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Cardiac Anesthesiology Made Ridiculously Simple - page 10 / 13





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have been suggested as a preventative measure for IMA spasm and myocardial ischemia, downside is hypotension, supply limited ischemia, and more fluid requirements to keep preload adequate. Magnesium is thought to be an anti-arrythmic, anti ischemic agent. Some people load with magnesium prior to CABG surgery (2 grams IV) others do not. The scientific evidence for many of these therapies is equivocal. Once again you have to communicate and ask your surgeon their preference. You will have to come to some sort of intelligent, professional compromise on prophylactic drug use.

Phosphodiesterase Inhibitors: Do not start a phosphodiesterase inhibitor (Amrinone, Milrinone) without talking to the cardiac surgeons. Do not choose it as first line inotrope. A phosphodiesterase inhibitor will vasodilate profoundly and will most likely require a second drug with vasoconstrictor properties.

Potassium: Low potassium is defined as less than 4.0 meq. It is associate with arrhythmia's. Replace if less than 4.0. High potassium depends on timing. Greater than 5.0 is common on bypass from the cardioplegia. You would like it to be below 5.0 but greater than 4.0 when you come off pump. The perfusionist can dialyze the patient if needed.

Hematocrit: Drops with the hemodilution of the bypass pump. If it is below 20 you need to correct. Between 20-25 you need to use clinical judgment. Talk to the surgeons, they may have an absolute rule and if you don't follow it, they will simply follow it in the unit and be irritated with you in the OR.

Post Bypass Hemodynamics: Systolic blood pressure greater than 80 mmHg is fine. If it is between 100 and 120 mmHg everyone will be happy. If it is greater than 120 mmHg the patient is hypertensive and there will be more bleeding. Cardiac index greater than 2.0 is fine. Pa Diastolic less than 20 mmHg, CVP less than 15 mmHg. If CVP is ever greater than PAD there is a problem: poor calibration or right ventricular failure. Always consider surgical manipulation of the heart if the chest is open or tamponade when it is closed, as a cause of hypotension.

Protamine: Fish semen in a bottle. There are allergic, anaphylactic, and histamine responses. Dose is personal but Protamine 10 mg will equalize Heparin 1000 units. Protamine comes as 10 mg per cc so if you used 30 cc of heparin, 30 cc of protamine will neutralize it. You are forming a weak salt between a base and an acid. You are titrating the response. You need to give the dose and then check the response by measuring the ACT. Some of the V/Q mismatch and shunt post op is caused by clearance of heparin-protamine complexes by the reticulo-endothelial system in the lung.

Protamine Administration: Give 10 mg = 1 cc peripherally and check for allergic response manifested as hypotension, broncospasm, rash, or pulmonary hypertension. Stop administration for problems. You can get severe hypotension from protamine, be ready with phenylephrine. Steroids, H1& H2 blockers, vasoconstrictors, inotropes, and returning to bypass can help. Allowing the heparin to spontaneously be metabolized is another option for severe reactions.

Then give the rest of the dose slowly. What is slowly? If you follow the PDR it would be about 2 hours. If you are at some institutions it would be 1 minute. Over 20 minutes is not unreasonable. Once 1/3 of the protamine is in tell the perfusionist so that they can stop the pump suckers and avoid clotting the pump. If you clot the pump and need to return to bypass you will be very, very, very unhappy.

Once all the protamine is in, tell the surgeons, and then check an ACT. You should return to baseline (120 - 130). If you have not, give more protamine. If you give pump blood after this point you may need to give more protamine. You can only find this out by measuring the ACT. Check the ACT after you give blood products from the pump or cell saver.

Post Bypass Bleeding: If there is bleeding post bypass, check the ACT. If elevated, correct it. If there was aspirin given in the last 4 days you may need platelets. If there is medical bleeding, you may need platelets. If there is surgical bleeding, they should fix it with a stitch or the bovie not infusions of platelets. Recently a new factor was discovered in the clotting cascade it is a 6-0 proline.

Returning to Bypass: If there is severe hypotension, bleeding, low cardiac output, other problems, you may need to return to bypass. If you have given the protamine, give another dose of heparin at 300 U/kg and check an ACT. Before the aortic cannula is removed, you should make a decision about whether you may need to return to bypass. If you are having severe problems maintaining the pressure despite inotropes, tell the surgeons. They will delay removing the aortic cannula or immediately return to bypass. It is very bad for the heart to be dilated by high filling pressure and then have low coronary perfusion pressure. You may have to return to bypass.

Balloon Pump: Very nice system for inadequate left ventricular function. The balloon pump needs an ECG signal and an arterial pressure signal. On the Datex monitor the slave cable plugs into channel 3. Channel 3 is usually the CVP channel. Plug the CVP

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