Disclaimer: I LOVE cardiac physiology. I spent the first decade of my career doing hearts almost every day at the New England Deaconess Hospital. Lots of liver transplants too. With my engineering mindset, cardiac physiology just clicked. However, there are a lot of nurses (and doctors too!) who really don’t understand cardiac physiology. It's a real shame, because cardiac physiology is easy to understand if you’ve been taught “how” things work versus just being given a bunch of numbers to memorize.
As the population of patients having surgery at ASCs continues to grow (patients are getting older and sicker) more patients will have an echocardiogram sent over as part of their preop medical clearance. It usually falls on the ASC’s preop nursing staff to figure out what to make of the testing that has been done. Is it sufficient? Does something else need to be done? Is it safe for this patient to have surgery at the facility?
Every echocardiogram (and nuclear medicine stress test, for that matter) will have a line that lists the Ejection Fraction, sometimes just listed as an “EF”. So, what the heck is an “EF” and what does it mean?
As an anesthesiologist with over 30 years of experience, I can tell you that if I could have only one piece of information on an older patient, it would be the patient’s Ejection Fraction. Some of my anesthesia colleagues may disagree with me, and that’s ok. But for me, knowing the status of the pump function, i.e., how well the patient’s heart is contracting, is the single most valuable piece of information I could know.
Why’s that? Because most anesthesia drugs, including Propofol and inhalational agents like Sevoflurane and Desflurane, cause BOTH decreased cardiac contractility AND vasodilation. That combination is a “double whammy” for blood pressure. With a normal EF, there’s plenty of room to compensate, but when starting with an EF that’s already compromised, a little additional decrease in contractility can lead to severely compromised cardiac function and a blood pressure that’s in the proverbial toilet.
Ejection fraction is actually very easy to understand, if you remember that the heart is simply a living pump. More precisely, it is two pumps, a low-pressure, right-sided pump (the right ventricle or RV) to pump blood through the lungs to the left side of the heart, and a high-pressure, left-sided pump (the left ventricle or LV) that pumps blood out of the heart through the aortic valve into the aorta and the rest of the patient’s body.
The left ventricle and the right ventricle of the heart fill with blood during diastole (the relaxation or filling phase of the cardiac cycle), and eject blood during systole (the contraction phase of the cardiac cycle). The left ventricle (the stronger and more important of the two pumps because it is the ventricle that pumps blood to the whole body) is filled with the most blood at the end of diastole, and is filled with the least blood at the end of systole. The difference between those two volumes, the left ventricular end diastolic volume and the left ventricular end systolic volume, is the amount of blood that actually got “ejected” out of the heart and into the aorta.
Hang in there – we’re almost done! Let’s put some numbers to this discussion so that it makes more sense. Let’s assume that the left ventricle when full (end diastolic volume) has 150cc of blood in it. It then contracts (systole), and at the end of systole, there’s 50 cc left. (These are normal numbers for a normal-sized adult with a healthy heart). If you do the math, 150cc – 50cc, you will see that 100cc got ejected. Therefore, as a fraction, it looks like this: 100cc ejected/150cc at end diastole. 100/150 is 2/3 expressed as a fraction and is 66% expressed as a percentage. So there you have it: 66% is a normal ejection fraction. In fact, 55-70% is considered a normal EF.
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