175 In Vitro Closed System Determination of Licox® Physiological Variables Sensitivity

INTRODUCTION: In Traumatic Brain Injuries can result in low brain tissue oxygen tension (PbtO2) and poor clinical outcomes in TBI patients. The Integra® Licox® brain tissue oxygen monitor is an FDA-approved clinical tool used to monitor PbtO2. METHODS: Using an isolated experimental chamber containing saline solution and bicarbonate buffer, in vitro Licox® probe readouts of oxygen partial pressure (pO2) were recorded while manipulating salinity, total hydrostatic pressure, and pH individually to determine the overall effect that on measured pO2 levels. RESULTS: Licox® probe readouts indicated increasing pO2 values with increasing salinity in a statistically significant and linear manner (p<0.05). Licox® probe readouts had no measurable effect across physiologic pH ranges on measured pO2 (p>0.05). There was no statistically significant difference in Licox readouts versus pH when tested in solutions with a pO2 of 20mmHg, 35mmHg and 50 mmHg (p >0.05). In buffered saline solutions of pO2 of 10 mmHg, 20 mmHg, 35 mmHg, and 50 mmHg, Licox® readouts did not differ in a statistically significant manner between hydrostatic pressures 0 mmHg above atmospheric pressure to 70 mmHg above atmospheric pressure (p>0.05). CONCLUSIONS: Hydrostatic pressure and pH alone do not have any appreciable effect on the accuracy of the Integra® Licox® brain tissue oxygen monitor. While salinity may influence measured oxygen values, this effect is modest in magnitude, and rather reflect a transient increase in pO2 as oxygen diffuses out of solution with increasing salinity. In the clinical setting, changes in PbtO2 as measured by Licox® probes represent true alterations in local brain tissue oxygenation.