Blood Pressure


Blood pressure level (mm Hg)

Category

Systolic

Diastolic

Normal

< 120

< 80

Prehypertension

120–139

80–89

High blood pressure

Stage 1 hypertension

140–159

90–99

Stage 2 hypertension

>=160

>=10

  • There are three types of sphygmomanometers used to measure blood pressure: mercury, aneroid, and digital.

  • In some patients the Korotkoff sounds will disappear as the systolic pressure is bled down. After an interval, the Korotkoff sounds reappear. This interval is referred to as the “auscultatory gap.” This pathophysiologic occurrence can lead to a marked under-estimation of systolic pressure if the cuff pressure is not elevated enough. It is for this reason that the rapid inflation of the blood pressure cuff to 180 mmHg was recommended above. The “auscultatory gap” is felt to be associated with carotid atherosclerosis and a decrease in arterial compliance in patients with increased blood pressure.

  • Aneroid and digital manometers may require periodic calibration.

  • Use a larger cuff on obese or heavily muscled subjects.

  • Use a smaller cuff for pediatric patients.

  • For pediatric patients a lower blood pressure may indicate the presence of dehydration.

  • Don’t place the cuff over clothing.

  • Flex and support the patient’s arm.

JNC Classification of blood pressure in adults

Classification

BP (mm Hg)

Normal systolic: less than 120
Diastolic: less than 80
Pre-hypertension 120-139/80-89
Stage 1 hypertension 140-159 (systolic)
or
90-99 (diastolic)
Stage 2 hypertension equal or more than 160 (systolic)
equal or more than 100 (diastolic)

Errors in blood pressure readings:

  • The cuff is not of the proper size: if the cuff is too small the blood pressure readings may be artifactually high.

  • If the cuff is too big, the readings may be artifactually low.

  • The cuff is positioned too loosely: the blood pressure may be artifactually low.

  • If the cuff is too small, the readings may be artifactually high.

  • The cuff is positioned too tight: the blood pressure may be artifactually high.

  • The center of the cuff bladder is not positioned over the brachial artery.

  • The cuff is inflated too slowly: a slow inflation causes venous congestion, which in turn causes the

  • Korotkoff sounds to be faint; this results in false readings with the systolic value being too low and the diastolic reading too high.

  • If the cuff is re-inflated immediately after an initial reading (trying to re-check the reading): a rapid re-inflation could cause venous distension, the Korotkoff sounds become more muffled.

  • The initial Korotkoff sound may be missed so the systolic reading would be falsely low, and the diastolic reading would be falsely high because the last Korotkoff sounds could not be heard.