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Measuring Body Temperature – Nursing Skills

Updated: May 26, 2022

Measuring body temperature is something that we’ve all done countless times throughout our lives, but as a nurse, this seemingly effortless skill has a very significant role. The patient’s temperature can tell you whether they’re stable, deteriorating, improving or have an allergic reaction. Hence using reliable thermometers and applying the proper technique is crucial.

These notes will explain the measurements taken when checking one’s temperature and the clinical nursing skills required to perform it. You can find the complete list of notes on clinical nursing skills here.

Measuring Body Temperature: Introduction

Before we learn how to measure our patient’s temperature, we need to understand what value we’re measuring and what it means. Our bodies have two temperatures:

  1. The Core Body Temperature: is the temperature of our blood supplying organs. The value reflects our body’s internal functions and is rarely affected by environmental factors.

  2. The Peripheral Body Temperature: is the temperature of our tissues, including our muscles and skin, which largely depends on environmental factors.

Our bodies have several mechanisms that regulate our core temperature. If we’re healthy, the heat production and heat loss cancel out, keeping our core within a narrow bracket of 36-37.5°Celsius (equivalent to 96.8-99.5°Fahrenheit). When the value goes below or over that range, it indicates that something is wrong with our body, and in addition, if the values reach extreme ends, they will cause a series of complications.

Medically, we refer to abnormalities in core temperatures as:

  1. Normothermia: Normal temperature ranging from 36-37.5°Celsius (96.8-99.5°Fahrenheit)

  2. Febrile/ Pyrexial: (Fever) A temperature higher than 37.5°C (99.5°F)

  3. Hyperthermia/ Hyperpyrexia: A temperature above 41.1°C (106°F)

  4. Hypothermia: A temperature lower than 35°C (95°F)

Research suggests that the enzyme-controlled chemical reactions in our bodies increase by 10% with every additional 1°C that goes above the normal range. If the core temperature reaches a value of 43°C (109.4°F), irreversible damage occurs in our bodies, leading to the death of several cells and enzymes. On the other hand, as our core temperature decreases, cellular processes and metabolism start to function significantly slower. And humans will lose consciousness if the core temperature falls below 33°C (91.4°F)

Measuring Body Temperature: Thermoregulation

Our bodies have several mechanisms that keep our core temperature within a normal range. The main thermoregulatory centre, however, is found in the hypothalamus within our brain, and it is made up of three main areas:

  1. The heat-loss centre

  2. The heat-promoting centre

  3. The pre-optic region

All three areas work together to keep the core body temperature within a normal range, also known as the homeostatic range.

The process of thermoregulation starts when the sensory receptors in our skin and organs sense a temperature change. The increase or decrease in temperature serves as an alert, telling the sensory receptors that something is causing a disturbance in the homeostatic range. Once the temperature change is noted, the sensory receptors send signals through the afferent pathways informing the thermoregulatory centre about the disruption. From there, the thermoregulatory centre analyses the information received and sends out another signal to the organs through the efferent neural pathways. The signal sent by the thermoregulatory centre will cause the organs to gain or lose heat as needed.

Even though the thermoregulatory centre can usually balance our body temperature quite well, we do other mechanisms as humans to help maintain a comfortable temperature. Such as adding or removing layers of clothing, taking warm or cold showers and drinking warm or cold fluids, and these behaviours assist our body in maintaining normothermia.

Measuring Body Temperature: Indications

As a nurse, you will frequently have to check your patient’s temperature as it falls within the four main parameters (vital signs) used to determine a patient’s physiological stability. However, in addition to routine checking, there are several reasons why you might check your patient’s temperature. These include:

  1. Obtaining a baseline temperature upon admission or before an intervention

  2. Determining the presence of hypothermia or hyperthermia

  3. In patients with a suspected or confirmed infection

  4. Evaluating the effectiveness of antimicrobial therapy in patients with infection

  5. Before administering blood products and during the administration, to identify an allergic reaction.

Measuring Body Temperature: Available Devices

You might think that measuring your patient’s body temperature is an easy task; however, it might be slightly challenging to measure it as accurately as possible. The value is dependent on several factors, including the measurement site, the quality of the instrument used, and the technique applied. In reality, obtaining an actual core temperature requires invasive equipment such as temperature probes that can be placed inside the oesophagus, pulmonary artery or urinary bladder. Such invasive approaches are only made in critically ill patients in intensive care units, as they can be very impractical and rather unnecessary to obtain.

