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The Clinical Relevance of MAP

Hemodynamic monitoring can provide us quite a bit of value not only in an ICU setting, but even in the back of an ambulance. If you're completing an interfacility transfer (IFT) or responding to an emergent 911 call - trending of vitals gives providers a glimpse into the patient's clinical condition. Moreover, it can corroborate our physical exam findings and helps us determine if our immediate interventions are making a difference or if the patient is getting worse. I've always been taught -- be quick to make a decision, but even quicker to change your mind when new information is presented. The new information could be data you collect directly OR new information provided by patients or bystanders.

Nearly every patient encounter has a non-invasive blood pressure documented, but did you know that your heart monitor doesn't measure your systolic and diastolic pressures directly. The machine actually measures MAP and then uses some calculations to estimate both your SBP and DBP. Most noninvasive blood pressure (NIBP) devices use the oscillometric method. Published studies of oscillometric methodology introduced varied algorithmic approaches for determination of systolic (SBP), diastolic (DBP), and mean arterial (MAP) blood pressures. While there is a general agreement about MAP determination, controversy exists about the determination of SBP and DBP. Accuracy of oscillometric devices have been questioned and validation studies have revealed problems. We will save that for another discussion.

In the image above the MAP is the number in parentheses next to the blood pressure reading in RED. You actually have the ability to calculate it yourself using the following equation:

MAP guides clinicians and is used to check whether there’s enough blood flow to supply blood to all your major organs.  Physiologic mechanisms are in place to ensure that the MAP remains at least 60 mmHg so that blood can effectively reach all tissues.

However, too much resistance and pressure may impede that flow (number).

“Resistance” refers to the way the width of a blood vessel impacts blood flow. For example, it’s harder for blood to flow through a narrow artery. As resistance in your arteries increases, blood pressure also increases while the flow of blood decreases.

Additionally, you can also think of MAP as the average pressure in your arteries throughout one cardiac cycle, which includes the series of events that happen every time your heart beats. The image below helps demonstrate this average pressure.

Hypotension, i.e., persistently low blood pressure, can be life-threatening - that comes as no surprise to us in the field. When the MAP maintenance is inadequate, vital organs do not receive the required blood supply, hypotensive shock ensues, and multi-organ failure quickly follows. Hypotension often results from severe bacteremia (sepsis) or hypovolemia. This condition can be treated pharmacologically with dopamine, push-dose Epi and other vasopressors per your local protocols. Thus, we see that MAP can serve to help diagnose both hypertensive (think TBI and/or head bleeds) and hypotensive states and provide diagnostic information for clinicians to make informed therapy decisions.

Bottom Line:

MAP is an important measurement that accounts for flow, resistance, and pressure within your arteries. It allows clinicians from all walks of life to evaluate how well blood flows through your body and whether it’s reaching all your major organs.

Most people do best with a MAP between 70 and 110 mm Hg. Anything much higher or lower can be a sign of an underlying problem. However, this is typically most applicable as a measurement for inpatient procedures and hospitalized patients. EMS should not just outright disregard it though.

January 22, 2024

Author: Joshua Ishmael, MBA, MLS(ASCP)CM, NRP

Pass with PASS, LLC.

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