Measuring body temperature using a tympanic thermometer (2024)

This article explains the rationale for measuring body temperature and outlines the procedure using a tympanic thermometer

Introduction

Body temperature is one of the key physiological observations that should be recorded when a patient is admitted to hospital, and monitored regularly as clinically appropriate. Slight changes in body temperature can be an indication of acute illness and are an important component of the National Early Warning Score 2 (NEWS2) (Royal College of Physicians, 2017).

Nurses need to know how to measure body temperature accurately and reliably, as inaccurate results may influence diagnosis and treatment, lead to a failure to identify patient deterioration and compromise patient safety (McCallum and Higgins, 2012). It is, therefore, important that nurses understand the significance of abnormal temperature readings and, when delegating this task to unregistered staff, ensure they are competent and know when to report concerns.

Regulation of body temperature

The body’s temperature is regulated by the thermoregulatory centre in the hypothalamus through various physiological mechanisms such as sweating, dilation/constriction of peripheral blood vessels and shivering (Waugh and Grant, 2018). Body temperature rises and falls in line with increases and decreases in metabolic rate. Heat is released during periods of increased metabolic activity, such as skeletal muscle, liver and digestive organs activity. Shivering – a repetitive muscular activity – increases heat production when there is a possibility that body temperature could fall below normal.

Heat is lost from the body in four ways:

• Radiation – movement of heat from exposed parts of the body with a higher temperature to the surroundings with a lower temperature. This is the most common mechanism of heat loss;
• Convection – heat transfer from the body by flow or movement of air, such as sitting in front of a fan;
• Conduction – heat transfer due to direct contact with cooler surfaces such as lying on a cold surface;
• Evaporation – sweating (Waugh and Grant, 2018).

Normal values

Body temperature represents the balance between heat production and heat loss, and a normal body temperature is generally accepted to be 36.9°C – the optimum temperature needed to maintain enzyme activity required for metabolism. However, in health, it can range from 36.0-37.5°C (Dougherty and Lister, 2015), and slight increases can occur in the evening, during exercise and in women following ovulation (Waugh and Grant, 2018). Box 1 outlines terms used to describe body temperature.

NEWS2

NEWS2 is based on a simple aggregate scoring system in which a score is allocated to measurements of physiological signs, including temperature; the other signs are respiration rate, oxygen saturation, systolic blood pressure, pulse rate and level of consciousness or new confusion (RCP, 2017). Abnormal temperature readings outside of the range of 36.0-38.0°C (RCP, 2017) are a significant finding, prompting increased frequency of monitoring as well as a response from a registered nurse (Table1).

Causes of pyrexia

There are many causes of pyrexia including:

• Infection;
• High ambient temperature – heat and humidity in the environment can reduce the amount of heat lost through the skin;
• Drugs – amphetamine derivatives, such as methylenedioxymethamphetamine (MDMA or ‘Ecstasy’) and anaesthetic drugs, can cause malignant hyperpyrexia;
• Stroke involving injury to the hypothalamus;
• Cardiac arrest – pyrexia is common in the first 48 hours after cardiac arrest (Nolan et al, 2015);
• Increased muscular activity following strenuous exercise or during prolonged seizures;
• Endocrine disorders, for example, thyroid storm;
• Myocardial infarction when there is an inflammatory response to heart-muscle damage.

Sometimes, patients present with a pyrexia of unknown origin; this is a consistently elevated body temperature >37.5°C for over two weeks with no diagnosis, despite investigations.

Sepsis and temperature

There is a common misconception that patients with sepsis will always present with a pyrexia. For example, in adults, a temperature of <36.o°C is considered an amber flag warning in a patient who is suspected of having sepsis and this requires prompt review.

In children <5 years who have a suspected diagnosis of sepsis, a temperature <36.0°C is considered a red flag warning sign.

Causes of hypothermia

There are many causes of hypothermia including:

• Exposure to a cold environment, for example immersion in cold water;
• Underlying illness such as hypothyroidism, hepatic encephalopathy and cerebrovascular accident;
• Social factors including poor accommodation/inadequate heating, malnourishment or alcohol misuse;
• Burns, which can lead to excessive heat loss.

Children (due to their immature regulatory systems) and older people (due to their altered thermoregulatory mechanisms) are at risk of developing hypothermia.

Sometimes hypothermia may be induced during certain types of cardiac surgery when it is used to protect the brain from periods of low blood flow. Targeted temperature management (formerly called therapeutic hypothermia) used post cardiopulmonary arrest, when the patient remains in a coma to protect the brain from low blood flow, is becoming increasingly common (Nolan et al, 2015).

