Mean Arterial Pressure Calculator

Mean Arterial Pressure formulas

As a measure of blood flow and tissue perfusion, the mean arterial pressure can be determined through two different methods.

The first to be described is the one present in the mean arterial pressure calculator, that accounts for two variables, systolic and diastolic blood pressure, where:

■ SBP (normal values 90 – 120 mmHg) is consistent with the forces that sends blood from the ventricle through to the arteries.

■ BDP (normal values 60 – 80 mmHg) is consistent with the blood pressure remaining in the arteries in between heart contractions.

It starts from: MAP = DBP + 1/3 PP (where PP = SBP – DBP).

Given the above it can also be written as: MAP = DBP + 1/3 (SBP – BDP).

This is turn evolves into: MAP = 2/3 DBP + 1/3 SBP.

The second method is more exact but requires laboratory testing in order to obtain the variables. In this case, MAP takes into account cardiac output (CO), systemic vascular resistance (SVR) and central venous pressure (CVP).

Therefore the formula is: MAP = (CO x SVR) + CVP.

MAP interpretation

The sum of two thirds DBP and one third SBP are considered to be a better indicator of blood flow than just the SBP because it accounts for the diastole as well. It can help clinicians set targets of blood pressure in order to improve therapy adhesion and outcomes in hypertension, stroke recover or other conditions.

The normal MAP is considered to be between 70 and 110 mmHg. Values above 60 indicate adequate tissue perfusion. In some cases, such as in stroke or sepsis, the threshold for adequate perfusion moves slightly higher, to 65 mmHg.

MAP values below 60 mmHg indicate that tissue perfusion is likely to be impaired and there is risk of ischemia. Some of the ways to address this clinically include hydration or certain medication (vasopressor, inotrope or vasodilator).

There are two minimal accepted blood pressure values to ensure adequate perfusion to the vital organs: systolic BP needs to be higher than 90 mmHg and diastolic BP needs to be higher than 60 mmHg.

Maintaining adequate levels of tissue perfusion is essential in sustaining cellular processes, it basically brings nutrition to the cells through blood and if the blood doesn’t circulate properly, ischemia occurs.

Hypertension, diabetes mellitus, obesity, lack of exercise are amongst the causes of impaired perfusion.

Blood pressure classification

The following table compares the systolic and diastolic pressure values with the thresholds for hypotension, normal range and the various degrees of hypertension severity, according to the American Heart Foundation:

References

1. Magder SA. The highs and lows of blood pressure: toward meaningful clinical targets in patients with shock. Crit Care Med. 2014; 42(5): 1241-51.

2. Klabunde R. (2011) Cardiovascular Physiology Concepts 2nd ed. Lippincott Williams & Wilkins.

3. Dillon DJ, Dougan N. Simultaneous measurement of mean arterial pressure with reference to both the phlebostatic axis and middle cranial fossa in the calculation of cerebral perfusion pressure. Br J Anaesth. 2016; 117(2):268-9.