Measuring blood pressure means that we'll be calculating the level of strength that your heart uses to pump blood around your body. This reading gives us a lot of valuable information about the patient's physiological state and is an excellent indicator of complications and deterioration. These notes will discuss the knowledge and nursing skills required when measuring blood pressure manually. You can find the notes on measuring blood pressure automatically over here.
Measuring Blood Pressure Manually: Introduction
Before we get into the how and why we measure blood pressure, we need to understand what we're actually measuring. Let's start off with some basic terminology; Millimetres of Mercury (mmHg) is the unit used to measure blood pressure. Systolic Blood Pressure is the pressure exerted on the arteries during ventricular systole, which means during heart contraction. The average systolic blood pressure in a healthy adult is 120mmHg, and it's written first whenever one documents blood pressure. Diastolic Blood Pressure is the pressure exerted on the arteries during ventricular diastole, which means during heart relaxation. The average diastolic blood pressure in a healthy adult is 80mmHg, and it's written last whenever one documents blood pressure.
Hypotension is the medical term for low blood pressure, and it refers to a systolic level of less than 90mmHg. Hypertension, on the other hand, is the medical term for high blood pressure, and it's divided into three stages:
Stage 1 Hypertension is when the systolic is between 130-139mmHg, while the diastolic is 80-89mmHg.
Stage 2 Hypertension has a systolic of 140 or higher and a diastolic of 90 or higher.
Stage 3 is called Hypertensive Crisis as it can be life-threatening. This is when the systolic is more than 180mmHg, and the diastolic is more than 120mmHg.
Measuring Blood Pressure Manually: The Korotkoff Sounds
If you've ever seen a blood pressure machine, you'll notice that it has two important things:
The Cuff that goes around a patient's arm, and
The Sphygmomanometer which is a fancy word for pressure gauge.
When the cuff is inflated, it squeezes the patient's arm and presses down on the brachial artery until it occludes its blood flow. A stethoscope is then placed over the brachial artery, and the cuff is released slowly until the blood flow through the brachial artery returns to normal. As the cuff is being released, you'll be listening through the stethoscope to identify the Korotkoff Sounds and looking at the Sphygmomanometer to see where the arrow is when you hear the sounds.
The Korotkoff Sounds are five different noises that you'll hear while blood is returning back to the artery. These sounds are described as:
Phase I: A clear tapping sound
Phase II: The tapping sound becomes softer and has a swishing element to it
Phase III: Sounds very similar to phase I but with a more sharpened and tap
Phase IV: The sounds become abruptly muffled
Phase V: No more sounds
In terms of measuring the blood pressure, what concerns you the most are Phase I, which represents the systolic blood pressure and Phase V, which represents the diastolic blood pressure.
Measuring Blood Pressure Manually: The Procedure
Start by gathering all the equipment needed to check a blood pressure manually, including:
The proper sized cuff: Cuffs come in many sizes ranging from tiny paediatric cuffs to extra large adult cuffs, and choosing the right size is crucial to getting an accurate blood pressure reading. As a guide, the cuff is the proper size if it encircles more than 80% of the patient's arm.
Sphygmomanometer: This can be both analogue or digital; either way, you should test it before approaching the patient to ensure it works.
Stethoscope: Check that you can hear well through it
Before going over to the patient, you should follow infection control guidelines and clean all the equipment with an alcohol swab. Get the patient's file and then go over to their bed.
Introduce yourself to the patient, apply an alcohol hand rub and explain why you'll be checking their blood pressure and what they can expect while you're doing it. Ask the patient about the risk factors that might affect their blood pressure measurement, including whether they've
been consuming alcohol, caffeinated drinks or tobacco in the last 15 minutes
having strenuous exercise before the procedure
been experiencing a high level of stress
been starved for a few hours (typically done before surgery or general anaesthesia)
Next, position your patient comfortably; preferably, they should be seated with their back supported and their legs uncrossed with their feet touching the ground. Unless contraindicated, place their left hand onto a table and use a pillow for support to keep the arm level with the heart. If the arm is placed higher or lower than the heart, the blood pressure reading will not be accurate.
Before placing the cuff around their arm, you should ask them to remove tight and bulky clothing and assess the arm for contraindications; these might include:
continuous IV infusions
trauma or previous surgery
fistula or venous problems
If there are no contraindications and the patient is seated comfortably, you can go ahead and start the procedure. All cuffs will have an Artery Index Marker, typically drawn on the cuff as a bold straight line. Align this marker with the brachial artery, and wrap the cuff around the patient's arm roughly 2cm above the brachial artery.
Place the Sphygmomanometer vertically, close to the patient, and at eye level to easily monitor it. Palpate the brachial artery, and use one of your hands to press the stethoscope's diaphragm over it. Place the ear tips of the stethoscope in your ears, and listen for the brachial pulse; once you locate it, you can gently begin to inflate the cuff. Continue listening to the pulse and note the reading when it disappears.
When you can no longer hear the brachial pulse, you should look at the Sphygmomanometer and inflate the cuff with an additional 30mmHg. This should be enough pressure to completely occlude the brachial artery. Keep the diaphragm of the stethoscope over the brachial artery and slowly start to deflate the cuff, maintaining a 2-3mm/second rate.
As the cuff deflates, listen carefully to identify the Korotkoff sounds. The first one to appear represents the systolic blood pressure, and the last one to appear represents the diastolic blood pressure. After listening to the last Kortkoff sounds, you can continue to deflate the cuff fully and unwrap it from the patient's arm.
Apply hand hygiene again, and document the reading on the patient's observation chart, noting any discrepancies from previous readings. You can use the hospital's protocol or the American Heart Association Blood Pressure Chart as a guide to understanding your patient's measurement. If the reading is not within a normal range, or if you note a large discrepancy from previous readings, you should immediately inform your senior nurse and the patient's medical team to implement a care plan.
However, you should keep in mind that sometimes an extreme value can result from an error during the measurement. Such errors can occur if the:
patient is agitated and restless during the measurement
equipment is defective
cuff is deflated too quickly, not level with the heart or the incorrect size
technique was performed poorly, or the observer was biased
patient has an irregular pulse
Great, that's all you need to know to pass your clinical nursing test on how to measure blood pressure manually! If you'd like to read the rest of the notes on clinical nursing skills, you can follow the link here.
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Jevon P (2020) Blood pressure 2: procedures for measuring blood pressure. Nursing Times [online]; 116: 8, 26-28 ,t6 n
Rehman S, Nelson VL. Blood Pressure Measurement. [Updated 2021 Sep 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482189/
Aronow W. S. (2017). Measurement of blood pressure. Annals of translational medicine, 5(3), 49. https://doi.org/10.21037/atm.2017.01.09