Neuro Anesthesia – Anesthesia for Special Operations

by Brian Warriner, MD

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    00:00 deflated one-lung anesthetic situation. We're going to move now to Cardiac Anesthesia, which is a very common type of anesthesia nowadays, but is a very unique form of anesthesia.

    00:08 In cardiac surgery, in open-heart surgery, the cardio-pulmonary bypass machine, which is shown in this picture, and which is operated by a highly skilled member of the team called a perfusionist, basically bypasses the patient's own heart and lungs. And it takes blood from the central circulation, through the machine, warms it, filters it, oxygenates it, sends it away to the brain, the kidney, the rest of the body, and completely bypasses the lung and the heart. And this leaves the surgeon with a heart that's immobile. And it makes it much easier to do the surgery if the heart is on standby. Some surgeons however prefer to have a beating heart and it is possible, under certain circumstances, to keep the heart beating and still do surgery on it. That's not the commonest way of doing it. The anesthesiologist is responsible for managing the patient while they're on cardio-pulmonary bypass.

    01:08 The surgeon is responsible for preserving the myocardium while the patient's heart is at rest. And the way this is done is one of two ways. Either very cold solutions with high potassium are forced through the coronary arteries. This causes cardioplegia, it causes the heart to stop working because of the high potassium. And the cold just cools the heart and reduces its oxygen demand. The other way of dealing with this is, again using high potassium solution, but this time blood, forcing it through the coronary arteries, and that'll stop the heart. And because you're putting blood through the heart, you're actually supplying oxygen to a heart that, because it's immobile, really doesn't have very high oxygen demands.

    01:56 The critical phase in cardiac surgery is Coming Off Bypass.

    02:02 And this is usually managed by the anesthesiologist, although there tends to be a fair amount of back and forth discussion going on between the surgeon, the anesthesiologist, and the perfusionist at this time.

    02:14 So these are just some valves that are replaced during open heart surgery. The top valve is a metal valve. And the advantage of a metal valve is that they're tough and they will last for 20, even 30 years. So, if you're a young person requiring valve surgery, you want a metal valve, because you don't want to come back again for as long as you possibly can. The negative with metal valves is that clots tend to form on the valves, so patients have to be anticoagulated for the rest of their lives. They have to take anticoagulation every day for the rest of their lives. And some people find that a totally intolerable situation.

    02:50 The lower two valves in this picture are tissue valves. They could be bovine, or they can be pig valves. And they're much safer in terms of embolic phenomena, they simply don't cause embolic phenomena, so you don't need to take anticoagulation. The negative with these valves unfortunately is they don't last as long as the metal valves.

    03:14 And they often need to be replaced every 10 years or so. And repeat cardiac surgery is infinitely riskier and more complex than first time cardiac surgery.

    03:26 The scarring that goes on in the chest after cardiac surgery is unbelievable. So getting back in and finding the portion of the heart you need to operate on can be extraordinarily challenging.

    03:38 So the anesthesiologist is responsible for protecting the heart prior to cardio-pulmonary bypass, which is particularly critical if the patient has ischemic heart disease, or is unstable. We have to be very careful to control tachycardia, and more importantly, not to cause tachycardia. Because tachycardia increases cardiac work and requires increased oxygen supply to the heart. If you've got ischemic heart disease, it means the vessels into the myocardium are blocked, so you can't increase oxygen supply to the heart. So you must keep the heart rate slow. Frequently, very potent inotropic drugs such as norepinephrine, epinephrine, dobutamine, dopamine and milrinone are given in bypass and coming off bypass. Anticoagulation is required during bypass, because the actual bypass tubing in the cardio-pulmonary bypass machine tends to induce clotting. And the last thing you ever want to see, and I'm thankful I have never seen it, is a generalized clotting forming in your cardio-pulmonary bypass. That's a fatal event. So we give very high doses of anticoagulant. And the drug we use is heparin. So these patients are very prone to bleeding. Once the patient's off cardio-pulmonary bypass, we reverse the heparin. But by then, there's been some damage to platelet, there's been some dilution of clotting factor, so bleeding is not uncommon. When we wean patients from bypass, they are sometimes extremely unstable. And it's our job as anesthesiologists to monitor and manage that during the transfer to the Cardiac Surgical Intensive Care Unit, and usually for the first few hours in that unit.

    05:26 Once the patients are stable, we can consider discontinuing ventilation, which has been continued following the surgery. And usually they stabilize over about 4 hours and we can usually extubate them later in the day of their surgery, and have them transferred to the Cardiac Ward the following day. I spent 20 years as a Cardiac Anesthesiologist, and the changes that occurred during that 20 years were phenomenal.

    05:56 The rate of damage to patients dropped dramatically, and the preservation of the myocardium improved dramatically. So death on the table and death immediately following, or nearly following surgery has become really quite uncommon.

    06:14 Most neurosurgical procedures require general anesthesia, but a few can be done with deep sedation. And we'll talk about those in a moment. One of the critical things about neurosurgery is the duration of the surgery.

    06:26 And surgeries of 10 to 12 hours are common. And the longest I've ever personally done was 27 hours.

    06:32 During that 27 hours, there were two surgeons and they took time off. One would come in and do some work and the other would go out and sleep. I unfortunately, had nobody to relieve me, so I spent the whole 27 hours awake trying to concentrate on taking care of this poor patient.

    06:50 The most critical aspect of neuro-anesthesia is the control of intra-cranial pressure.

