Blood pressure measurement is the non-invasive measurement of the pressure exerted by the circulating blood on the walls of the body's arteries.
The purpose of non-invasive blood pressure measurement is to detect any changes from normal values, which may indicate disease. Measurement is also performed to monitor the effectiveness of medication and other methods used to control elevated blood pressure.
Blood pressure should be routinely checked every one to two years and may be monitored more closely during illnesses that affect blood pressure or during medical treatments which may change blood pressure. Measurement can be taken as often as every few minutes.
As there may be no prior knowledge of the patient's previous blood pressure for comparison, a wide range of normal values apply to patients of different ages. The inflated cuff can cause discomfort, and this should be taken into account when dealing with very ill patients. Patients with a history of sickle cell anemia should not have non-invasive blood pressure measurements made with a typical blood pressure cuff, because the sickling process can be initiated by the pressure on the arm. Blood pressure measurements should occur on a limb free of intravascular catheters and arterial venous fistulas (joined artery and vein) used for chronic dialysis.
Blood pressure is usually recorded by measuring the force of the blood during the contraction of the ventricles (lower chambers of the heart) as blood is pumped from the heart to the rest of the body (systolic pressure), and during the period when the heart is relaxed between beats and pressure is lowest (diastolic pressure).
The cardiac output, resistance, quality, and quantity of blood circulating through the heart, and the condition of the arterial walls are all factors that influence the blood pressure. Hypertension is an elevation in the blood pressure above normal values, with the diastolic pressure being the indicator most commonly used.
Hypotension is a reduction in the blood pressure below normal values. If a very high or very low pressure is taken, the blood pressure reading may be inaccurate and should be repeated immediately, prior to the initiation of medical treatment.
The non-invasive blood pressure is taken using a sphygmomanometer , a hand bulb pump, and a cuff.
The sphygmomanometer may be electronic or mercury-based. The mercury-based unit has a manually inflatable cuff attached by tubing to the unit that contains mercury and is calibrated in millimeters of mercury. The electronic unit is similar, but is mercury free and inflates and deflates automatically with the reading displayed digitally. The electronic units are also calibrated to display the measurement in millimeters of mercury. Blood pressure can be measured with either unit, although electronic units are becoming more commonplace in both home care and clinical use.
Children and adults with smaller or larger than average-sized limbs require special sized cuffs appropriate for their needs. The blood pressure cuff is usually placed on the arm, but can also be used on the leg.
To record blood pressure, the patient may be seated or lying down. The cuff will be positioned so that it is level with the heart. With an electronic unit the cuff is placed in accordance with manufacturer instructions on the bare upper arm, on the bare wrist, or on the bare index finger.
If the blood pressure is monitored with a manual system, a cuff is placed level with the heart and wrapped firmly but not too tightly around the bare arm 1 in (2.5 cm) above the elbow, with any creases in the cuff smoothed out. Leg measurements, require the cuff to be positioned below the groin on the bare leg over the femoral artery.
Following the manufacturer's guidelines (electronic models), the cuff is inflated and then deflated automatically. The reading is displayed and recorded by the user. The results are charted with the systolic pressure first, then by the diastolic pressure in the following manner, xxx/xx (e.g., 120/70). A manual system requires a stethoscope be placed over the artery, the cuff is then inflated until the artery is occluded and no sound is heard through the stethoscope.
The cuff is then inflated a further 10 mm Hg above the last sound heard. The valve in the pump is slowly opened no faster than 5 mm Hg per second to deflate the pressure in the cuff to the point where a tapping sound is heard over the artery. This point is noted as the systolic pressure. The sounds continue as the pressure in the cuff is released and the artery is no longer occluded. At this point, the noises are no longer heard and this is noted as the diastolic pressure.
With children, the tapping noise changes to a soft muffled sound. That point is noted as the diastolic pressure, as commonly in children, sounds continue to be heard as the cuff deflates to zero.
Medical staff should explain the procedure fully to the patient and reassure him or her that recording blood pressure is part of normal health checks and that it is necessary to ensure the patient's health is being correctly monitored. The appropriate-sized cuff should be used for the patient to give an accurate reading.
The test can be performed at any time, but is best performed when the patient has been resting for at least five minutes so that any exertion, such as climbing stairs prior to the test, will not unduly influence the outcome of the reading.
Devices should be checked and calibrated annually by a qualified technician to ensure accurate readings.
The patient should be made comfortable. The medical staff should be notified if the blood pressure measurement is above or below normal values so treatment can be initiated, continued, or adjusted. Repeated measurements are required for screening purposes and continuity of care.
The normal values for blood pressure measurement is a systolic pressure of 120 mm Hg and a diastolic pressure of 70–80 mm Hg. Mild hypertension is a diastolic pressure above 90 mm Hg. The American Heart Association states that a systolic pressure above 130–139 mm Hg needs to be watched carefully. Significant hypertension is a systolic pressure above 200 mm Hg. The blood pressure measurement is recorded and compared with normal ranges for the patient's age and medical condition. Based on the results, a decision is made as to whether any further action is required. Hypertension increases the risk of serious diseases such as heart attack and stroke.
Hypotension is demonstrated by with a systolic blood pressure under 80 mm Hg. Treatment options depend on the patient's current health and may include blood or saline administration. Drugs to improve heart rate and function may also be administered.
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Margaret A Stockley, RGN
Allison J. Spiwak, MSBME