MAP, or mean arterial pressure, is defined as the average pressure in a patient’s arteries during one cardiac cycle. It is considered a better indicator of perfusion to vital organs than systolic blood pressure (SBP). True MAP can only be determined by invasive monitoring and complex calculations; however it can also be calculated using a formula of the SBP and the diastolic blood pressure (DBP). 

To calculate a mean arterial pressure, double the diastolic blood pressure and add the sum to the systolic blood pressure. Then divide by 3. For example, if a patient’s blood pressure is 83 mm Hg/50 mm Hg, his MAP would be 61 mm Hg. Here are the steps for this calculation:

MAP = SBP + 2 (DBP)
                3

MAP = 83 +2 (50)
                3

MAP = 83 +100
             3

MAP = 183
           3

MAP = 61 mm HG

Another way to calculate the MAP is to first calculate the pulse pressure (subtract the DBP from the SBP) and divide that by 3, then add the DBP:

MAP = 1/3 (SBP – DBP) + DBP

MAP = 1/3 (83-50) + 50

MAP = 1/3 (33) + 50

MAP = 11 + 50

MAP = 61 mm Hg

There are several clinical situations in which it is especially important to monitor mean arterial pressure. In patients with sepsis, vasopressors are often titrated based on the MAP. In the guidelines of the Surviving Sepsis Campaign, it is recommended that mean arterial pressure (MAP) be maintained ≥ 65 mm Hg. Also, in patients with head injury or stroke, treatment may be dependent on the patient’s MAP. 

In what other clinical situations do you monitor MAP?  

References
Surviving Sepsis CampaignAccessed December 8, 2011. 
Smeltzer, S. C., Bare, B. G., Hinkle, J. L., & Cheever, K. H. (2010). Brunner & Suddarth's Textbook of Medical-Surgical Nursing, Twelfth Edition. Philadelpha: Wolters Kluwer Health/ Lippincott Williams & Wilkins.