Mean arterial pressure explained

Mean arterial pressure

In medicine, the mean arterial pressure (MAP) is an average calculated blood pressure in an individual during a single cardiac cycle.[1] Although methods of estimating MAP vary, a common calculation is to take one-third of the pulse pressure (the difference between the systolic and diastolic pressures), and add that amount to the diastolic pressure.[2] [3] A normal MAP is about 90 mmHg.[4]

MAP is altered by cardiac output and systemic vascular resistance.[5] It is used clinically to estimate the risk of cardiovascular diseases, where a MAP of 90 mmHg or less is low risk, and a MAP of greater than 96 mmHg represents "stage one hypertension" with increased risk.[3] [4]

Testing

Mean arterial pressure can be measured directly or estimate from systolic and diastolic blood pressure by using a formula. The least invasive method is the use of a blood pressure cuff which gives the values to calculate an estimate of the mean pressure. A similar method is to use a oscillometric blood pressure device that works by a cuff only method where a microprocessor determines the systolic and diastolic blood pressure.[6] Invasively, an arterial catheter with a transducer is placed and the mean pressure is determined by the subsequent waveform.

Estimating MAP

While MAP can only be measured directly by invasive monitoring, it can be estimated by using a formula in which the lower (diastolic) blood pressure is doubled and added to the higher (systolic) blood pressure and that composite sum then is divided by 3 to estimate MAP.[2]

Thus, a common way to estimate mean arterial pressure is to take one-third of the pulse pressure added to the diastolic pressure:[2] [3] [7]

MAP ≈ DP+1/3(SP-DP)

where:

Systolic pressure minus diastolic pressure equals the pulse pressure which may be substituted in.Another way to find the MAP is to use the systemic vascular resistance equated (

R

), which is represented mathematically by the formula

R=\DeltaP/Q

where

\DeltaP

is the change in pressure across the systemic circulation from its beginning to its end and

Q

is the flow through the vasculature (equal to cardiac output).

In other words:

SVR=(MAP-CVP)/CO

Therefore, MAP can be determined by rearranging the equation to:

MAP=(CO ⋅ SVR)+CVP

where:

CO

is cardiac output

SVR

is systemic vascular resistance

CVP

is central venous pressure and usually is small enough to be neglected in this formula.[8]

This is only valid at normal resting heart rates during which

MAP

can be approximated using the measured systolic (

SP

) and diastolic (

DP

) blood pressures:[9] [10]

Elevated heart rate

At high heart rates

MAP

is more closely approximated by the arithmetic mean of systolic and diastolic pressures because of the change in shape of the arterial pressure pulse.

For a more accurate formula of

MAP

for elevated heart rates use:

MAP\simeqDP+0.01 x \exp(4.14-40.74/HR) x PP

Where

Most accurate

The version of the MAP equation multiplying 0.412 by pulse pressure and adding diastolic blood is indicated to correlate better than other versions of the equation with left ventricular hypertrophy, carotid wall thickness and aortic stiffness.[12] It is expressed:

MAP=DBP+(0.412 x PP)

where:

Young patients

For young patients with congenital heart disease a slight alteration to the factor used found to be more precise. This was written as:

MAP=DBP+(0.475 x PP)

where:

This added precision means cerebral blood flow can be more accurately maintained in uncontrolled hypertension.[13]

Neonates

For neonates, because of their altered physiology, a different formula has been proposed for a more precise reading:

MAP=DBP+(0.466 x PP)

where:

It has also been suggested that when getting readings from a neonates radial arterial line, mean arterial pressure can be approximated by averaging the systolic and diastolic pressure.[14]

Other formula versions

Other formulas used to estimate mean arterial pressure are:

MAP=DBP+(0.33PP)+5

[15]

or

MAP=DBP+[0.33+(0.0012 x HR)] x PP

[16]

or

MAP=DAP+PP/3

[17]

or

MAP=DAP+(PP/3)+5mmHg

[18]

Clinical significance

Thresholds for 24 hr. mean arterial pressure (MAP)!24 hr. MAP category!24 hr. MAP
Normal< 90 mmHg
Elevated blood pressure90 to < 92 mmHg
Stage 1 hypertension92 to < 96 mmHg
Stage 2 hypertension> 96 mmHg

Mean arterial pressure is a major determinant of the perfusion pressure seen by organs in the body. MAP levels greater than 90 mmHg increase the risk stepwise of having higher risk of cardiovascular diseases, such as stroke, and mortality.[3]

Hypotension

When assessing hypotension, the context of the baseline blood pressure needs to be considered. Acute decreases in mean arterial pressure of around 25% put people at increased risk for organ damage and potential mortality.[19] Even one minute at a MAP of 50 mmHg, or accumulative effects over short periods, increases the risk of mortality by 5%, and can result in organ failure or complications.[20] [21]

In people hospitalized with shock, a MAP of 65 mmHg lasting for more than two hours was associated with higher mortality.[22] In people with sepsis, the vasopressor dosage may be titrated on the basis of estimated MAP.

