How to Check Blood Pressure with a Sphygmomanometer

Primer on Blood Pressure:

How blood pressure works



Correct blood pressure measurements are essential to diagnosing and treating high blood pressure. Accordingly, a specific set of techniques and procedures have been developed which describe the proper method for obtaining the most accurate blood pressure readings possible.

Following a few simple rules is important to get an accurate reading:
  • First, your patient should not smoke or drink alcohol or coffee within 15 minutes of a blood pressure measurement.
  • Second, the length of the bladder on the device should be 80 percent of the circumference of the upper arm. This means that heavy or very muscular people with thick arms need a larger bladder, while children need a smaller bladder.
  • Third, posture is important. Your patient should sit with his/her back supported and his/her elbow at about the level of his/her heart with his/her arm supported. The patient's legs should not be dangling. It's better if he/she rests for several minutes in that position before the measurement. Don't talk during the measurement.
Step 1 - Leaving the cuff's lower edge about an inch above the bend of the elbow, place the cuff over the patient's bare arm, close the cuff around the arm, and then stick the Velcro together at the ends of the cuff.

Step 2 -  Place the earpieces of the stethoscope in your ears and place the stethoscope bell at the side of the cuff away from the patient's heart and over the brachial artery.

Step 3 -  Tighten the screw at the side of the rubber bulb and squeeze the bulb. Air is pumped into the bulb, and thus the cuff expands.

Step 4 -  The cuff is inflated until the blood flow through the brachial artery stops. With sufficient compression, the cuff cuts off blood flow through the artery, and no sound is heard in the stethoscope. The pressure in the cuff is increased rapidly to 30 millimeters of mercury above the point that no blood flow is taking place through the cuff when no sound can be heard in the stethoscope or when a pulse can no longer be felt in the wrist.

Step 5 -  Turn the screw again to loosen the valve in the bulb and to lessen the air pressure. Pressure is then decreased so that the rate of drop is 2 millimeters per second. When the pressure falls to the point that blood begins to flow through the artery again, the number that the column of mercury has risen to at the first sound heard in the stethoscope is the systolic blood pressure (SBP), the first number in the blood pressure reading.

Step 6 -  Look at the column of mercury to see the number at that pressure point.

Step 7 -  When the cuff decompresses to the point that blood flows freely in the artery, the sound is no longer heard in the stethoscope. The number next to the top of the column of mercury when the sound ceases is the diastolic blood pressure (DBP), the second number in the blood pressure reading.

Step 8 -  Again, look at the column of mercury to see the number at that pressure point.

Step 9 - Record the SBP and the DBP numbers immediately (don't depend on your memory), and note the arm (right or left) used for taking the measurement.

Step 10 -  If the first measurement is elevated, take another measurement in the same arm after 60 seconds. Then the other arm is measured. The arm that has the higher blood pressure is the one that's used in the future (they're often the same). The average of the two measurements in the arm that supplies the more abnormal reading is considered to be the correct blood pressure.



Measure the blood pressure while the patient is in a standing position especially in the event that the patient experiences lightheadedness on standing. If a fall of 20 or more millimeters of mercury occurs in systolic blood pressure or 10 or more in diastolic blood pressure, the patient is considered to have orthostatic hypotension, an abnormally great fall in blood pressure with standing.

If blood pressure isn't normal, don't start any treatment on the basis of one office visit. This is treatment for life and should be done only after confirmation at a second and even a third office visit. It may even be that blood pressure in the doctor's office is not an accurate assessment of blood pressure despite using entirely correct techniques. A blood pressure reading that's greater than 180/120 millimeters of mercury (mm Hg) requires immediate treatment.

Typically, blood pressure is higher in the mornings and lower in the evenings. If the blood pressure reading is a concern or masked or white coat hypertension is suspected, a 24 hour blood pressure study may be required to assess the patient's overall blood pressure profile.



Blood Pressure Measurement