Would you consider a dose of 2l of oxygen for treatment emphysema a high dose or low dose?

Low. This is low dose oxygen and equal to roughly 27 percent inspired oxygen (we breath 21 percent).
Neither... Oxygen is prescribed like any other medicine; the patient is given the amount necessary to maintain the patient's oxygen level within an acceptable range. Too much oxygen or too little oxygen are both dangerous for the patient.Therefore, the amount prescribed must be carefully monitored by the physician so the amount needed is given.