Recording baseline observations and temperature measurement are among the vital components of core assessments in clinical practice. Human body temperature is well balanced to provide optimum conditions for tissue metabolism. Measurement of body temperature is important for two reasons. First, to give insight into the metabolic and homeostatic activity of the body and, second, to provide information about the possible cause of any abnormal state and contributing to accurate diagnosis (Blows, 2018). Each physiological condition has a particular set point: this is the physiological value around which the normal range fluctuates. The head thorax temperature is normally around 37°C. Yet peripheral temperature it is typically 2°C–4°C cooler than core temperature. This gradient is maintained by tonic thermoregulatory vasoconstriction (Bindu et al, 2017).
Thermoregulation
Thermoregulation is a process that allows the body to maintain its core internal temperature. Thermoregulation has three mechanisms: afferent sensing, central control and efferent responses. The body must have the ability to switch from increased heat production when it is cold to increased heat loss when it is hot (Blows, 2018). This process is finely tuned and sensitive to changes in both internal and external temperatures. Thermoreceptors are responsive to various thermatic cues in different parts of the body, and receptors to cold and heat are present in the skin. The aim, as with any homeostatic mechanisms, is to stabilise the normal state—referred to as normothermia—to sustain average body temperature and distribute heat evenly to all the tissues. This involves sensory feedback to the brain and an output effector to organs to stimulate changes in temperature (Figure 1).
Figure 1. Physiological process of thermoregulation
The hypothalamus controls thermoregulation. Stimuli affecting the receptor at the start of the afferent pathway carry nerve impulses from the receptor to the hypothalamus. This informs the hypothalamus of a change in internal temperature. The hypothalamus triggers an action in response to the stimulus. Nerve impulses pass from the hypothalamus, via the efferent pathway, to the skin, glands, organs, muscles and the nervous system, which respond by making appropriate changes to regulate the body's temperature. If the temperature rises, the effector organ will take action to lower it and vice versa (Blows, 2018). Vasodilation is the process in which blood vessels close to the skin surface widen allowing heat to be lost from the blood. The reverse, vasoconstriction, is the narrowing of the blood vessels that take away blood from the surface of the skin to prevent heat loss (Blows, 2018).
Heat is generated by the basal metabolic system, through the consumption of food and by muscle contraction, such as shivering, voluntary activity and behaviours. An example of a behavioural action to react to changes in environmental temperature would be to put on another layer of clothing when feeling cold (Campbell, 2011). The methods by which the hypothalamus controls our behaviour and physiology are usually effective at regulating our body temperature.
Heat loss
According to Woodhead and Fudge (2012), patients may experience heat loss via four methods: evaporation, convection, conduction, and radiation. These methods can often be used in a therapeutic sense when caring for a patient and are summarised below (Potter et al, 2017):
Evaporation
During evaporation, the hypothalamus signals to the sweat glands to release sweat through ducts on the surface of the skin. When the sweat evaporates, this causes heat loss.
Convection
This is heat loss via air movement. For example, the use of a fan to cool a patient down is a way to promote heat loss through convection. This method is more effective if the skin is slightly moist.
Conduction
If a patient who had hyperthermia were to use an ice pack or a cold flannel to chill themselves, they would be promoting heat loss through conduction. Heat will always travel from hot to cold because the particles that have the higher temperature are more active.
Radiation
When there is a transfer of heat from the surface of one object to the surface of another without contact being made. For example, a patient without a blanket is going to radiate more heat than a patient who is covered. In addition, a patient who is standing up will radiate more heat than someone lying in the foetal position.
Core temperature
Core temperatures vary from person to person. Factors that influence body temperature include age, sex (due to metabolic rates and hormone differences), changes in hormones, heart rate, stress, obesity, metabolic processes, and long-term illnesses such as cancer (Obermeyer et al, 2017). Body temperature cycles in harmony with an individual's sleep-wake cycle. Temperature decreases during the nocturnal sleep phase and increases during the wake phase repeatedly within a 24-hour circadian rhythm. Temperature can also vary due to external factors such as altitude, which reduces calorigenic response.
