Mean arterial pressure

In medicine, the mean arterial pressure (MAP) is an average blood pressure in an individual during a single cardiac cycle.^[1]

Calculation

The Systemic Vascular Resistance (SVR), denoted ${\displaystyle R}$ is represented mathematically by the formula

${\displaystyle R=\Delta P/Q}$,^[2] 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)

another type of equation is:

${\displaystyle MAP=[Systolic+2(Diastolic)]/3}$

In other words:

Systemic Vascular Resistance = (Mean Arterial Pressure - Mean Venous Pressure) / Cardiac Output

Therefore, Mean arterial pressure can be determined from:^[3]

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

where:

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

Estimation

While MAP can only be measured directly by invasive monitoring. The MAP can be estimated by using a formula in which the lower (diastolic) blood pressure is doubled and added to the higher (systolic) blood pressure and that composite sum then is divided by 3 to estimate MAP. In patients with sepsis, the vasopressor dosage may be titrated on the basis of estimated MAP.^[4]

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:^[5][6][7]

${\displaystyle MAP\simeq DP+{\frac {1}{3}}(SP-DP)}$

or equivalently

${\displaystyle MAP\simeq {\frac {2}{3}}(DP)+{\frac {1}{3}}(SP)}$

or equivalently

${\displaystyle MAP\simeq {\frac {(2\times DP)+SP}{3}}}$

or equivalently

${\displaystyle MAP\simeq DP+{\frac {1}{3}}PP}$

where ${\displaystyle PP}$ is the pulse pressure, ${\displaystyle SP-DP}$

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 generalized formula of ${\displaystyle MAP}$:

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

Where HR is the heart rate.^[8]

Clinical significance

${\displaystyle MAP}$ is considered to be the perfusion pressure seen by organs in the body.

It is believed that a ${\displaystyle MAP}$ that is greater than 70 mmHg is enough to sustain the organs of the average person. ${\displaystyle MAP}$ is normally between 65 and 110 mmHg.^[9] 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.^[10][11] MAP may be used similarly to systolic blood pressure in monitoring and treating for target blood pressure. Both have been shown advantageous targets for sepsis, major trauma, stroke, intracranial bleed, and hypertensive emergencies.^[12]

If the ${\displaystyle MAP}$ falls below this number for an appreciable time, vital organs will not get enough oxygen perfusion, and will become hypoxic, a condition called ischemia.

See also

• Blood pressure
• Hypertension
• Hypotension
• Ambulatory blood pressure
• Pulse pressure

References

External links

• Mean Arterial Pressure Calculator
• More Information on usage of the Mean Arterial Pressure