## **Core Concept**
The Fick principle is a method used to calculate cardiac output (CO) based on the difference in oxygen content between arterial and venous blood and the rate of oxygen consumption. It is given by the formula: CO = Oxygen consumption / (Arteriovenous oxygen difference).

## **Why the Correct Answer is Right**
To calculate cardiac output using the Fick principle, we use the formula: CO = Oxygen consumption / (Arteriovenous oxygen difference). Given that the oxygen consumption is 300 ml/min, the arterial oxygen concentration is 20 ml/100ml, and the mixed venous oxygen concentration is 16 ml/100ml, the arteriovenous oxygen difference is 20 - 16 = 4 ml/100ml. First, convert the oxygen difference into ml/ml: 4 ml/100ml = 0.04 ml/ml. Then, calculate the cardiac output: CO = 300 ml/min / 0.04 ml/ml = 300 / 0.04 = 7500 ml/min. To convert ml/min to liters/min, divide by 1000 (since 1 liter = 1000 ml): 7500 ml/min / 1000 = 7.5 liters/min.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because the calculation does not match the provided numbers and does not correctly apply the Fick principle.
- **Option B:** This option is incorrect because, similar to option A, it does not align with the correct calculation based on the given values for oxygen consumption and arteriovenous oxygen difference.
- **Option D:** This option is incorrect as it suggests a much lower cardiac output than what is calculated using the provided values.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Fick principle assumes that the oxygen consumption and the arteriovenous oxygen difference are accurately measured. In clinical practice, cardiac output can also be measured by other methods such as thermodilution or Doppler echocardiography. However, the Fick principle remains a fundamental concept in understanding cardiac physiology.

## **Correct Answer:** . 7.5