What is the math behind the formula for MAP?

DragonClaw

Emergency Medical Texan
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I get it's the Mean Arterial Pressure, but a mean is an average. What are they averaging if you divide the difference of the systolic and diastolic by 3?

I can't find anything more specific than the formula and notes of basic resistance in the vessels
 

FiremanMike

Just a dude
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There’s several formulas out there, some probably far more accurate, but the one I’ve always used is (SBP + 2*DBP)/3

So really what this this formula does is take the constant arterial pressure at rest (DBP) and then add in the pressure thst the heart exerts against the arteries when it pumps (SBP) to give you an overall average pressure..
 

mgr22

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I get it's the Mean Arterial Pressure, but a mean is an average. What are they averaging if you divide the difference of the systolic and diastolic by 3?

I can't find anything more specific than the formula and notes of basic resistance in the vessels
As FiremanMike pointed out, it's not just an average, but a weighted average, where DBP has twice the impact of SBP. You're not dividing the difference between SBP and DBP by 3. That would be a much smaller, meaningless number that would equal one third of the pulse pressure.

'Course there's always a chance the AHA will introduce OTOPP as a key predictor of ROSC.
 

E tank

Caution: Paralyzing Agent
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If you look at an arterial pressure wave form, there are no straight lines and the area under the curve has kind of a wave type shape. Because of this we can't use a straight arithmetic mean or average of the numbers. If the numbers on the wave form, when plotted on a graph, made straight lines, we could. But they don't, so we can't. The values form curved lines and so MAP requires a geometric mean calculation.
 
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OP
DragonClaw

DragonClaw

Emergency Medical Texan
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If you look at an arterial pressure wave form, there are no straight lines and the area under the curve has kind of a wave type shape. Because of this we can't use a straight arithmetic mean or average of the numbers. If the numbers on the wave form, when plotted on a graph, made straight lines, we could. But they don't, so we can't. The values form curved lines and so MAP requires a geometric mean calculation.
Is that kind of like a scatteplot with Line of Best Fit?
 

RedBlanketRunner

Opheophagus Hannah Cuddler
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"Since MAP is a product of Cardiac Output (CO) and Systemic Vascular Resistance (SVR) [MAP = CO x SVR], variations in SVR make the relationship between MAP and CO often unreliable (for example, a patient with a poor CO but high SVR such as a patient in cardiogenic shock may have an acceptable MAP but a CO that is too low to provide adequate perfusion to tissues)"
 

silver

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"Since MAP is a product of Cardiac Output (CO) and Systemic Vascular Resistance (SVR) [MAP = CO x SVR], variations in SVR make the relationship between MAP and CO often unreliable (for example, a patient with a poor CO but high SVR such as a patient in cardiogenic shock may have an acceptable MAP but a CO that is too low to provide adequate perfusion to tissues)"
What is this a quote from?

The relationship is very reliable. However CO and MAP do not equal tissue perfusion.
 
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GMCmedic

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I want to but like...

Stuff
_____

My head

I'm enjoying the discussion though. We're all learning, right?

Just recognize that what you learn in this thread could potentially cause you to over think test questions.

There is good information here and the discussion looks to be headed towards great information. However, the direction they're headed, personal opinion here, is above your average street medics education level.
 

RedBlanketRunner

Opheophagus Hannah Cuddler
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There is good information here and the discussion looks to be headed towards great information. However, the direction they're headed, personal opinion here, is above your average street medics education level.
Education - Training dilemma; a paradox if you will. Excessive information, especially theoretical, can lead to inattentiveness which can produce skipping or missing steps in procedures and protocols, sometimes crucial. On the other hand having a solid background on the purpose, why there are those P&Ps, can lead to thinking on your feet, giving greater scope to a persons functions., especially at critical times such as assessments and trend monitoring.
In the classrom, the professor droning on monotone rote as the class starts nodding off vs an animated enthusiastic prof that continuously strives for student involvement to get salient points driven home.

At one hospital there were two CPR refresher course certified instructors. One, a nurse who was in charge of all continuing ed and updating literature who hadn't worked with patients in over a decade and the other, an NA who worked ER part time and ambulance EMT II ACLS etc. The nurse refreshers were rote, 2 solid hours of theory. The NA filled her course with war stories and practical tips and suggestions along with fielding lots of questions. Constant low key friction between the two.
 
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