Room-air resting ABG is gold standard.
PaO2 of 55 mmHg or less or SaO2 of 88% or less on RA consistently @ rest, with exercise, or with sleep
Pt with PaO2 of 56 - 59 mmHg plus evidence of cor pulmonale (P pulmonale on ECG, lower ext. edema secondary to RHF) PH, or 2° polycythemia (Hct: >55%), or CHF.
Annual evaluation necessary.