Anesthetist Student Blog



Applied Physiology Lecture 4: CEA & Stenting9-29-11**The exam will be based on Neurophysiology. He just gives us the skeleton of it, but we have to read and know all the other stuff too**Carotid Endarterectomy : the slides are a bunch of crap b/c there is really no clear-cut answer. The Carotid is a major blood vessel in the neck/ a major landmark which is important for placing a lot of the lines we place: central, EJ, etc. It starts as a common carotid artery which then splits into the L and R carotids. The R is more internal and is usually the more common site for stenosis. The L is usually more external and it comes directly off the aorta, whereas the R does not (comes off indirectly). This is an important vessel for cardiac issues. For most cardiac procedures, you will stop the lungs and heart and put the pt on a heart/lung machine to circulate and breathe for them. However, there are some procedures where you can’t even do this. You actually have to stop the machine at the appropriate time (circ-arrest) to do the procedure, but you still have to perfuse the brain. How? Retrograde perfusion through the L carotid artery (b/c it is directly off of the aorta). There is a carotid bulb on this vessel which houses the chemoreceptors and baroreceptors. These sense that there is less blood flow and that the brain needs more. Inside the lumen of the stenosed vessel is complete crap. No matter how much you dilate, with stenosis, your blood flow through that vessel will still be crap. So, if you hypo-perfuse, you get less blood flow. What are some symptoms of low blood flow to the brain/ stenosis? TiredLethargicSyncope (this is fainting due to lack of blood flow to the brain. It’s your body’s defense mechanism. If you pass out, you lie flat, and the blood can flow to the brain more easily instead of fighting against gravity).If the crap in the lumen breaks off, you will see small infarcts in the brain. The territory of the carotid supplies can be anterior and posterior. When you get these small infarcts, you will actually see stars, which tell you that you are having a TIA (transient ischemic attack), which may also lead to temporary blindness (amurosis fugax). You could also have headaches, temporary loss of consciousness and a stroke. To maintain the blood flow, you have to keep pumping more blood to the brain, which will ↑ the pressure in the brain (ICP). When stenosis starts (smoking makes this happen super fast), you see higher pressures in the brain. The autoregulation curve is 50-150mmHg (textbook value…it’s actually 70-150mmHg), but with a patient with chronic stenosis, this curve has shifted up higher than normal. If you drop the pressure too far below their own autoregulation pressure range, they will not have adequate CPP. The vertebral artery serves as collateral blood flow to the carotid artery. These 4 arteries (R & L of each) meet in the brain to form the Circle of Willis which ensures enough backup blood flow to the entire brain even if one of the incoming vessels is occluded. If the R sided vessel is stenosed, hopefully the L side is ok. Carotids and vertebrals supply both the anterior and posterior circulation of the brain. 2921635-109855You should be able to palpate your own carotid artery; use the sternocleidomastoid muscle as a landmark. The carotid is a decently big blood vessel. Chances are, if it is stenosed, then the little coronary artery vessels are as well, which leads to cardiac issues for obvious reasons. In fact, 50% of patients with carotid artery stenosis do have some stenosis of the coronary arteries. The amount of the stenosis is also important. When you see the patient’s report, it may read: L ICA 80-90% R ICA 60-70%. This means that the left internal carotid artery is blocked 80-90%, etc. It may also read as: ↑ Vel R ICA. This means there is an ↑ velocity in the right side, so you know there is a smaller lumen/ stenosis.00You should be able to palpate your own carotid artery; use the sternocleidomastoid muscle as a landmark. The carotid is a decently big blood vessel. Chances are, if it is stenosed, then the little coronary artery vessels are as well, which leads to cardiac issues for obvious reasons. In fact, 50% of patients with carotid artery stenosis do have some stenosis of the coronary arteries. The amount of the stenosis is also important. When you see the patient’s report, it may read: L ICA 80-90% R ICA 60-70%. This means that the left internal carotid artery is blocked 80-90%, etc. It may also read as: ↑ Vel R ICA. This means there is an ↑ velocity in the right side, so you know there is a smaller lumen/ stenosis.When this is the case, you can put a stethoscope on the neck and hear a carotid bruit (a systolic sound heard over the artery due to turbulent flow/ narrowing of vessel). Ex: pt is 86y.o. Has lost vision temporarily 5-6x this year, and