MAP may be used like systolic blood pressure in monitoring and treating target blood pressure. Both are used as targets for assessing sepsis, major trauma, stroke, and intracranial bleeding.[23]

Hypertension

In younger people, elevated MAP is used more commonly than pulse pressure in the prediction of stroke. However in older people, MAP is less predictive of stroke and a better predictor of cardiovascular disease.[24] [25]

See also

Notes and References

  1. Zheng L, Sun Z, Li J, Zhang R, Zhang X, Liu S, Li J, Xu C, Hu D, Sun Y . 6 . Pulse pressure and mean arterial pressure in relation to ischemic stroke among patients with uncontrolled hypertension in rural areas of China . Stroke . 39 . 7 . 1932–1937 . July 2008 . 18451345 . 10.1161/STROKEAHA.107.510677 . free .
  2. Web site: Calculating the mean arterial pressure (MAP) . Nursing Center . 8 December 2011 .
  3. Melgarejo JD, Yang WY, Thijs L, Li Y, Asayama K, Hansen TW, Wei FF, Kikuya M, Ohkubo T, Dolan E, Stolarz-Skrzypek K, Huang QF, Tikhonoff V, Malyutina S, Casiglia E, Lind L, Sandoya E, Filipovský J, Gilis-Malinowska N, Narkiewicz K, Kawecka-Jaszcz K, Boggia J, Wang JG, Imai Y, Vanassche T, Verhamme P, Janssens S, O'Brien E, Maestre GE, Staessen JA, Zhang ZY . 3 . Association of Fatal and Nonfatal Cardiovascular Outcomes With 24-Hour Mean Arterial Pressure . Hypertension . 77 . 1 . 39–48 . January 2021 . 33296250 . 10.1161/HYPERTENSIONAHA.120.14929 . 7720872 .
  4. Web site: Understanding Blood Pressure Readings . American Heart Association . 3 June 2023 . 2023.
  5. Book: DeMers D, Wachs D . Physiology, Mean Arterial Pressure . 2022 . http://www.ncbi.nlm.nih.gov/books/NBK538226/ . StatPearls . Treasure Island (FL) . StatPearls Publishing . 30855814 . 2022-05-22.
  6. Lewis PS . Oscillometric measurement of blood pressure: a simplified explanation. A technical note on behalf of the British and Irish Hypertension Society . Journal of Human Hypertension . 33 . 5 . 349–351 . May 2019 . 30926901 . 10.1038/s41371-019-0196-9 . 8076036 .
  7. Web site: Mean arterial pressure calculator . PhysiologyWeb . 3 June 2023 . 2023.
  8. Web site: Mean Arterial Pressure . Cardiovascular Physiology Concepts . Klabunde RE . Marian University College of Osteopathic Medicine .
  9. Book: Nosek TM . Essentials of Human Physiology . Section 3/3ch7/s3ch7_4 . http://humanphysiology.tuars.com/program/section3/3ch7/s3ch7_4.htm . https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section3/3ch7/s3ch7_4.htm . 2016-03-24.
  10. Web site: Cardiovascular Physiology (page 3) . 12 September 2006 . World of Anesthesia . Nuffield Dept.of Anaesthetics, University of Oxford . https://web.archive.org/web/20061211084819/http://www.nda.ox.ac.uk/wfsa/html/u10/u1002_03.htm. 2006-12-11.
  11. Moran D, Epstein Y, Keren G, Laor A, Sherez J, Shapiro Y . Calculation of mean arterial pressure during exercise as a function of heart rate . Applied Human Science . 14 . 6 . 293–295 . November 1995 . 8591100 . 10.2114/ahs.14.293 . free .
  12. Papaioannou TG, Protogerou AD, Vrachatis D, Konstantonis G, Aissopou E, Argyris A, Nasothimiou E, Gialafos EJ, Karamanou M, Tousoulis D, Sfikakis PP . 3 . Mean arterial pressure values calculated using seven different methods and their associations with target organ deterioration in a single-center study of 1878 individuals . Hypertension Research . 39 . 9 . 640–647 . September 2016 . 27194570 . 10.1038/hr.2016.41 . 11382793 . free .
  13. Meaney E, Alva F, Moguel R, Meaney A, Alva J, Webel R . Formula and nomogram for the sphygmomanometric calculation of the mean arterial pressure . Heart . 84 . 1 . 64 . July 2000 . 10862592 . 10.1136/heart.84.1.64 . 1729401 .
