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Cardiac Anesthesiology Made Ridiculously Simple - page 9 / 13





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  • c.

    Check the requirements for coming off pump. Warm, Rhythm, Monitors On, Ventilator On, Perfusion (resistance reasonable).

  • d.

    Be ready to change your plan.

Why does the patient "go on bypass"? and How does the patient "come off bypass"?: The bypass system is basically a large plastic pipe with lots of holes placed through the right atrial appendage into the inferior vena cava. The large plastic pipe is full of fluid and hooked to the venous reservoir. The pipe is clamped with a large clamp. Note: Before attempting any of this activity, (not recommended in the privacy of your own home) make sure you have fulfilled the criteria for going on bypass (HADDSUE) or coming off bypass (WRMVP) as noted above. NEVER LET THEM GO ON PUMP IF YOU HAVE NOT HEPARINIZED. Having an ACT greater than 450 is very reassuring but not absolutely essential in dire and I mean dire emergencies. Other than the dire emergency. ACT must be greater than 450.

The simple explanation for going on bypass is the perfusionist removes the clamp from the venous drain line and a siphon effect drains blood from the right atrium and inferior vena cava into the venous reservoir. It is important to maintain the siphon effect to keep this flow going. Since, there is no or less blood going into the right ventricle, the cardiac output drops. The perfusionist then turns on the pump and returns the blood to through the aortic cannula into the patient's aorta. If all is working well the blood will be heated/cooled and oxygenated by the heater/cooler/oxygenator before being pumped through the filter and back into the aorta. Unclamping the venous drain line reduces the right atrial pressure and diverts blood into the pump. The perfusionist will say something like "Full flow" which means they have 4 or 5 liters a minute of venous drainage and are able to pump 4 to 5 liters/min into the patient. At this point you can turn off the ventilator. Pulmonary artery pressures should be non-pulsatile.

Coming off pump is the exact reverse situation. You fulfill all the criteria for coming off pump. (WRMVP), i.e. the patient is warm, the heart is beating, the monitors are turned on, the ventilator is turned on, and you have adjusted the resistance and inotropic state to an appropriate level. The perfusionist then partially occludes the venous drain line. This reduces the amount of blood draining into the venous reservoir. The right atrial pressure increases and blood starts to go into the right ventricle and out the pulmonary artery. At this point you can have a pump flow that is a fraction of the total systemic blood flow with the rest produced by the heart. The surgeon will say something like, Leave some in and come to 4 liter/min. You will notice that the pulmonary artery and systemic pressures become pulsatile. They will then drop to say 2 liter/min then 1 liter/min. They are watching the right and left ventricles to make sure they are not distending. They also watch the pressures and slowly load the heart. When they say something like "Give a hundred". What they are telling the perfusionist is to leave 100 cc less blood in the reservoir. The perfusionist may be draining 2 liters/min of blood from the patient and pumping 2 liter/min to the patient. They are supposed to pump 100 more cc of blood than they withdrew. It is an inexact science. But you get the idea.

The surgeon will then clamp the venous drain line and you can tell that you are truly off pump. They will remove the venous cannula. If you have a kind surgeon, they will place it in a bucket of saline and then drain the blood back to the reservoir keeping the line full of saline. This allows the perfusionist to start hemo concentrating the blood in the system but keeps the venous line ready in case you have to return to bypass. The arterial line is still in place so the perfusionist can give fluid. When the patient's blood volume is low you will hear - "give a hundred". The perfusionist basically unclamps the arterial line with the pump on and drains 100 cc of fluid from the reservoir.

Who weans the patient from bypass and who gives volume orders? This varies by institution and surgeon. At some institutions the anesthesiologist does at others the surgeon does. If you are not ready to wean a patient, say so. If you think the patient needs to go back on bypass, tell the surgeon to put the cannulas back in. If the patient is doing poorly, tell them not to take out the arterial cannula. If you need more volume, ask for it. You are part of the team. This is one surgery where it is essential that you be able to tell the surgeon what to do, and when to do it. When things are going bad, communication is key. It is essential that it is a team process. They need to know what you need and what is going on. If something is not working, they need to know about it. They can and will most likely try to fix it.

Inotropes and Vasoactive Compounds: If you are using a drug that requires an infusion and where the effects of an incorrect or fluctuating dose would be difficult to manage, use an infusion pump. This includes (dopamine, dobutamine, epinephrine, norepinephrine, nitroprusside, nitroglycerin, neosynephrine, and propofol). The fluctuations caused by relying on gravity drips are unacceptable. Gravity is reliable, back pressure is not. All drugs must be mixed in concentrations approved by the pharmacy. The labels with the appropriate concentration are in a black box in the anesthesia machine. If you mix it and label it with the yellow label then the ICU nurses will not throw it away when you get to the ICU. If you mix some weird concentration, label it poorly, or then put it on a dial-a-flow, the nurses will throw away your drugs and the patient will get less than optimal care.

Prophylactic Drugs: Some surgeons believe that prophylactic high dose steroids are thought to reduce the immune reaction to bypass or reduce neural injury. Scientific evidence for these theories is limited. Downside to steroids are infections and poor wound healing. Some surgeons believe in prophylactic inotropes or vasodilators. Post bypass prophylatic nitroglycerin infusions

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