In my classes, some nurses ask me what is the most important BP, the systolic or the diastolic. Of course the answer is somewhere in between. It's the Mean Arterial Pressure (MAP).
Where systolic BP represents the peak pressure as a wave of blood pulses through arteries, the diastolic blood pressure represents the net pressure in the blood vessel during relaxation.
The MAP represents perfusion of organs like brain heart kidneys etc. If a person is deteriorating, it is the MAP that is really the most important number.
MAP is a calculation of 1/3 of pulse pressure plus diastolic.
If bp is 110/68
Pulse pressure(PP) is S-D
So 110-68 = 42
PP=42.
MAP= 1/3PP+D
MAP= (42/3)+68
MAP= 14+68
MAP= 82
MAP normal range in adults is 65-120. For the MAP to be too low means organs are not being adequately perfused with oxygen.
This lack of perfusion (hypoperfusion) is called ischaemia.
That Magic MAP >65 is good.
In hypotension (low blood pressure), the MAP suffers.
If the brain is poorly perfused the consequence is agitation, restlessness, confusion and worsening altered levels of consciousness.
If heart is poorly perfused the consequence is poor cardiac output, chest pain, ECG changes.
If kidneys are poorly perfused, renal output suffers.
All these are related to this mean arterial pressure.
So let's look at a low BP.
80/50
MAP=1/3PP+D
PP=30
MAP= (30/3)+50
MAP= 10+50
MAP= 60 !!!
Can you see that this is substandard? Globally this person would not be perfuming their vital organs optimally.
This is just one of the topics I cover in our Basic Nursing Assessment Seminar. Check out our dates in my web page.
No comments:
Post a Comment