2070 In Vitro Closed System Determination of Licox® Temperature Sensitivity

INTRODUCTION: Acute Traumatic Brain Injuries (TBI) can result in brain tissue hypoxia leading to neuronal damage. The Integra® Licox® oxygen monitor, is an FDA-approved brain tissue monitor that uses Clark polarographic electrodes to measure brain oxygenation (PbtO2) in humans. METHODS: Using an isolated experimental chamber containing saline solution and bicarbonate buffer, in vitro Licox® probe readouts of pO2 were recorded while heating and cooling solution to determine the overall effect that changes in temperature would have on measured pO2 levels. RESULTS: For pO2 values between 10-40 mmHg, the probe was sensitive to warming in saline buffer solutions indicated by a positive linear relationship (p<0.0001). Solutions at equilibrium at 10 mmHg, 20 mmHg, 30 mmHg, and 40 mmHg pO2 rose by Δ pO2 1.05 ± 0.081 mmHg/oC, Δ pO2 1.11 ± 0.035 mmHg/°C, Δ pO2 0.97 ± 0.026 mmHg/°C, Δ pO2 0.73 ± 0.06 ± 0.026 mmHg/°C respectively. When the same buffer solutions were cooled, there was a less significant negative linear trend observed for the same range of pO2 values (p<0.001). Licox® readouts were not statistically significant between hydrostatic pressures of 5 mmHg, 15 mmHg, or 25 mmHg above atmosphere (p > 0.05). CONCLUSIONS: 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 who found a (Δ PbtO2 = 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 temperature changes may reflect aspects of instrumentation performance as opposed to clinically relevant fluctuations in tissue O2 metabolism.