Carbon Dioxide Reactivity of Brain Tissue Oxygenation after Pediatric Traumatic Brain Injury

Background: We investigated how changes in partial pressure of brain tissue oxygenation (PbtO(2)) relate to end-tidal carbon dioxide (EtCO(2)) after pediatric traumatic brain injury (TBI). Methods: Dynamic structural equation modeling (DSEM) was used to investigate associations between EtCO(2) and PbtO(2), with positive associations indicating intact CO(2) reactivity of PbtO(2,) and negative associations indicating impaired reactivity. Sub-analyses were performed to investigate associations of PbtO(2) to intracranial pressure (ICP), arterial blood pressure (ABP) and cerebral regional oximetry (rSO(2)). Results: Among 14 patients, a positive association between PbtO(2) and EtCO(2) was demonstrated (SRC 0.05, 95% CI [0.04, 0.06]), with 9 patients demonstrating intact CO(2) reactivity and 5 patients demonstrating impaired reactivity. Patients demonstrating intact CO(2) reactivity had positive associations between PbtO(2) and ICP (0.22 [0.21, 0.23]), whereas patients with impaired reactivity had negative associations (−0.28 [−0.29, −0.28]). Patients demonstrating intact CO(2) reactivity had negative associations between PbtO(2) and rSO(2) (−0.08 [−0.09, −0.08]), whereas patients with impaired reactivity had positive associations (−0.15 [0.14, 0.16]). Compared to patients with intact CO(2) reactivity(,) those with impaired reactivity had increased ICP (p < 0.0000), lower PbtO(2) (p < 0.0000) and higher PRx (p = 0.0134). Conclusion: After TBI, CO(2) reactivity of PbtO(2) can be heterogenous, necessitating further work investigating factors contributing toward impaired reactivity.