[[Partial pressure of Oxygen]], that is, amount of oxygen in the blood (normally referred to as Dissolved Oxygen).

Monitoring the partial pressure of oxygen in brain tissue ([[PbtO2]]) is an important tool for traumatic brain injury (TBI) but is invasive and inconvenient for real-time monitoring. 

[[Near-infrared spectroscopy]] (NIRS), which can monitor hemoglobin parameters in the brain tissue, has been used widely as a noninvasive tool for assessing cerebral ischemia and hypoxia. Therefore, it may have the potential as a noninvasive tool for estimating the change of PbtO2.