Blood Pressure Assessment
Defined as the lateral force exerted by blood on the arterial walls, blood pressure depends on the force of ventricular contractions, arterial wall elasticity, peripheral vascular resistance, and blood volume and viscosity. Systolic, or maximum, pressure occurs during left ventricular contraction and reflects the integrity of the heart, arteries, and arterioles. Diastolic, or minimum, pressure occurs during left ventricular relaxation and directly indicates blood vessel resistance.
Pulse pressure, the difference between systolic and diastolic pressures, varies inversely with arterial elasticity. Rigid vessels, incapable of distention and recoil, produce high systolic pressure and low diastolic pressure. Normally, systolic pressure exceeds diastolic pressure by about 40 mm Hg. Narrowed pulse pressure—a difference of less than 30 mm Hg—occurs when systolic pressure falls and diastolic pressure rises. These changes reflect reduced stroke volume, increased peripheral resistance, or both. Widened pulse pressure—a difference of more than 50 mm Hg between systolic and diastolic pressures—occurs when systolic pressure rises and diastolic pressure remains constant, or when systolic pressure rises and diastolic pressure falls. These changes reflect increased stroke volume, decreased peripheral resistance, or both.
Frequent blood pressure measurement is critical after serious injury, surgery, or anesthesia and during any illness or condition that threatens cardiovascular stability. (Frequent measurement may be performed with an automated vital signs monitor.) Regular measurement is indicated for patients with a history of hypertension or hypotension, and annual screening is recommended for all adults.
Blood pressure should be measured using the recommendations set by the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC VII). Until recently, patients with hypertension were stratified based on blood pressure readings alone. However, the JNC VII also considers the patient’s individual risk factors, meaning that those with more risk factors are treated more aggressively. (See Classification of blood pressure, page 78.)
Equipment
Aneroid sphygmomanometer ▪ stethoscope ▪ alcohol pad ▪ automated vital signs monitor (if available).
The sphygmomanometer consists of an inflatable compression cuff linked to a manual air pump and an aneroid gauge. A recently calibrated aneroid gauge should be used. To obtain an accurate reading, rest the gauge in any position but view it directly from the front. Cuffs come in sizes ranging from newborn to extra-large adult. Disposable cuffs and thigh cuffs are available.
The automated vital signs monitor is a noninvasive device that measures pulse rate, systolic and diastolic pressures, and mean arterial pressure at preset intervals. (See Using an electronic vital signs monitor, page 79.)
Preparation of Equipment
Carefully choose a cuff of appropriate size for the patient; the bladder should encircle at least 80% of the upper arm. An excessively narrow cuff may cause a falsely high pressure reading; an excessively wide one, a falsely low reading. (For information on other situations that can cause false-high or false-low readings, see Correcting problems of blood pressure measurement, page 80.) If you aren’t using your own stethoscope, disinfect the earpieces with an alcohol pad before placing them in your ears to avoid cross-contamination.
To use an automated vital signs monitor, collect the monitor, dual air hose, and pressure cuff. Then make sure the monitor unit is firmly positioned near the patient’s bed.
Implementation
Confirm the patient’s identity using at least two patient identifiers according to your facility’s policy.4
Classification of Blood Pressure
The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure recommends that a person’s risk factors be considered in the treatment of hypertension. The patient with more risk factors should be treated more aggressively.
| Category | SBP MM HG | DBP MM HG | |
|---|---|---|---|
| Normal | less than 120 | and | less than 80 |
| Prehypertension | 120 to 139 | or | 80 to 89 |
| Hypertension, stage 1 | 140 to 159 | or | 90 to 99 |
| Hypertension, stage 2 | 160 or higher | or | 100 or higher |
| Key: SBP = systolic blood pressure; DBP = diastolic blood pressure. Adapted from the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. (2003). NIH Publication No. 03-5231. Bethesda, Md: National Institutes of Health; National Heart, Lung, and Blood Institute; National High Blood Pressure Education Program. | |||
Have the patient rest for at least 5 minutes before measuring his blood pressure. Make sure he hasn’t smoked or had caffeine for at least 30 minutes.
Tell the patient that you’re going to take his blood pressure.
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