How is systolic blood pressure (SBP) measured?

From the Guidelines

Systolic blood pressure is measured using a sphygmomanometer, which consists of an inflatable cuff, pressure gauge, and stethoscope, and the most accurate method involves wrapping the cuff around the upper arm at heart level, inflating it until blood flow stops, and then slowly deflating it while listening for the first audible sound (Korotkoff phase 1) with a stethoscope, as recommended by the American Journal of Kidney Diseases in 2020 1. To measure SBP, the following steps should be taken:

• The patient should be seated quietly for at least 5 minutes before measurement, with feet flat on the floor, back supported, and arm supported at heart level, as stated in the 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults 1.
• The cuff should be wrapped around the upper arm at the level of the right atrium, and the correct cuff size should be used, such that the bladder encircles 80% of the arm, as specified in the 2019 AHA/ACC clinical performance and quality measures for adults with high blood pressure 1.
• Multiple readings should be taken, with at least 2 readings obtained on at least 2 occasions, and the average calculated, as recommended by the 2019 AHA/ACC clinical performance and quality measures for adults with high blood pressure 1.
• The first audible sound (Korotkoff phase 1) indicates the systolic pressure, which represents the maximum pressure exerted by the heart when it contracts, and the reading is recorded in millimeters of mercury (mmHg), as described in the 2020 American Journal of Kidney Diseases article 1. The importance of accurate SBP measurement is highlighted by the fact that systolic pressure is a key indicator of cardiovascular health, and elevated levels can increase the risk of cardiovascular disease and mortality, as noted in the 2018 Journal of the American College of Cardiology article 1. Key considerations for accurate SBP measurement include:
• Using a validated BP measurement device and ensuring it is calibrated periodically, as stated in the 2019 AHA/ACC clinical performance and quality measures for adults with high blood pressure 1.
• Supporting the patient's arm and positioning the cuff at the level of the right atrium, as specified in the 2019 AHA/ACC clinical performance and quality measures for adults with high blood pressure 1.
• Using the correct cuff size and noting if a larger or smaller cuff is used, as recommended in the 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults 1. Overall, accurate measurement of SBP is crucial for diagnosing and managing hypertension, and healthcare providers should follow established guidelines and protocols to ensure reliable and consistent measurements, as emphasized in the 2020 American Journal of Kidney Diseases article 1.

From the Research

Measuring Systolic Blood Pressure (SBP)

• Systolic blood pressure (SBP) can be measured using various techniques, including the auscultatory Korotkoff-based sphygmomanometry and oscillometry 2.
• The auscultatory Korotkoff-based technique is relatively accurate but is limited to a physician's office, while automatic oscillometry can be used at home by the patient and is preferred even in clinics 2.
• However, the accuracy of automatic oscillometry is low, and errors of 10-15 mmHg are common 2.

Techniques for Measuring SBP

• Manual measurement of blood pressure using an aneroid sphygmomanometer is an essential clinical skill, and nurses must be competent in performing this procedure and taking accurate readings 3.
• Automated blood pressure devices, such as automated sphygmomanometers, have been embraced by clinicians for their convenience and ease of use, but it is essential to be aware of their limitations and select the correct device dependent upon the clinical need 4.
• A systematic review and meta-analysis found that automated blood pressure monitors appear to be accurate in measuring SBP but not diastolic blood pressure (DBP) in patients with atrial fibrillation 5.

Factors Affecting SBP Measurement

• The measurement of SBP can be affected by various factors, including the patient's condition, the device used, and the technique employed 2, 4, 5.
• The use of automated oscillometric blood pressure measurement devices can result in differences between measured and calculated mean arterial pressure (MAP) 6.
• Age, SBP, DBP, and type of device are all independently related to the difference between measured and calculated MAP 6.