Let's start with some basics.
I also take "cO2" to be in reference to Carbon Dioxide (CO2) and not content of Oxygen.
Also, here is the link for some to review OXYGEN.
http://www.ccmtutorials.com/rs/oxygen/index.htm
Hyperoxygenation is NOT Hyperventilation.
Hyperoxygenation is an increase in PaO2.
Hyperventilation is a decrease in PaCO2.
Giving oxygen does not decrease the PaCO2. In some cases it may increase the PaCO2
due mainly to an increase in the ratio of dead space to tidal volume (Vd/Vt) which is probably from reversal of hypoxic pulmonary vasoconstriction. This is another discussion for those who follow the recipe "NEVER give more than 2 L NC to a patient with COPD".
When learning to intubate, some Paramedic students use the term "hyperventilate" when actually it should be "hyperoxygenate". The goal is to increase PaO2. You want to maintain or achieve a normal CO2 (normocapnia) and not hypocapnia. If you still think you hyperventilate the patient, please review the AHA position on this issue as to why the ventilatory rate has been changed in the ACLS guidelines.
High levels of CO2 will cause cerebral vasodilation. However, we no longer hyperventilate (decrease PaCO2) a head injury due to the chances of vasoconstriction or inducing spasm. We maintain the CO2 levels at the lower range of normal.
Now for the delivery terminology.
When taking about physiological effects of oxygen, refer to the FiO2. "High Flow" tells one little in the medical world since a 24% Venturi mask is a high flow device. A NRBM is not.
For ischemic CVAs, there are several issues to consider rather than a blanket recipe of "2 - 4 L NC".
What is the blood pressure? Diastolic and/or Systolic too high or too low? Adequate perfusion?
Airway? Snoring? Aspiration? Pre-existing pulmonary and/or cardiac conditions?
We will often maintain close to normal oxygenation and will usually try to achieve that through SpO2 unless we know other conditions that may influence delivery such as anemia or sickle cell. We rarely do an Arterial Blood Gas (ABG) due to the possibilty thrombolytic treatment but can find many of the values needed from venous lab work. What isn't in print can usually be calculated.
It is also not uncommon to see different positions on reperfusion theories and tissue ischemia concerning hyperoxygenation by a high FiO2 system or possibly HBO. The patient's "oxygen clock" will be closely monitored during this time.
There's still a lot of research to be done. In the ICU, we have the capability to monitor cerebral perfusion, O2 consumption, ABGs and SjvO2. I can tell you that no two patients are always given the same amount of oxygen (FiO2) to stay within the guidelines of the parameters chosen for THAT patient by the etiology and extent of their injury or other systemic injuries and complications.