What is blood pressure and how is it measured?
Before diving into the step-by-step process, it’s important to understand what blood pressure is and why it is measured. The amount of pressure (or force) of blood on the walls of the arteries as it travels through them is known as blood pressure.
It is recorded as two numbers:
- Systolic blood pressure (SBP): This is the top number. It denotes the pressure (or force) in the arteries when the heart beats.
- Diastolic blood pressure (DBP): This is the bottom number. This is the pressure in the arteries when the heart is at rest between beats.
Regular blood pressure for an adult is less than 120/80. Several factors, such as age, medications, activity level, and overall health status can affect blood pressure.
Equipment needed to take blood pressure manually
To manually measure blood pressure, you will need the following equipment:
Stethoscope: This is used to listen to the Korotkoff sounds, which are the pulse sounds of blood flow heard as the cuff pressure is released.
Sphygmomanometer: This is the piece of equipment that is applied to the patient. Parts included are:
- An inflatable cuff and bladder (which is wrapped around the patient’s arm)
- A bulb (the part you squeeze) to inflate the cuff
- A valve (which is on the bulb and goes in two positions, closed and opened). The valve is what you twist to release and deflate the cuff so you can hear the Korotkoff sounds
- Pressure gauge
- Two tubes: One tube attaches to the pressure gauge to the cuff and bladder. The second tube attaches the bulb and air release valve to the cuff and bladder.
Steps to take blood pressure manually
The more you practice how to take blood pressure manually, the better at it, you will become. The steps on how to do this are as follows:
Step 1: Before taking Reading
- Use a quiet, calm environment.
- Ensure patient is seated comfortably with back supported.
- Remove tight clothing from arm.
- Avoid caffeine, nicotine, and exercise for 30 minutes prior.
Step 2: Prepare the patient
- Ensure your patient is relaxed. If ambulatory, ask your patient to go to the bathroom to empty their bladder. Next, your patient should be seated for at least five minutes before you measure their blood pressure. Once seated, ensure they’re sitting comfortably with their back supported, their feet flat on the floor, and their ankles and legs uncrossed.
- Position the arm correctly. The patient’s arm should be supported on a flat surface at the same level as their heart with their palm facing up. The patient’s arm should be free of clothing to avoid obscuring the Korotkoff sounds.
- Avoid recent activities that are known to raise blood pressure. Confirm your patient has not smoked, consumed caffeine, or engaged in any physical activity at least 30 minutes prior to taking their blood pressure, as these can temporarily elevate it. Ask your patient not to talk during the measurement.
Step 3: Apply the cuff — size and placement matter
- Choose the appropriately sized cuff. Using a cuff that is too small or large can lead to inaccurate readings. Using a cuff that is too small can result in a falsely higher blood pressure reading. Conversely, using a cuff that is too large can result in a falsely lower reading.
- Consider the cuff length and width. The cuff should cover approximately 75% to 100% of the total circumference around the upper arm. The width of the cuff should be at a height (wide enough) to cover at least 40% to 80% of the length from the shoulder to the elbow.
- Place the cuff on the arm correctly. First, palpate the brachial artery. Place the lower edge of the cuff on the upper arm, approximately one inch (2.5 cm) above the bend of the elbow. The artery marker on the cuff should align with the brachial artery, which is located slightly medial on the inner aspect of the arm. The cuff should fit firmly but not too tight. Make sure you can fit one finger under the cuff to ensure it’s not too tight or too loose.
Step 4: Estimate the systolic pressure
- Palpate the brachial pulse. Before using the stethoscope to auscultate and obtain your patient’s blood pressure, palpate their brachial pulse.
- Inflate the cuff. While palpating the brachial pulse, inflate the blood pressure cuff until you can no longer feel it. Look at the gauge to see the pressure reading when their palpable pulse disappears. This number is their estimated systolic pressure.
- Deflate the cuff. Slowly release the pressure and allow their arm to rest for one minute before proceeding.