  14. Gevers M, Hack WW, Ree EF, Lafeber HN, Westerhof N . Calculated mean arterial blood pressure in critically ill neonates . Basic Research in Cardiology . 88 . 1 . 80–85 . 1993 . 8471006 . 10.1007/BF00788533 . 27547225 .
  15. Chemla D, Hébert JL, Zamani K, Coirault C, Lecarpentier Y . Estimation of mean aortic pressure . English . Lancet . 354 . 9178 . 596 . August 1999 . 10470724 . 10.1016/S0140-6736(05)77948-4 . 20720814 . free .
  16. Razminia M, Trivedi A, Molnar J, Elbzour M, Guerrero M, Salem Y, Ahmed A, Khosla S, Lubell DL . 6 . Validation of a new formula for mean arterial pressure calculation: the new formula is superior to the standard formula . Catheterization and Cardiovascular Interventions . 63 . 4 . 419–425 . December 2004 . 15558774 . 10.1002/ccd.20217 . 25022922 .
  17. Chemla D, Nitenberg A . A call for improving mean aortic pressure estimation . American Journal of Hypertension . 18 . 6 . 891 . June 2005 . 15925755 . 10.1016/j.amjhyper.2004.10.025 . free .
  18. Chemla D, Hébert JL, Aptecar E, Mazoit JX, Zamani K, Frank R, Fontaine G, Nitenberg A, Lecarpentier Y . 6 . Empirical estimates of mean aortic pressure: advantages, drawbacks and implications for pressure redundancy . Clinical Science . 103 . 1 . 7–13 . July 2002 . 12095398 . 10.1042/cs1030007 .
  19. Book: Jones D, Francesco L . 2017 . Hypotension . McKean SC, Ross JJ, Dressler DD, Scheurer DB . Principles and Practice of Hospital Medicine . 2nd . McGraw Hill . https://accessmedicine.mhmedical.com/content.aspx?bookid=1872&sectionid=146976893 . 978-0-07-184313-3 .
  20. Nicklas JY, Beckmann D, Killat J, Petzoldt M, Reuter DA, Rösch T, Saugel B . Continuous noninvasive arterial blood pressure monitoring using the vascular unloading technology during complex gastrointestinal endoscopy: a prospective observational study . Journal of Clinical Monitoring and Computing . 33 . 1 . 25–30 . February 2019 . 29556885 . 10.1007/s10877-018-0131-6 . 4025532 .
  21. Maheshwari K, Khanna S, Bajracharya GR, Makarova N, Riter Q, Raza S, Cywinski JB, Argalious M, Kurz A, Sessler DI . A Randomized Trial of Continuous Noninvasive Blood Pressure Monitoring During Noncardiac Surgery . Anesthesia and Analgesia . 127 . 2 . 424–431 . August 2018 . 29916861 . 6072385 . 10.1213/ANE.0000000000003482 .
  22. 3 . Vincent . Jean-Louis . Nielsen . Nathan D. . Shapiro . Nathan I. . Gerbasi . Margaret E. . Grossman . Aaron . Doroff . Robin . Zeng . Feng . Young . Paul J. . Russell . James A. . Mean arterial pressure and mortality in patients with distributive shock: a retrospective analysis of the MIMIC-III database . Annals of Intensive Care . 8 . 1 . 2018-11-08 . 107 . 2110-5820 . 10.1186/s13613-018-0448-9 . 30411243. 6223403 . free .
  23. Magder SA . The highs and lows of blood pressure: toward meaningful clinical targets in patients with shock . Critical Care Medicine . 42 . 5 . 1241–1251 . May 2014 . 24736333 . 10.1097/ccm.0000000000000324 . 39745357 .
  24. Book: Wong ND, Franklin SS . 2017 . Epidemiology of hypertension. . Fuster V, Harrington RA, Narula J, Eapen ZJ . Hurst's The Heart . 14th . McGraw Hill . https://accessmedicine.mhmedical.com/content.aspx?bookid=2046&sectionid=176572658 . 978-0-07-184324-9 .
  25. Verdecchia P, Schillaci G, Reboldi G, Franklin SS, Porcellati C . Different prognostic impact of 24-hour mean blood pressure and pulse pressure on stroke and coronary artery disease in essential hypertension . Circulation . 103 . 21 . 2579–84 . May 2001 . 11382727 . 10.1161/01.cir.103.21.2579 . 13521935 . free .

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