Abstract
Object
Periods of brain tissue ischemia are common after severe head injury, and their occurrence and duration are negatively correlated with outcome. Accurate and reliable measurement of brain tissue oxygenation (Bti pO2) may be a key to improve patient outcome after severe head injury. Knowledge of stability and accuracy of the Bti pO2 systems is crucial. We have therefore conducted a bench test study of new Neurovent-PTO® (NV) and Licox® (LX) oxygen tension catheters to evaluate the sensor accuracy, response time to different oxygen tensions, response to temperature changes and long-term stability.
Methods
For all experiments five new fluorescent NV sensors and five new electrochemical LX sensors were used. The catheter probes were placed into a container filled with a buffer solution. The solution was equilibrated with five high precision calibration gases. The accuracy of the probes was recorded after an equilibration period of 20 min in O2 concentrations of 5, 10, 20, 30 and 40 mmHg at 37.0 ± 0.2°C. The probe response to an increase in temperature from 37.0°C to 38.5°C to 40.0°C in two different gases with O2 concentrations of 10 and 20 mmHg were analysed. We also recorded the time for reaching 90% of a new oxygen concentration level when switching from one concentration to another. Finally, to test if there was a time-dependant drift in pO2 recordings, all sensors were left in 10 mmHg O2 solution for 10 days, and recordings were taken every 24 h.
Results
In all gas concentrations, NV and LX sensors measured pO2 with high accuracy and stability in vitro (mean differences from calculated values were for NV 0.76–1.6 mmHg and for LX −0.46–0.26 mmHg). Both sensors showed a shorter response time to pO2 increase (for NV 56 ± 22 s and for LX 78 ± 21 s) compared to pO2 decrease (for NV 131 ± 42 s and for LX 215 ± 63 s). NV pO2 values were more stable for changes in temperature, while LX sensors showed larger standard deviations with increasing temperature (the difference from the calculated values in 19.7 mmHg O2 at 40°C were for NV probes between 0.5 and 1.7 mmHg and LX between −2.3 and 1.9 mmHg). Both sensors gave stable results with low standard deviations during long-term (10 days) use, but with a slight elevation of measured pO2 levels by time.
Conclusions
Both NV and LX were accurate in detecting different oxygen tensions, and they did not deviate over longer recording times. However, LX needed a significantly longer time to detect changes in pO2 levels compared to NV. Furthermore, LX probes showed an increased standard deviation with higher temperatures.
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Acknowledgements
The study was supported by The Swedish Research Council. We would like to acknowledge Lars Berglund, Ph.D., Uppsala Clinical Research Center, Uppsala University for statistical advice.
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Financial support: Swedish Research Council
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Purins, K., Enblad, P., Sandhagen, B. et al. Brain tissue oxygen monitoring: a study of in vitro accuracy and stability of Neurovent-PTO and Licox sensors. Acta Neurochir 152, 681–688 (2010). https://doi.org/10.1007/s00701-009-0532-x
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DOI: https://doi.org/10.1007/s00701-009-0532-x