Step 5: Measure the blood pressure
- Ensure good placement of the stethoscope. Position your stethoscope’s diaphragm over the brachial artery, just below the cuff’s edge.
- Inflate the cuff. Quickly inflate the cuff to 20 to 30 mmHg above the estimated systolic pressure you just obtained.
- Slowly deflate the cuff. Release the air at a rate of 2 to 3 mmHg per second while listening through your stethoscope.
Step 6: Identify the Korotkoff sounds
Knowing how to take blood pressure manually requires you to know what Korotkoff sounds are. Korotkoff sounds are the circulatory pulse sounds you hear when auscultating an artery with a stethoscope when taking a BP manually.
- First Korotkoff sound (systolic pressure): As the pressure in the cuff is released, listen for the first pulse sound, known as the first Korotkoff sound. The reading at the time of hearing the first Korotkoff sound is known as the systolic pressure.
- Disappearance of the Korotkoff sound (diastolic pressure): Continue to slowly release the pressure at a rate of 2 to 3 mmHg per second, as you continue to listen with your stethoscope. The point at which the sound stops indicates the level of the diastolic blood pressure.
Step 7: Record the reading
Document the blood pressure reading as systolic over diastolic (example: 120/80). State in your documentation which arm was used, the patient’s position (sitting, lying, or standing), and any additional relevant factors that may have influenced the reading. Two examples: The patient continued to speak throughout the measurement, or the patient was anxious and hyperventilating.
How to Interpret the Blood Pressure Reading
- A normal blood pressure is a systolic pressure of less than 120 mmHg and a diastolic pressure of less than 80 mmHg.
- An elevated blood pressure occurs when the systolic pressure is between 120-129 mmHg, and the diastolic pressure is less than 80 mmHg.
- Hypertension Stage 1 occurs when the systolic pressure is between 130-139 mmHg, or the diastolic pressure is between 80-89 mmHg.
- Hypertension Stage 2 occurs when the systolic pressure is greater or equal to 140, or the diastolic pressure is greater or equal to 90 mmHg.
For a patient to be diagnosed as having hypertension, they need an average reading based on 2 readings or more that are obtained on 2 or more occasions.
Common Errors:
- Bladder cuff too narrow or wide;
- Limb being assessed is unsupported;
- Insufficient rest before the assessment;
- Repeating the assessment too quickly;
- Cuff not wrapped tightly and evenly;
- Deflating the cuff to quickly;
- Deflating the cuff too slowly;
- Failure to use the same site for consistency;
- Limb being assessed is measured while above their heart level.
REFERENCES
- Carole Jakucs, How to Take Blood Pressure Manually retrieved from https://www.nurse.com/nursing-resources/how-to-guides/how-to-take-blood-pressure-manually/
- Shahbabu, B. (2016). Which is More Accurate in Measuring the Blood Pressure? A Digital or an Aneroid Sphygmomanometer. JOURNAL OF CLINICAL AND DIAGNOSTIC RESEARCH. doi: 10.7860/jcdr/2016/14351.7458
- Centers for Disease Control and Prevention. (2021, September 27). Measure your blood pressure. Centers for Disease Control and Prevention. Retrieved February 16, 2022, from https://www.cdc.gov/bloodpressure/measure.htm
- Editorial Team. How to Take Someone’s Blood Pressure (Manually). Melbourne (VIC): Ausmed [Internet]; 2020 March 19 Available from: https://www.ausmed.com.au/learn/explainers/manual-blood-pressure.
- 2017 Guideline for High Blood Pressure in Adults – American College of Cardiology. (2018). Retrieved from https://www.acc.org/latest-in-cardiology/ten-points-to-remember/2017/11/09/11/41/2017-guideline-for-high-blood-pressure-in-adults
- Ernstmeyer K, Christman E, editors. Nursing Fundamentals [Internet]. 2nd edition. Eau Claire (WI): Chippewa Valley Technical College; 2024. PART IV, NURSING PROCESS. Available from: https://www.ncbi.nlm.nih.gov/books/NBK610818/
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