In addition, body temperature will vary, depending on the site where the temperature is taken. Axillary temperature is usually 0.3°–0.6°C lower than oral temperature. A rectal temperature measurement is usually 0.3°-0.6°C higher than one taken orally. Rectal readings are generally considered to be middle ground between accuracy, however this method has implications in terms of patient preference and infection control. Tympanic readings are the most accurate due to the proximity to the hypothalamus (Gasim et al, 2013) and the tympanic membrane shares an arterial blood supply originating from the carotid artery. The pulmonary artery catheter is the gold standard method for measuring core body temperature. Dunleavy (2010) found a difference of 0.8°C or greater between tympanic temperature and pulmonary artery catheter temperature. However, this method is invasive and performed only with patients in intensive care units. The clinical decision on where to take a temperature can often be down to the type of thermometer available, patient preference and the clinical area where the investigation is taking place.
Core temperature is a vital sign because this is the temperature at which the body's organs must function. For the body to balance the temperature, mechanisms must be in place to ensure that heat gain equals the heat lost (Blows, 2018). Any variations in body temperature are indicators that homeostasis has not been maintained. It is considered a vital indicator for diagnosis of clinical conditions(Tables 1–3).
Table 1. Temperature values
| Hypothermia Pyrexia >38.0°C | <35.0°C |
| Normal range in accordance with definitions: | 35.1°−37.9°C |
| Optimal range for homeostasis | 36.5°−37.5°C |
Table 2. Causes of temperature changes
| Causes of raised temperature | Causes of low temperature |
|---|---|
| Toxins | Cold weather |
| Drug reactions | Alcohol |
| Infection | Drug use |
| Brain disorders affecting the hypothalamus | Diabetes |
| Neoplasms | Low thyroid |
| Auto immune diseases | Infection |
Table 3. Morbidities associated with body temperature
| Sepsis | Fever, shivering, or feeling very cold is one of the six signs of sepsis |
| Febrile convulsions | These indicate two things in children aged under 7 years: a pyrexia caused by infection or a hypothalamus that is too immature to cope with the high temperature |
| Pulmonary embolism | Usually a raised temperature to 38 – 38.5 and among one of the leading causes of hospital associated complications and preventable deaths (Saad et al, 2018) |
| Meningitis | A fever and headache pain are among the first symptoms of meningitis |
| COVID-19 | Raised temperature to 37.8°C or greater is one of the key signs of COVID-19 |
Temperature changes
Temperature, which is defined as ‘the degree of internal heat of the body’ (White et al, 2011), should always be recorded when conducting vital signs monitoring checks (Bickley, 2016). Temperature monitoring is a fundamental nursing skill and, when assessing a patient's temperature, it is important to place the numerical value of the reading in the context of the patient's presenting condition and symptoms. The assessment of temperature as an initial clinical examination allows practitioners to gain a greater insight into the patient's current condition, so that more appropriate treatment and care can be given. Temperature monitoring should also be used to measure the effectiveness of, and track the side effects arising from, any intervention delivered to the patient (Bickley, 2016), such as taking a temperature preoperatively to monitor the effects of an anaesthetic.
Several factors can affect temperature, such as presenting clinical conditions, infections, brain function and injury, cardiac function including hypotension, bleeding and haemorrhage, the patient's age and body mass index, and the environment (Blows, 2018).
When body temperature is in the normal range, tissue and cells continue to work efficiently and effectively (Potter et al, 2017). When a patient's temperature starts to rise or fall, this can cause serious physiological issues, but it can also be a key indicator for diagnosis. Prolonged hypothermia causes vasoconstriction, and bradycardia is a heat-preservation mechanism. Such changes will affect the delivery of oxygen to cells (Dutton and Finch, 2018) and will result in slowed breathing, lack of co-ordination, irritability, confusion and sleepy behaviour.
Hyperthermia refers to a group of heat-related conditions characterised by an abnormally high temperature and hypothermia refers to the condition of having an abnormally low body temperature. The symptoms of hyperthermia and hypothermia have different presentations, which are listed in Table 4.
