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Effect of Vapours on Cardiac Function – Respiration and Cardiovascular System

by Brian Warriner, MD
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    00:00 blood flow to vital organs, including the heart. This graph gives you an idea of how the vapours affect cardiac function. On the upper graph to the left, you can see how mean arterial blood pressure is affected by the vapours, and basically all of them cause a decrease in blood pressure, at least mean arterial pressure.

    00:19 But there is a bit of a difference with Desflurane, which tends to come down and then stabilize a bit, and with Sevoflurane that also does that. Comes down, there's a drop in blood pressure, and then there's a stabilization.

    00:31 So you don't have to worry about it continuing to drop quite so much. On the right upper graph you're looking at cardiac output affected by vapours. And you can see that Desflurane has a very slight effect on cardiac output. Initially a bit of a drop, and then it tends to come back and stabilize. Sevoflurane, a bit more profound, but the older drugs, Isoflurane and particularly Halothane, are continuing drop in cardiac output as the concentration of the vapours increased. On the left lower graph we're looking at Systemic Vascular Resistance. So this is the resistance against which the heart works when it contracts. And you can see that Isoflurane causes quite a profound drop in peripheral resistance, as does Desflurane. This can be a good thing in the presence of poor cardiac output, because it improves the ability of the heart to eject blood against a lower resistance. However, it may result in hypotension and decreased blood flow to organs.

    01:31 In the bottom slide to the right is Heart Rate, and you can see that Desflurane initially causes very little change in heart rate and then, as you increase it, there is fairly marked increase in heart rate. Isoflurane, on the other hand, causes quite a nice stable increase in heart rate, and it stays pretty much at a level that doesn't change for a period after that. Heart rate's critical in these patients, because increases in heart rate increase oxygen demand by the heart. And so, we don't like to see tachycardia, particularly in middle aged people or older people. So how about the induction drugs? We already mentioned Propofol and Pentothal.

    02:13 We're now going to talk about Ketamine and how it affects cardiac function.

    02:19 Ketamine is often used in patients who appear to be volume depleted at the time of surgery or have had trauma, because it increases heart rate and increases blood pressure moderately.

    02:31 The problem is that it can lead to increases in blood pressure that are unacceptable, and it can lead to tachycardia or increased heart rate that's unacceptable. On the good side, it acts as a pain killer. So less opioids needs to be used. You can give Ketamine without a whole lot of extra narcotic on board. The problem with Ketamine, and one of the reasons why it isn't as widely used as it might otherwise be, is that people have what are called Emergence Phenomena when they start to wake up from Ketamine, which can include hallucinations and quite strange behaviour. Patients will wake up and be picking at things in the air, they'll think they see bugs.

    03:13 They'll be very concerned about noises in the room. So, at the time Ketamine was used fairly regularly in the early 80's, the recovery rooms were often kept dark and very, very quiet. Which meant you really couldn't see your patient and monitor them adequately. So that was totally unacceptable and we no longer accept that as a property within our recovery rooms. Etomidate, which is a drug that has been available in the United States for many years, but in many other countries hasn't been available, because it wasn't marketed due to cost constraints, is a very good drug to use in patients who have had brain trauma. Because it has very little effect on intracerebral blood pressure, has very little effect upon the cardiovascular system, and oxygen, cerebral oxygen delivery tends to remain stable. But it's not a perfect drug. It suppresses the release of cortisol from the adrenal cortex. And this may interfere with the body's ability to handle the stress of trauma, surgery, or anesthesia. And there are some reports that suggest, that unexpected death following surgery. Not at the time of surgery, but in the weeks to maybe a month following surgery, that unexpected death is higher in patients who have had Etomidate. So, what does the anesthesiologist do about these changes? Low blood pressure can reduce blood flow, thus oxygen supply to vital organs.

    04:43 Rapid heart rates can increase the work of the heart and increase the need for myocardial oxygen, which is difficult to supply in the presence of low blood pressure.

    04:55 A blood pressure that is too high is also unacceptable, as it can lead to strokes, an increased cardiac work, which may cause cardiac ischemia or heart attacks.

    05:07 So the anesthesiologist can modify these variables by careful administration of either stimulating drugs, such as Ephedrine or Phenylephrine, Epinephrine or Norepinephrine, which increase blood pressure and heart rate. Of course, all of these drugs have their pros and cons.

    05:25 So careful understanding of each is necessary before one uses them. For instance, Phenylephrine will increase blood pressure quite nicely, but only for a very short period of time and often causes quite a profound drop in heart rate, whereas the others all increase heart rate and tend to increase blood pressure. Constant monitoring of the patient's condition, during and after anesthesia, has shown to be the most important aspect of anesthesiology.


    About the Lecture

    The lecture Effect of Vapours on Cardiac Function – Respiration and Cardiovascular System by Brian Warriner, MD is from the course Anesthesiology: Introduction.


    Author of lecture Effect of Vapours on Cardiac Function – Respiration and Cardiovascular System

     Brian Warriner, MD

    Brian Warriner, MD


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