What is the Mean Arterial Pressure (MAP) for a blood pressure reading of 87/51?

Mean Arterial Pressure Calculation for Blood Pressure 87/51

The mean arterial pressure (MAP) for a blood pressure reading of 87/51 mmHg is 63 mmHg when calculated using the standard formula: MAP = DBP + [(SBP - DBP) × 1/3].

Standard MAP Calculation Formula

• The most widely used formula for calculating MAP is: MAP = Diastolic BP + [(Systolic BP - Diastolic BP) × 1/3] 1
• Using this formula for BP 87/51: MAP = 51 + [(87 - 51) × 1/3] = 51 + [36 × 1/3] = 51 + 12 = 63 mmHg 1

Alternative Calculation Methods

• Some research suggests that the standard formula may not be optimal in all situations, as it assumes a fixed ratio between systole and diastole 1, 2
• A more accurate heart rate-corrected formula has been proposed: MAP = DBP + [0.33 + (HR × 0.0012)] × [PP], where PP is pulse pressure (SBP - DBP) 1
• Without heart rate information in this case, we must rely on the standard formula 1

Clinical Significance of MAP

• MAP represents the average arterial pressure during a single cardiac cycle 3
• It is considered the perfusion pressure seen by organs in the body 3
• A MAP of 65 mmHg is often used as a target threshold in critical care settings to ensure adequate organ perfusion 3
• For this blood pressure (87/51), the calculated MAP of 63 mmHg is slightly below this common target 3

Variations in MAP Calculation

• Research has shown differences between measured MAP (directly from devices) and calculated MAP 4
• These differences can be influenced by:
  • Age of the patient 2, 4
  • Heart rate 1, 5
  • Type of measurement device 2, 4
  • Arterial location of measurement 2

Special Considerations

• In neonates, MAP may be better approximated by adding 46.6% of pulse pressure to diastolic pressure rather than the standard 33% used in adults 6
• During exercise, the systolic fraction of the cardiac cycle changes with heart rate, which affects MAP calculation 5
• Different devices may yield different MAP values - oscillometric devices often display directly measured MAP that can differ from calculated values 2, 4

Clinical Context

• A MAP of 63 mmHg may be considered low in many clinical contexts 3
• In septic shock management, current guidelines recommend maintaining MAP ≥65 mmHg 3
• In trauma without brain injury, a lower MAP may be acceptable until bleeding is controlled 3
• In patients with traumatic brain injury, a higher MAP (≥80 mmHg) is often targeted 3