Wednesday, June 19, 2024

Vital Signs in Adults: How to Measure Them


Vital signs are a group of important medical signs that define the status of the body’s life-sustaining or vital functions. They are the indicators of health. Measurement or monitoring of vital signs is an important step in clinical evaluation and patient monitoring. Through vital signs, a patient’s condition can be communicated universally and is an important tool in emergency departments.

Traditionally there are four vital signs namely:

  • Body temperature
  • Pulse rate or heart rate
  • Respiratory rate
  • Blood Pressure

Vital Signs of Body Temperature

The normal body temperature or normothermia/ euthermia is a temperature range found in humans. The body temperature varies and depends on age, gender, time of the day, exertion, health status, part of the body, emotional state, and consciousness level.

Normal Range

The normal range for body temperature of an average healthy adult is 97.7 to 99.5-degree Fahrenheit or 36.5 to 37.5 degrees Celsius.

Temperature classification
Core  (rectal, esophageal, etc.)
Hypothermia <35.0 °C (95.0 °F)
Normal 36.5–37.5 °C (97.7–99.5 °F)
Fever >37.5 or 38.3 °C (99.5 or 100.9 °F)
Hyperthermia >37.5 or 38.3 °C (99.5 or 100.9 °F)
Hyperpyrexia >40.0 or 41.0 °C (104.0 or 105.8 °F)
Note: The difference between fever and hyperthermia is the underlying mechanism. Different sources have different cut-offs for fever, hyperthermia and hyperpyrexia.


How to Measure

Temperature can be measured from mouth, ear, axilla, skin, or rectum, and it varies with the site.

  • Oral Temperature– Most commonly used. The thermometer is placed under the tongue and lips are closed tightly around it.
  • Tympanic temperature– thermometer is inserted in the ear canal to measure the temperature. It is less accurate
  • Axillary Temperature– thermometer is placed in the axilla and the patient adducts the arm to hold it.
  • Rectal Temperature– the thermometer is inserted into the rectum to measure the temperature. This method is very inconvenient but is usually considered the ‘gold standard’ method as it measures the internal temperature of the body.
  • Skin Temperature– digital thermometers are used for measuring skin temperature. It is placed 3-5cm away from the skin for measuring. This method is being used a lot especially since the COVID-19 pandemic started to avoid cross-contamination.

Vital Signs of Pulse Rate

Pulse rate is the waves of blood created by the contraction of the left ventricle of the heart in the arteries, during a cardiac cycle, in one minute. It is similar to measuring the heart rate.

Normal Range

The range of 60-100 beats per minute or bpm is considered the normal pulse rate in an average adult. Rates less than 60 bpm are called bradycardia and those more than 100 bpm are called tachycardia

(0–3 months old)
(3 – 6 months)
(6 – 12 months)
(1 – 10 years)
children over 10 years
& adults, including seniors
adult athletes
99-149 89–119 79-119 69–129 59–99 39–59


How to Measure

Pulse rate is measured by palpating any artery that can be compressed near the body surface such as carotid artery in the neck, radial artery in the wrist, femoral artery at the groin, popliteal artery behind the knee, posterior tibial artery near the ankle joint, and dorsalis pedis artery in the foot.

The radial pulse is measured using three fingers. To measure, place the index and finger over the underside of the wrist, below the base of the thumb, and press with flat fingers until the pulse is felt. Now, count the pulses or beats for 1 minute or 30 seconds and then multiply by 2.

In the day-to-day, clinical practice radial artery is palpated for measuring the peripheral pulse rate. Apart from measuring the pulse rate, pulse volume, rhythm, symmetry and amplitude is also important to check to identify any problem.

Vital Signs of Respiratory Rate

The Respiratory rate is defined as the number of breaths an individual takes in one minute. One breath consists of both inhalation and exhalation. Parameters to look for here are – the rate, the depth, and the pattern of breathing.

Normal Range

12-20 breaths per minute are the normal range of respiratory rate for an average adult. In the pediatric population, however, the normal respiratory rate is defined by the particular age group (see the table below).

0-3 months 34 to 57
3 to <6 months 33 to 55
6 to <9 months 31 to 52
9 to <12 months 30 to 50
12 to <18 months 28 to 46
18 to <24 months 25 to 40
2 to <3 years 22 to 34
3 to <4 years 21 to 29
4 to <6 years 20 to 27
6 to <8 years 18 to 24
8 to <12 years 16 to 22
12 to <15 years 15 to 21
15 to 18 years 13 to 19

Reference- Fleming S, Thompson M, Stevens R, Heneghan C, Plüddemann A, Maconochie I, Tarassenko L, Mant D. Normal ranges of heart rate and respiratory rate in children from birth to 18 years of age: a systematic review of observational studies. Lancet. 2011 Mar 19;377(9770):1011-8. doi: 10.1016/S0140-6736(10)62226-X. PMID: 21411136; PMCID: PMC3789232.

