Differences in Intracranial Temperature Measurements – A Systematic Analysis Between the Licox® and Hemedex® Systems

Background: Multimodality brain monitoring includes intracranial temperature (ICT) measurements.Different ICT readings have been reported from Licox ® and Hemedex ® systems used in the same patient with the Hummingbird ® "SynergyDuo Ventricular" introducer.Methods: To investigate the differences we report an analysis of causes for different ICT readings.In keeping with the radial brain ICT gradient model model we calculated ICTs according to the sensors' penetration depths and compared the results to clinical data from six patients.Results: The ICT accuracy is ±0.2°C for Licox ® and ±0.3°C for Hemedex ® so any ICT difference ±0.5°C between the systems is not significant.The Hemedex ® -ICT sensor is placed 15.5mm deeper than the Licox ® -ICT sensor with the Hummingbird ® .The calculated ICT from the model range from -0.7°C to -1.0°C for a 37.5°C arterial temperature, and a 22°C ambient temperature.The ICT (ICT Licox ® -ICT Hemedex ® ) in six patients were -0.6°C,SD = 0.7°C, median = -0.6°C,max = 0.4°C, min = -5.7°C,range 6.1°C.41.1% of recorded data lie within the accuracy range of ±0.5°C.53.8% lie within a range between -0.5°C and -1.5°C, and represent the differences which can be explained by different sensor insertion depths and the model.Only 5% were outliers with ICT < -1.5°C.Conclusions: This study shows that the discrepancy in ICT measurements using different sensors can be explained by (a) the ICT measurement accuracies/specifications, and (b) different insertion depths.Other causes may include (c) environmental conditions and (d) unknown factors secondary to body -and/or brain physiology.