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In this third post in an occasional series questioning some of the basics of paediatric assessment, we will look at measuring temperature in children.  It’s one of the few vital signs that parents measure themselves before entering the emergency department. But just how accurate is their assessment?

When a neonate is brought into the department, it can really make a difference if their temperature is normal or just a few points of a degree over.  Those extra digits may mean the difference between a watchful eye, careful safety netting, and a full septic workup. When a 2-year-old is brought in following a seizure, a fever may mean you are less likely to do a full workup. (Editors note: though afebrile febrile seizures can occur).

Everybody’s got the fever, that is something you all know
Fever isn’t such a new thing, fever started long ago

He feels warm to me…

Whenever I was ill as a child, my mother would put her cool hand on my forehead, declare, “You don’t have a fever,” and package me off to school. Was she right to do that? Is a caregiver’s touch enough to determine if a child is febrile or not?

A 1984 study found that mothers correctly identified that their child had a fever 52.3% of the time (though at least they were better at recognising when there was no fever, being right 93.9% of the time). When the study authors limited the results to children under two years of age, mothers were much more accurate and picked up 90% of cases. Bonadio et al., reassuringly, found that children with a reported temperature at home but not in the emergency department were highly unlikely to have a serious bacterial illness. However, one African study using mothers and medical students found that they could detect a fever on 4 out of 5 occasions but also overestimated its presence.

Mercury thermometers have fallen by the wayside now, and parents have many other means to check their children’s temperature. Scientists, trying to improve on what nature has given us – the hand – have developed a plastic-encased strip with thermophototropic chemicals that respond to changes in skin temperature. A study of one brand found that only detected 13 out of 40 children with a fever. Could mother know best?

Most guidelines, including the NICE guidelines, suggest that the parents’ subjective perception should be considered valid and taken seriously by healthcare providers.

Does how the baby is dressed make a difference?

Most studies that look at this really common question involve small numbers of participants. Bundling up a child in layers and layers of swaddling may raise the skin temperature by up to 2.5°C with a minimal rise in rectal temperature.

Does it matter where the thermometer is put?

The current NICE guidelines make the following recommendations:-

In infants under 4 weeks, measure body temperature with an electronic thermometer in the axilla [2007]

In children aged 4 weeks to 5 years, use one of the following:-

The Royal Children’s Hospital in Melbourne defines a fever as a rectal temperature greater than 38°C.

Deviation of measured temperature from true core – after Robinson JL, Seal RF, Spady DW, Joffres MR. Comparison of esophageal, rectal, axillary, bladder, tympanic, and pulmonary artery temperatures in children. The Journal of pediatrics. 1998 Oct 31;133(4):553-6

It can be difficult to measure the temperature in a child, especially a cranky, wriggly one.  For most parents of a modern generation, a thermometer up the bottom is not an acceptable way to take it. Several studies have compared different sites to a reference standard to determine the gap between the core and the outside world.  Many of these were done in the days of mercury thermometers and showed an unacceptable variation between sites, even when the temperature was repeated at the same site. The most accurate data comes from experimental studies in small groups of children undergoing cardiac surgery.

Axillary

The axillary temperature may be altered by a number of environmental and physiological factors. As the thermometer does not directly overlie the axillary artery, it may cause localized cooling and a falsely low reading. Chemical dot thermometers may differ formal readings by ±0.4 degrees, though they have not been compared with a gold (or even brass standard). An axillary thermometer has a sensitivity of around 30%. With such poor sensitivity, surprisingly, NICE recommends it.

Rectal

Whilst rectal temperatures are still taken, especially in neonates, they may lag behind core temperature (as determined by a pulmonary artery or oeseophageal temperature detection) and be an inaccurate indicator of febrile status. It is easy to appreciate how the recorded temperature may vary according to how far the probe has been inserted and in the presence or absence of stool.  Rectal temperature is also slow to change in reaction to changes in blood temperature (as demonstrated in anaesthetized cardiac cases).

Oral

Parents can use both simple electronic and pacifier (dummy)- based devices, but the challenge is often getting the child to suckle long enough for a temperature to register.

Tympanic

Theoretically, the tympanic membrane temperature approximates the hypothalamus’s temperature (the centre for thermoregulation). Under correct operating conditions, it certainly appears to be more accurate than axillary or rectal measurements. Improved accuracy can be achieved by pretending the thermometer is an otoscope and pulling back on the pinna in the same way, thus allowing the instrument to visualize the tympanic membrane. Those available for purchase and home use do not mention this in their instructions, so caregivers may under-report the fever.

And what about those magic wands we have in hospital?

