Vital signs - Blood pressure (BP): Nursing skills

As a healthcare professional, you will need to measure your patient’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 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.

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’s 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.

This 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.

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.

There are several factors that determine what a person’s blood pressure is at any given time. The first factor is the cardiac output, which is the total volume of blood the heart ejects in one minute. The cardiac output depends on the heart rate, or the number of times the heart beats per minute, and the stroke volume, or the volume of blood the left ventricle ejects with every heartbeat.

Stroke volume in turn is affected by factors like preload, or how much blood the ventricle can fill with before it contracts; the contractility, or how forcefully the heart contracts with each beat; as well as afterload, or the amount of resistance the ventricles must overcome to push blood out of the heart.

So, left ventricular afterload is affected by aortic pressure, valve diseases, and systemic vascular resistance. Focusing for a minute on systemic vascular resistance, this is the resistance from systemic blood vessels to blood flow. In other words, how readily blood vessels allow blood to flow through them. Now, systemic vascular resistance is mainly affected by changes in the vessel lumen, which is determined by vasodilating and vasoconstricting factors.

The relationship between the systemic vascular resistance and cardiac output as a whole is what determines blood pressure.

Let’s look at some other factors that can influence blood pressure. Blood pressure can vary between sexes, since sex hormones like estrogen can have a protective effect on blood pressure. Age is also an important factor, where blood pressure typically goes up as a person gets older. Other factors include obesity, stress, pain, certain medications, smoking, and alcohol use.

It’s also important to recognize that blood pressure in any patient is highly variable. This means blood pressure readings often differ by the time of day, where they’re typically higher in the morning and lower following a meal. 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. One last important variation to remember is that a person’s blood pressure may be higher in a healthcare setting than it is at home, sometimes referred to as “white coat hypertension.”

In adults and children aged 13 years and older, blood pressure should be below 120 systolic and below 80 diastolic.

Normal blood pressure for younger children is based on biological sex, age, and height, and should be between the 50th and 90th percentile for these criteria when diagnosing hypertension.

On the other hand, a simplified range of normal blood pressure values can be used to decide which children need a repeat blood pressure measurement or further evaluation of their blood pressure.

These ranges are based on age; so, for school-aged children 6 to 12 years old, normal systolic blood pressure is 97 to 120 mmHg, and diastolic blood pressure is 57 to 80 mmHg. Preschoolers from age 3 to 5 normally have a systolic blood pressure of 89 to 112 mmHg and a diastolic blood pressure of 46 to 72 mmHg. Toddlers from 1 to 2 years old have a normal systolic blood pressure of 86 to 106 mmHg and a diastolic pressure of 42 to 63 mmHg. Finally, infants under 1 year of age normally have the lowest blood pressure, which ranges from 72 to 104 mmHg systolic and 37 to 56 mmHg diastolic.

So, hypertension is defined as persistently higher than normal values of blood pressure, which, in adults and children aged 13 years and older, means 130 mmHg or more for the systolic blood pressure or 80 mmHg or more for the diastolic blood pressure. In children under age 13 years, hypertension is diagnosed if measurements are persistently above the 95th percentile for their age. On the other hand, hypotension for adults is when blood pressure falls below 90 mmHg for the systolic or 60 mmHg for the diastolic.

Now, defining hypotension in children is a bit more complex. It’s based on the systolic blood pressure and age, and there are some important cutoffs to keep in mind.

In neonates a systolic blood pressure of less than 60 mmHg is considered hypotension, in infants it is less than 70 mmHg.

For children 1 to 10 years of age, it’s less than 70 plus the child’s age, multiplied by 2; and for children over 10 years old a systolic blood pressure of less than 90 mmHg is considered hypotensive.

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 patients could experience lightheadedness and fainting, also known as syncope, when they stand or sit up due to decreased blood flow to the brain.

Now, when measuring a patient’s blood pressure, there are some common tips to keep in mind. Do not take the blood pressure on an arm that’s injured, in a cast, or is on the same side as a mastectomy.

Now, for an accurate measurement, ensure that the patient is in a comfortable position with their legs uncrossed, feet flat on the floor, and their back supported. They should be calm; should not be talking;

and check to make sure they haven’t recently consumed caffeine or smoked.

It’s also important to choose the proper cuff size for the patient.