The majority of emboli occur on aortic cannulation, cross clamp placement, cross clamp removal, side bitter placement, side bitter removal, weaning from bypass, and aortic cannula removal. It is best not to have high glucose or overly warm temperatures ( 37oC) during any of the embolic times. 95% of patients suffer subtle neuro-psychiatric changes consistent with multiple small emboli.
Check List for Getting Off Bypass:
WRMVP: Wide receiver most valuable player.
Warm: What is the bladder and blood temp?
Rhythm: Are they in NSR or do you need to pace? Is the rate adequate?
Monitors On: Turn em back on if you turned them off for bypass. Turn back on the alarms.
Ventilation: Turn on the ventilator. Easy to forget and you look very stupid.
Perfusion: What is the pump flow.
Weaning from bypass: You need to have a plan. What was the ventricular function prior to bypass? How long was the cross clamp? What does the heart look like now? What is the resistance now? Once you have a plan communicate with the surgeon. If you plan to use a drug with prolonged side effects ask them what they think (amrinone, milrinone). They may have an opinion that should be considered. Have some inotrope ready. You should be able to wean 80-90% of first time CABG patient's from bypass with no inotropes. Calcium chloride is commonly used. Excessive doses ( 2g) have been associated with pancreatitis.
A standard weaning plan would be to calculate the systemic vascular resistance (SVR):
SVR = [(MAP - CVP)/CO]*80
MAP: Mean Arterial Pressure
CVP: Central Venous Pressure
CO: Cardiac Output (Can be obtained by asking the perfusionist what the pump flow is)
SVR should be in the 1000 to 1200 wood units. It routinely will be 600 to 800 and the cardiac output necessary to develop a reasonable pressure post bypass will be too high. Vasoconstrictors (phenylephrine) or a catecholamine with some vasocontrictive effects (dopamine, epinephrine, norepinephrine) are commonly necessary to raise the resistance to reasonable levels. Here is an example. The MAP is 50 and the CVP is 10. You ask the perfusionist and he tells you the pump flow is 5 liters/min. That gives a SVR of (50-10)/5*80 which equals 640 wood units.
Let's take two approaches. The first is to come off pump and let the heart try to pump sufficiently to develop a reasonable pressure. Once off pump the SVR will be 640, the MAP will be 50 and the BP will be about 70/40. The problem is not cardiac in nature. The problem is simply low resistance. An inotrope is not needed a vasocontrictor is.
If the SVR had been raised to 1200 prior to coming off pump, the 5 liter/min cardiac output would yield a MAP of 65 with a CVP of 10. The BP would then be about 95/50 and all would be well.
A reasonable approach to weaning from bypass is to:
a. Make an educated guess as to the inotropic state of the ventricle. If it was lousy prior to bypass, it will most likely still be lousy and an inotrope will be necessary. If the inotropic state of the ventricle was ok prior to bypass and cross clamp times were reasonable (60 minutes or less) then it is likely no inotropes will be needed.
b. Calculate the resistance and correct it.