Assessment of Blood Pressure

With each cardiac contraction, the heart pumps blood into the arterial tree. The pressure within the cardiac cycle reaches a systolic peak and a diastolic trough that are measured and reported as the blood pressure. The difference between the systolic and diastolic pressures is known as the pulse pressure. Normal blood pressure in adults is now considered a systolic reading less than 130 and a diastolic reading less than 85. A systolic reading between 130-139 is considered "high normal" as is a diastolic of 85-89. Hypertension is defined as blood pressure equal to or in excess of 140/90.

The accurate assessment of blood pressure is a critical skill to master. There are several steps involved in measuring blood pressure accurately including:

Patient preparation.
Careful selection of the proper cuff size.
Accurate placement of the cuff.
Accurate positioning of the patient's arm.
Accurate determination of the blood pressure.

Observational studies of physicians however show that many physicians do not attend to these details and therefore are likely to record an erroneous reading.

Patient preparation:

Before blood pressure measurement, patients should:

Rest for 5 minutes.
Avoid tobacco and caffeine for the preceding 30 minutes.
Remove all clothing from the arm to be used.
Have blood pressure measured on an arm free of fistulas, lymphedema or significant scarring, with the arm resting at the level of the heart.

Selection of cuff size:

Cuffs that are too short or too narrow for a given patient may provide a falsely elevated blood pressure reading and lead to an erroneous diagnosis of hypertension. The proper cuff size depends upon the circumference of the patient's upper arm.

The length of the bladder in the cuff should be 80% of the circumference of the upper arm.
The width of the bladder should be 40% of the circumference of the upper arm.
For many adults a standard adult cuff will suffice.
If the length of the bladder is too small, a large adult cuff, or possibly a thigh cuff, will be needed.
On rare occasions, a pediatric cuff many be needed if the upper arm is particularly small.

Click on the video icon for a review accurate placement of the cuff and positioning of the patient's arm.

Click on the video icon for a review the technique for accurate measurement of blood pressure.

Click on the interactive icon to practice measurement of blood pressure.

Additional measurements:

Blood pressure should be measured in both arms at least once on each patient, in the sitting, supine and standing position in patient's suspected of volume depletion, and in a lower extremity in patients with hypertension.

Common problems:

Several problems may be encountered when attempting to accurately assess blood pressure. These include patient anxiety, sounds that are inaudible, the presence of arrhythmias, marked respiratory variation in systolic pressure, or the presence of an auscultatory gap. Be sure to avoid repetitive inflations of the cuff in quick succession as this too can cause an erroneous determination.