Mean arterial pressure

The most common formula for calculating mean arterial pressure is:

${\displaystyle MAP=DP+1/3(SP-DP)}$[6]

where:

• DP = diastolic pressure
• SP = systolic pressure
• MAP = mean arterial pressure

Systolic pressure minus diastolic pressure equals the pulse pressure which may be substituted in.[2]

Blood pressure cuff

Another way to find the MAP is to use the Systemic Vascular Resistance equated (${\displaystyle R}$), which is represented mathematically by the formula

${\displaystyle R=\Delta P/Q}$

where ${\displaystyle \Delta P}$ is the change in pressure across the systemic circulation from its beginning to its end and ${\displaystyle Q}$ is the flow through the vasculature (equal to cardiac output).

In other words:

${\displaystyle SVR=(MAP-CVP)/CO}$

Therefore, Mean arterial pressure can be determined by rearranging the equation to:

${\displaystyle MAP=(CO\cdot SVR)+CVP}$

where:

• ${\displaystyle CO}$ is cardiac output
• ${\displaystyle SVR}$ is systemic vascular resistance
• ${\displaystyle CVP}$ is central venous pressure and usually is small enough to be neglected in this formula.[7]

This is only valid at normal resting heart rates during which ${\displaystyle MAP}$ can be approximated using the measured systolic (${\displaystyle SP}$) and diastolic (${\displaystyle DP}$) blood pressures:[8][9][10]

At high heart rates ${\displaystyle MAP}$ is more closely approximated by the arithmetic mean of systolic and diastolic pressures because of the change in shape of the arterial pressure pulse.

For a more accurate formula of ${\displaystyle MAP}$ for elevated heart rates use:

${\displaystyle MAP\simeq DP+0.01\times \exp(4.14-40.74/HR)\times PP}$

Where

• HR = heart rate.
• DP = diastolic pressure
• MAP = mean arterial pressure
• PP = pulse pressure which is systolic minus diastolic pressure[11]

The version of the MAP equation multiplying 0.412 by pulse pressure and adding diastolic blood is indicated to correlate better than other versions of the equation with left ventricular hypertrophy, carotid wall thickness and aortic stiffness.[12] It is expressed:

${\displaystyle MAP=DBP+(0.412\times PP)}$

where:

• DBP = diastolic pressure
• MAP = mean arterial pressure
• PP = pulse pressure

For young patients with congenital heart disease a slight alteration to the factor used found to be more precise. This was written as:

${\displaystyle MAP=DBP+(0.475\times PP)}$

where:

• DBP = diastolic pressure
• MAP = mean arterial pressure
• PP = pulse pressure

This added precision means cerebral blood flow can be more accurately maintained in uncontrolled hypertension.[13]

For neonates, because of their altered physiology, a different formula has been proposed for a more precise reading:

${\displaystyle MAP=DBP+(0.466\times PP)}$

where:

• DBP = diastolic pressure
• MAP = mean arterial pressure
• PP = pulse pressure

It has also been suggested that when getting readings from a neonates radial arterial line, mean arterial pressure can be approximated by averaging the systolic and diastolic pressure.[14]

Other formulas used to calculate mean arterial pressure are:

${\displaystyle MAP=DBP+0.33(PP+5)}$[15]

or

${\displaystyle MAP=DBP+[0.33+(0.0012\times HR)]\times PP}$[16]

or

${\displaystyle MAP=DAP+PP/3}$[17]

or

${\displaystyle MAP=DAP+PP/3+5mmHg}$[18]

• MAP = mean arterial pressure
• PP = pulse pressure
• DAP = diastolic aortic pressure
• DPB = diastolic blood pressure

In patients with sepsis, the vasopressor dosage may be titrated on the basis of estimated MAP.[5]

Even 1 minute at a mean arterial pressure of 50 mmHg, or accumulative effects over short periods, increases the risk of mortality by 5% and can result in organ failure or complications.[21][22] MAP may be used like systolic blood pressure in monitoring and treating target blood pressure. Both have been shown advantageous targets for sepsis, major trauma, stroke, intracranial bleed. If the MAP falls below the target number for an appreciable time, vital organs will not get enough oxygen perfusion, and will become hypoxic, a condition called ischemia.[23]

As the 24 hour mean arterial pressure increases, so does the risk of adverse cardiovascular events. MAP shows information about both the systolic and diastolic blood pressure In the management of high blood pressure, so it can be evaluated to ensure perfusion is maintained to the organs.[19]