Not all monitors give you the same numbers! The physiological idea behind cerebral oxygen monitoring is that the PbrO 2 value accurately represents the balance between oxygen delivery and oxygen consumption in brain cells, and that changes in PbrO 2 will therefore reflect pathophysiological alterations. These changes could then be used to guide treatments to prevent or mitigate hypoxic injury [56] . PbrO 2 has been frequently monitored using a Licox system (LX, Integra Neuroscience, Biot, France), the only available device until a couple of years ago. Recently, a different manufacturer (Raumedic, Münchberg, Germany) introduced a new probe, the Neurovent-PTO (NV). Dengler [57] compared the performance of the two systems in 11 comatose traumatic brain injury (TBI) or aSAH patients during dynamic changes in inspirational oxygen fraction and mean arterial pressure. PbrO 2 was recorded continuously in patients using the two probes which were placed side-by-side in the same cerebrovascular region. Once a steady baseline value was reached, FiO 2 was increased by 20% for 10 min. Once the baseline was again achieved, MAP was increased by 20 mmHg for 10 min. The PbrO 2 values of both probes differed significantly at all times. The LX probe reacted significantly faster to changes in FiO 2 and MAP. Limits of agreement ranged between -32.1 and 20.0 mmHg. Mean LX values were 6.1 mmHg lower than NV values. Even if the examined patient cohort was rather small, the data suggest that LX and NV probes measure different PbrO 2 values in routine monitoring as well as during phases of dynamic changes in FiO 2 and MAP. These data therefore do not support the view that both probes can be used interchangeably. The practical advice for the clinician is to be aware of the performance of the system they are using and to adapt treatment thresholds accordingly.