Reliability issues in human brain temperature measurement
IntroductionThe influence of brain temperature on clinical outcome after severe brain trauma is currently poorly understood. When brain temperature is measured directly, different values between the inside and outside of the head can occur.
It is not yet clear if these differences are 'real'or due to measurement error.
Methods: The aim of this study was to assess the performance and measurement uncertainty of body and brain temperature sensors currently in use in neurocritical care. Two organic fixed-point, ultra stable temperature sources were used as the temperature references.
Two different types of brain sensor (brain type 1 and brain type 2) and one body type sensor were tested under rigorous laboratory conditions and at the bedside. Measurement uncertainty was calculated using internationally recognised methods.
Results: Average differences between the 26degreesC reference temperature source and the clinical temperature sensors were +0.11degreesC (brain type 1), +0.24degreesC (brain type 2) and -0.15degreesC (body type), respectively.
For the 36degreesC temperature reference source, average differences between the reference source and clinical thermometers were, -0.02degreesC, +0.09degreesC and -0.03degreesC for brain type 1, brain type 2, and body type sensor, respectively. Repeat calibrations the following day confirmed that these results were within the calculated uncertainties.
The results of the immersion tests revealed that the reading of the body type sensor was sensitive to position, with differences in temperature of -0.5degreesC to -1.4degreesC observed on withdrawing the thermometer from the base of the isothermal environment by 4 cm and 8 cm respectively. Taking into account all the factors tested during the calibration experiments, the measurement uncertainty of the clinical sensors against the (nominal) 26degreesC and 36degreesC temperature reference sources for the brain type 1, brain type 2 and body type sensors were +/-0.18degreesC, +/-0.10degreesC and +/-0.12degreesC, respectively
Conclusions: The results show that brain temperature sensors are fundamentally accurate and the measurements are precise to within 0.1-0.2degreesC.
Subtle dissociation between brain and body temperature in excess of 0.1-0.2degreesC is likely to be real. Body temperature sensors need to be secured in position to ensure that measurements are reliable.
Author: Charmaine ChildsGraham Machin
Credits/Source: Critical Care 2009, 13:R106
Published on: 2009-07-02
Copyright by the authors listed above - made available via BioMedCentral (Open Access). Please
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