Chapter 2

BLOOD PRESSURE MEASUREMENT

• Accurate blood pressure measurement is the only method for the diagnosis of hypertension.

• Measure the blood pressure in the right arm while the patient is sitting with back supported or while lying flat on his back. Urine voided if needed. No food intake, coffee or smoking for two hour before the procedure. Talking should be avoided for 5 minutes prior to measurement.

• Appropriate cuff size and palpatory blood pressure measurement are essential.

• Take systolic blood pressure at first appearance of sounds at 3 consecutive beats. Take diastolic blood pressure at complete disappearance of sounds.

• Take the lower of at least two readings.

• This procedure has many sources of inaccuracy, which commonly cause wrong decisions. Care must be given to all steps of the process.

The Sphygmomanometer

There are three basic components to the sphygmomanometer: the manometer, the cuff and the connecting tubing, and the valve.

The Manometer

• The two commercially available types of manometer (mercury and aneroid) need periodic check.

• Aneroid manometers need to be calibrated against a subjected manometer using a T-tube. The mercury sphygmomanometer is subjected to mercury loss (leading to subnormal readings), introduction of air into the system (leading to bubbling and exaggerated readings), and breaking of the glass manometer tube (leading to injury and toxic hazards).

• With a deflated cuff, the manometer should read at the zero point. The mercury manometer should not bubble when the cuff is inflated while the manometer is stable on a horizontal surface. The presence of air means that the manometer needs re-filling and re-calibration.

The Cuff

• The cuff size must match the arm size to avoid tissue pressure dissipation that necessitates over-inflation, leading to false high readings if the cuff is too small.

• The width of the rubber bladder inside the fabric cuff (not the fabric itself) should be more than 40 % of the circumference of the mid-upper arm. The standard 12 cm cuff is good for most patients.

• For blood pressure measurement in adults, the physician should have at least one more cuff with 15 cm wide bladder for obese patients, and preferably a thigh cuff.

• Those taking care of children should possess a range of small cuffs.

• If the exact cuff size is lacking, it is better to use a larger than a smaller cuff.

• Rubber bladders and tubing may crack and leak with use, leading to poor control of inflation/deflation. The faulty piece must be changed.

• To exclude air leak from the system, make sure that the inflated cuff stays inflated at steady pressure when the valve is closed.

The Valve

• Valve governs the deflation rate which is essential for accurate blood pressure measurement.

• To check for valve function, make sure that the inflated cuff stays inflated at steady pressure when the valve is closed and that it can be deflated smoothly and slowly with valve rotation between the index and thumb.

The Stethoscope

• Tubing should be long enough for convenience but not more than 40 cm to prevent damping of sounds. There should be no air leak.

• The cone is better for listening to low frequency vibrations (the major component of the late stages of Korotkov sounds). The cone will - thus - be more accurate for sharp localization of sound disappearance, indicative of the diastolic blood pressure.

• The limitation of the cone is its limited field of reception. If it is not exactly over the brachial artery, it may miss some or all of Korotkov sounds.

• The diaphragm should only be used in the very obese arm when it becomes difficult to localize the brachial pulse in the antecubital region.

Blood Pressure Measurement Procedure

Before Taking Blood Pressure

• The patient should avoid smoking, eating and coffee for at least two hours prior to measurement. Urine should be voided if necessary.

• Talking should be voided five minutes before and during blood pressure measurement.

• Blood pressure should be measured in a quiet room with comfortable temperature.

Patient Position

• Blood pressure is to be measured in the supine or sitting positions. The abducted supinated arm should be at the heart level and supported on a pillow.

• In the sitting position, the back should be supported and the feet on the ground. The arm should be slightly flexed and supported on a desk.

• In the standing position, the arm should rest supported on either a high table, the shoulder of the examiner or in the armpit of the examiner, depending on the relative height of the patient and the examiner.

• In case of measuring the popliteal blood pressure, the patient should be in the prone position with the knee slightly flexed. The normal popliteal systolic blood pressure is about 20 mmHg higher than the brachial.

The Procedure

• The cuff should be applied directly to the skin, with no clothing intervening. Tight sleeves should be taken off before cuff application.

• Palpate the brachial artery and center the bladder over the artery.

• Wrap the cuff tightly around the arm. The edge of the cuff should be 3 cm above the elbow crease.

• Close the valve and inflate the cuff first rapidly to about 70 mmHg, then by 10 mmHg at a time while the other hand feels for the radial pulse at the wrist. The pulse occlusion pressure (POP) is identified, and then release all pressure. Raise the arm above the level of the head for a few seconds to prevent venous engorgement.

• Close the valve and rapidly inflate the cuff to 30 mmHg above the POP identified from the previous step. Rapid inflation is essential to minimize venous engorgement which attenuates the Korotkov sounds. The cuff is then deflated slowly (at 2 mmHg/sec) while the cone of the stethoscope is firmly applied over the brachial artery but not touching the tubing or the cuff.

• The mercury manometer should be viewed from a distance of 1-3 feet and the eye level should be at the mid-point of the manometer. It is not essential to keep the manometer at heart level. The upper level of the convex top of the mercury column should be taken as the height of that column. For the aneroid sphygmomanometer, similar viewing distance should be observed.

• Record the blood pressure to the nearest 2 mmHg.

The Korotkov Sounds

Stage I: appearance of sound, read as systolic blood pressure.

Stage IV: sudden reduction of sound, read as diastolic blood pressure when there is a wide pulse pressure (anemia, aortic incompetence, etc …) or when sounds continue to zero blood pressure.

Stage V: disappearance of all sound, read as diastolic blood pressure in all other patients.

Augmentation of the Korotkov Sounds

• Occasionally the Korotkov sounds are damped. This occur when the cuff has been repeatedly inflated with incomplete deflation (resulting in venous stasis with poor reflow) and occasionally with an obese arm.

• · Two maneuvers can augment Korotkov sounds:

Special Practical Issues

How Many Readings?

• Take the lower of at least two readings1-2 minutes apart. If the difference in systolic or diastolic blood pressure between these two readings is more than 6 mmHg, a third reading is needed, and the lowest reading is taken.

One or Both Arms? Which Arm?

• If the radial pulse volume is equal in both arms, the right arm blood pressure is measured.

• The arm with neuromuscular disease, skeletal deformity or vascular abnormality (venous or lymphatic obstruction, arteriovenous fistula or dialysis shunt) should be avoided.

• Use the same arm and same body position in the follow - up.

Supine, Sitting or Standing Blood Pressure?

• There is usually no difference between supine and sitting blood pressures. However, the standing blood pressure should be taken in the following situations to detect postural hypotension:

• The standing blood pressure should be measured two minutes after standing.

Rhythm disturbances:

• With an irregular pulse (atrial fibrillation, frequent premature beats) take the average of four blood pressure readings or equate systolic blood pressure with the consistent presence of sounds.

• With a profoundly slow pulse (e.g., complete heart block):

Special Considerations for Elderly Patients:

• The auscultatory gap (a phase of silence after sound appearance, followed by reappearance) is more frequent in the elderly. This leads to a serious error if palpatory blood pressure is not taken prior to auscultation. Cuff inflation to a level within this gap leads to under-estimation of systolic blood pressure.

• Stiff arterial walls may cause over-estimation of blood pressure (pseudohypertension). This phenomenon should be suspected when:

- Target organ damage is absent despite high blood pressure readings.

- Symptoms of hypotension while sphygmomanometer pressure is high.

- Arterial wall is felt while inflating sphygmomanometer cuff above systolic pressure and absence of arterial pulsations (Osler maneuver).

- Resistant hypertension in the elderly.