mean arterial pressure.

By impactEDnurse • May 31st, 2007 • Category: clinical skills, the nurses desk:

We all diligently watch our patients blood pressure, recording it in our observation charts…but do we pay enough attention to the mean arterial pressure (MAP)? That innocent little number placed in brackets or hiding off to one side of the monitor screen.
What the heck is that number? Is it important? Should I record it?

MAP is defined as the average arterial blood pressure during a single cardiac cycle.
The reason that it is so important is that it reflects the haemodynamic perfusion pressure of the vital organs.

how is it calculated?

The simple way to calculate the patients MAP is to use the following formula:
MAP = [ (2 x diastolic) + systolic ] divided by 3.

The reason that the diastolic value is multiplied by 2, is that the diastolic portion of the cardiac cycle is twice as long as the systolic. Or you could say, it takes twice as long for the ventricles to fill with blood as it takes for them to pump it out….. at a normal resting heart-rate.

In a bradycardic or tachycardic patient this relationship between systolic and diastolic values changes, and the formula is not as accurate. When using non-invasive BP monitoring (BP cuff around the patients arm) the monitor uses this formula to determine the MAP, so it is less accurate in the unstable patient.

During invasive monitoring of BP (using an arterial line) a complex formula is used that is way beyond my understanding to attain a much more accurate and real time value.
OK, if you must know… it is obtained via Fourier analysis of the arterial waveform, or as the time-weighted integral of the instantaneous pressures derived from the area under the curve of the pressure-time.
Whatever.

do I need to watch it?

Definitely. I guess a rough analogy would be that the MAP is the oil gauge for your patients motor.
A MAP of at least 60 is necessary to perfuse the coronary arteries, brain, and kidneys. Normal range is around 70 – 110 mmHg.

It is a vital sign to monitor anytime the patient has a potential problem with perfusion of his organs. Some examples (and there are many more) might include:

  • a patient with septic shock on vasopressors.
  • head injured patients.
  • Cardiac patients on vasodilator (GTN) infusion.
  • Patient with a dissecting abdominal aneurysm who needs to have his BP controlled within a narrow range so as not to cause increased bleeding.

In a head injured patient, the brain is at risk of ischaemi injury due to insufficient blood flow if the MAP falls below 50. On the other hand, a MAP above 160 reflects excess cerebral blood flow and may result in raised intercrainial pressures.

is it true that women are worse than men at reading a MAP?

Now, if you think I am brave enough to tackle that question you must be crazy!

impactEDnurse is also known as Ian Miller, a nurse with over 26 years experience working in a busy emergency department in, Australia. This site in no way reflects the opinions of that hospital. All stories (although based on actual experiences) have been changed to protect patient confidentiality.
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12 Responses »

  1. Not Telling on May 31st, 2007 at 8:36 pm:

    ;)

  2. beajerry on June 3rd, 2007 at 4:41 pm:

    MAP is like oil pressure gauge – that’s a good analogy!

  3. Ernst on June 7th, 2007 at 4:22 am:

    Excelent explanation! I am 72 years old live in Germany had a heart attack 1993! BP was 185/120 and cholesterol 250 at that time! My actual numbers are 105/60, and 155 Total cholesterol.-Take ONLY 100 ASS every morning, lots of excercice, low fat foods, fruits, brocoli, flax seeds, walnuts, brazil nuts, quark cheese, mushels and fish every day, plus chicken liver and massdamer cheese and MOST OF ALL.. GARLIC!! I smoke 20 to 30 cigarretes a day ALLWAYS with Water Filter!! Check my blood P.at least 2 times a day!! Can still swim 25 m. en less than…30 seconds!! What do you think? Regards..

  4. Grumpy on June 9th, 2007 at 11:38 am:

    What do I think? … Well I too am 72 and I live in Australia. I’ve had a dodgy heart for a while, not assisted by a drive-through attempt at a coronary biopsy. My BP varies with the phase of the moon (as does my facial hair). I take a couple of kilos of pills each morning, take daily exercise when I check the mail, eat from a cornucopia of forbidden fare, have been known to down the odd bottle of wine with a scotch chaser or two and could probably swim 25m in less than 20 seconds (in a downward direction). But at least I don’t smoke. What do YOU think? Cheers.

  5. Ernst on June 10th, 2007 at 6:40 pm:

    Hallo Grumpy.. my congratulations!, its almost 10 am and I enjoyed your comments greatly!!Humor is one of the best medicines in the world!..and it looks like you take lots every day!! It may be the ONLY reason why you are still ALIVE !!.. Leaving jokes aside.. I am a High Sea Merchant Marine Captain 1st Class. my daily rutine and diet is a recopilation of on the spot experiences of 43 years at sea visiting about 65 countries!! The main problem of aging is the stifnes of the arteries..which is caused mainly by FREE RADICALS who weaken our cells (oxidation). If you could slower this process. (you can not stop it)you could live longer and healthier. So you need ANTI-OXIDANTS to do it!!Not once or twice a day, but OFFEN meaning NOT ONLY at meals.. but between meals also.. My daily diet does just THAT!!Provides my sells CONSTANTLY with NATURAL antioxidants..A small glass of orange juice (0.1 L) + 10 or 15 gramms of flax seeds + brazil nuts+walnuts+wheatgerm..all of them grinded and mixed together is a good way to achieve this!! be happy.. don´t worry!! regards
    Ernst

  6. jokergirl on June 12th, 2007 at 6:24 pm:

    Is it bad that when I saw the word “Fourier” in your article, I went “Yay! Finally something medical I can understand!”?
    (Yes, I’m an engineer and currently addicted to med/nursing blogs – why do you ask?)

    I wonder though – would the MEP change depending on where you measure it, especially if you have a trauma?

    ;)

  7. jokergirl on June 12th, 2007 at 6:25 pm:

    MAP even. I need more coffee.

  8. Bonnie on January 18th, 2008 at 11:14 pm:

    How serious is a MAP Greater tha 110?

  9. BOLA LAJIDE on February 6th, 2008 at 3:09 am:

    KEEP IT SIMPLE STUPID==KISS

    EXCELLENT .YOU KEEP IT SIMPLE FOR THE STUPIDS TO KNOW
    THANKS

  10. audie-pierre bernardin on February 26th, 2010 at 3:30 pm:

    i m taking care of a patient who is suspected of early septic shock.her B/P has fallen to60/40 .she’started on levophed gtt the parameter for her MAP is to be kept at 65 to 70.what is the significance of this.

  11. Gaby on May 31st, 2010 at 2:53 am:

    Audie, MAP is a tool that gives us an indicator of blood pressure and whether it is adequate enough to provide 02 supply to vital organs. The normal range is 70-110 and if it falls too low it is indicating that the blood pressure is too low and will not perfuse the organs adequately and therefore we will start to see some organ failure. The reason this patient needs to have his/her MAP between 65-70 in order to be able to perfuse his/her organs. As impactEDnurse stated, at least 60 is required to perfuse the coronary arteries, brain, and kidneys.

  12. lefty the earthworm on August 18th, 2010 at 11:25 pm:

    thanks for the explanation! my 9 year old daughter has had many episodes of “idiopathic” ag metabolic acidosis over the years so we’ve spent far too much time in ed’s. the map is just one number i’ve heard discussed. every time i ask what it means it seems no one knows (of course that’s not the way they say it)

    i have a few questions:

    1) for kids, are the map guidelines different? i know that my daughter’s has been too low (the one that stands out to me was 39 with a 80/18), but when she is well it can be as high as the low 70’s.

    2) when is a recurring low map something to address? when is a recurring low map not something to address?

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