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Blood pressure: Clinical skills notes




Blood pressure


As a nurse, you will need to measure your client’s blood pressure. Blood pressure refers to the force that the blood exerts on the walls of the arteries. Now, a blood pressure measurement has two values. The first and the highest is the systolic blood pressure, which is the force that the blood exerts on the walls of the arteries during systole, or when the heart contracts to pump blood through the body. The second one is the diastolic blood pressure, which is the pressure on the walls of the arteries during diastole, or when the heart relaxes and refills with blood between heartbeats.

Figure 1: The difference between systolic and diastolic blood pressure.

Importance of maintaining normal blood pressure

Now, maintaining normal blood pressure is essential to ensure that tissues around the body are receiving an adequate amount of oxygen and nutrients from the blood. If blood pressure gets too low, the brain, heart, and other vital organs might stop functioning normally because they’re not getting enough blood.

In contrast, blood pressure that is too high, can create a serious problem for the blood vessels and the organs they supply. Just like a garden hose that’s always under high pressure, in the long term, blood vessels may develop tiny cracks and tears that can lead to serious problems, like myocardial infarctions, or heart attacks; strokes, or brain attacks; and aneurysms, or bulges of a weakened blood vessel wall. Increased blood pressure can damage small blood vessels, like those seen in the kidney and eyes, leading to kidney failure and vision loss.

Figure 2: High blood pressure can lead to serious complications.

Chronic increased blood pressure also makes it hard for the heart to pump blood out against the increased pressure. Over time, the heart gets overworked and this can lead to heart failure.

Factors influencing blood pressure

There are several factors that can increase or decrease blood pressure. The first factor is the cardiac output, which is the total volume of blood the heart ejects in one minute. The more blood the heart pumps out, the higher the blood pressure. The cardiac output depends mainly on the heart rate, or the number of times the heart beats per minute; the contractility, or how forcefully the heart contracts with each beat; as well as the total volume of blood circulating throughout the entire body at that time.

Another factor influencing the blood pressure is resistance, which refers to the physical and mechanical pushback the blood gets from things like vasoconstriction, or narrowing of the blood vessel. The narrower the blood vessel, the higher the blood pressure.

Now, blood pressure may also vary depending on the biological sex, where biological males typically have a higher blood pressure than biological females; ethnicity, where people of African descent are likely to develop higher blood pressure; as well as different age groups, where blood pressure typically goes up with age. Other factors include obesity, stress, pain, smoking, and alcohol.

Figure 3: Factors that can affect blood pressure.

It is also important to recognize that blood pressure in any client is highly variable.This means blood pressure readings often differ by the time of day, so they’re typically lowest in the morning and following a meal, especially if it’s high in salt. Also, the readings may vary by the season and by other factors; for example, they may increase with physical activity, fear, or pain and decrease when the person is lying down.

Normal blood pressure values among different age groups

So, for those 13 years and older, they normally have a systolic blood pressure of less than 120 millimeters of mercury, or mmHg, and a diastolic blood pressure of less than 80 mmHg. For school-aged children between 5 and 12 years old, systolic blood pressure is 84 to 120 mmHg, and diastolic blood pressure is 54 to 80 mmHg. Preschoolers from 3 to 5 normally have a systolic blood pressure of 82 to 110 mmHg and a diastolic blood pressure of 50 to 78 mmHg. Toddlers from 1 to 3 have a normal systolic blood pressure of 80 to 112 mmHg and a diastolic pressure of 50 to 80 mmHg. Finally, infants under 1 year of age normally have the lowest blood pressure, which ranges from 74 to 100 mmHg systolic and 50 to 70 mmHg diastolic.

Figure 4: Normal systolic and diastolic blood pressure values by age group.

Hypertension, hypotension, and orthostatic hypotension

So, hypertension is defined as persistently higher than normal values of blood pressure, which, in adults, means 130 mmHg or more for the systolic blood pressure and 80 mmHg or more for the diastolic blood pressure. On the other hand, hypotension for adults is when blood pressure falls below 90 mmHg for the systolic and 60 mmHg for the diastolic.

A variant of that is orthostatic hypotension, which is when blood pressure falls when a person goes from a lying down position to a standing position. This is more common in the elderly, and these clients could experience lightheadedness and fainting when they stand or sit up due to decreased blood flow to the brain.

