The role of lung function in brain tissue oxygenation following traumatic brain injury

Object. Previous studies have demonstrated that periods of low brain tissue oxygen tension (PbtO(2)) are associated with poor outcome after head trauma but have primarily focused on cerebral and hemodynamic factors as causes of low PbtO(2). The purpose of this study was to investigate the influence of lung function on PbtO(2) with an oxygen challenge (increase in fraction of inspired oxygen [FiO(2)] concentration to 1.0). Methods. This prospective observational cohort study was performed in the neurointensive care unit of the Level I trauma center at San Francisco General Hospital. Thirty-seven patients with severe traumatic brain injury (TBI) undergoing brain tissue oxygen monitoring as part of regular care underwent an oxygen challenge, consisting of an increase in FiO(2) concentration from baseline to 1.0 for 20 minutes. Partial pressure of arterial oxygen (PaO2), PbtO(2), and the ratio of PaO2 to FiO(2) (the PF ratio) were determined before and after oxygen challenge. Results. Patients with higher PF ratios achieved greater PbtO(2) during oxygen challenge than those with a low PF ratio because they achieved a higher PaO2 after an oxygen challenge. Lung function, specifically the PF ratio, is a major determinant of the maximal PbtO(2) attained during an oxygen challenge. Conclusions. Given that patients with TBI are at risk for pulmonary complications such as pneumonia, severe atelectasis, and adult respiratory distress syndrome, lung function must be considered when interpreting brain tissue oxygenation.