Is an art line MAP a calculated number?
Started by ultraconsrvativ
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ultraconsrvativ said:
Yes. Its a calculated number.
MAP= (2)(diastolic) + (1/3)(systolic) or something close to that. Check with UT or an analagous I-just-took-my-boards stud.
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......for the exact formula.jetproppilot said:
I think most of the modern monitors use area under the curve - may help avoid inaccuracy in the calculated MAP due to damping, placement of a-line in the foot etc. I think Marino ICU book talks about this.
heartICU said:
Area under the curve = Integral a-->b of f(x) dx.
The formula is diastolic diastolic + 1/3 systolic-diastolic, which is easier to calculate as (2*diastolic +systolic)/3. The two times I've seen a-line in the past few weeks, the MAP displayed has not equaled this calculation, not has it even been close enough for me to chalk it up to a math rounding error. Either the machine is using an adjusted calculation based on heart rate, or it's doing some calculus or some calculations to approximate calculus (or I'm just plain wrong).
This paper finds that a better way is diastolic + 0.412 (systolic-diastolic). Perhaps if (when) I feel especially nerdy I'll whip that one out some day.
This paper finds that a better way is diastolic + 0.412 (systolic-diastolic). Perhaps if (when) I feel especially nerdy I'll whip that one out some day.
Adcadet said:
I think what you guys are referring to is how to calculate/estimate MAP from an NIBP (BP cuff pressure). In a manual BP, the MAP is a calculated value.
However, with an automatic BP cuff, the MAP is the most accurate parameter & the SBP & DBP are derived from a statistical algorithm known as oscillometry. And, the further away from "normal", whatever that is, the higher the error factor is in the SBP & DBP.
Now, with modern monitors & an a-line, it does involve calculus & other mathematical voodoo.
The long & short of it - a manual cuff, an automatic cuff & an a-line are 3 different methods of estimating a natural phenomenon: blood pressure. All three have merits & short-comings. All three require a practitioner to 'know' when to trust & when to discount the numbers they provide. Afterall, it is the patient & not some spurious numbers that we should be treating.
MAP in art lines is just the average blood pressure (a measured term) derived by the area under the curve (integral) divided by the time it takes to produce that curve (ie: from nadir to nadir).
So all three art-line numbers (the systolic, diastolic, and MAP) are measured numbers. The formula MAP = (systolic - diastolic)/3 + diastolic is just an estimate of the MAP using the fact that the heart spends more time in diastole than systole. This estimate is assuming the HR is at 60 (or is it 80?.. can't remember), so it is highly inaccurate at other heart rates.
So all three art-line numbers (the systolic, diastolic, and MAP) are measured numbers. The formula MAP = (systolic - diastolic)/3 + diastolic is just an estimate of the MAP using the fact that the heart spends more time in diastole than systole. This estimate is assuming the HR is at 60 (or is it 80?.. can't remember), so it is highly inaccurate at other heart rates.
