Question

Ejection fraction calculation method?
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Answer 1

Answer:

Ejection fraction and stroke volume are two parameters that are commonly measured in the ICU to evaluate cardiac performance. However, stroke volume and ejection fraction do not always change in parallel and are affected differently by changes in loading conditions.

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Stroke volume is the difference between end-diastolic and end-systolic volumes; it is the volume ejected with each heart beat. The normal range is 50 to 100 ml. In the ICU, stroke volume is usually measured by a pulmonary artery catheter and is reported as cardiac output.

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Ejection fraction is the proportion of diastolic volume ejected during ventricular contraction (see Equation 1-2). The normal range of left ventricular ejection fraction is 55% to 75%. In the ICU, ejection fraction is usually estimated by echocardiography.

These two parameters are related by the end-diastolic volume. Thus, a patient with an ejection fraction of 60% and an end-diastolic volume of 90 ml has a stroke volume of 54 ml. Similarly, a patient with an ejection fraction of 30% and an end-diastolic volume of 180 ml also has a stroke volume of 54 ml. Therefore, if ventricular volumes are high, it is possible to have a low ejection fraction but a normal stroke volume (as in chronic stable heart failure) or a low-normal ejection fraction and a high cardiac output (as in septic shock).

Stroke volume is influenced by preload and afterload, whereas ejection fraction is relatively preload independent but is affected by changes in afterload. Both are influenced by contractility. Cardiac output is the parameter that determines total oxygen delivery to the tissues and is therefore of the greater interest in critically unwell patients. However, ejection fraction and ventricular volumes are predictive of survival following myocardial infarction and cardiac surgery; therefore, they too are important.8,9

Explanation:

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