# mean arterial pressure.

May 312007

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.
• 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!

### 30 Responses to “mean arterial pressure.”

1. Hello. Just curious… As you mention, MAP is less accurate in an unstable patient or someone who is brady/tachy. Just wondering why we bother doing it at all. I understand the concept of monitoring perfusion, etc. Is it something to watch as a red flag for more invasive monitoring ie: art line monitoring?

2. Thank you, for a beautiful description of MAP…always love to use your material as a reference.

James

3. Never heard about MAP before today, I had been taking medication for high blood pressure for10 years, until I found a Dr. that told me that I could get rid of the pills with alternative medicine, been off the pills for three months now, and there are days that I worry about my readings, even though most of them are within normal range, I can have 116/90 with a heart rate of 62, and couldn’t understand why. I couldn’t understand the explanation for the formula until I read yours, THANK YOU SO MUCH! for such a short, clear explanation.

4. Question:

We use Phillips monitors in my facility. I have noticed the numbers in the brackets after the BP is taken is not always the exact MAP. It states it’s the “mean arterial pressure (device) #.”

It’s usually a few numbers off from the actual calculated MAP, but I’m very curious of this other reading the monitor’s calculating (formula).

• EDRN, I noticed this too. I asked around to the CCU nurses, the CCU MD, a medical resident and a cardiologist. No one had an explanation for the difference. I am going to try to find out from Phillips. I happened to be caring for a patient on pressors with parameters dependent on the MAP. It was the difference between titrating down or not. I googled it and found your comment!!

5. I love MAP especially in resus because it helps to confuse the junior doctors. The last textbook I read said that a MAP < 70 resulted in inadequate perfusion of the kidneys: now if they pack up you're basically in the doo doo! In trauma though, where there is the potential for blood loss, a MAP of 70 is about right – this is known as permissive hypotension.

I also love fluids, especially Hartmann's, which is much more expensive than normal saline: I always get the doctors to prescribe this for my favourite patients!

• oooooh….not supposed to have “favourite” patients …. ;D

6. Thank you for that great explaination of MAP, you made it so easy to understand.

7. I am commenting because I am a PCT at my local hospital. I work on the medical/surgical floor and they say NOT to chart MAP; however, I believe it is a very important component of the vital signs, especially if it is too high or low. What are the opinions of those here? Thank you.

• If the pt is in the M/S wing, they do not need MAP for the most part. Usually MAP readings are used for critical care units (ICU/ER etc.)

I understand your principle “why not chart it anyways” but it comes down to logistics; it’s not a main vitals sign for M/S pt’s and there are other values that nurses look for that patients that are not profusing efficiently (SIRS criteria, HR, BP <90 sys, compensation etc.).

• I got called out on supplying a MAP when doing a manual BP but then got asked by another colleague for the formula. Great explanation btw it shows why its worked out how it is… thankyou.

8. I have a theory that real time map is relevent in hypertension and that the long term effects on organ systems is also influnced by mean pulse rates. That is, hytpertension of the same magnitude will have more negative effects on target organs such as the heart and kidneys as the mean pulse rate increases. Additionally, a normotensive patient would be effectively hypertensive with a high mean heart rate. Therefore, the role of mean heart rate should be considered evaluating patients for hypertension and in evaluating the overall cardiovascular system in normotensive patients. Your thoughts on this subject?? Thanks, Windham Bremer M.D.

9. Thanks for the explanation

This is very helpful as I prepare for my NCLEX. I have been going through your blog like crazy. It has been ver helpful. Simple, direct, easy to understand and humorous. Keep up the good work and thanks Ian

10. Thank you for your succinct explanation of MAP!

11. OMG!!! Your straight forward, clear explanation on MAP just saved my life after 6 hours of exam study!! Thank you!!

12. 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?

13. 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.

14. 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.

15. KEEP IT SIMPLE STUPID==KISS

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

16. How serious is a MAP Greater tha 110?

17. MAP even. I need more coffee.

18. 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?

19. 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.. donÂ´t worry!! regards
Ernst

20. 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.

• Mate I think your a champion!

21. 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..

• Hey……………..you sound a whole lot like me, other than I cannot swim. I probably do not eat quite as well as you, but I do try to get something of everything (moderation). I also smoke about 25 cigs a day………..been doing so for 57 years now, although probably not that many during my earlier/working years.

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

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