Vital Signs : Temperature measurement


The largest volume of research identified during the  literature search   addressed   various aspects     of      temperature measurement.  These  studies highlight  the  large  range  of methods  and  body  sites  that are used for the measurement of  temperature  (see  table three).  Because  of  the  volume of  research,  comparisons  of different  temperature measurement  methods  will  be summarised  as  a  separate systematic review. Summarised in  this  practice  information sheet  are  studies  addressing aspects of oral, rectal axillary and tympanic temperatures. 

General Issues
While  much  attention  has focused   on   measurement accuracy, one study evaluated touch as a screen for fever and found  that  while  mothers  and medical students overestimated the  incidence  of  fever  when using touch, they rarely missed its  presence  in  a  child.  The results  of  this  study  perhaps challenge  the  current  focus  of research  on  the  accuracy  of measurements  using  tenths  of a  degree,  when  simple  touch is  an  accurate  measure  for fever.  The  use  of  temperature as a discharge criterion for an ambulatory  surgical  unit  has been   studied,   but   results suggest  it  is  not  useful  in neither     rapid     or     deep differentiating  readiness  for Oral Temperatures Studies  evaluating  measurements from the different areas of the mouth recommend using either the right or left posterior sublingual  pocket,  as  these result   in   higher   recorded temperatures. 



Evaluation  of  the  impact  of oxygen    therapy    on    oral temperatures  have  reported contradictory results regarding its  statistical  significance, however  no  study  reported  a clinically  significant  effect. 

Similarly, different  rates  of oxygen flow, from 2 litres to 6 litres per minute, and warmed or  cooled  inspired  gas,  were found not to have an influence on oral temperature measurements.  Two  studies found  that  rapid  respiratory rates had a small influence on oral  temperatures,  but  these results  were  contradicted  by another   study   that   found breathing,     alone     or in combination, had any significant   effect   on   oral temperatures.

Studies   have   shown   that drinking hot or cold water has a    significant    impact    on recorded  oral  temperatures, and  it  has  been  suggested waiting 15 to 20 minutes after drinks  to  ensure  accuracy. Smoking does not change oral temperature measurements.
Researchers have evaluated the of the temperature accuracy time  required  for  mercury thermometers  to  accurately record   the   person's   oral temperature. One study found that with healthy adults, using a  two  minute  insertion  time resulted    in    27%    of    the temperature  readings  having an  error  of  at  least  0.3°C.  A study  assessing  thermometer insertion  time  in  afebrile  and febrile adults, suggested a six minute  insertion  time  as  a compromise  between  optimal time  and  clinical  practicality while another recommended a seven minute insertion time to ensure the majority of afebrile and  febrile  temperatures  are correctly recorded. However, a survey  of  nurses  showed  that most     left     the     mercury thermometer  in  the  mouth  for less than 3 minutes.

Axillary Temperature
There has been only limited re- search  focusing  on  axillary temperatures.   One   study evaluated axillary temperature measurements  in  elderly  females, and found great variation  between  individuals.
While  the mean axillary temperatures were approximately 36°C, the wide range of tem- peratures  encountered  prevented  the  identification  of  a single figure that could be considered  the  "normal"  axillary temperature.  Another  study evaluated  the  influence  of  intravenous infusions, via upper limbs of neonates, on axillary temperatures and found there was little significance in terms

Tympanic Temperature
There has been considerable research addressing tympanic temperature measurements ranging from the influence of infection and cerumen on measurement accuracy, to optimal technique. Studies have evaluated the impact of otitis media on tympanic temperatures and suggest it has little effect. While some studies have reported a statistically significant difference in tympanic temperatures between ears in people with unilateral otitis media, this difference was approximately 0.1°C and so of little clinical importance. The presence of cerumen  does  influence  tympanic  temperature  readings,  and  while  results  are  variable,  they  suggest  a significant  proportion  of the  temperature readings taken from  the occluded ear  will be  more  than 0.3°C lower than the ear that is not occluded.
Studies  evaluating  technique  suggest  an  ear  tug  should  be  used  during  the  measurement  of  tympanic temperatures, as this is reported to straighten the external auditory canal. Failure to use the ear tug means infrared thermometers are only partially directed at  the  tympanic membrane. The tug technique  in adults has  been described  as  pulling  the  pinna  (auricle  of  ear)  in  an  upward  and  backward  direction,  and  in infants it is pulling the pinna in a backward direction.
Evaluations  of  the  impact  of  ambient  temperatures  on  tympanic  temperatures  suggest  that  while  a  hot environment can significantly affect readings, cold appears to have little effect.
Cost  analyses of the different  temperature measurement methods suggest  infrared measurements may be the  most  cost  effective  despite  the  greater  initial  costs.  These  savings  are  the  result  of  the  rapid  reading capabilities of these instruments, and the labour cost savings that result.

Rectal Temperature
Many  studies  have  compared  the  different  methods  of  temperature  measurement,  and  commonly  rectal temperatures are used as the standard comparison. However, these studies will be summarised in a separate systematic  review.  The  most  common  reported issue  related  to  rectal temperature  measurement  is  that  of rectal perforation, which appears to be a risk primarily for the newborn and very young. Other reported complications include peritonitis secondary to rectal perforation, and one case of intra-spinal migration of a rectal thermometer in a two year old, which broke during routine rectal temperature measurement. A ten year  review of hospital records identified 16 children admitted to a surgical unit  with broken or  retained rectal thermometers. In response to this problem axillary temperature measurements have been recommended in  preference  to  the  rectal  measurements.  With  the  advent  of  infrared  tympanic  thermometers,  these complications are likely to become less common.





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