20 = 35, lowest tolerated
26 = 50
40 = 75
55 = 88 medicare standard for continuous O2 Tx.
60 = 90 "knee of O2-Hb dissociation curve; hypoxic drive and erythrocytosis are expected below this level
80 = 95 low normal arterial range
100 = 97 upper normal arterial range
In a patient with history of cigarette smoking (e.g.,1 pack a day over the past 50 years) who has erythrocytosis in the setting of chronic heavy tobacco use, ask if there is a history of sleep apnea. Such patients may need work-up to determine the cause for erythrocytosis. In the setting of 50 pack-year tobacco use, secondary polycythemia is the most likely etiology, but evaluation for polycythemia vera (JAK2 mutation) and sleep apnea should be considered if not previously pursued.