Oxygen therapy in COPD: when to start and how to monitor

Not every COPD patient with low oxygen levels meets the threshold for long-term supplementary oxygen therapy—this lesson covers the exact cutoffs and when they apply. 

When your patient with COPD also has pulmonary hypertension or heart failure, the indications for oxygen therapy change. And if they're planning to fly? The picture shifts again. Comorbidities adjust the thresholds, and knowing when to use oxygen therapy—and how to monitor your patient after starting—ensures it's used appropriately. This lesson covers these and other practical considerations for managing oxygen therapy in COPD.

In this lesson from our COPD Essentials course you'll learn how to:

• Identify the PaO₂ and saturation thresholds for supplementary oxygen therapy
• Apply adjusted thresholds when comorbidities are present
• Monitor patients after starting long-term oxygen therapy
• Recognize when pulse oximetry may overestimate oxygen saturation
• Assess whether your patient needs supplemental oxygen during air travel

PaO₂ and oxygenation

[00:00] 

The partial pressure of oxygen, or PaO₂, is a critical component of arterial blood gas, or ABG, analysis, providing information about how well the lungs are doing with respect to oxygenation. 

Measuring oxygenation: PaO₂ units and conversion

[00:13]

The standard international unit for partial pressure is kPa, but in clinical practice, mmHg is more commonly used. To convert between the two, remember that 1 mmHg = 0.133 kPa. To go from mmHg to kPa, multiply by 0.133. And to go from kPa to mmHg, divide by 0.133. In this Medmastery course, we'll stick with mmHg, but knowing this conversion is helpful since you'll encounter both units in different contexts.

Oxygen saturation in COPD: PaO₂ levels

[00:54] 

Normal PaO₂ levels typically range between 75 and 100 mmHg when breathing room air at sea level. Deviations from this range can indicate respiratory disorders, lung diseases, or that oxygen therapy is not sufficiently improving oxygenation as expected. 

Supplementary oxygen therapy in COPD

When to use oxygen therapy in COPD

[01:16] 

Studies have shown that supplemental long-term oxygen for more than 15 hours per day in patients with severe resting hypoxemia increases survival. On the other hand, oxygen does not benefit patients with stable COPD experiencing slightly lower than normal arterial oxygen levels, partly due to their adaptation to mild hypoxia and a diminished respiratory drive with supplemental oxygen.

Which COPD patients benefit from supplemental oxygen

[01:44] 

Long-term oxygen supplementation is needed in patients with a PaO₂ less than 55 mmHg or an oxygen saturation below 88%. And if their condition is complicated with pulmonary hypertension or congestive heart failure, the magic number is a PaO₂ below 60 mmHg. These patients should have their ABG tested at least twice over a three-week period to confirm that the levels are low enough for oxygen therapy.

Monitoring oxygen saturation during oxygen therapy

[02:18] 

After starting long-term oxygen, your patient should be reevaluated in two months with a repeat ABG test or oxygen saturation measurements using pulse oximetry. This evaluation should be conducted while the patient is breathing room air or at the prescribed oxygen flow rate. The results of this reevaluation will help you decide if the patient still needs to be on oxygen or whether an adjustment to the flow rate is needed. The goal of oxygen supplementation is to keep oxygen saturations of the blood above 90%.

Pulse oximetry limitations in patients with darker skin tone

[02:56] 

An important consideration is that some pulse oximetry machines falsely overstate the blood oxygen in patients with darker skin pigments. For this reason, in patients with darker skin, an ABG may provide a more accurate measurement of oxygen saturation compared to pulse oximetry.

Supplemental oxygen needs at altitude in COPD

[03:17] 

Now, if your patient is planning to travel by air, temporary oxygen therapy may be needed because of the decreased partial pressure of oxygen at altitude. Patients with resting oxygen saturations more than 95% and a six-minute walk oxygen saturation greater than 84% will likely not need supplemental oxygen on an airplane. But patients with moderate to severe hypoxemia at sea level will need supplemental oxygen during air travel at 3 liters per minute by nasal cannula.