their doctor found stenosis, so they sent the pt to a vascular surgeon. He has been sent for PAD (preoperative assessment __________________) and needs to the stenosis in the R carotid cleared. You need additional tests, pt history, etc. What should you ask for?Exercise tolerance/ METSCardiac Hx of MIDiabeticSmokerThe pt says everything is fine. He has never had an MI, he plays tennis 6x/wk. Would you send him to a cardiologist? Probably, if you have time. The cardiologist does an echo of the patient’s heart and finds that he has a cardiac ejection fraction of 60-65%, which is really good. You should also get an EKG (it is normal). So, you would also ask for a stress test. The stress test comes back +. The pt’s echo looks normal. If his blood vessel supplying the left ventricle (main highway) is 100% occluded, the blood takes the smaller collateral vessels (side streets). So, the muscle looks good on the echo b/c, at a normal heart rate, the muscle is getting enough blood flow. However, when you stress the muscle out, the collateral vessels (side streets) can’t keep up with the necessary blood flow demand (volume of traffic) anymore, so the heart starts to become ischemic which shows up under stress. So, if you put him under anesthesia, you can’t guarantee that his HR will stay 72-75. It may go over 100 b/c he can’t take it. When this happens in the stress test, we can stop the test. If this happens on the OR table with his carotid wide open, we really can’t stop, so we can see why the stress test is useful. There is a 45-50% chance that the smaller vessels are occluded. This patient had an acute troponin leak (MI) and coded on the OR and it took 45min to get him back. We can also look in the vessels with radioactive dye using a cardiac catheter to see if there’s an occlusion. However, the risk vs. benefit is not really worth it when we already know that ? these patients will have the smaller vessel occlusion. Additionally, doing this test would not affect your anesthetic plan. You know that his carotid and his smaller coronary vessels are both occluded, so which do you do first, the carotid or the open heart? If you do the open heart surgery first, the guy will stroke out and die. If you do the carotid first, the guy could have an MI on the table. Both issues together lead to huge complications b/c you have to give tons of heparin, which could lead to a massive bleed out from the neck, etc. Our tennis playing patient has 70% stenosis on one side and 40% on the other. We used to do both of these procedures combined, but it presented many problems, so now we don’t do that. Which do we do first? It depends on which is the most pressing issue for the patient. You must maintain a high CPP b/c of the shifted autoregulation curve. If he is having an MI, do the heart surgery first. If he is having TIAs, do the carotid first. 25120605080We also perform carotid plaque removals in patients with high carotid occlusion (ex: 99%) who are asymptomatic b/c there are good results from this procedure, and b/c if left untreated, the patient could have a stroke. This stroke is usually followed by a heart attack in these pts, which happens in most cases which are left untreated. You would clamp the carotid artery on either side of the plaque occlusion, open the artery, and take the crap out. The part of the brain fed by this artery still gets blood flow, but the supply is compromised. Is this good enough, or do you need to shunt the blood passed this operation? 020000We also perform carotid plaque removals in patients with high carotid occlusion (ex: 99%) who are asymptomatic b/c there are good results from this procedure, and b/c if left untreated, the patient could have a stroke. This stroke is usually followed by a heart attack in these pts, which happens in most cases which are left untreated. You would clamp the carotid artery on either side of the plaque occlusion, open the artery, and take the crap out. The part of the brain fed by this artery still gets blood flow, but the supply is compromised. Is this good enough, or do you need to shunt the blood passed this operation? 26644605080If shunting is necessary, you can use a Pruitt shunt. In this situation, the artery is still clamped on both sides, but the blood is allowed to flow passed via the shunt. When you are using a shunt, the blood is passing through a more narrow lumen, so you have to keep the blood pressure up to be able to get enough blood through to the brain. The HR may ↑ to accomplish this and produce tachycardia. However, remember that ? of these patients have occluded coronary arteries as well, so the ↑ HR may be too much work, cause stress, which can lead to ischemia= conflicting goals. 