In Vitro Closed System Determination of Licox® Temperature Sensitivity

Introduction: Acute Traumatic Brain Injuries (TBI) are commonly associated with transient or sustained brain tissue hypoxia leading to neuronal damage and poor outcomes. Currently, the Integra® Licox® brain tissue oxygen monitor is an FDA-approved device used to monitor brain tissue oxygenation (PbtO2) in humans.

Methods: Confidence for use of the Licox® in critically ill patients is dependent on understanding the impact of tissue factors such as salinity, pH, hydrostatic pressure, and temperature on device performance and measurement of tissue oxygen partial pressure (pO2). Our study focused on the performance of the Licox® probe with variations in temperature within the physiological range. Using a closed system in vitro model, temperature was altered to determine its influence on Licox® performance over a range of pO2 and hydrostatic pressure values.

Results: The probe was found to be sensitive to warming and high temperatures in saline buffer solutions with pO2 values between 10-40mmHg. This was described by a linear (p < 0.0001) rise in pO2 with temperature. The pO2 for all saline buffer solutions rose by 0.75 ± 0.086mmHg/oC (p < 0.0001) during heating. The device was less sensitive to cooling although a negative trend was observed for the same range of pO2 values. There were no differences between the slopes of the warming curves for variations in hydrostatic pressure at pO2 of 20 mmHg (p> 0.05).

Conclusion : In our closed system model, the Licox® probe exhibited significant variations in output with alterations in temperature at fixed levels of O2. These variations are similar in magnitude with those reported in vivo by who found a (ΔPbtO2 = 0.9 ± 6.1 mmHg, p = 0.022) when TBI patients experienced episodes of temperature increases (Rass et.al.,2021). These results suggest that variations in measured values of PbtO2 during periods of temperature change may reflect aspects of instrumentation performance rather than fluctuations in tissue O2 metabolism.