نظرة سريرية عامة
Mean arterial pressure represents the average pressure driving systemic blood flow over a cardiac cycle. Because the heart normally spends more time in diastole than systole, MAP is not the simple arithmetic mean of systolic and diastolic pressure. At typical heart rates it is estimated by adding one third of the pulse pressure to the diastolic pressure. A directly measured arterial waveform provides a time-integrated value and may differ from this bedside approximation.
MAP is used as one piece of hemodynamic assessment in shock, perioperative care, traumatic brain injury, renal perfusion concerns, and vasoactive-drug titration. Many sepsis protocols begin with a target near 65 mmHg in adults receiving vasopressors, but this is an initial population-level target. The appropriate pressure for a particular patient depends on chronic hypertension, age, pregnancy, cerebrovascular or coronary disease, intracranial pressure, and observable organ perfusion.
دواعي الاستخدام
- Rapid estimation of organ perfusion pressure
- Hemodynamic monitoring in shock and critical illness
- Titration context for fluids and vasoactive therapy
القيود والسلامة
Confirm that the cuff size and position are appropriate and repeat unexpected values. Oscillometric devices directly estimate MAP and algorithmically derive systolic and diastolic values, so recomputing MAP from the displayed endpoints can differ from the monitor. Severe hypotension, vasoconstriction, arrhythmia, movement, and poor limb perfusion reduce noninvasive accuracy. When decisions are high stakes or vasoactive therapy changes rapidly, consider an arterial catheter when clinically indicated.
MAP cannot show whether cardiac output, oxygen delivery, or microcirculatory flow is adequate. Evaluate mentation, skin perfusion, capillary refill, urine output, lactate trend, bedside ultrasound, and the suspected shock phenotype. A value above 65 mmHg is not proof of adequate perfusion, and a transient value below 65 mmHg is not by itself a mandate for fluids; excess fluid can be harmful. Treat the cause and use dynamic assessment of likely fluid responsiveness.
- Approximation is less accurate with marked tachycardia or irregular rhythm
- Cuff measurements may be unreliable in shock, arrhythmia, movement, or inappropriate cuff sizing
- A universal MAP target is not appropriate for every patient
المعادلة
MAP ≈ DBP + ⅓(SBP − DBP), equivalent to (SBP + 2 × DBP) ÷ 3 at ordinary heart rates
تفسير النتائج
- < 65 mmHg — Low pressure in many critically ill adults: May be associated with inadequate organ perfusion, depending on baseline and duration. Verify promptly; assess shock phenotype and perfusion, then treat the cause.
- 65–69 mmHg — Borderline / common initial target zone: May be adequate for some patients and insufficient for others. Individualize to chronic BP, neurologic context, and end-organ response.
- ≥ 70 mmHg — Often adequate pressure: Does not guarantee adequate flow or oxygen delivery. Continue clinical monitoring; avoid unnecessary escalation based on pressure alone.
المراجع
- Evans L, et al. Surviving Sepsis Campaign Guidelines 2021.
- Asfar P, et al. High versus low blood-pressure target in septic shock. NEJM. 2014.
- Magder S. The meaning of blood pressure. Crit Care. 2018.
الأسئلة الشائعة
Why is MAP not (SBP + DBP) divided by two?
At normal heart rates diastole lasts longer than systole. Weighting diastolic pressure twice better approximates the cycle average.
Is 65 mmHg always the correct target?
No. It is a common initial target in vasopressor-treated septic shock, then individualized using baseline pressure, comorbidity, perfusion response, and treatment harms.
Does a low MAP automatically mean the patient needs fluid?
No. Determine the cause and fluid responsiveness. Cardiogenic, obstructive, or distributive shock may require different interventions, and excess fluid can worsen outcomes.