    06:56 We've talked a little bit about that in earlier discussions. If intra-cranial pressure is lowered too aggressively, cerebral blood flow can be reduced and stroke could occur, ischemic brain damage can occur. Vapours increase cerebral blood flow, which is a good thing, but they can increase intra-cranial pressure as well, and that's not good. Propofol will decrease intra-cranial pressure, but the decrease in cerebral blood flow that can occur at the same time is not a good thing. Ketamine will increase cerebral blood flow, which is good, but it can increase intra-cranial pressure as well, which is not good. So Etomidate, which is the drug that's most often used in patients with brain trauma, is used largely because it has very little effect on either cerebral blood flow, and it does decrease intra-cranial pressure. So the combination is a good combination. Narcotics have little effect on cerebral blood flow or intra-cranial pressure in patients who are ventilated. And so, we can give narcotics to prevent severe pain. Intra-cranial pressure can be reduced by having the patient hyperventilate before induction. This tends to lower arterial carbon dioxide which lowers intra-cranial pressure. And then, once the patient is asleep and intubated, we provide them with mild hyperventilation and try to control that pressure from that perspective. We can also give Osmotic diuretics such as Mannitol or Loop diuretics such as Furosemide to reduce the water in the brain. And that can reduce the pressure in the brain as well. So certain surgical procedures in the brain can be performed without general anesthesia. Burr holes, which are just holes in the cranium, can be given in the presence just of local infiltration of the skin. And it's possible in those patients to drill a hole and relief blood in the brain and let the blood flow out.

    08:56 And this is a procedure that's actually been done for hundreds of years, actually thousands of years. There are pictures from the Egyptian era of holes being made in the brain or in the skull to reduce blood in the intracranial space. But some modern procedures, such as Deep brain stimulation for patients with Parkinson's disease, can be done with virtually nothing, except local anesthesia and a little sedation. This is a very interesting procedure. We give the patient a little bit of sedation, the surgeon puts local wherever they want to put it, drills a hole through the cranium and then passes probes deeply into the brain and stimulates them.

    09:38 And by so doing, they can find the nerve centers that cause, are causing Parkinsonism rigidity or tremor.

    09:50 And they can ablate those areas by sending an electrical shock down the, down the probe.

    09:56 And I've had patients who have come into the operating room so rigid they could barely move, and leave the operating room after 8 or 10 hours, it's not a short procedure, mobile, talking, immediately feeling better. So it's quite a remarkable treatment and one that is really quite new and is not done everywhere in the world. So, Complications of neuro-anesthesia. The most important one, and one that is unfortunately not uncommon, is Massive Hemorrhage. It's extremely difficult to treat and I'm not going to spend a lot of time on this, because the actual amount of bleeding relative to what happens when an aorta ruptures is actually quite small. The problem is, there's no way to relieve the pressure in the brain when hemorrhage occurs. So, it means making bigger and bigger craniotomies and let, trying to let out more and more blood. It's very difficult. Cerebrovascular accidents or strokes occur. These can be due to embolic phenomena or when the brain is being manipulated by the surgery, surgeon, it's always possible that certain areas of the brain will have their blood supply occluded. And that area of the brain will then develop an ischemic injury or a stroke.

    11:08 There could be permanent damage to the brain from increased intra-cranial pressure. And this is a situation which we see relatively rarely, thank goodness, but when it does occur, it's usually an extraordinarily bad sign.

    11:20 The patient fails to awaken for anesthesia and this isn't because there's something the matter with the anesthetic, it's because there's something seriously the matter with the brain. What you try to do in that situation is, you try to find a cause for the failure to awaken. And if it's a surgical cause, you go back in and try to correct it, if it's an anesthesia cause you try to correct it. But in most cases, it's caused by the brain itself being so damaged by the previous increased intra-cranial pressure or the injury that occurred prior to the patient coming to the operating room, that they just simply don't wake up. And these are patients who end up in a chronic vegetative state and may last for many months, or even years in some cases, before they finally die. So in summary, in this lecture we've discussed a number of specialized areas of anesthesia. We've discussed Pediatric Anesthesia and some of the differences that the anesthetist has to be aware of when dealing with children. They are not small adults.

    12:20 We've also talked about Thoracic Anesthesia and the highly risky process of putting an endobronchial tube in place and isolating one lung, and doing one-lung ventilation. Special training is often required for people who are going to do this on a regular basis, but every anesthesiologist has to be aware of the principles, and has to be able to deal with potential emergency patients who require one-lung anesthesia. We talked about Cardiac Anesthesia and some of the complications associated with that. And we talked a little bit about Cardio-pulmonary bypass.

    12:56 We ended by talking about Neuro-anesthesia, about some of the Risks and Dangers associated with neuro-anesthesia. But also, very briefly, about some of the Opportunities in neuro-anesthesia, and some of the good things that are happening in our Development of New Surgical Procedures for patients of all kinds.

    About the Lecture

    The lecture Neuro Anesthesia – Anesthesia for Special Operations by Brian Warriner, MD is from the course Anesthesia in special situations.

    Included Quiz Questions

    1. Often requires isolation of the heart and lungs by cardio-pulmonary bypass.
    2. Is associated with a high incidence of “death on the table“.
    3. Has never been complicated with “recall”.
    4. Uses anticoagulation to prevent bleeding during surgery.
    1. Can often be done under local anesthesia and sedation.
    2. Always requires general anesthesia for adequate control of pain and awareness.
    3. Like cardiac surgery, requires intra-operative anti-coagulation.
    4. Is never associated with failure to awaken.

    Author of lecture Neuro Anesthesia – Anesthesia for Special Operations

     Brian Warriner, MD

    Brian Warriner, MD

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