Calculate Mean Arterial Pressure using the standard clinical formula. Septic shock target ≥65 mmHg, vasopressor thresholds, organ perfusion interpretation, and EMR-ready documentation.
Alternative to NE; increased arrhythmia risk vs norepinephrine
Phenylephrine
0.5–6 mcg/kg/min
Pure α1 agonist — vasoconstriction only
Tachycardia-induced hypotension; vasodilatory shock when NE unavailable
Doses are typical adult ranges — adjust for weight, renal function, and clinical response. Always follow local formulary and ICU protocols.
Mean Arterial Pressure — Clinical Reference
Mean Arterial Pressure (MAP) is the time-weighted average arterial pressure throughout the cardiac cycle and the single most important hemodynamic value for assessing organ perfusion. Unlike systolic or diastolic blood pressure alone, MAP directly reflects the driving pressure that pushes blood through the systemic vasculature to vital organs — the brain, kidneys, liver, and heart. A MAP below 65 mmHg is the clinical threshold for inadequate organ perfusion in most adults.
MAP Formula — Why Diastole Is Weighted More
The standard clinical formula is MAP = [SBP + (2 × DBP)] / 3. Diastolic pressure is weighted twice because the heart spends approximately two-thirds of the cardiac cycle in diastole (relaxation) and only one-third in systole (contraction). At normal resting heart rates (60–80 bpm), systole lasts approximately 0.3 seconds and diastole lasts approximately 0.5–0.7 seconds. The formula is equivalent to: MAP = DBP + (Pulse Pressure / 3), where Pulse Pressure = SBP − DBP.
MAP in Septic Shock — Surviving Sepsis Campaign Guidelines
The Surviving Sepsis Campaign 2021 guidelines recommend a MAP target of ≥65 mmHg as the initial resuscitation goal in septic shock. Norepinephrine (noradrenaline) is the first-line vasopressor — it increases MAP through α1-mediated vasoconstriction with minimal increase in heart rate. Vasopressin (0.03–0.04 units/min) is added to norepinephrine to either raise MAP further or reduce norepinephrine dose. For patients with chronic hypertension, a higher MAP target of 70–80 mmHg may be needed to maintain cerebral autoregulation.
Pulse Pressure — Interpreting the Gap
Normal pulse pressure: 40 mmHg (SBP 120, DBP 80) — represents normal stroke volume and aortic compliance
What is the difference between MAP and blood pressure?
Blood pressure is reported as two values — systolic (peak during contraction) and diastolic (minimum during relaxation). MAP is a single value representing the average perfusion pressure throughout the entire cardiac cycle. MAP is more clinically relevant than SBP or DBP alone because it accounts for the time spent at each pressure phase. Organ blood flow is driven by MAP (specifically: Organ Flow = MAP ÷ Vascular Resistance), not by systolic pressure alone.
Why is MAP ≥65 mmHg the septic shock target?
The MAP ≥65 mmHg threshold is derived from multiple studies showing that renal blood flow, cerebral perfusion, and mesenteric circulation are maintained above this level in most adults. The landmark SEPSISPAM trial (Asfar et al., NEJM 2014) found no mortality benefit of targeting MAP 80–85 mmHg versus 65–70 mmHg in septic shock — except in patients with chronic hypertension, who had lower rates of new renal replacement therapy with the higher target. The Surviving Sepsis Campaign therefore recommends 65 mmHg as the minimum target for most patients, with individualisation for those with chronic hypertension or known renal disease.
Is MAP different from an arterial line (A-line) reading?
Yes — the formula-based MAP (from a cuff BP) is an approximation. An arterial line (A-line) calculates MAP electronically by integrating the area under the arterial pressure waveform, which is more accurate — especially at extremes of heart rate or in states of poor peripheral perfusion where cuff measurements are unreliable. In critically ill patients receiving vasopressors, an A-line provides continuous, beat-to-beat MAP monitoring and is strongly preferred over intermittent cuff measurements.
Can MAP be normal with a low systolic blood pressure?
Yes. Consider SBP 90, DBP 70: MAP = (90 + 140) / 3 = 77 mmHg — a normal MAP despite a low systolic. This is common in young patients with low vascular resistance (e.g., distributive shock early stages) or athletes with physiologically low resting SBP. Conversely, isolated systolic hypertension in elderly patients (e.g., SBP 180, DBP 70) produces a MAP of 107 mmHg — high MAP with a wide pulse pressure reflecting reduced aortic compliance. This is why MAP is more informative than SBP or DBP alone for perfusion assessment.