blood often cause the arterioles to stay dilated and, therefore, keeps the peripheral vascular resistance markedly low. And that leads to very low blood pressure and low blood flow into critical organs: the brain, the heart, and the kidneys.

    05:34 So here you see it in a table, all of it put together. The defense mechanisms maintain a normal blood pressure and are overwhelmed because the… resulting in the blood pressure decrease. There are circulating components of the immune system that help fight bacteria but also cause peripheral dilation of the arterioles and decrease in peripheral resistance and a decrease in blood pressure, and that… the normal constriction of the blood pressures to… of the arterioles to raise the blood pressure doesn't occur. In fact, the opposite occurs: The vessels dilate. Peripheral resistance goes down. Blood pressure falls catastrophically.

    06:15 What about therapy? Well, there's a number of therapies. First of all, you want to increase the blood volume, because when the arterioles dilate, they markedly increase the volume of blood that's needed to fill the system. So if it's a hemorrhage, you often give blood.

    06:33 If it's a severe infection, we may give plasma—that is, the fluid component of blood—or other fluids to, in a sense, what we call "fill up the tank." Also, there are pharmacological agents that can be given that constrict the arterioles and raise the peripheral vascular resistance. For example, we can give adrenaline or noradrenaline, which constricts the peripheral arterioles, raises the resistance, and raises the blood pressure.

    07:02 We can even use mechanical devices, and there's a whole array of mechanical devices. The one that's best known and used very commonly is the so-called intra-aortic balloon counterpulsation device. You can see that a hotdog-shaped balloon is inserted into the aorta, and it's attached to a pump that pumps helium gas in and out of the balloon (helium gas because it can be very rapidly pumped in and out of the balloon). Each time the heart contracts, the balloon contracts. And each time the heart relaxes, the balloon inflates. And what that does is it increases blood pressure during diastole and it helps move the blood out of the heart during systole, so it increases cardiac output. Well, there are a whole variety of small heart–lung machines and a whole bunch of other equipment that's used in very sophisticated intensive care units that also help to maintain blood pressure in patients with severe shock. It's way beyond the level of specialization of this talk, but it's important to know that there's a whole variety of little pumps that can be put on catheters, that can be inserted into blood vessels, and that can help maintain cardiac output and maintain blood pressure while you're getting the patient over whatever catastrophic illness has caused the shock state. It is important that urgent and aggressive therapy be done early in the shock state before there is serious damage to the heart, the kidneys, and the brain. So, for example, a patient who's having a large blood volume loss from some injury: It's really important to get blood transfusion in there to get the blood pressure up. We often talk about, in trauma, the golden hour: the first hour after a serious injury where, let's say, an artery has been cut and the patient's bleeding copiously.

    08:59 If you get lots of blood into that patient during the first hour, there's a very good chance the patient will survive. If the blood transfusions don't occur for several hours, the chance of survival is much less. And, of course, emergency surgery: Let's take the trauma example. There's the patient, you know, who is bleeding from a torn artery.

    09:21 Obviously, the most important thing is to get in there and repair that artery so that you stop the bleeding. Or if there's a big abscess in the abdomen, filled with bacteria, that's putting bacteria into the bloodstream, you need to get a surgeon in there to drain that abscess and get all that pus and bacteria out of the abdomen. And then, of course, you have to use drugs as well: antibiotics and so forth. So you have to treat the underlying illness, and you have to treat aggressively and early, as quickly as you can, both with medicines and, when needed, with surgical intervention.

    09:55 So, in summary: • Remember that hypertension is a chronic condition of increased blood pressure, and it's often unnoticed by the patient. As I said in the last lecture, it's the silent killer. And chronic hypertension can damage the heart, the arteries; lead to heart attacks and strokes and kidney failure and so forth.

    10:16 And there's lots of effective medicines for hypertension.

    10:21 • However, what's important is that the opposite of hypertension can be equally life-threatening: hypotension. It's quite common, and often, it's something simple and straightforward.

    10:33 For example, when somebody has a simple faint—you know, they see blood or they see something very upsetting—suddenly, the vagus nerve dilates the blood vessels. The peripheral resistance falls. The blood pressure falls, and the patient may faint. Well, that's not a serious illness, as long as the patient doesn't fall and break a bone. And usually, patients recover pretty quickly. However, that's a more benign form of hypotension.

    10:58 • Severe hypotension, such as shock, occurs (as I have mentioned) through a number of serious illnesses. It is not only low blood pressure but very poor blood flow to critical organs. And many patients who go into shock don't survive, particularly if they don't get urgent care.

    About the Lecture

    The lecture Arterial Diseases – Hypotension and Shock by Joseph Alpert, MD is from the course Arterial Diseases. It contains the following chapters:

    • Hypotension and shock - Definition
    • Hypotension and shock - Pathogenesis
    • Hypotension and shock - Therapy
    • Hypotension and shock - Summary

    Included Quiz Questions

    1. Patients with hypotension usually complain of headache
    2. Patients with hypotension often complain of dizziness
    3. The skin of patients with hypotension can be warm and dry or moist and damp
    4. Patients with a systolic blood pressure less than 100 mm Hg are usually said to be hypotensive
    1. Hyperthyroidism
    2. Myocardial infarction
    3. Gastrointestinal hemorrhage
    4. Vasovagal syncope
    1. Decreased levels of blood adrenaline (epinephrine) and noradrenaline (norepinephrine)
    2. Organ malfunction
    3. Decreased urine output
    4. Circulating substances that depress blood pressure
    1. Intensive tube feeding with a high protein nutritional supplement
    2. Intravenous infusion of noradrenaline (norepinephrine)
    3. Infusion of blood
    4. Urgent surgery

    Author of lecture Arterial Diseases – Hypotension and Shock

     Joseph Alpert, MD

    Joseph Alpert, MD

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