This article will explain how to measure and record blood pressure using a sphygmomanometer (Figure 1). There are many other types of machines for recording blood pressure, such as electronic devices, but these may not be readily available. They can also be difficult to maintain and therefore may give inaccurate readings.
Blood pressure is the force of blood against the walls of the arteries. Blood pressure is recorded as two numbers, the systolic pressure (the pressure when the heart beats) over the diastolic pressure (the pressure when the heart relaxes between beats).
We record this with the systolic pressure first (on the top) and the diastolic pressure second (below). For example, if the systolic pressure is 120 mmHg (millimetres of mercury) and the diastolic pressure is 80 mmHg, we would describe the blood pressure as ‘120 over 80’, written 120/80.
All patients must be assessed for fitness before they undergo surgery. As part of this assessment, it important to measure and record the patient's blood pressure. There are two reasons for this:
It provides an initial recording (a ‘baseline’). If the blood pressure falls suddenly below this baseline after surgery, we are alerted to the fact that the patient may be experiencing complications.
It allows us to confirm that the patient is fit enough to undergo surgery. A high blood pressure reading, or indeed a very low blood pressure reading, could suggest that the patient has other medical problems, e.g. an undiagnosed heart condition. He or she may need further medical tests and possibly medication to stabilise the blood pressure before undergoing surgery.
When measuring a patient's blood pressure, the nurse should be aware of factors that can affect the reading and possibly give a false reading, which could lead to unnecessary medical investigations. These factors include:
blood pressure cuff is too small or is placed over clothing
the patient has recently exercised
the patient is cold or otherwise uncomfortable (e.g., they may need to use the toilet first)
the patient has consumed alcohol or caffeine less than 30 minutes before the reading
the patient is anxious or stressed
the patient is talking during the procedure.
Figure 1. Sphygmomanometer (wall-mounted)
Figure 2. The arm is supported on a level surface. The cuff is around the upper arm and the stethoscope is over the brachial artery, in the bend of the elbow
Blood pressure may vary according to whether the patient is lying down, sitting or standing. It is normally recorded with the patient sitting.
blood pressure cuffs: small, medium, large
patient's care notes or observation chart
Ask whether the patient needs the toilet.
Ask the patient to sit down. The patient should have rested for 3–5 minutes before starting the procedure.
Explain to the patient what you are going to do. This will help reduce their anxiety.
Explain the sensation of the cuff tightening on their arm and reassure them that this is safe.
Ask the patient to loosen any tight clothing or remove long-sleeved garments so that it is possible to access the upper arm. Do not use an arm that may have a medical problem.
Place the cuff around the upper arm and secure.
Connect the cuff tubing to the sphygmo-manometer tubing and secure.
Rest the patient's arm on a surface that is level with their arm.
Place the stethoscope over the brachial artery (in the bend of the elbow) and listen to the pulse (Figure 2).
Pump up the cuff slowly and listen for when the pulse disappears. This is an indication to stop inflating the cuff.
Start to deflate the cuff very slowly whilst watching the mercury level in the sphygmomanometer.
Note the sphygmomanometer reading (the number the mercury has reached) when the pulse reappears: record this as the systolic pressure.
Deflate the cuff further until the pulse disappears: record this reading as the diastolic pressure.
Record these two measurements, first the systolic and then the diastolic (e.g., 120/80), in the patient's notes or chart.
Tell the patient the blood pressure reading.
Disinfect the stethoscope drum and ear pieces with the alcohol wipe.
Report an extremely low or high reading to the clinically qualified person in charge of the patient's care.
Dianne Pickering, Nurse Advisor (retired), Community Eye Health Journalmoc.liamtoh@nagol_ennaid.
Sue Stevens, Nurse Advisor (retired), Community Eye Health Journal.
Articles from Community Eye Health are provided here courtesy of International Centre for Eye Health
Vital Signs: Blood Pressure
CHILD AND FAMILY ASSESSMENT AND PREPARATION
Assess for signs of hypotension, including weak pulse, diaphoresis, pallor, and dizziness.
Assess for signs of hypertension, including headache, bounding pulse, and flushing.
Explain to the child and family why monitoring is important, how it is done, and equipment used. Use language that is appropriate for developmental level (e.g., “I’m going to see how your heart is working. You will feel like your arm is getting a hug.”).
In nonemergent situations:
Show child equipment and let child handle equipment.
Demonstrate on family member, other staff, or stuffed animal how procedure is done and how equipment is used, as age appropriate.
Measure BP after 5 minutes of rest, when possible, to ensure the most accurate reading because agitation may falsely elevate the results. Position child’s arm (extremity) at heart level during the rest; a level below the heart may cause false high readings, a level above the heart may cause false low readings.
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Learn how to take a manual blood pressure! As a nurse or healthcare professional, it is essential that you know how to take a manual blood pressure, and many nursing students must pass a blood pressure measurement skills check-off in nursing school. The manual blood pressure reading is obtained with a sphygmomanometer (aneroid manometer gauge and blood pressure cuff) and stethoscope.
Once obtained, the nurse records it with the systolic reading (this is the first sound heard) over the diastolic blood pressure reading (the point when the sound stops). For example, a blood pressure reading may look something like this: 114/76. The 114 is the systolic reading and the 76 is the diastolic reading.
