Increased Brain Tissue Oxygen Monitoring Threshold to Improve Hospital Course in Traumatic Brain Injury Patients

Introduction This article is a retrospective analysis of the neurosurgical census at our institution to determine an optimal threshold for brain tissue oxygenation (PbtO2). The use of brain tissue oxygen monitoring has been in place for approximately three decades but data suggesting optimal thresholds to improve outcomes have been lacking. Though there are multiple modalities to monitor cerebral oxygenation, the monitoring of brain tissue oxygen tension has been deemed the gold standard. Still, it is not clear exactly how reductions in PbtO2 should be treated or what appropriate thresholds to treat might be. The aim of our study was to determine if our threshold of 28 mmHg for a good functional outcome could be correlated to the Glasgow Coma Scale (GCS) and Glasgow Outcome Scale (GOS). Methods A retrospective analysis of the Arrowhead Regional Medical Center (ARMC) Neurosurgery Census was performed. Patients from 2017-2019 who had placement of Licox® cerebral oxygen monitoring sensors (Integra® Lifesciences, Plainsboro Township, New Jersey) were included in the analysis. Fifteen patients were consecutively identified, all of which presented with traumatic brain injury (TBI). Data on age, gender, days in the intensive care unit (ICU), days before discharge or end of medical care, admission GCS, hospital length of stay, GOS, maximum and minimum PbtO2 values for five days following insertion, minimum and maximum intracranial pressures (ICPs), and brain temperature were included for analysis. Patient data were separated into two groups; those with consistently higher PbtO2 scores (≥ 28 mmHg; n = 7) and those with inconsistent/lower PbtO2 scores (< 28 mmHg; n = 8). Standard student t-tests were used to find potential statistical differences between the groups (α = 0.05). Results There were seven patients in the consistently high PbtO2 category (≥ 28 mmHg) and eight patients in the inconsistent/low PbtO2 category (<28 mmHg). The average maximum and minimum PbtO2 for the group displaying worse outcomes (as defined by GCS/GOS) was 23.0 mmHg and 14 mmHg, respectively. Those with consistent Day 2 PbtO2 scores of ≥ 28 mmHg had significantly higher GCS scores at discharge/end of medical care (p < 0.05). Average GCS for the patient group with >28 mmHg PbtO2 averaged over Days 2-5 group was 11.4 (n=7). Average GCS for the <28 group was 7.0 (n=8). The GCS for the >28 group was 63% higher than found in the <28 group (p = 0.03). GOS scores were significantly higher in those with consistently higher PbtO2 (≥ 28) than those with lower PbtO2 scores (< 28). The averages were 3.5 in the higher PbtO2 group as compared to 2 in the lower PbtO2 group. Conclusion Along with ICP monitors and monitoring in the assessment of CPP, brain tissue oxygenation allows yet another metric by which to optimize treatment in TBI patients. At our institution, a PbtO2 level of ≥ 28 mmHg is targeted in order to facilitate a good functional outcome in TBI patients. Keeping patients at this level improves GCS and GOS at discharge/end of medical treatment.