Monitoring brain tissue oxygen tension in brain-injured patients reveals hypoxic episodes in normal-appearing and in peri-focal tissue

Objective: We compared brain tissue oxygen tension (PtiO₂) measured in peri-focal and in normal-appearing brain parenchyma on computerized tomography (CT) in patients following traumatic brain injury (TBI). Design: Prospective observational study. Setting: Neurointensive care unit. Patients and participants: Thirty-two consecutive TBI patients were subjected to PtiO ₂ monitoring. Interventions: Peri-focal tissue was identified by the presence of a hypodense area of the contusion and/or within 1 cm from the core of the contusion. The position of the tip of the PtiO₂ probe was assessed at follow-up CT scan. Measurements and results: Mean PtiO₂ in the peri-contusional tissue was 19.7 ± 2.1 mmHg and was lower than PtiO₂ in normal-appearing tissue (25.5 ± 1.5 mmHg, p <0.05), despite a greater cerebral perfusion pressure (CPP) (73.7 ± 2.3 mmHg vs. 67.4 ± 1.4 mmHg, p <0.05). We observed both in peri-focal tissue and in normal-appearing tissue episodes of brain hypoxia (PtiO ₂ <20 mmHg for at least 10 min), whose median duration was longer in peri-focal tissue than in normal-appearing tissue (51% vs. 34% of monitoring time, p <0.01). In peri-focal tissue, we observed a progressive PtiO ₂ increase from pathologic to normal values (p <0.01). Conclusions: Multiple episodes of brain hypoxia occurred over the first 5 days following severe TBI. PtiO₂ was lower in peri-contusional tissue than in normal-appearing tissue. In peri-contusional tissue, a progressive increase of PtiO₂ from pathologic to normal values was observed over time, suggestive of an improvement at microcirculatory level.