00If shunting is necessary, you can use a Pruitt shunt. In this situation, the artery is still clamped on both sides, but the blood is allowed to flow passed via the shunt. When you are using a shunt, the blood is passing through a more narrow lumen, so you have to keep the blood pressure up to be able to get enough blood through to the brain. The HR may ↑ to accomplish this and produce tachycardia. However, remember that ? of these patients have occluded coronary arteries as well, so the ↑ HR may be too much work, cause stress, which can lead to ischemia= conflicting goals. If you are in this situation , and you ↓ pressure, the heart will be happy, but then the brain is not happy b/c it is no longer getting enough blood flow. So, do you want a dead patient or a brain dead patient? In heart surgery, you would clamp the aorta at low pressure (b/c it will tear if clamped at high pressures) and run the patient on a heart/lung bypass machine at MAPs of around 40-60. But autoregulation is 70-150mmHg, and this guy’s curve is even higher, so the CPP has to be higher than it is here for the brain, but this ↑ in pressure is bad for the heart. You have to have acute control of HR and bp, but you can only control HR on this pt. Cooling the pt wouldn’t help either b/c it would just make the pt bleed more. The carotid bulb has baroreceptors and chemoreceptors. Chemoreceptors detect ↑ PCO2, etc. Baroreceptors detect ↑ HR and ↓ bp in response (supplied by Glossopharyngeal nerve IX and give feedback via Vagus nerve X). If you do the carotid surgery on one side, these are both compromised. You can’t do carotid surgery on both sides at once b/c thesesurgeries at once, along with the fentanyl and GETA would mean very bad news for the patient. So instead, you do the second side 3-6 months later.Which side do you do first? Whichever has the higher % of occlusion. If the pt has 98% blockage on R and 90% on the L, then you would do the R first. However, you’re seriously occluding the blood flow to the brain, so you have to ↑ pressure significantly for CPP while maintaining HR to avoid an MI. You would want to order lab tests for this patient: Pt/ptt/INREchocardiogramStress testThe stress test is useful b/c if ischemia happened at a HR of 90, then you know they have a much higher chance of having an MI compared to someone in whom ischemia began at a HR of 120. A _______________________ catheter is better. If they can put a metal stent in and fix the heart, should you go ahead and do the carotid while you’re at it? No, b/c after placing a stent in the coronary vasculature, the risk of MI is actually ↑ for 30days afterward, even more so than it was before the stent was placed. There are 2 types of stents that can be used:BMS – bare metal stentDES – drug eluding stent (constantly oozes chemotherapeutic agent to prevent clotting)If you use a BMS instead of a DES, you have to use aspirin and plavix (makes the platelets not sticky) for the rest of your life. You have to continue this treatment for at least 30 days regardless of which stent you get, but we don’t actually know how long it takes for the DES stent to release the proper amount of drug to appropriately equilibrate throughout the body, so you actually need to stay on these drugs for at least a year regardless of the stent used. DES is useful, though, so the pt doesn’t have to be on aspirin and plavix for the rest of their life. If you know the pt will need surgery after 30 days, you would use a BMS from the start anyway b/c, when you stop aspirin and plavix for the surgery and give __________________, it won’t clot up (Heparin? Warfarin?) . The DES needs aspirin and plavix for 1 year. If you stop drugs before surgery, the DES will clot in seconds and they will die on the table. To fix the carotid, you clamp the artery, which compromises the blood flow to the brain. Now blood is static on either side of the clamp, so it will clot. To prevent this, give heparin first (about 7,000 units for a 70kg pt), or even the best surgeon in the world could lose the patient. (Heparin= 100units/kg)You could do a pt/ptt/INR test to make sure the heaprain has taken the proper effect, but it takes forver, so it’s actually better to use ACT (activated clotting time) b/c the test is done right there so it’s more convenient and it’s also more accurate. Normal clotting time is about 90-110sec. You want the heparin to give you a clotting time of >200sec. If the patient is getting open heart surgery and is on a heart/lung machine, you want >400sec. MAKE SURE YOU HAVE >200SEC before the surgeon clamps. If your IV is occluded and the drug doesn’t go in, and you clamp without doing the test, you will kill the patient. Just wait the 5min to check the ACT. You want to place a large bore IV and an A line for carotid surgery. These are necessary b/c you need to use the A line to draw back blood for the ACT and get beat-to-beat blood pressure readings. You also need the large bore IV to get the drug in fast. You can actually do this procedure awake. The advantage is that an awake pt