Why does a nurse need to know how to check a manual blood pressure when there are digital devices that will perform this skill?
Digital or automatic devices may not be available at all times. In addition, manual blood pressure measurement devices provide a more accurate blood pressure reading than digital ones. According to a study by Journal of Clinical and Diagnostic Research, an aneroid device (which is used during a manual blood pressure measurement) is more accurate than a digital device [1].
Therefore, as a nurse you should always reassess a suspicious blood pressure reading with a manual blood pressure measurement.
Video on How to Take a Blood Pressure Manually
Steps on How to Take a Blood Pressure Manually
Here are the steps to take a manual blood pressure. Note: Before taking a patient’s blood pressure, always verify the specific steps required by your healthcare facility or nursing school, as guidelines or protocols may change over time.
1. Perform hand hygiene and gather your supplies.
- Supplies needed: stethoscope, sphygmomanometer (blood pressure cuff with aneroid manometer gauge), cleaning supplies, towels or pillow for support (if needed)
- Tip: always use an appropriately sized blood pressure cuff
2. Have the patient sitting or lying down with their back supported. Their arm should be positioned at heart level. If necessary, use towels or a pillow to support the arm, and make sure the palms are facing up (supinated). Be sure the legs are also uncrossed. For best results, the patient should urinate before the procedure, avoid eating or drinking anything for 30 minutes before the measurement is taken, and should remain quiet [2].
- Find the brachial artery near the proximal (top) portion of the elbow’s bend (in the cubital fossa area):
- This is the most common site for checking the blood pressure and is a major artery in the upper arm that divides into the radial and ulnar artery.
- To find this artery, extend the elbow joint and have the palm facing upward. The pulse point is found near the top of the cubital fossa, which is a triangular area that is in front of the elbow.
3. Place and secure the blood pressure cuff on the patient’s upper arm. Place it about 2 inches above the elbow. In addition, make sure the arrow on the blood pressure cuff is lined up with the brachial artery. In addition, be sure the cuff is secured over the bare skin, and attach the gauge (aneroid manometer) so that you can easily read it as you palpate.
4. First, we will estimate the systolic pressure by palpating the brachial artery and inflating the cuff to the point where the pulse disappears. Turn the bulb’s valve clockwise to tighten. Make sure the gauge is at zero, and pump until you no longer feel the brachial artery’s pulse. Note that number on the gauge when you no longer feel the brachial artery, as this is the estimated systolic pressure. Then deflate the cuff by turning the bulb’s valve counterclockwise, and wait 30 to 60 seconds.
- Why do we do this? By first estimating the systolic pressure, we can avoid missing the auscultatory gap in certain patients. The auscultatory gap is an abnormal silence during auscultation that can lead the clinician to obtain an inaccurate systolic reading, which is the first sound heard during auscultation. This gap occurs in SOME patients (not all), especially if they have hypertension.
5. Place your stethoscope in your ears, palpate the brachial artery again, and place the bell of the stethoscope lightly on the brachial pulse site (you can use the diaphragm rather than the bell if you want, but the bell is the best for hearing low pitched sounds).
6. Verify the gauge is at zero, and inflate the cuff 30 mmHg above the number at which you felt the brachial artery’s pulse disappear when estimating the systolic pressure. For example, if the brachial artery’s pulse disappeared at 100 mmHg, inflate the cuff to 130 mmHg.
7. Next, deflate the cuff slowly by turning the bulb’s valve counterclockwise until the needle drops at a speed of about 2 mmHg per second.
8. Listen carefully for the very first sound to appear, and note the point on the gauge when you heard it. This is the systolic blood pressure number (top number) of your blood pressure reading.
9. Continue to allow the air to slowly leave the cuff, and note the point on the gauge when the sound stops completely. This is the diastolic blood pressure number, which is the lower number in a blood pressure reading. Note: In the past, the diastolic number may be referred to as the last faint sound heard (also known as the Korotkoff phase 4 sound). However, many newer guidelines suggest the diastolic pressure is the point at which the sound is no longer heard (also known as Korotkoff phase 5, which is silence).
The video below demonstrates a blood pressure measurement with audible systolic and diastolic sounds as you watch the gauge:
10. Open the bulb’s valve completely by turning it counterclockwise, allowing the cuff to deflate.
11. Remove the cuff from the patient’s arm.
12. Clean the cuff and devices used, and perform hand hygiene.
13. Document per your facility’s protocols, making sure to include necessary information such as the blood pressure reading, the patient’s position (sitting or lying), and the arm used to measure the blood pressure.
How to Interpret the Blood Pressure Reading
Here are the blood pressure guidelines published by the American College of Cardiology, last updated in 2017 [3]:
- 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 [3].
References:
1. 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
2. Centers for Disease Control and Prevention. (2021, September 27). Measure your blood pressure. Centers for Disease Control and Prevention. Retrieved February 16, 2022, from //www.cdc.gov/bloodpressure/measure.htm
3. 2017 Guideline for High Blood Pressure in Adults – American College of Cardiology. (2018). Retrieved from //www.acc.org/latest-in-cardiology/ten-points-to-remember/2017/11/09/11/41/2017-guideline-for-high-blood-pressure-in-adults