A Guide to Measuring Blood Pressure

Edited by Adam Da Costa Gomes

Proper technique is critical when measuring blood pressure, yet it remains one of the most inaccurately performed measurements in clinical medicine. Blood pressure is consistently overestimated by at least 10/5 mmHg during routine clinical practice measurements, potentially leading to the over-diagnosis of hypertension. Today, we will look at proper patient preparation, cuff placement, and both in-clinic and at-home measurement methods.

Purpose of Measuring Blood Pressure

First, let’s review why we measure blood pressure. Measuring blood pressure helps to estimate a patient’s risk of experiencing a cardiovascular event such as a myocardial infarction. Blood pressure can also serve as a marker of effectiveness and safety of various medications. Finally, measuring blood pressure can aid in the diagnosis of hypertension, prompting health care professionals to take action and initiate therapeutic interventions to prevent progression or complications. Conversations about blood pressure are a great way to facilitate shared decision-making between practitioner and patient and are a great launching point to developing mutually-agreed-upon care goals.

Patient Preparation Tips

DOs

• Quiet room with comfortable temperature

• Rest for at least 5 mins before measurement

• Calmly seated with back well-supported and arm supported at the level of the heart

• Feet flat on the floor

• Bladder & bowel comfortable

• Stay silent prior & during the procedure

DON’Ts

• Caffeine, smoking, or nicotine in the preceding 30 mins

• Use of substances containing adrenergic stimulants such as phenylephrine or pseudoephedrine

• Tight clothing on arm or forearm

• Crossed legs

• Acute anxiety, stress, or pain

This short video from the American Medical Association provides 7 simple tips to get an accurate blood pressure reading, and quantitatively displays how much certain factors can raise the blood pressure reading.

Proper Cuff Placement

Blood pressure cuffs, also called “bladders,” are offered in different sizes, so be sure to select the correct size for your patient’s arm. The width of the cuff should be approximately 40% of the patient’s arm circumference, and the length of the cuff should cover 80-100% of the patient’s arm circumference.

When placing the cuff around the patient’s arm, ensure that the centre (usually marked with a line) is placed over the brachial artery, which runs along the medial side of the arm. The lower edge of the cuff should be about 2-3 cm above the elbow crease.

When securing the cuff, ensure it is not too tight nor too loose. With the cuff deflated, you should be able to fit 1-2 fingers between the cuff and the arm.

Measurement in Clinics

While the auscultation method may still be used in some practices today, we will be focusing on the oscillometric (electronic) method, as it is the preferred method for determining blood pressure in-office.

The oscillometric method, also called “Automated Office Blood Pressure Measurement” (AOBP), does not require the healthcare professional to be in the room for any of the readings. This helps to reduce “white coat hypertension” in which the blood pressure readings in the office are higher due to the presence of a healthcare professional in the room. Once the cuff is properly fitted to the patient, the healthcare professional can leave the room while the device takes multiple blood pressure measurements at 1- to 2-minute intervals. The average of the readings is then displayed.

During the first clinic visit, blood pressure measurements should be performed from both arms. The arm yielding the higher blood pressure reading should then be used for subsequent visits.

Omron HEM-907

Examples of oscillometric devices include the Omron HEM-907 and the Sun Tech CT40. It is important to note that oscillometric devices require recalibration at least every 2 years.

At-Home Assessment

Self-measuring blood pressure at home is preferred over getting it measured in a clinic, as it eliminates the chances of white coat hypertension and predicts health outcomes better than in-office blood pressure readings. At-home measurements can also identify masked hypertension, where office readings are lower than home readings. It is especially important for patients to measure and record their blood pressure at home if they have inadequately controlled hypertension, issues with adherence, or diabetes.

There are two methods for monitoring blood pressure at home:

Ambulatory Blood Pressure Monitoring (ABPM)

ABPM provides fully-automated blood pressure measurements over a period of 24 hours. The cuff is connected to a small oscillometric monitor that can be worn on a belt or in a pouch. The monitor takes a reading every 15-30 minutes while awake, and every 30-60 minutes while asleep. The readings can then be downloaded onto a computer. Some guidelines state that ABPM is the preferred method to diagnose hypertension as it can predict clinical outcomes better than conventional methods of blood pressure measurement, however its cost and inconvenience limit its use.

Automated Blood Pressure Monitor Set-Up

Home Blood Pressure Measurement (HBPM)

HBPM, also called “self-measurement,” refers to the patient using their own blood pressure monitor at home and is similar to AOBP. A fully automated upper-arm device is preferred, and the device must be validated. Two readings should be taken each morning and evening for 4-7 days. The first reading should be discarded and only the second reading should be recorded. This is because first readings are consistently higher than second readings.

There is strong evidence for the superiority of self-measurements over office measurements for predicting various cardiovascular outcomes. Further, HBPM has moderate agreement with ABPM values, however there is no strong evidence to say that ABPM is superior to HBPM.

When counselling patients on monitoring blood pressure at home, show them this helpful video!

Wrap-Up

Monitoring blood pressure is essential in preventing disease progression. However, when done incorrectly, it may cause more harm than good. It is important to take the time to re-evaluate your blood pressure measurement technique based on the recommendations and adjust if needed. Help patients obtain more accurate measurements in the clinic by educating them on how to properly prepare for their appointment. Be sure to also educate them on how to conduct proper at-home assessments, and encourage them to use a Blood Pressure Log to help them keep track of their blood pressure readings.

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References

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