Common care tips

Now, when you’re asked to measure a client’s blood pressure, there are some common tips you need to remember:

  • Do not take the blood pressure on an arm that’s injured, in a cast, or has an IV or dialysis access site.
  • Even if we measure blood pressure under the same conditions, a client’s blood pressure may vary.
  • For an accurate measurement, ensure that the client is in a comfortable position and not talking, remains calm, and hasn’t recently smoked or consumed caffeine.
  • Choosing proper cuff size:
    • An overly small cuff causes the blood pressure to read too high, while an overly large cuff causes the blood pressure to read too low.
    • The width of the cuff’s bladder should amount to about 40% of the circumference of the upper arm, and the length of the cuff’s bladder should amount to no less than 80% of the circumference of the upper arm.
  • The arm should be held at the heart level. 
    • If it’s held too low, the blood pressure might read higher than it really is. 
    • If it’s held too high, the blood pressure might read lower than it really is.
  • If the cuff is wrapped too loosely, the reading might come out too high.
  • Deflation speed is important:
    • If the cuff is deflated too slowly, then the diastolic blood pressure might read higher than it really is. 
    • If the cuff is deflated too quickly, the diastolic blood pressure might read too high and the systolic blood pressure too low.
  • If the cuff isn’t inflated enough, the systolic blood pressure might again read too low.

Figure 5: Tips for proper positioning and use of the blood pressure cuff.

Measuring Blood Pressure with a Manual Sphygmomanometer

  • Before taking a client's blood pressure, gather the supplies you’ll need, including a blood pressure gauge, or manual sphygmomanometer; a stethoscope; and alcohol wipes. 
  • Remember to also always practice hand hygiene.

Figure 6: Supplies needed to take blood pressure; and don't forget to practice hand hygiene!

  • Support the arm at the heart level with their palm up and help the client expose their arm from their clothing.
  • Disinfect the earpieces, diaphragm, and bell of the stethoscope with the alcohol wipes. 
  • Identify the brachial artery on the inner side of the elbow and wrap the deflated cuff around the arm. The bladder of the cuff should be centered 2.5 centimeters, or about 1 inch, above the brachial artery. Make sure the arrow on the cuff is also aligned with the brachial artery. 
  • Palpate the radial or brachial pulse with one hand as you inflate the cuff with the other.
  • Once the pulse disappears, read the pressure on the gauge and continue to inflate a further 20 to 30 millimeters of mercury. 
  • Fully deflate the cuff and wait 15 to 30 seconds.
    • if you know the client’s usual systolic blood pressure, you may skip this step and start at the next one.

Figure 7: Client and blood pressure cuff positioning.

  • Place the diaphragm or bell of the stethoscope over the artery, ensuring an airtight seal, and place the earpieces in your ears.
  • Quickly reinflate the cuff to the previous level or, if you’ve skipped that, 30 mmHg above the client’s usual systolic blood pressure.
  • Slowly deflate the cuff at a rate of about two to three millimeters of mercury per second.
  • When you hear two consecutive beats, read the pressure on the gauge. What you’re hearing is the Phase I Korotkoff sound, and the reading on the gauge is the systolic blood pressure.
  • As you continue to deflate the cuff, the sound will begin to muffle, and this is the Phase IV Korotkoff sound. Then it will disappear entirely, and this is the Phase V Korotkoff sound. The reading on the gauge when the sound disappears entirely is the diastolic blood pressure.

Figure 8: The readings associated with the Phase I and V Korotkoff sounds indicate the systolic and diastolic blood pressures, respectively.

  • You can then fully deflate the cuff, remove it from the client’s arm and take the earpieces of the stethoscope off.
  • Finally, assist the client into a comfortable position, disinfect the stethoscope with the alcohol wipes, and practice hand hygiene.

Measuring Blood Pressure with an Automated Sphygmomanometer

So far, we’ve discussed the manual approach to measuring blood pressure. This is quick, convenient, and non-invasive. However, your facility may use an electronic blood pressure cuff, also known as an automated sphygmomanometer.

The procedure is almost the same; however, you’ll only need the sphygmomanometer.
  • Practice hand hygiene and assist the client to a comfortable position. 
  • Expose the client’s arm and wrap the cuff over the same site as previously explained, ensuring the bladder of the cuff is centered above the brachial artery. 
  • However, instead of manually inflating and deflating the device while you listen for the Korotkoff sounds, just select the appropriate mode and activate the device. 
  • The measurement will then be visible on the display screen. If an abnormal measurement is obtained, consider repeating the procedure with the manual approach.

Figure 9: The procedure for using an automated sphygmomanometer is very similar to the one for using a manual one, except you select the appropriate mode, activate the device, and read the measurement that displays on the screen. 


When obtaining a client’s blood pressure, be sure to document:
  • the date and time you did the procedure 
  • the blood pressure reading 
  • the method with which it was taken 
  • and your observations