Temporal Patterns in Brain Tissue and Systemic Oxygenation Associated with Mortality After Severe Traumatic Brain Injury in Children

Background: Brain tissue hypoxia is an independent risk factor for unfavorable outcomes in traumatic brain injury (TBI); however, systemic hyperoxemia encountered in the prevention and/or response to brain tissue hypoxia may also impact risk of mortality. We aimed to identify temporal patterns of partial pressure of oxygen in brain tissue (PbtO), partial pressure of arterial oxygen (PaO), and PbtO/PaO ratio associated with mortality in children with severe TBI.

Methods: Data were extracted from the electronic medical record of a quaternary care children's hospital with a level I trauma center for patients ≤ 18 years old with severe TBI and the presence of PbtO and/or intracranial pressure monitors. Temporal analyses were performed for the first 5 days of hospitalization by using locally estimated scatterplot smoothing for less than 1,000 observations and generalized additive models with integrated smoothness estimation for more than 1,000 observations.

Results: A total of 138 intracranial pressure-monitored patients with TBI (median 5.0 [1.9-12.8] years; 65% boys; admission Glasgow Coma Scale score 4 [3-7]; mortality 18%), 71 with PbtO monitors and 67 without PbtO monitors were included. Distinct patterns in PbtO, PaO, and PbtO/PaO were evident between survivors and nonsurvivors over the first 5 days of hospitalization. Time-series analyses showed lower PbtO values on day 1 and days 3-5 and lower PbtO/PaO ratios on days 1, 2, and 5 among patients who died. Analysis of receiver operating characteristics curves using Youden's index identified a PbtO of 30 mm Hg and a PbtO/PaO ratio of 0.12 as the cut points for discriminating between survivors and nonsurvivors. Univariate logistic regression identified PbtO < 30 mm Hg, hyperoxemia (PaO ≥ 300 mm Hg), and PbtO/PaO ratio < 0.12 to be independently associated with mortality.

Conclusions: Lower PbtO, higher PaO, and lower PbtO/PaO ratio, consistent with impaired oxygen diffusion into brain tissue, were associated with mortality in this cohort of children with severe TBI. These results corroborate our prior work that suggests targeting a higher PbtO threshold than recommended in current guidelines and highlight the potential use of the PbtO/PaO ratio in the management of severe pediatric TBI.