How do you measure mean systemic arterial pressure (MAP)?

From the Guidelines

Mean systemic pressure (MSP) is typically measured in experimental settings by temporarily stopping blood flow through the heart, but in clinical practice, it is estimated using indirect methods such as measuring central venous pressure (CVP) or using mathematical models that incorporate measurements of cardiac output, CVP, and mean arterial pressure 1.

Measurement Techniques

• In experimental settings, MSP is measured by stopping blood flow through the heart and allowing pressures throughout the circulatory system to equilibrate.
• In clinical practice, direct measurement is not feasible, so MSP is estimated using indirect methods.

Indirect Measurement Methods

• Measuring central venous pressure (CVP) during circulatory arrest situations like cardiac arrest or during cardiopulmonary bypass.
• Using mathematical models that incorporate measurements of cardiac output, CVP, and mean arterial pressure.
• The zero-flow pressure extrapolation technique plots the relationship between venous return and right atrial pressure, then extrapolates to the pressure at zero flow, which represents MSP.

Importance of MSP

• MSP reflects the elastic recoil pressure of the entire circulatory system and serves as the driving force for venous return to the heart.
• Normal MSP values range from 7-10 mmHg in humans, though this can vary with blood volume status and vascular tone.

Clinical Considerations

• The provided evidence 1 focuses on blood pressure measurements and guidelines, but does not directly address the measurement of mean systemic pressure.
• However, understanding blood pressure measurements is crucial in estimating MSP, as it is closely related to cardiac output and vascular tone.

From the Research

Measuring Mean Systemic Pressure

To measure mean systemic pressure, the following methods can be employed:

• Invasive measurement using an arterial catheter, which is considered the most accurate method 2, 3, 4
• Noninvasive intermittent methods using an occluding upper arm cuff, which can be performed manually or automatically 2
• Vascular unloading technique with a finger plethysmographic sensor for continuous and noninvasive blood pressure monitoring 2
• Bedside assessment using minimally invasive monitoring of continuous cardiac output and right atrial pressure (Pra), by performing a series of end-inspiratory hold maneuvers in ventilator-dependent patients 5

Key Considerations

When measuring mean systemic pressure, it is essential to consider the following:

• The choice of catheter insertion site, type of arterial catheter, and placement technique 3, 4
• The use of a flush device with a constant flow and a fast flush valve connected to normal saline under pressure 4
• The incorporation of salts for radiopacity and the use of heparin-coating, which may increase thrombogenicity 4
• The potential for distortion of pressure wave and the importance of minimizing connections and using low volume, low compliance, low resistance devices 4

Clinical Applications

Measuring mean systemic pressure has significant implications in clinical practice, including:

• Monitoring blood pressure in perioperative and intensive care medicine 2, 3
• Assessing the control of vascular capacitance and distinguishing between passive and active mechanisms of blood volume redistribution 5
• Evaluating the effects of inotropic stimulation and essential hypertension on pulsatile components of blood pressure 6