is the best monitor you have. Have them squeeze their rubber ducky every 5 minutes, and the sound of the squeak will tell you they are still with you. Also, if they do not have proper blood flow, they will pass out. If they are having a stroke, their tongue will protrude. You just block their nerve supply (block 2 nerves: ________________ & _______________________). However, the surgeon may prefer to do the surgery asleep. If so, you need the EEG to be able to see if they stroke out, etc. If you see a flat line, you know that blood flow has been occluded there and they are having a stroke. A raw EEG has 16-20 channels. It is processed so it is smaller, and represented many different ways (3D, telephone poles, shades of gray, etc). 174625010160To measure stump pressure, you insert the needle here in the brainstem. It measures the pressure of the blood that goes into this tube/ column of blood. At least 50mmHg is considered good; <50mmHg is bad. It’s not hard ot measure, you simply put a stopcock on, flip the valve so the blood flows into the column, and the measurement only takes like 2 seconds. However, stump pressure actually has no consistent correlation to EEGs. EEGs also have false (+)s and false (-)s. 020000To measure stump pressure, you insert the needle here in the brainstem. It measures the pressure of the blood that goes into this tube/ column of blood. At least 50mmHg is considered good; <50mmHg is bad. It’s not hard ot measure, you simply put a stopcock on, flip the valve so the blood flows into the column, and the measurement only takes like 2 seconds. However, stump pressure actually has no consistent correlation to EEGs. EEGs also have false (+)s and false (-)s. 1574165476250To do regional anesthesia, you put your block posterior to the sternocleidomastoid muscle at about the level of C2-C4 and go deep to do a deep cervical plexus block. The problem is that you could inject into the phrenic nerve (cause paralysis of the diaphragm) or the vertebral artery (cause systemic toxicity), or you could paralyze the brainstem.020000To do regional anesthesia, you put your block posterior to the sternocleidomastoid muscle at about the level of C2-C4 and go deep to do a deep cervical plexus block. The problem is that you could inject into the phrenic nerve (cause paralysis of the diaphragm) or the vertebral artery (cause systemic toxicity), or you could paralyze the brainstem.If you did this procedure awake, you could use regional anesthesia. If you do it asleep, you would probablyuse a shunt. Using a blind shunt risks dissection of the carotid artery, especially upon insertion. 16598901738630So, you could do a superficial cervical plexus block using the mastoid process, the sternocleidomastoid muscle, and C6 as your landmarks. The problem is, you could inject into the carotid (cause systemic toxicity), etc. 00So, you could do a superficial cervical plexus block using the mastoid process, the sternocleidomastoid muscle, and C6 as your landmarks. The problem is, you could inject into the carotid (cause systemic toxicity), etc. Either way, you need minimal sedation during the anesthesia for this procedure if being done awake b/c you need to be able to know if they have altered mental status. Ex: our patient has stopped squeezing his ducky, his tongue is to the side, so you know he is completely stroking out. So, what do you first? First, you secure the airway. The problem is that his neck is wide open and to the side under the drapes, so this is not easy. This is why we are moving more away from awake carotid surgeries. If the patient is operated on asleep, however, you need to wake them up as fast as possible at the end of the case b/c it is the only way you will know if they have stroked out during the case or not. Carotid surgeries utilize a patch closure b/c this is best. They do not sew the slice in the carotid shut like a normal suture b/c you can run into all kinds of problems with this. For example, a smoker with secretions, someone who is coughing and bucking, or any other way that you get ↑ pressure these could all reopen the carotid artery. Also, a patch adds extra space and makes the lumen of the vessel bigger. The chances of re-stenosis are high, so the lumen is bigger. If the patient had a good airway, you can extubate them semi-deep. If they had a difficult airway, then you have to extubate them awake regardless of the potential for ↑ pressure on the carotid. Some big complications of this surgery include stroke, MI, cardiac mortality and neck hematomas. If the patient gets a neck hematoma, they will experience shortness of breath. You need to secure the airway and open the neck to let the blood out. %0cc of blood sitting in the neck takes up a lot of room and can compress the airway. SLIDES:CEA Stenting:There are 2 different types of stroke-Hemorrhagic (from a bleed) – for this type of stroke, you