Table 4. Signs of hyperthermia verses hypothermia
| Hyperthermia | Hypothermia |
|---|---|
| ▪ Dizziness | ▪ Shivering |
| ▪ Weakness | ▪ Exhaustion or feeling very tired |
| ▪ Nausea | ▪ Confusion |
| ▪ Thirst | ▪ Slurred speech |
| ▪ Headache | ▪ Drowsiness |
Hyperthermia, or pyrexia, is often described as having a prolonged core temperature of above 38°C (Robertson and Hill, 2019). The consequences of pyrexia are vasodilation and an initial hypotension, as the body attempts to release the heat through radiation. The heart will usually become tachycardic to compensate for the circulating volume, as it tries to maintain the delivery of oxygen to cells. This is a compensatory mechanism, known as cardiac compensation, to promote blood flow and oxygen delivery to cells to prevent cell death and organ failure. The volumes of blood and urine are reduced due to loss of water through increased perspiration (Dutton and Finch, 2018). Body protein is rapidly broken down, leading to increased excretion of nitrogenous products in the urine. When the body temperature rises rapidly, the affected person may feel cold due to the evaporation occurring on the surface of their skin.
Intraoperative temperature regulation
Intraoperative inadvertent changes in body temperature are common with an incident rate of up to about 90% (Bindu et al, 2017). Fluctuations in temperature have harmful physiological effects and can adversely affect the patient outcome. Under anaesthesia, patients rely on automimic responses and external thermal management for thermoregulation (Bindu et al, 2017). The National Institute for Health and Care Excellence (NICE) (2016) recommends that temperature measurement is taken as follows:
- One hour prior to surgery
- Every 30 minutes intraoperatively
- At 15-minute intervals postanaesthetic
- Once the patient is on the ward either 4-hourly or, if active warming is required, every 30 minutes.
Hyperthermia can have a profound effect on the brain as is because the by-products of increased cellular metabolism can contribute to a raise in intracranial pressure. Intraoperative hyperthermia can be caused by a variety of mechanisms, which include (Bindu et al, 2017):
- Exposure of body surface
- Cold irrigation fluid
- Skin preparation
- Duration of surgery
- Induced reduction in metabolic rate by 20-30%
- Muscle relaxants, which prevent shivering
- Intravenous sedatives/anaesthetics, which increase or lower shivering threshold
- Vasodilators, which promote heat loss.
Intraoperative temperature requires serious monitoring to ensure regulation.
Evidence-based practice
Clinical staff involved in thermometry require education and training prior to performing the practice. Training is required to improve technique and for consistency in approach and location. Potter et al (2017) suggested that taking temperature via the tympanic membrane is the most easily accessible method to monitor a patient's core temperature. It maintains the patient's dignity and is a relatively non-invasive, pain-free method to take a temperature (Robertson and Hill, 2019). If done correctly, the process should take 2–5 seconds. The tympanic membrane is sensitive to core temperature changes, which allows for an accurate reading. However, it does not provide a continuous measurement and readings may often be distorted if the ear has a build-up of earwax. In addition, it is not appropriate for use with small children because their ear canal is too small to accommodate the device. An alternative is to monitor temperature via the skin: this uses a wearable thermometer that adheres to the skin and continuously monitors the patient's temperature. However, it should be borne in mind that this type of thermometer is less sensitive to core body temperature changes and readings can be distorted by sweat (Campbell, 2011).
Infrared tympanic membrane thermometers are considered ideal because the tympanic membrane and the hypothalamus share an arterial blood supply originating from the carotid artery; therefore, the tympanic membrane is considered to directly reflect core temperature (Gasim et al, 2013). Such thermometers are easy to use and are favoured over a conventional mercury thermometer provided its accuracy is guaranteed.
Thermometry is recommended in many clinical guidelines. Initially, clinicians will identify the need to monitor a patient's temperature, alongside other routine vital observations, which are undertaken in both primary and secondary care settings. One of the key drivers for temperature monitoring is the updated National Early Warning Score 2 (NEWS 2). NEWS 2 requires a temperature reading to be documented to support potential recognition of deteriorating patients and to prompt an escalation of care, if necessary (Royal College of Physicians (RCP) (2017). Furthermore, temperature monitoring is imperative when sepsis is considered to be a potential differential diagnosis, instigating the need for blood cultures for patients who have a body temperature more than 38°C, instigating the use of Sepsis Six guidelines (Dellinger, 2013; NICE, 2017; Blakemore, 2019).
