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Vital Signs: How to Take a Blood Pressure

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Blood pressure is measured by listening for Korotkoff sounds as the blood surges through the arteries.
What is blood pressure?
Blood pressure is the pressure exerted on the wall of the artery or vein as blood is pumped through the body.

Blood does not flow readily, it surges along with each beat of the heart. The walls of the arteries are thicker than the veins and as such much more force is generated allowing us to record that pressure.

As the blood is pumped through the vessels a turbulence is heard. These sounds are created by turbulence as the blood begins to flow through the arteries after the blood pressure cuff has temporarily stopped the flow by the pressure exerted as it was inflated.

When the sound is first heard, this is the
systolic pressure; and when the sound ceases as the turbulence ends, the diastolic pressure is determined.

Systolic and Diastolic pressure
As blood is pumped through the body it exerts pressure on the veins and arteries. The systolic pressure is the pressure as the heart contracts and pumps the blood. The diastolic pressure is the pressure in the vessels when the heart is at rest between beats.

Blood pressure is recorded as a fraction such as 110/70. The systolic pressure is the top number and the diastolic number is the bottom number.

Influencing Factors:
Factors that can influence blood pressure readings include proper cuff size for the size of the arm, activity, emotions, posture, medications, alcohol consumption, temperature and diet.

Taking the BP
To take a blood pressure, the person should be sitting comfortably and relaxed. Legs uncrossed. Sleeves are pushed up or the shirt removed to reveal a naked arm as clothing can interfere with the pressure of the inflated cuff as well as hearing the Korotkoff sounds.

If taking the BP over clothing it should be thin enough to not interfere with the pressure exerted by the cuff, and you should be able to hear clearly. The best option is over bare skin.

The cuff of the sphygmomanometer is placed on the upper arm. It is centered over the brachial artery which is located in the crook of the elbow. The gauge should be placed so it can be easily read. There is usually a place on the cuff to clip it on. Once the cuff is secured, raise the arm to heart level, place your arm underneath it to support it or rest on a table. And ask the person to relax their arm.

Palpate (feel for) the brachial pulse and place the diaphragm of the stethoscope over this spot. Place the ear pieces on the stethoscope into your ears. Listen to the brachial pulse.

Close the valve on the bladder of the cuff and begin to squeeze the bulb. Continue squeezing until the needle on the gauge reads at least 180 or until it is 10mmHg above where you last heard the pulse as you inflated the cuff. Some people cannot hear this and so it is usually pumped up to 180-200mmHg on the gauge.

Open the valve slowly and allow the cuff to deflate by 5mmHg/second while you listen to the artery.

When you first hear the Korotkoff sound this is the systolic pressure. Continue deflating the cuff until you no longer hear the Korotkoff sound. This is the diastolic pressure. At this point you can open the valve completely to allow the cuff to deflate rapidly.

If you did not hear clearly, or the pressure is high or very low, wait at least one minute before repeating the procedure.

What Should the BP Be?
Age, heath status, medications and many other factors can determine what a good blood pressure should be for each individual.

Each individual's situation can be very different depending on any underlying disease processes, general health, diet and exercise patterns.

In general, optimal blood pressure is considered less than 120 systolic and 60 -70 diastolic.

According to the American Heart Association, a blood pressure of less than 120/80 is optimal. Blood pressure of more than 140 systolic or 80 diastolic is considered to be high.

Some Precautions
Never take a blood pressure in an arm with:
  • an any IV access or heplock in place
  • a dialysis or other fistula or shunt in place
  • on the same side as a mastectomy or hemiparesis from a stroke or injury does not collect, nor use your data.

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