How does one get hypoxic brain injury?

Lack of blood flow: This usually results from a lack of blood flow to the brain for a period of time. How long is required will vary from individual to individual. This can occur when there is an interruption of cerebral blood flow, usually due to cardiac arrest, with blood flow restored a short time afterwards.

O2 & circulation: In general, if you can't get enough oxygen in your blood (pe, suffocation, lung disease, tracheal injury...) or cannot circulate blood to your brain (bad heart/acute or chronic, vascular injury, stroke, brain swelling...) you will suffer hopoxic brain injury in a short time.

Lack of oxygen: Hypoxia means a lack of oxygen. inadequate oxygen can be acquired from a cardiac/respiratory arrest, from being overcome as a result of a fire, carbon monoxide intoxication, severe respiratory distress.