In fact, the most common temperature reading methods are with non-invasive devices such as probes that can be placed in the rectal cavity, mouth, auditory canal or simply placed over the temporal area or axillary area. However, these devices only give an estimated measurement of the actual core temperature, and the values tend to vary between one area or another.

1. Oral Temperature

Using an oral thermometer is relatively reliable, but it is essential to place the probe correctly. Most research articles recommend obtaining the most accurate reading if the probe is placed posteriorly into the sublingual pocket. This spot is very close to the sublingual artery, reflecting the core body temperature. However, the estimated temperature value can be altered if your patient has recently ingested food or fluid, has tachypnoea or is on oxygen therapy.

2. Axillary Temperature

The probes used to measure axillary temperatures are typically the same probes used to measure oral temperatures, with some devices asking the user to specify the site. If you’re going to measure your patient’s axillary temperature, you’ll need to place the probe’s tip in the centre of the armpit and ask your patient to squeeze their arm close to their chest. This method is arguably one of the least reliable ways to measure core body temperature, as there are no main blood vessels surrounding the area. In addition, the axillary temperature can be influenced by environmental factors and by perspiration.

3. Rectal Temperature

Using a rectal thermometer is one of the most accurate ways of measuring a true core body temperature, but it presents several disadvantages:

  1. Uncomfortable for the patients

  2. Intrudes on the patient’s privacy

  3. Faeces can generate a false reading (as the probe needs to be directly touching the intestinal wall)

  4. It does not detect immediate changes in temperature due to the low blood flow in the rectum

4. Tympanic Thermometer

For the tympanic thermometer to function effectively, it needs to be placed inside the external auditory canal, where it can sense the reflected infrared emissions from the tympanic membrane. This value reflects the core temperature of the hypothalamus. Despite its frequent use, the tympanic thermometer is not always accurate. Its values can be affected if your patient has ear wax or if the probe is not aimed correctly. Moreover, users frequently report errors in their devices.

5. Temporal Thermometer

Like the tympanic thermometer, the device used to measure the tympanic temperature senses infrared emissions radiating from the skin. The device needs to be held a few inches away from the forehead, making it quick and easy to use. However, its reliability and accuracy have not been widely tested, making it unreliable.

Measuring Body Temperature: The Procedure

Start by ensuring that the thermometer device is available and functioning, and read the manual on how to use it. The device is very easy to use in most cases, but its settings might vary from one brand to another. Ensure that the thermometer is set to an adult or paediatric depending on your patient and that the mode is consistent with the approach you'll be taking (i.e. Oral/ axillary/ rectal etc.)

The devices will often have single-use covers placed over the probe to maintain a good hygienic practice, so before you leave the nursing station, make sure that the covers are available.

Once you have the thermometer in hand, grab the patient's file and go to their bed. Introduce yourself, apply an alcohol hand rub and explain why you'll be checking their temperature. Go over the selected method and assess the risk factors for obtaining an inaccurate reading (i.e. If you're taking an oral temperature reading, ask the patient whether they've recently consumed a hot or cold drink).

Turn on the thermometer device and place the probe in the appropriate area, keeping it steady. If you're checking the temperature orally, make sure that the patient keeps their mouth closed and avoid asking them any questions, so you don't prompt talking. Wait for the beeping sound on the device, which would indicate that it has read the temperature value.

Once you have the reading, dispose of the single-use cover and re-apply the alcohol hand rub. Document the patient's temperature on their chart and compare it to the previous readings. Explain the value to your patient, and if the patient has normothermia, no action is necessary.

If the reading is abnormal (too high or too low), you must inform the medical team and follow their instructions.


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