would give coagulants. Ischemic (from a clot) - this can affect anterior or posterior circulation. For this type of stroke, you would give anticoagulants. It is important to have the proper diagnosis b/c they have opposite treatments. If we have the stroke team on the case from the first moment they start stroking, they will take them to the ER, through triage, then to the MRI (neuro-interventional radiology), then they can get the clot with a retractor or TPA. The outcome in this situation is amazing. However, if there is any time delay at all, 25% of these patients die. We are part of the stroke team. We intubate them b/c their GCS score doesn’t meet the proper criteria due to ischemia. If there is a bleed inside of the brain (the actual parenchyma/ tissue), they will go into a coma. If there is a bleed on top of the brain, they will get a severe headache. We can see this with the Hess-Hunt classification. 4072255684530Don’t worry about the stroke algorithm in anesthesia. You just get them to the right people (above). If the patient is paralyzed, a GCS score of <8 may not really count. You have to establish a baseline based on what their highest level of activity is and judge it off of that. 400000Don’t worry about the stroke algorithm in anesthesia. You just get them to the right people (above). If the patient is paralyzed, a GCS score of <8 may not really count. You have to establish a baseline based on what their highest level of activity is and judge it off of that. 40671755080**Know this classification for the test!!!! This is only for hemorrhagic strokes!!!**00**Know this classification for the test!!!! This is only for hemorrhagic strokes!!!**TIA for carotid. Use aspirin and plavix (T___________ is the old drug). There is no clear cut answer as to which to do first. It depends on the case. If the blood vessel is stenosed (slide 15), you can put a stent in the carotid, but it will push all the crap in it to the side and the crap will break off and go into the brain. To prevent this, they put an umbrella above it first, then open the stent. Now the extra stuff will ↑ the pressure and the baroreceptors will cause bradycardia. So, have atropine and glycopyrrolate ready during these procedures. You also need to already have the pads on the pt b/c you may have to shock them out of A-fib. This is an endovascular reaction. We want them awake. The biggest problem is that the stents become re-stenosed 50% of the time. If this is a patient with completely occluded coronary arteries, go endovascular b/c surgery presents a risk for MI whereas the endovascular procedures do not. You want to protect the brain from ischemia as well, so you have to apply all the principles of MAP, CPP, etc, or wake them up quickly. For awake, you want to keep them awake and very light. (Slide 25) there is not much difference b/w the outcomes of regular vs. GETA. How to do regional, potential complications (nerves). EEG stump pressures. Can do Xenon washout, etc, but this is not really done. Use a rubber bungee cord around the carotid on both ends where it is clamped while it is cleaned out and the patch is sewn in. Any ↑ in bp can cause the patch to tear. If the site starts to tear, you can pull up on the bungees and occlude either side of the vessel to stop the bleeding. Blood loss is usually minimal unless the clamps come off, then it’s really bad. The patch leaves a bigger lumen in the vessel, so you will get more blood to the brain at first after the procedure (hyperemia), which is also bad. You need to ↓ the bp at this point. Use a shunt (the one pictured above). (Slide 42) Very important!!!At this point you would send them to the ICU b/c they will be very well monitored. They may have a hematoma, delayed stroke in their head, hyperemia (headache), a seizure, or an MI (within 24 hrs). Ex: Pt w/ COPD and a bad subclavian vein, but the surgeon needs a central line. He also has 90% occlusion on the R carotid, but the L is clean. He is anticoagulated and 700lbs with a yeast infection (can’t do femoral). So, do you use the R or the L jugular vein? The L is clean and the R has occlusion. Let’s say you go for the L and you get the carotid instead, now he’s bleeding everywhere and you’ve given him an occlusion. Now let’s say you go on the R, but you get the carotid again. You need to do an ultra-sound guided carotid in the R side to not give him 100% occlusion (which is what would happen if you went in the L). Make sure to read: M&M, Barash, Miller and Secrets. The test will be all inclusive so study hard. On a side note, chlorohexadane is a prep solution used before surgery. You’re supposed to prep, let it dry, then clean it before inserting the needle b/c the epidural space is very sensitive. Even 0.01cc of this in the epidural space could cause face-down paralysis. ................
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