Measuring temperature

Indications for measuring body temperature include:

• Baseline observation on admission/first consultation and as part of NEWS2 assessment;
• Routine bedside observations, and other vital signs, to help the early detection of acute illness and deterioration;
• Observations associated with a transfusion of blood products to detect signs of transfusion reaction;
• Assessment in acute illness as part of ABCDE approach. Nurses should manually check skin temperature as part of the assessment of circulation (C) – cool peripheries could indicate circulatory shock – and measure body temperature as part of exposure (E);
• As part of the NEWS2 assessment.

Frequency of measurements

The National Institute for Health and Care Excellence (2007) recommends that adult patients in acute hospitals should have physiological observations, including body temperature, recorded at initial assessment or admission and then subsequently monitored at least every 12 hours, unless a decision has been made at a senior level to increase or decrease the frequency of monitoring.

Methods for measuring body temperature

Methods for measuring body temperature include:

• Tympanic thermometer – commonly used in clinical practice (Fig 1);
• Single-use chemical dot thermometer – commonly used with infants and small children;
• Rectal thermometer – frequently used when hypothermia is suspected;
• Oesophageal/nasopharyngeal probes, bladder probe or pulmonary artery catheter: reliable methods, but generally only used on critical care units.

Forehead chemical thermometers are unreliable and should not be used by health professionals (NICE, 2019).

The same site should be used for consecutive temperature measurements and documented, as switching between sites can produce readings that are difficult to interpret (Jevon and Joshi, 2020).

Tympanic temperature measurement

The tympanic membrane shares the same carotid blood supply as the hypothalamus: measurement of tympanic membrane temperature and, therefore, reflects core temperature (Jevon and Joshi, 2020).

Care should be taken when using the tympanic thermometer as poor technique can render the measurement inaccurate. Temperature differences between the opening of the ear canal and the tympanic membrane can be as much as 2.8°C (Jevon and Joshi, 2020).

To ensure accurate temperature measurements, the tympanic thermometer probe should be positioned to fit snugly in the ear canal. This will prevent ambient air at the opening of the ear canal from entering it, resulting in a false low temperature measurement. Size of the external acoustic meatus (ear canal), presence of cerumen (ear wax), operator technique and the patient’s position can affect the accuracy of the measurement.

Arslan et al (2011) found that readings using a tympanic thermometer in patients who had been lying on one ear were significantly higher in that ear than in the exposed ear. The study involved 68 healthy young people who had no signs of discharge or infection of the ear or upper respiratory tract infection. Dougherty and Lister (2015) suggest that patients should not lie on their side for 20minutes before their temperature is measured using a tympanic thermometer.

Infection prevention

The thermometer is an important tool for clinical assessment but can become contaminated by micro-organisms. Adherence to local infection prevention and control policies, including the cleaning of equipment, is essential. Non-sterile gloves are not required routinely for this procedure. Nurses need to assess individual patients for the risk of exposure to blood and body fluids (Royal College of Nursing, 2020) and to be aware of local policies for glove use.

Procedure using an electronic tympanic thermometer

Equipment:

• Electronic tympanic thermometer that has been cleaned and maintained according to local policy;
• Clean disposable probe tip;
• Waste bag.

1. Decontaminate hands and assemble equipment.
2. Introduce yourself to the patient, explain the procedure and gain consent.
3. Ascertain which ear was used for previous readings and use the same ear for subsequent readings.
4. Ensure the patient is in a comfortable position.
5. Decontaminate hands.
6. Inspect the ear canal for any problem that may affect the accuracy of the reading including the presence of cerumen, ear discharge and foreign bodies. If you identify a problem select a different site and document and report your concerns.
7. Turn on electronic thermometer and attach a new probe tip following manufacturer’s recommendations (Fig2a).
8. Gently pull the pinna of the ear upwards and backwards (Fig2b).
9. Insert the thermometer into external acoustic meatus and ensure there is a snug fit (Fig2c).
10. Press the button on the device to measure the temperature and a reading will appear.
11. Remove the thermometer from the ear canal and dispose of the probe tip into waste bag.
12. Ensure the patient is comfortable and decontaminate your hands.
13. Document the reading, including date and time, and site where the reading was taken. If NEWS2 is being used, calculate the score once other observations are completed and record on NEWS chart or handheld device. If necessary, ensure local protocols for escalation are followed.
14. Ensure that electronic tympanic thermometer is cleaned and stored according to the manufacturer’s guidelines.