The NICE (2016) Clinical Guideline 65 (Hypothermia: prevention and management in adults having surgery) identifies that during the intraoperative phase (total anaesthesia time), the patient's temperature should be measured and documented before induction of anaesthesia, and then every 30 minutes until the end of surgery. The importance of temperature monitoring is so crucial that standard critical incident reporting should be considered for any patient arriving at the theatre suite with a temperature below 36.0°C, and induction of anaesthesia should not begin unless the patient's temperature is 36.0°C or higher (unless there is a need to expedite surgery because of clinical urgency, for example bleeding or critical limb ischaemia).
For infants and children aged between 4 weeks and 5 years, an electronic/chemical dot thermometer in the axilla or an infrared tympanic thermometer should be used (NICE, 2019). For children aged 5 years and upwards, an electronic/chemical dot thermometer in the axilla or mouth, or an infrared tympanic thermometer should be used (Foley, 2015). Appropriate use of thermometry supports early discharge—for example in the children having case of day surgery—and a full set of observations should be undertaken on discharge. This should include temperature, pulse, respiratory rate, blood pressure and oxygen saturations (RCN, 2017).
Sepsis
With reference to the NICE guidance (NICE, 2017), there is key guidance relating to thermometry in diagnosis and monitoring of sepsis. Although the focus of this article is to explore temperature monitoring, it is imperative that sepsis is considered when performing any patient assessment or activity. The NICE (2017) NG51 sepsis guideline specifies that clinicians must ‘assess temperature, heart rate, respiratory rate, blood pressure, level of consciousness and oxygen saturation in young people and adults with suspected sepsis’ when undertaking a face-to-face assessment of patients with suspected sepsis.
A raised temperature is recognised as a key indicator in diagnosing sepsis, and ongoing temperature monitoring will indicate the progression of the infection (Mai et al, 2018). Robertson and Hill, 2019 identify that many patients with an aggregate NEWS 2 of score 5 or higher are critically unwell, and indeed national hospital mortality rates are in the region of 20% for patients who have a NEWS 2 of 5 or higher. It is important to note, however, that this is an aggregate score. It is entirely possible to have a NEWS 2 score of 5 without any evidence of organ dysfunction—eg a patient receiving 28% oxygen who has a respiratory rate of 21, but has normal oxygen saturations, and a temperature of 38.3°C, is a good example of this. Therefore, it is recommended that pure use of the NEWS 2 score is limited to help identify signs of sepsis, and it is therefore recommended that health professionals do not assume that everyone with a NEWS 2 of 5 or above has sepsis.
According to NICE (2017) a tympanic temperature of less that 36°C is indicated as moderate to high risk criteria in the sepsis risk stratification tool.
Suspected COVID-19
There is an emerging consensus on best practice for measuring temperature in patients known to have or suspected of having COVID-19. It is now recognised that temperature screening supports the detection of patients with SARS-CoV-2. Even though hand-held infrared thermometers are convenient to check whether a patient has an elevated body temperature, they are not sufficiently accurate for screening purposes. The non-profit healthcare research organisation ECRI (2020) suggests that temperature screening based on infrared alone or alongside a questionnaire for is ineffective as a mass screening tool to identify people infected with SARS-CoV-2; the ECRI conclusions are based on a review of evidence from two large systematic reviews, three simulation studies, and six diagnostic cohort studies (not included in the systematic reviews).
Under best-case scenarios, simulation studies suggest that such screening will miss more than half of infected individuals. Infrared temperature measurement is ineffective for mass screening for SARS-CoV-2 because of the low number of infected individuals who will have fever at the time of screening, as well as due to inconsistent technique by operators. Recent Office for National Statistics data on the prevalence of SARS-CoV-2 in the population show that the false positive rate is high (>95%). The major confounders regarding accuracy of temperature measurement are environmental temperature, humidity, gender, whether the person regularly exercises and age. Howe (2020) suggests that, if a patient's temperature needs to be taken, then tympanic temperature is more reliable than forehead temperature.
