Background: We investigated how changes in partial pressure of brain tissue oxygenation (PbtO2) relate to end-tidal carbon dioxide (EtCO2) after pediatric traumatic brain injury (TBI). Methods: Dynamic structural equation modeling (DSEM) was used to investigate associations between EtCO2 and PbtO2, with positive associations indicating intact CO2 reactivity of PbtO2, and negative associations indicating impaired reactivity. Sub-analyses were performed to investigate associations of PbtO2 to intracranial pressure (ICP), arterial blood pressure (ABP) and cerebral regional oximetry (rSO2). Results: Among 14 patients, a positive association between PbtO2 and EtCO2 was demonstrated (SRC 0.05, 95% CI [0.04, 0.06]), with 9 patients demonstrating intact CO2 reactivity and 5 patients demonstrating impaired reactivity. Patients demonstrating intact CO2 reactivity had positive associations between PbtO2 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 CO2 reactivity had negative associations between PbtO2 and rSO2 (−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 CO2 reactivity, those with impaired reactivity had increased ICP (p < 0.0000), lower PbtO2 (p < 0.0000) and higher PRx (p = 0.0134). Conclusion: After TBI, CO2 reactivity of PbtO2 can be heterogenous, necessitating further work investigating factors contributing toward impaired reactivity.
Keywords: brain tissue oxygenation; carbon dioxide reactivity; traumatic brain injury.