Equipment, technique, and common errors

The stethoscope is used to amplify body sounds, making them louder. It consists of earpieces, binaural tubes (one for each earpiece), rubber or plastic tubing, and a chestpiece. For best results, the earpieces should fit snugly and comfortably in your ears. When placing them in your ears, make sure the earpieces are facing forward, toward your face, for the best fit.

The chest piece consists of two parts: the diaphragm and the bell. The diaphragm is the larger, flat side of the chestpiece, which is covered by a thin, plastic disk. The diaphragm - best at amplifying high-pitched sounds, such as bowel and lung sounds-must be placed firmly against the skin for proper amplification of sound.

The bell is the cone-shaped side of the stethoscope chestpiece. It should be held lightly against the skin to amplify sound. The bell is best at amplifying low-pitched sounds, such as vascular and heart sounds.

When placed on the patient’s arm, the cuff should cover two-thirds of the distance from the elbow to the shoulder. The lower edge of the cuff should be 2 to 3 cm (about 2 finger widths, or 1 inch) above the elbow or antecubital space to allow plenty of room to place the stethoscope without touching the cuff. If the stethoscope touches the cuff during the blood pressure reading, the sound of the deflating cuff may interfere with your ability to hear the correct reading. The patient’s sleeve must be above the antecubital space; if the sleeve is tight, ask the patient to remove the arm from the sleeve. This is done for two reasons: tight clothing can restrict normal blood flow in the brachial artery, altering the blood pressure, and placing the stethoscope over clothing makes it difficult to hear blood pressure sounds. Provide a patient gown if needed to maintain the patient’s privacy.

Blood pressure cuffs and stethoscopes are available in drug and retail stores for patients to use to measure their own blood pressure at home. These units can be aneroid, electronic, or computerized sphygmomanometers. If you have patients who are monitoring their pressure at home, be sure they understand the mechanics of obtaining an accurate reading. It is best to have the patient bring the equipment to the office and demonstrate its use. While the patient is showing you the home equipment, you will have an ideal opportunity to check technique and calibration and answer any questions the patient may have about the use of the equipment. This is also a good opportunity to reinforce treatment plans, such as medication, diet, and exercise. It is helpful for a patient who is monitoring blood pressure readings at home to keep a log and review it with the provider during visits to help detect blood pressure variations during normal daily activities.

Some providers will want the BP taken on the leg when a patient has undergone a bilateral mastectomy with lymph node removal or has an arteriovenous shunt (used for dialysis). This is to reduce the risk of lymphedema. If a patient has had a mastectomy on one side, the opposite side can be used for BP. When using the leg, the BP can be taken at either the thigh or ankle. When using the thigh, a cuff designed for the thigh should be used, and the popliteal artery would be auscultated. For the ankle, a regular cuff could be used, and the posterior tibial artery would be auscultated. It can be difficult to hear Korotkoff sounds at the posterior tibial artery, and a Doppler may need to be used. For either location, the patient should be supine (lying down) so that the leg is at the same level as the heart. The cuff should encompass 80% of the circumference of either the thigh or the ankle.

Effects of body position on blood pressure measurement

Blood pressure is usually taken with the patient in either the sitting or the supine position. However, the diastolic pressure can be as much as 5 mm Hg higher when patients sit than when they are supine. In addition, if the patient’s back is not supported and there is some muscle tension in the body (as occurs when the patient is seated on an examination table rather than in a chair), the diastolic pressure may be increased by 6 mm Hg. If patients cross their legs during the reading, the systolic pressure may be raised by 2 to 8 mm Hg. The position of the patient’s arm can also have a major influence when the blood pressure is measured. If the upper arm is below the level of the right atrium (e.g., dangling at the patient’s side), the reading is artificially elevated; if the arm is above the heart level, the reading is lowered. Or if the patient holds up the arm, muscular tension will raise the pressure. The arm should be placed at the level of the heart on a table next to an exam room chair or resting on the arm of the chair to avoid these issues. Patients should also have their feet flat on the floor. Having the legs crossed at the knee can raise the blood pressure. If a patient has a full bladder, it can artificially raise the pressure up to 10 points. Ask patients if they need to use the restroom before taking vital signs.

Blood pressure cuff sizes:

Common causes of errors in blood pressure readings

• The limb used for measurement is above the level of the heart.
• The bladder in the cuff is not completely deflated before a reading is started or retaken.
• The pressure in the cuff is released too rapidly.
• The patient is nervous, uncomfortable, or anxious (may cause a reading to be higher than the patient’s actual blood pressure).
• The patient consumed caffeine or smoked cigarettes within 30 minutes of the blood pressure measurement.
• The cuff was applied improperly.
• The cuff is too large, too small, too loose, or too tight.
• The cuff was not placed around the arm smoothly.
• The bladder is not centered over the artery, or the bladder bulges out from the cover.
• There was a failure to wait 1 to 2 minutes between measurements.
• Instruments are defective:
  • Air leaks in the valve
  • Air leaks in the bladder
  • Aneroid needle not calibrated to zero