Mean Arterial Pressure (MAP) Calculator

About the Mean Arterial Pressure (MAP) Calculator

Mean arterial pressure (MAP) is the average pressure in your arteries over one whole heartbeat. It is closer to the pressure that pushes blood through your organs than the top number alone, which is why intensive care teams watch it. A cuff gives two numbers, systolic and diastolic, and MAP is worked out from them: the usual formula is the diastolic pressure plus one third of the difference between the two.

Enter a reading and this calculator gives the standard MAP, the alternatives published since — Meaney’s 0.412 form, Razminia’s heart-rate-corrected formula and three others — each with your numbers worked through, plus pulse pressure and where the result sits against the published reference points: 60 mmHg, 65 mmHg (the first target in septic shock) and the usual 70–100 mmHg.

Without a pass, the free preview shows the standard MAP in full, with what it means, every warning and the first rows of the formula table; the pulse pressure, the rest of the formula table, the scale and Copy result come with a Pro pass.

Common uses

• Working out the MAP from a home or clinic blood pressure reading.
• Checking a MAP against the 65 mmHg target while studying sepsis or critical care.
• Seeing how much the choice of formula changes the result, especially at a fast heart rate.
• Finding the pulse pressure and proportional pulse pressure of a reading.

The formulas

SBP is the systolic pressure, DBP the diastolic and PP the pulse pressure (SBP − DBP), all in mmHg; HR is the heart rate per minute.

• Standard: DBP + ⅓ × PP, the same as (SBP + 2 × DBP) ÷ 3. The heart spends about two thirds of each beat in diastole at a resting rate, so the diastolic pressure counts twice.
• Meaney: DBP + 0.412 × PP.
• Razminia: DBP + (0.33 + 0.0012 × HR) × PP. At faster heart rates more of each beat is systole, so the systolic pressure gets more weight.
• Wezler: 0.42 × SBP + 0.58 × DBP.
• Chemla: DBP + ⅓ × PP + 5, and the geometric mean √(SBP × DBP).

A comparison against pressure measured directly inside an artery (in pigs) found every one of these within about 3 mmHg of the true mean: the standard formula read about 2 mmHg low and 0.412 about 1 mmHg high.

What the number means

• The normal range of MAP is generally given as 70 to 100 mmHg.
• A MAP below about 60 mmHg is associated with reduced blood flow to the organs.
• For adults in septic shock who need drugs to raise their blood pressure, the Surviving Sepsis Campaign recommends a first target MAP of 65 mmHg rather than higher targets.
• Low blood pressure on its own is not always a problem: the NHS defines it as below 90/60 mmHg, and notes it can simply be because someone is fit and healthy. What matters is whether it causes symptoms such as dizziness or fainting.
• A high MAP usually comes with high blood pressure readings. For the category of a reading (normal, elevated, hypertension) use the blood pressure checker.

Pulse pressure

Pulse pressure is the systolic minus the diastolic pressure: 40 mmHg for a reading of 120/80. Divided by the systolic pressure it becomes the proportional pulse pressure. In a study of 50 people with chronic heart failure, a proportional pulse pressure below 25% picked out a low cardiac output (cardiac index below 2.2 L/min/m²) with 91% sensitivity and 83% specificity. The calculator points this out, but it only applies in that setting.

Why your monitor may show a different MAP

Automatic cuffs measure the pressure oscillations in the cuff and work out MAP with their own maker’s method, so the MAP shown on a monitor can differ by a few mmHg from any formula. An arterial line in intensive care measures it directly.

Sources

• Tien LYH et al., Optimal calculation of mean pressure from pulse pressure, American Journal of Hypertension — the six formulas, their accuracy, the 70–100 and 60 mmHg reference points and oscillometric monitors.
• Meaney E et al., Formula and nomogram for the sphygmomanometric calculation of the mean arterial pressure, Heart.
• Razminia M et al., Validation of a new formula for mean arterial pressure calculation, Catheterization and Cardiovascular Interventions.
• Evans L et al., Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock, recommendation 9.
• Stevenson LW, Perloff JK, The limited reliability of physical signs for estimating hemodynamics in chronic heart failure, JAMA.
• NHS, Low blood pressure (hypotension).

Limitations

• One cuff reading is a snapshot: blood pressure changes from minute to minute, so repeat readings matter more than any single MAP.
• The formulas estimate the mean from two numbers; they cannot see the shape of the pressure wave, which an arterial line records.
• The reference points describe adults. Children have lower normal pressures.
• This page does not diagnose or treat low or high blood pressure. If a low reading comes with fainting, confusion or breathlessness, get medical help straight away.

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