What is the cardiac output of a patient whose heart rate is 72 beats per minute with a stroke volume of 90 mL/contraction?

This method, known as the 6-second method, involves counting the number of QRS complexes in a 6-second interval on the electrocardiogram (ECG) strip and then multiplying that number by 10 to calculate the heart rate per minute. The advantage of this method is that it provides a relatively quick estimate of the heart rate.
A. Printing a 1-minute ECG strip and counting the number of QRS complexes in (option A) is incorrect because it can be time-consuming and may not be practical in situations where a quick estimate is needed.
B. Calculating the number of small squares between one QRS complex and the next and dividing into 1500 in (option B) is incorrect because it is a method used to calculate heart rate, known as the "1500 method," but it is not as quick as the 6-second method and requires more time and measurement precision.
D. Counting the number of large squares in the R-R interval and dividing by 300 is another method used to calculate heart rate, known as the "300 method," but it is also less quick and less accurate for assessing heart rate in patients with regular rhythms.
It's important to note that if the heart rhythm is irregular, these methods may not provide an accurate estimate of the heart rate, and a longer monitoring period or a different approach may be necessary.

Heart rate: 72 beats per minute Stroke volume: 90 mL/contraction

Cardiac output = Heart rate × Stroke volume

Cardiac output = 72 beats/minute × 90 mL/contraction

To simplify the calculation, you can convert the units:

72 beats/minute × 90 mL/contraction = (72 × 90) beats/minute × mL/contraction

Now, perform the multiplication:

72 × 90 = 6,480

Therefore, the cardiac output is 6,480 mL per minute.

The correct answer is:

C. 6,480 mL