Correlation between brain tissue oxygen tension and regional cerebral oximetry in uninjured human brain under conditions of changing ventilation strategy

Controversy surrounds regional cerebral oximetry (rSO(2)) because extracranial contamination and unmeasured changes in cerebral arterial:venous ratio confound readings. Correlation of rSO(2) with brain tissue oxygen (PbrO(2)), a “gold standard” for cerebral oxygenation, could help resolve this controversy but PbrO(2) measurement is highly invasive. This was a prospective cohort study. The primary aim was to evaluate correlation between PbrO(2) and rSO(2) and the secondary aim was to investigate the relationship between changing ventilation regimens and measurement of PbrO(2) and rSO(2). Patients scheduled for elective removal of cerebral metastases were anesthetized with propofol and remifentanil, targeted to a BIS range 40–60. rSO(2) was measured using the INVOS 5100B monitor and PbrO(2) using the Licox brain monitoring system. The Licox probe was placed into an area of normal brain within the tumor excision corridor. FiO(2) and minute ventilation were sequentially adjusted to achieve two set points: (1) FiO(2) 0.3 and paCO(2) 30 mmHg, (2) FiO(2) 1.0 and paCO(2) 40 mmHg. PbrO(2) and rSO(2) were recorded at each. Nine participants were included in the final analysis, which showed a positive Spearman’s correlation (r = 0.50, p = 0.036) between PbrO(2) and rSO(2). From set point 1 to set point 2, PbrO(2) increased from median 6.0, IQR 4.0–11.3 to median 22.5, IQR 9.8–43.6, p = 0.015; rSO(2) increased from median 68.0, IQR 62.5–80.5 to median 83.0, IQR 74.0–90.0, p = 0.047. Correlation between PbrO(2) and rSO(2) is evident. Increasing FiO(2) and PaCO(2) results in significant increases in cerebral oxygenation measured by both monitors.