Mean Arterial Pressure Calculator

How does this mean arterial pressure calculator work?

This is a health tool that is designed to obtain the mean arterial pressure (MAP) which describes an average blood pressure during a cardiac cycle based on:

1) Systolic blood pressure (SBP) – consistent with the force that pushes blood through the arteries when the heart beats/contracts. Normal values are considered between 90 and 120 mmHg.

2) Diastolic blood pressure (DBP) – consistent with the blood pressure in the arteries between heart contractions. Normal values are considered between 60 and 80 mmHg.

The mean arterial pressure calculator can be applied in numerous cases and provides a good indicator of blood flow and tissue perfusion, comparable to SBP as it takes account of the diastole factor as well.

Mean arterial pressure formula

While the mean arterial pressure exact determination MAP = (CO x SVR) + CVP takes account of:

CO – cardiac output

SVR – systemic vascular resistance

CVP – central venous pressure

At normal resting heart rates MAP can be estimated through SBP and DBP with any of the following formulas:

MAP = DBP + 1/3 PP where PP = SBP – DBP therefore MAP = DBP + 1/3 (SBP – DBP)

or

MAP = 2/3 DBP + 1/3 SBP

or

MAP = (2 x DBP + SBP)/3

(double the diastolic pressure, add it to the systolic pressure and divide this sum by three)

Example calculation: SBP = 120 mmHg, DBP = 90 mmHg.

MAP = 90 + 1/3 (120 – 90) = 100 mmHg

MAP = 2/3 x 90 + 1/3 x 120 = 60 + 40 = 100 mmHg

MAP interpretation

This is an indicator widely used as a blood pressure target along with systolic blood pressure in clinical guidelines. It is demonstrated that the use of blood pressure targets improves outcome in conditions such as hypertension, trauma or stroke.

Normal mean arterial values are situated between 70 and 110 mmHg.

MAP >60 mmHg – indicates adequate tissue perfusion with a necessary minimum of 65 mmHg for patients in shock/ sepsis.

MAP <60 mmHg – impaired tissue perfusion, not enough oxygen delivered to vital organs, risk of ischemia.

Low MAP values are to be addressed with hydration, vasopressor, inotrope or vasodilator medication.

Tissue perfusion

This and oxygenation are essential in sustaining metabolic cellular processes. The concept of tissue perfusion encompasses blood flow and nutritional supply. Amongst the factors that regulate it, there is a minimum acceptable blood pressure for adequate perfusion to vital organs and this is more than 90 mmHg systolic BP and more than 60 mmHg diastolic BP. When this doesn’t function properly, hypoxia and then ischemia develops and can even progress to necrosis.

Risk factors for an impaired perfusion:

- Age, Gender (in case of male the risk is higher than in case of female), family history

- Sedentarism

- Smoking

- Hypertension

- Obesity

- Diabetes mellitus

Blood pressure classification

According to the American Heart Foundation.

References

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

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

3) Gottrup F. (1994) Physiology and measurement of tissue perfusion. Ann Chir Gynaecol; 83(3):183-9.