Those ‘magic wands’ or temporal artery thermometers (TATs), as they are actually called, work by detecting the heat radiated by the skin over the temporal artery. A meta-analysis published in BMJ Open earlier this year found a significant deviation in the level of agreement between TATs and reference standards in the order of ±1°C.

There is a real challenge when it comes to parsing all of this. So many of the studies compare one technique with another, which is already inaccurate, and only those studies that compare a peripheral method with a true core method hold much validity. Even when this is considered, it seems that most methods overestimate at lower temperatures and underestimate at higher ones. With sensitivities for some devices reported to be as low as 22%, we might miss four out of five children with a fever!

What does all of this mean for me?

Mothers are generally very good at knowing if their child has a fever (as long as the child is under two; otherwise, you might as well just flip a coin). Most home methods of determining temperature, such as forehead strips and off-the-shelf in-ear thermometers, are not sufficiently accurate and so should be considered another data point, not an absolute.

When measuring temperature in hospitals, the methods suggested by NICE are NOT the most accurate and are compared to a brass rather than gold standard (rectal temp versus oesophageal or PA temp).

It seems (to me, at least) that tympanic membrane thermometry (if performed correctly – pull the pinna back) is the most accurate method until something more high-tech comes along. Perhaps something like a contactless thermal imaging camera?

Apologies to our American cousins

Given that the scale, first devised by German physicist Daniel Fahrenheit in 1724, is only used in a small part of the world, I’ve stuck to Celsius in this post. If you want to know more about this scientific schism so you can sound more erudite at your next dinner party, then read this article.

References

Craig JV, Lancaster GA, Williamson PR, Smyth RL. Temperature measured at the axilla compared with rectum in children and young people: a systematic review. BMJ. 2000 Apr 29;320(7243):1174-8.

Keeley D. Taking infants’ temperatures. BMJ: British Medical Journal. 1992 Apr 11;304(6832):931.

Muma BK, Treloar DJ, Wurmlinger K, Peterson E, Vitae A. Comparison of rectal, axillary, and tympanic membrane temperatures in infants and young children. Annals of emergency medicine. 1991 Jan 31;20(1):41-4.

Robinson JL, Seal RF, Spady DW, Joffres MR. Comparison of esophageal, rectal, axillary, bladder, tympanic, and pulmonary artery temperatures in children. The Journal of Pediatrics. 1998 Oct 31;133(4):553-6.

Jefferies S, Weatherall M, Young P, Beasley R. A systematic review of the accuracy of peripheral thermometry in estimating core temperatures among febrile critically ill patients. Critical Care and Resuscitation. 2011 Sep;13(3):194.

Allegaert K, Casteels K, Van Gorp I, Bogaert G. Tympanic, infrared skin, and temporal artery scan thermometers compared with rectal measurement in children: a real-life assessment. Current Therapeutic Research. 2014 Dec 31;76:34-8.

Davis T. NICE guideline: feverish illness in children—assessment and initial management in children younger than 5 years. Archives of disease in childhood-Education & practice edition. 2013 Sep 17:edpract-2013.

Reynolds M, Bonham L, Gueck M, Hammond K, Lowery J, Redel C, Rodriguez C, Smith S, Stanton A, Sukosd S, Craft M. Are temporal artery temperatures accurate enough to replace rectal temperature measurement in pediatric ED patients?. Journal of Emergency Nursing. 2014 Jan 31;40(1):46-50.

Niven DJ, Gaudet JE, Laupland KB, Mrklas KJ, Roberts DJ, Stelfox HT. Accuracy of peripheral thermometers for estimating temperature: a systematic review and meta-analysis. Annals of internal medicine. 2015 Nov 17;163(10):768-77.

Reisinger KS, Kao J, Grant DM. Inaccuracy of the Clinitemp skin thermometer. Pediatrics. 1979 Jul 1;64(1):4-6.

Banco L, Veltri D. Ability of mothers to subjectively assess the presence of fever in their children. American Journal of Diseases of Children. 1984 Oct 1;138(10):976-8.

Callanan D. Detecting fever in young infants: reliability of perceived, pacifier, and temporal artery temperatures in infants younger than 3 months of age. Pediatric emergency care. 2003 Aug 1;19(4):240-3.

BONADIO WA, HEGENBARTH M, ZACHARIASON M. Correlating reported fever in young infants with subsequent temperature patterns and rate of serious bacterial infections. The Pediatric infectious disease journal. 1990 Mar 1;9(3):158-60.

El-Radhi AS, Barry W. Thermometry in paediatric practice. Archives of disease in childhood. 2006 Apr 1;91(4):351-6.

Whybrew K, Murray M, Morley C. Diagnosing fever by touch: observational study. BMJ. 1998 Aug 1;317(7154):321-30.

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