Rates lower or higher than the range mentioned above are termed bradypnea and tachypnea respectively.

Bradypnea which is described as a respiratory rate of fewer than 12 breaths per minute can be caused due to many reasons like- respiratory failure, metabolic dysfunctions, or use of central nervous system depressants, etc.

Tachypnea is a respiratory rate over 20 breaths per minute and could occur both in physiological or pathological conditions. Exercise, pregnancy, emotional changes are some of the physiological factors, whereas pain, pneumonia, asthma, pulmonary embolism, anxiety, are some of the pathological factors that can lead to tachypnea.

Apnoea- is the term used to describe inhibition of respiration for a total of 15 seconds. It can be caused by swallowing, hyperventilation, Hering-Breuer deflation reflex, or sleep (sleep apnoea).

How to Measure

Respiratory rate can be simply measured by observing the patient and counting the number of times the chest rises for 1 minute.

Other methods like impedance pneumography and capnography are also used for measuring the respiratory rate. These are used in patient monitoring.

Vital Signs of Blood Pressure

Blood pressure is defined as the force exerted by the circulating blood on the walls of blood vessels. Blood pressure has two measurements- systolic blood pressure (SBP) and diastolic blood pressure (DBP). The difference between systolic and diastolic blood pressure is defined as pulse pressure.

Systolic blood pressure is the pressure exerted on the walls of large arteries during maximum contraction of the heart (during one heartbeat), and diastolic blood pressure is the minimum pressure exerted on large arterial walls between two heartbeats.

Normal Range

Instead of one single normal value, a range of normal blood pressure is defined. In adults, 120/80 blood pressure is considered to be normal where 120 is the systolic blood pressure and 80 is the diastolic blood pressure.

The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH) classification of office blood pressure (BP)a and definitions of hypertension gradeb.
Category Systolic BP,
Diastolic BP,
Optimal < 120 < 80
Normal 120–129 80–84
High normal 130–139 85–89
Grade 1 hypertension 140–159 90–99
Grade 2 hypertension 160–179 100–109
Grade 3 hypertension ≥ 180 ≥ 110
Isolated systolic hypertensionb ≥ 140 < 90
The same classification is used for all ages from 16 years.

a BP category is defined according to seated clinic BP and by the highest level of BP, whether systolic or diastolic.

b Isolated systolic hypertension is graded 1, 2, or 3 according to systolic BP values in the ranges indicated.

Normal blood pressure ranges for pediatric population-

Stage Approximate age Systolic BP,
Diastolic BP,
Infants 0 to 12 months 75–100 50–70
Toddlers and preschoolers 1 to 5 years 80–110 50–80
School age 6 to 12 years 85–120 50–80
Adolescents 13 to 18 years 95–140 60–90

Reference- p. 6. Revised 6/10. By Theresa Kirkpatrick and Kateri Tobias. UCLA Health System

How to Measure

In regular clinical practice, non-invasive measuring is done by using a stethoscope for auscultation and watching the aneroid, electric, or mercury (not used much now) sphygmomanometer. However, automated or semiautomated devices that are more popular these days use the oscillatory method to measure the BP. These devices measure the amplitude of blood pressure oscillations on the arterial wall.

Usually, blood pressure is measured from the left arm unless otherwise required. The brachial artery is the commonest site to take the measurement.

Auscultation method:

  • Firstly, make the patient comfortable. Make sure they have not consumed caffeinated items, smoked, etc., at least one hour before the measurement, and let them rest for about five minutes before measuring the BP.
  • Ask the patient to loosen or remove tight or full-sleeved clothing so that the upper arm is accessible. Choose the arm for measurement based on the patient’s medical history.
  • Place the pressure cuff around the upper arm and connect it to the sphygmomanometer tubing.
  • Place the patient’s arm on a comfortable surface such that it is flexed and is at the level of the heart.
  • Place the stethoscope over the brachial artery and listen to the pulse.
  • Inflate the cuff slowly and listen when the pulse disappears. As soon as it occurs, stop the inflation.
  • Now start deflating the cuff slowly and keep an eye on the mercury level or the needle in the sphygmomanometer.
  • Note down the sphygmomanometer reading when the pulse sound reappears- this is systolic blood pressure.
  • Keep deflating the cuff, and the reading where the pulse sound disappears is the diastolic blood pressure.

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