Anyone Can Take A Blood Pressure. Right?

The taking of blood pressure is one of the most commonly performed of medical procedures. According to the literature, most of the time it is done incorrectly.

This is significant because differences of as little as 5mmHg can determine whether or not an appropriate e diagnosis of Hypertension is made. Inaccurate readings can lead to diagnostic errors (ie "white coat" or "masked" hypertension) or unnecessary investigation and treatments, with the attendant costs, both financial and medical.

As you have no doubt noticed in your office, readings often vary, even from minute to minute. This is why a standardized measurement technique is recommended, including multiple readings.

Errors in the taking of blood pressure can relate to the patient, the equipment and the technique.

According to the recommendations of the Canadian Hypertension Society:

The Patient should:

• Have no caffeine in the preceding hour (how often do the patients present to the office holding a cup of "Tim's")
• No smoking in the preceding 15-30 minutes
• No use of substances containing adrenergic stimulants such as may be present in nasal decongestants or eye drops.
• Have an empty bladder.
• Be calm with a warm office temperature environment.
• Have no tight clothing on arm or forearm. (No, you can't just role the sleeve up)
 

Moreover, the patient:

• Should be seated calmly for 5 minutes with the back well supported (not on the examining table) and the arm supported at the level of the heart. The feet should touch the floor and the legs should not be crossed.
• Should be checked for postural changes (if over age 65, taking antihypertensive drugs or diabetic), by taking a reading after 1-5 minutes in a standing position.
 

The Equipment:

• The cuff size should be such that the bladder goes around the arm and covers 80% of its circumference. The width of the cuff should be at least 40% of the circumference of the arm.
• The system must be able to generate a pressure of 30 mmHg above the systolic pressure in less than 5 seconds, and should not leak.
• If (still) using a mercury manometer, the column of mercury must be at zero before starting and the meniscus must be easily visible, at eye level and able to rise easily when pressure is applied.
• The needle of the aneroid device must be at zero when the cuff is empty, and the device should be calibrated every six to twelve months.
• When oscillometric devices are used the conditions should be the same as with the auscultatory method.
 

The Technique:

• Use a cuff with the proper size. Adjust the cuff on the arm about 2-3 cm above the anticubital fossa
• Inflate the cuff quickly to 20mmHg above the systolic pressure, identified by the disappearance of the radial pulse.
• Deflate the cuff at a rate of 2-3 mmHg/second or heartbeat.
• Note the systolic pressure when a clear sound is repeated. (Phase 1 of Korotkoff)
• Note the diastolic pressure when the repeated sound disappears (Phase 5), except in children when the recommendation is to hold until the sounds are muffled (Phase 4). For patients in whom the sound does not disappear, use Phase 4 as the reference.
• Don't "round off" the reading to values ending in 5 or 0.
• If the Korotkoff sounds are weak, have the patient raise his/her arm and flex and extend his/her hand five to ten times. The reading can then be taken again on the lowered arm.
• At the first "hypertension visit", take the reading in both arms and take two readings several minutes apart. If one of the arms consistently reads higher (more than 5-10 mmHg), use that arm for future readings.

If you're not already following these guidelines, you should start to do so - and don't forget to check the technique of the nurses with whom you work. It's all in the interest of accuracy, and the patient is the ultimate beneficiary. If not measured properly, BP measurements are not reliable. Physicians do not believe them, and patients do not believe them. This situation may initiate what is called "professional inertia". Therapeutic decisions may be postponed or delayed. BP measurement with a proper technique is very important and a major step in assessing our patient's cardiovascular risk.

For an interesting and entertaining CME program on office blood pressure measurement and related technologies, visit:

- John Hickey

Thanks to Dr. Denis Drouin, Dr. Brian Gore and Dr. Janusz Kaczorowski, all members of the CHEP Implementation Committee, for their review of the draft copy of this article.

Reference:

2005 Canadian Hypertension Education Program Recommendations.