From the Guidelines
The formula to calculate Mean Arterial Pressure (MAP) is MAP = [(2 × Diastolic Blood Pressure) + Systolic Blood Pressure] ÷ 3. This formula provides an approximation of the average arterial pressure during a single cardiac cycle. MAP is an important clinical parameter that represents the perfusion pressure experienced by organs in the body. The formula gives more weight to the diastolic pressure because diastole typically lasts longer than systole in the cardiac cycle. For example, if a patient has a blood pressure of 120/80 mmHg, the MAP would be [(2 × 80) + 120] ÷ 3 = 280 ÷ 3 = 93.3 mmHg. In clinical practice, a normal MAP ranges from 70-100 mmHg. Values below 60 mmHg are concerning as they may indicate inadequate organ perfusion, particularly to vital organs like the brain and kidneys. MAP can be measured directly through an arterial line or calculated using this formula when only non-invasive blood pressure readings are available 1.
Key Points to Consider
- The provided evidence does not directly address the formula for calculating MAP, but it emphasizes the importance of maintaining adequate MAP in various clinical scenarios, such as septic shock and traumatic brain injury.
- The formula MAP = [(2 × Diastolic Blood Pressure) + Systolic Blood Pressure] ÷ 3 is a widely accepted method for estimating MAP.
- Clinical guidelines often recommend targeting a specific MAP range, such as ≥ 65 mmHg in septic shock, to ensure adequate organ perfusion 1.
- The choice of vasopressor and the target MAP may vary depending on the patient's condition and the clinical context.
- It is essential to consider the individual patient's needs and to monitor their response to treatment closely.
Clinical Application
In clinical practice, calculating MAP is crucial for assessing the adequacy of blood pressure and organ perfusion. By using the formula MAP = [(2 × Diastolic Blood Pressure) + Systolic Blood Pressure] ÷ 3, healthcare providers can estimate MAP and make informed decisions about patient care. For example, if a patient has a blood pressure of 100/60 mmHg, their MAP would be [(2 × 60) + 100] ÷ 3 = 220 ÷ 3 = 73.3 mmHg, which is within the normal range. However, if the patient's blood pressure drops to 80/50 mmHg, their MAP would be [(2 × 50) + 80] ÷ 3 = 180 ÷ 3 = 60 mmHg, which may indicate inadequate organ perfusion and require intervention. Healthcare providers should consult the most recent and relevant clinical guidelines, such as those from the Surviving Sepsis Campaign 1, to determine the optimal MAP target for their patients.
From the Research
Formula for Mean Arterial Pressure (MAP)
The formula to calculate Mean Arterial Pressure (MAP) can be expressed in several ways based on different studies:
- MAP = dBP + St.PP, where dBP is diastolic blood pressure, St is the fraction of systole from the heart cycle, and PP is pulse pressure 2
- MAP = DP + [0.33 + (HR x 0.0012)] x [PP], where DP is diastolic pressure, HR is heart rate, and PP is pulse pressure 3
- MAP = DP + 1/3(SP - DP), where DP is diastolic pressure and SP is systolic pressure, is a standard equation but may not be accurate during exercise 4
- MAP = DP + Fs(SP - DP), where Fs is the fraction of the cardiac cycle comprising systole, is a more accurate method during exercise 4
- MAP can also be approximated by adding 46.6% of PP to DAP (diastolic arterial pressure) in neonates 5
Key Considerations
- The standard equation for MAP (MAP = DP + 1/3(SP - DP)) may not be accurate during exercise due to changes in the systolic:diastolic period ratio as heart rate increases 4
- The use of a heart rate-corrected MAP formula can provide more accurate results, especially during exercise or in patients with varying heart rates 2, 3
- Different patient populations, such as neonates, may require different formulas or considerations for calculating MAP 5