The mean arterial pressure (MAP) can tell healthcare providers how well your blood flow is and if your tissues are getting enough blood. The MAP is usually calculated in all patients that are in the emergency room, but most importantly in cases of trauma or septic shock. Mean arterial pressure will help tell the doctors whether measures need to be taken to lower the blood pressure or raise it to increase the perfusion of blood.
The article will help you understand the MAP, how it is used, how to calculate, and what is done for different levels (high and low).
MAP is used to describe average blood pressure in an individual during a single cardiac cycle. The mean arterial pressure tells the doctor about how well the body is able to perfuse blood to the vital organs in the body. The systolic blood pressure is not an adequate predictor of perfusion, so calculating the MAP can reveal the actual pressure of blood against the arterial walls. The actual calculation is done with a formula that includes systolic blood pressure and diastolic blood pressure. Most blood pressure machines in the hospital calculate MAP for you. In the intensive care unit setting, the actual MAP can be monitored with invasive monitors i.e. arterial line. Invasive monitoring of pressures is the most accurate, but not necessary unless you are in the intensive care unit.
Calculating the MAP involves doubling the diastolic blood pressure and adding that total to the systolic blood pressure. Then you divide that total by 3. The result will be your mean arterial pressure. For example; a blood pressure of 83/50, has a MAP of 61. This is how you calculate the MAP:
50 + 50 = 100
83 + 100 = 183
183/3 = 61 MAP
The MAP is important in cases where a patient’s arterial pressure needs to be kept in a range to effectively get blood to the organs. There are certain drugs given to do this function and the doses are based on these pressures. When a patient has severe sepsis and the kidneys shut down due to low blood flow, knowing this number is the difference between life and death. This is also the case in severe heart attacks, strokes, head injuries, and major blood loss.
The normal ranges for blood pressure and mean arterial pressure are:
Below are the definitions of what it means when the MAP is not in a normal range and what is done to correct the problem:
A MAP that is above 105mmHg indicates the heart has to work much harder than it should and can cause stress on the heart. When the pressure goes too high and stress on the heart increases, fatty deposits build up on the inside of the arteries. These are called “atheroma” and can lead to advanced heart disease, blood clots, heart attacks or stroke. If the blood pressure remains high and the MAP remains elevated, the heart muscle will enlarge and grow thicker. It will also weaken the muscle. If the MAP is elevated even just a moderate amount it can lead to a shorter life span. If the MAP is severely elevated, then the life expectancy is only a few years without treatment.
If the MAP goes up critically in a short amount of time, this is a medical emergency because the increased blood flow to the organs can cause organ failure.
Treatment – A high MAP that happens over long-term needs to be treated with blood pressure medications to bring down the blood pressure, in order to prevent arterial and organ damage.
When the MAP increases suddenly, emergency measures need to be taken to lower the pressure within a 24 to 48hour period. Intravenous blood pressure medications will be given in the hospital and you will be monitored closely.
This can be fatal if left untreated. A low MAP is any pressure reading that is less than 60 mmHg. When the mean arterial pressure goes too low it means there is less blood getting to the vital organs and could cause you to go into shock. Without enough blood, organs can fail. A MAP can be low even if the systolic (top number) blood pressure is 80 to 100 mmHg. This is why it is important to calculate the MAP on every patient that goes into the acute care setting.
Causes of low MAP include:
Any condition that causes the body to lose blood pressure can cause a low MAP, so this is not limited to the conditions above.
Treatment – Low MAP is a medical emergency and if untreated will cause organ failure and possible death. This is treated with vasopressor medications that cause the blood vessels to constrict and raise the pressure. If the condition is caused by fluid or blood loss, intravenous fluids or blood transfusions will be given along with the vasopressors.
The mean arterial pressure is regulated by the body in healthy people and usually is unchanged. When you exercise, your body compensates for changes in MAP by reflex. This is done through baroreceptors that are inside your arterial walls.
You will notice if your blood pressure goes up during exercise, your MAP will stay relatively the same. Here is how it works:
As you go through your day doing just about anything, your blood pressure is constantly being monitored by your central nervous system and changes made to certain functions to keep it pretty constants. This is done by the baroreceptor reflexes. These receptors read the stretching of the arterial walls, your heart, and your veins. When the blood pressure goes up and they stretch, the receptors send a signal to a control center in your brain telling it to relax the walls or tighten them. This can quickly restore blood pressure and MAP in healthy people.