Medical AIMean arterial pressure (MAP) calculator
Mean arterial pressure estimates the average pressure driving blood to the organs across the cardiac cycle. Because diastole lasts longer than systole, it is weighted toward the diastolic pressure. A MAP of around 65 mmHg is a commonly cited floor for adequate organ perfusion in resuscitation.
How to measure each input
- Obtain a reliable blood pressure
- Use a correctly sized cuff with the arm at heart level after the patient has rested, or an invasive arterial line in unstable patients. A poorly fitting cuff or motion artefact distorts the MAP.
- Estimate versus measured MAP
- MAP = DBP + 1/3 pulse pressure is an estimate. Arterial-line monitors compute MAP by integrating the pressure waveform, which is more accurate, especially at abnormal heart rates or rhythms.
- Heart rate dependence
- The one-third weighting assumes a normal heart rate. At tachycardia, systole occupies a larger share of the cycle and the formula underestimates true MAP; the opposite holds at bradycardia.
- Use trends and perfusion markers
- Read MAP alongside lactate, urine output, capillary refill, and mentation rather than as an isolated number. A single value can mislead if perfusion is otherwise compromised.
Interpretation
| Band | Meaning |
|---|---|
| < 65 mmHg, below the common perfusion floor | Below the 65 mmHg MAP commonly cited as a resuscitation target floor (for example in sepsis). Sustained low MAP risks organ hypoperfusion. Assess volume status and consider vasopressors per the clinical context. |
| 65 to 69 mmHg, borderline at target | At or just above the commonly cited 65 mmHg target. Adequate for many patients but offers little margin; reassess trend, perfusion markers (lactate, urine output, mentation), and any individualised target. |
| 70 to 100 mmHg, typical range | Within the usual range for an adult. Generally consistent with adequate organ perfusion, though target ranges are condition-specific. |
| > 100 mmHg, elevated | Elevated mean arterial pressure. Interpret in context (pain, anxiety, chronic hypertension, raised intracranial pressure, or a target organ at risk such as in aortic dissection, where a lower MAP is often desired). |
Pitfalls, exclusions and caveats
- MAP = DBP + 1/3 pulse pressure is an approximation valid at normal heart rates. It diverges from waveform-derived MAP during tachycardia, bradycardia, and irregular rhythms.
- The 65 mmHg target is a population default, not a universal goal. Higher targets may suit chronic hypertensives, and lower targets suit conditions such as aortic dissection or active haemorrhage before control.
- Cuff (oscillometric) MAP and invasive arterial-line MAP can differ, particularly in shock, arrhythmia, peripheral vascular disease, or with an inappropriate cuff size.
- MAP reflects perfusion pressure, not flow or oxygen delivery. An adequate MAP does not guarantee adequate tissue perfusion if cardiac output or microcirculation is impaired.
- A negative or near-zero pulse pressure usually signals a measurement error (diastolic recorded above systolic) and should prompt re-measurement.
- In raised intracranial pressure, cerebral perfusion pressure (MAP minus ICP) is the relevant target, not MAP alone.
MAP = DBP + (SBP - DBP)/3, equivalently (SBP + 2 x DBP)/3. Pulse pressure = SBP - DBP. The one-third rule is an approximation valid at normal heart rates.Mean arterial pressure is a standard physiological calculation. This implementation is an educational tool and is not affiliated with any guideline body. Perfusion targets are condition-specific and should follow the relevant guideline.
Frequently asked
How do you calculate mean arterial pressure?
MAP = diastolic pressure + one third of the pulse pressure, which is the same as (systolic + 2 x diastolic) / 3. For 120/80, MAP is (120 + 160) / 3, which is about 93 mmHg.
What is a normal mean arterial pressure?
A typical adult MAP is roughly 70 to 100 mmHg. Around 65 mmHg is a commonly cited floor for organ perfusion in resuscitation, though the right target depends on the patient and condition.
Why is MAP weighted toward the diastolic pressure?
At a normal heart rate the heart spends about twice as long in diastole as in systole, so the average pressure sits closer to the diastolic value. That is why the formula adds only one third of the pulse pressure to the diastolic pressure.
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