Genius 3 Tympanic Thermometer
The Genius 3™ Tympanic Thermometer is an adjusted mode ear thermometer that provides fast and accurate measurements of patient temperatures. The device is an in-ear canal thermometer which options for site-adjusted readings, namely oral and rectal temperatures.
The default mode of operation of the Genius 3 is the ear mode. This mode offers temperature measurements without adjustment, recording the actual temperature of the tympanic membrane in the range of 33°-42°C (91.4°-107.6°F). If the user chooses to use the oral or rectal modes, the temperature measurement reading is adjusted to display the oral or rectal equivalent, which differ very slightly. This is in contrast with most other tympanic thermometers, which display an estimate of oral of an oral-equivalent temperature as their default setting. The Genius 3 temperature readings are made using peak select technology, which records and analyses up to 100 temperature readings, selecting the highest one in 1–2 seconds.
The thermometer comes with a base that can store up to 32 single-use probe covers, which can be easily attached without the need to touch them, and a used probe is easily ejected into a waste container (Figure 1). The device can be switched between Fahrenheit and Celsius scales, with readings displayed on an LCD screen.
Figure 1. Genius 3 Tympanic Thermometer: attaching a single-use probe from the storage case, disposing a used cover and the probe's LCD display
From 2017, all thermometers must adhere to the new ISO 80601-2-56;2017 (https://www.iso.org/standard/67348.html) basic safety and performance standard. This replaced the previous ISO with strengthened requirements and test procedures for the verification of the laboratory accuracy of all types of electrical clinical thermometers and the validation of the clinical accuracy of the thermometer that operates in adjusted mode. Devices, such as the Genius 3, must meet the following criteria:
- Accuracy: +/-0.3°C
- Measurement response time: 1-2 seconds
- Ambient operating range: 16°C to 33°C (60.8°F to 91.4°F)
- Storage temperature range: -25° to 55°C
Box 1 summarises the main features of the Genius 3 thermometer.
Box 1.Features of the Genius 3 Tympanic Thermometer
- Accuracy +/-0.3°C
- Provides a temperature measurement in 1–2 seconds
- A programmable display allows the thermometer to be customised according to hospital protocol
- No-touch disposable, single-use probe covers are designed to prevent cross-contamination
- LCD temperature display screen
- F°/C° toggle button customises temperature read-outs to follow facility protocol
- Pulse timer allows for pulse and respiration monitoring on one single device
- Base stores up to 32 probe covers
- Recalibration required
- Extended battery life: one thermometer can take 15 000 readings on a full charge of 3AAA batteries
Source: Cardinal Health, 2019
Considerations
To ensure that thermometers remain within accuracy range and to reduce the risk of misdiagnosis or delay in treatment they need to be regularly recalibrated. In the case of the Genius 3 recalibration needs to be carried out periodically (Medicines and Healthcare products Regulatory Agency (MHRA), 2020). This to ensure that thermometers remain within their accuracy range and reduce the risk of misdiagnosis or treatment delay.
A further consideration could be the cost of the Genius 3 Tympanic Thermometer and the probe covers required for each single use. Although it may appear expensive in comparison with other tympanic thermometers, the device offers high accuracy and is non-patient; Because the Genius 3 is a non-invasive device, it is quick, comfortable and easy to use with both adults and children older than 4 months (MHRA, 2020). Younger children have smaller ear canals.
Case studies
The following case studies, which were undertaken by registered nurses in a large acute hospital in the UK, indicate that the Genius 3 Tympanic Thermometer is a front runner in thermometry due to its versatile and effective features, 2-second temperature recording time, temperature probe cover storage, and pulse and respiratory timer features, which are present all in a single device. The patients' names have been changed.
Case study 1
The Genius 3 Tympanic Thermometer was used to undertake a temperature reading of a patient who presented within an acute secondary care setting. Daniel Smith, a 39-year-old male patient, required a vital observation due to his shortness of breath and inability to talk in full sentences. The nurse used an ABCDE (airway, breath, circulation, disability, exposure) approach to provide a structured and systematic assessment.
