Question

Direct Fick method of measuring cardiac output requires estimation of:

• A. O2 content of arterial blood
• B. O2 consumption per unit time
• C. Arteriovenous O2 difference
• D. All of the above

Hint:

Cardiac output = O2 consumption / A-V O2 difference, so every listed quantity is needed.

Answer 1

The Correct Option is D

Step 1: Think of the lungs as the organ that adds oxygen to the blood. The Fick method exploits the fact that whatever oxygen the body burns per minute must have been loaded onto the blood as it passed through the lungs.

Step 2: Mathematically, $CO = \dfrac{VO_2}{C_aO_2 - C_vO_2}$, where $VO_2$ is oxygen consumed per minute, $C_aO_2$ is arterial oxygen content and $C_vO_2$ is mixed venous oxygen content.

Step 3: To plug numbers into this equation you require three measurements: oxygen consumption per unit time, the oxygen content of arterial blood, and the gap between arterial and venous oxygen (the A-V difference). Each option in the question names one of these mandatory inputs.

Step 4: Because no single measurement is sufficient on its own, all of them together are needed.

\[\boxed{All\ of\ the\ above}\]