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30 mL/beat
2%
3/146
40 mL/beat
83%
121/146
50 mL/beat
6%
9/146
60 mL/beat
3%
4/146
70 mL/beat
1%
2/146
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Using the Fick Principle, where Cardiac Output (CO) = oxygen consumption (VO2) / arteriovenous oxygen difference (CaO2-CvO2), the cardiac output is determined to be 4 L/min. Plugging into and rearranging the equation CO = SV x HR gives a value for cardiac stroke volume in this patient of 40 mL. In theory, the greatest level of accuracy in using the Fick Principle to calculate CO is achieved through the measurement of O2 content in both the pulmonary arteries and veins. In practice however, peripheral arterial blood is often used as a surrogate for pulmonary venous blood. The true Fick method of calculating cardiac output or stroke volume is rarely used due to the difficulty of obtaining the requisite variables for gas concentrations and oxygen consumption. As a result, an assumed value for oxygen consumption of 125 ml O2/min/m^2 body surface area is commonly used. Illustration A summarizes the calculations used to reach the above answer. Incorrect Answers: Answers 1,3,4,5: The stroke volume calculated using the Fick Principle, CO=SVxHR relationship, and above values is 40 mL; see Illustration A for further detail.
4.5
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