The disability assessment, which checks neurology and consciousness, also includes temperature measurement. Mr Smith's temperature was taken from his ear following the manufacturer guidelines (Figure 1). In addition, the thermometer timer supports 1-minute timings, enabling the nurse to capture Mr Smith's respiratory rate and pulse rate. The nurse asked the patient if the device caused any distress, and the patient replied that he was comfortable and did not have any pain from the temperature probe. Within 2 seconds the assessment was completed and Mr Smith's temperature was recorded as 38.8°C. This indicated pyrexia and that Mr Smith required further investigations, with the result that blood cultures were performed in line with local hospital policy. He was diagnosed with community-acquired pneumonia.
The Genius 3 Tympanic Thermometer performed well; the hands-free, battery-powered probe applicator enabled rapid, clean agile measurement of Mr Smith's temperature. Most importantly, it helped to identify a fever (a body temperature of >38°C), which instigated further investigations and a diagnosis.
Case study 2
Michelle Barton, who is 26 years old, is receiving mental health treatment in a mental health trust. She presented to her mental health centre for her annual physical health check and, as part of the national and local COVID-19 guidelines the nurse took Ms Barton's temperature on arrival. Ms Barton reported that she had walked to the centre and, although it was cold outside, she was wearing lots of layers and was feeling very hot and sweaty.
Using the handheld infrared forehead thermometer, the nurse recorded Ms Barton's temperature as 32°C. Using clinical judgement, the nurse decided to recheck the temperature using a Genius 3 Tympanic Thermometer. The thermometer gave a reading of 37°C, which was a more accurate reading for a patient who had walked for 30 minutes to reach the clinic. To be sure of the accuracy of the temperature reading, the nurse took three readings. Ms Barton commented that the temperature check was comfortable.
The Genius 3 Tympanic Thermometer performed well, providing a quick and accurate temperature recording, which ensured that the nurse could continue with Ms Barton's annual physical health check.
Case Study 3
Lisa Oliveira is a 33-year-old female student studying nursing at university and, along with her peers, she was in lockdown in November last year. Over the winter months, Ms Oliveira and her peers have been worried about coronavirus, as well as the more usual seasonal infections such as common colds and flu.
Before joining her clinical placement Ms Oliveira was required to have an occupation health check with a nurse. Ms Oliveira mentioned to the nurse that she had been worried about going on placement during the COVID-19 pandemic and was feeling hot and anxious. The nurse took Ms Oliveira's vital observations, which were within normal parameters. Her temperature was 36.2°C. The nurse did not observe any physical abnormalities during this health check and was able to refer Ms Oliveira to the health and wellbeing team at the university to support her anxiety, as well as requesting that she contact her GP while the referral was being processes.
The nurse was asked for feedback on the Genius 3 Tympanic Thermometer and she responded that she was impressed by the timely and immediate temperature recording. She also liked the clear display and the three beeps as a prompt indicator that the temperature reading was ready.
Conclusion
Thermometry is vital in nursing practice for assessment and diagnosis and more recently as a core assessment for COVID-19. Early recognition of changes in temperature can lead to timely treatment, track interventions or side effects and improve outcomes for patients. The use of a tympanic thermometer, notably the Genius 3 Tympanic Thermometer, has proved to be accurate in temperature reading, easy to use and comfortable for patients.
KEY POINTS
- Understand the importance of temperature monitoring observations
- Understand the physiology of temperature regulation
- Be aware of the underpinning evidence for the use of thermometry. Temperature monitoring is a fundamental skill used by nurses in clinical practice. It is a vital sign that is significant and must be acknowledged as such. Using the right equipment and the correct route of measurement, ie the ear (tympanic thermometer), is important for obtaining accurate readings
- Ensure the patient has given consent for the procedure, that infection control policy has been followed, and that the relevant documentation is accurate and legible
- Escalate any concerns—and always advocate for your patient
CPD reflective questions
- On which parts of the body can body temperatures be recorded? Do you have the equipment to take body temperature, and what method could you use in those aged 5 years or older plus and those aged under 5 years?
- Are you aware of Sepsis Six guidance and, if so, do you have this education noted in your clinical setting? Consider organising a team to produce a project and poster about sepsis and the six steps to treat it
- Think about what thermometry devices you use in your clinical setting and explore all the functions, including the need for calibration. Consider arranging a teaching session for your colleagues