Medical Assistant Chapter 19: Vital Signs

In this chapter, we’ll be discussing how to take and record vital signs as a medical assistant. You’ll learn the proper techniques for taking blood pressure, temperature, pulse, and respiratory rate.

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Vital signs are measurements of the body’s most basic functions. They provide an overall picture of the body’s well-being and are used to detect or monitor medical problems. The four main vital signs measured by medical assistants are blood pressure, pulse, temperature, and respirations.

Body Temperature

There are several methods for measuring temperature, each with its own degree of accuracy. The most common methods are:
-Oral (by mouth)
-Rectal (in the rectum)
-Axillary (under the arm)
-Tympanic membrane (ear drum)

Oral temperature is the most frequently used method in adults. It is quick and easy, but may not be accurate if the patient has had hot or cold beverages, smoked cigarettes, or exercised within the last hour. Rectal temperature is taken by placing a lubricated thermometer into the rectum for three to five minutes. This method is most accurate, but may be uncomfortable for the patient. Axillary temperature is taken by placing the thermometer under the arm and holding it in place for three to five minutes. This method is less accurate than oral or rectal methods, but may be used when those methods cannot be used due to patient factors (such as mental status or age). Tympanic membrane temperature is taken by placing a special thermometer into the ear canal and holding it in place for two minutes. This method is quick and easy, but may not be accurate if there is ear wax present or if the patients ear canal is small.

Blood Pressure

Blood pressure (BP) is a vital sign, a measure of the force that blood exerts on the walls of your arteries as it travels through your body. systolic pressure and diastolic pressure. Diastolic is the bottom number (the one in the middle) and measures the pressure in your arteries between heartbeats. Systolic is the top number, which measures the pressure in your arteries as your heart contracts and pumps blood through your body


The act of respiration is the result of the coordinated contraction of the diaphragm and intercostal muscles. Contraction of the diaphragm flattens it and increases the volume of the thoracic cavity. This decrease in pressure within the lungs causes air to flow into them. The air flows until the pressure within the lungs equals that of the outside atmospheric pressure.

The rate, depth, and rhythm of respiration are under both voluntary and involuntary control. Voluntary control occurs when a person is aware of the need to change his or her breathing pattern, such as when preparing to lift a heavy object or during strenuous exercise. The involuntary control is provided by centers located in the medulla oblongata and pons that control both inspiratory and expiratory effort. These centers are stimulated by changes in carbon dioxide concentrations and pH levels in the blood and cerebrospinal fluid surrounding them.


Pulse is the number of times the heart beats per minute and is commonly taken at the radial artery, which is located on the thumb side of the wrist. The normal pulse rate for adults ranges from 60 to 100 beats per minute. To take a radial pulse:

-Locate the radial artery on the thumb side of the wrist.
-Place your fingers gently on the artery.
-Do not use your thumb, as you may inadvertently miscalculate your own pulse.
-You may need to press lightly to feel a pulse.
-Count the number of beats in 60 seconds or for 30 seconds and multiply by 2.

Height and Weight

Human height is determined by a combination of genetics and environmental factors, such as nutrition and exercise. The average height for an adult male is just over 5 feet 9 inches, while the average height for an adult female is just under 5 feet 4 inches.
Weight, too, is determined by both genetics and environment. An average adult male weighs around 195 pounds, while an average adult female weighs around 168 pounds. However, weight can vary greatly from person to person, and even within the same individual over time.

There are several different ways to measure height and weight. The most common method is to use a ruler or tape measure to obtainheight, and a scale to measure weight. However, other methods do exist, such as the Body Mass Index (BMI).
The BMI is a mathematical formula that takes into account both height and weight when determining whether someone is underweight, overweight, or of normal weight.

When taking vital signs, it is important to use the same method each time in order to obtain accurate results. For example, if you use a ruler to measure someone’s height one time, be sure to use a ruler every time after that in order to obtain an accurate measurement. The same goes for weight – if you use a scale one time, be sure to use a scale every time after that in order ensure accuracy.

Body Mass Index

Body mass index (BMI) is a measure of body fat based on height and weight that applies to both adult men and women. BMI is not a perfect measure, but it is the best population-level measure of body fat we have. A person’s BMI can be calculated using their height and weight, and is often used as a screening tool to identify whether someone is overweight or obese.

BMI can be used to screen for overweight and obesity in adults. A BMI of 25.0 or greater is considered overweight, and a BMI of 30.0 or greater is considered obese. However, BMI does have some limitations. First, it does not directly measure body fat percentage. Second, it does not account for different body types (e.g., athletes vs. non-athletes). Finally, BMI may overestimate body fat in those with a muscular build, and underestimate body fat in older adults and those of Asian descent.

Despite its limitations, BMI is still the best population-level measure of overweight and obesity that we have. If you are concerned about your weight, talk to your healthcare provider about ways to manage your weight safely.

Head circumference

Head circumference is a measurement of the distance around the outside of a person’s head. It is typically measured with a tape measure, and can be used to assess the size and development of the brain in infants and young children. Head circumference can also be used to diagnose certain medical conditions, such as hydrocephalus (a buildup of fluid in the brain).

Waist circumference

Waist circumference (WC) is a good indicator of intra-abdominal fat, which surrounds the internal organs and is more closely linked with cardiovascular disease and diabetes than subcutaneous fat. WC is measured at the midpoint between the lower ribs and the iliac crest, using a measuring tape placed horizontally around the abdomen. The ideal WC for men is less than 102 cm (40 inches) and for women is less than 88 cm (35 inches).

Hip circumference

Hip circumference (HC) is a clinical measurement used to assess malnutrition, obesity, and risk for certain chronic diseases.

To measure HC, find the greatest circumference around the buttocks and thighs. Place the measuring tape at the top of the iliac crest (the bony point on the hip), wrap it around the buttocks and thighs, and bring it back to the starting point. The HC measurement is recorded in centimeters (cm).

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