Can Normal Oxygen Levels at Rest Hide Exercise Problems After COVID?
Yes. In this study, 43% of COVID pneumonia patients with normal oxygen at rest showed significant oxygen drops during a walking test. Normal blood gas readings at discharge cannot predict whether patients will struggle with exercise.
Researchers in Italy studied 70 patients ready for discharge after COVID-19 pneumonia. Even though all had normal oxygen levels at rest, nearly half experienced significant oxygen desaturation when they exercised. Most concerning, 83% of those who desaturated dropped below 90% oxygen during the test.
What the Study Found
The researchers had patients perform a 6-minute walking test before hospital discharge:
- Desaturation rate: 43% (30 of 70 patients) had oxygen drops of 4% or more
- Severe drops: 83% of desaturators fell below 90% SpO2 during walking
- Resting oxygen: Mean PaO2 was 75.8 mmHg (normal range)
- Average age: 66.1 years, 71.4% male
- Mean walking distance: 347 meters
Key Differences Between Groups
Patients who experienced oxygen drops during exercise (desaturators) differed from those who didn’t:
- Longer hospital stays: 30.5 vs 21.9 days in acute care
- Higher heart rates: 125 vs 117 beats per minute at end of walk test
- More breathlessness: Higher dyspnea scores during exercise
- Higher lung ultrasound scores: 11.8 vs 7.4
Importantly, resting blood oxygen levels and the A-aO2 gradient (a measure of lung function) did not differ between the two groups.
Dr. Kumar’s Take
This study reveals a critical gap in how we assess COVID recovery. We’ve been relying on blood gases at rest to determine when patients are ready for discharge. But normal numbers at rest can mask significant problems that only appear with exertion.
Nearly half the patients who looked fine sitting still had real oxygen problems when they tried to walk. This means we may be sending patients home who will struggle with daily activities like climbing stairs or walking to the mailbox.
The practical takeaway is clear: if you’ve recovered from COVID pneumonia and still feel breathless with activity, you’re not imagining it. There may be a real oxygen delivery problem that only shows up during exercise.
Lung Ultrasound as a Screening Tool
The study found that lung ultrasound could help identify patients at risk:
- LU score above 8.5 predicted exercise-induced desaturation
- Patients with higher scores were 4.4 times more likely to desaturate during exercise
- The test had 67% sensitivity and 61% specificity
Lung ultrasound has advantages: it’s quick, doesn’t expose patients to radiation, can be done at bedside, and was already being used to monitor COVID pneumonia progression.
Study Details
- Location: Two pulmonary rehabilitation centers in Italy (Pavia and Lumezzane-Brescia)
- Time period: April 15 to May 30, 2020
- Participants: 70 patients discharged after COVID-19 pneumonia
- Prior treatment: 57% had non-invasive ventilation, 27% required invasive mechanical ventilation
- Pre-existing conditions: 10% had COPD, 15.7% had diabetes
Important Limitations
- No data on pulmonary thromboembolism (blood clots in lungs)
- Conducted during early pandemic with limited CT angiography access
- Lung ultrasound had moderate (not high) accuracy
- Study conducted at rehabilitation centers, may not represent all patients
Practical Takeaways
- Normal oxygen at rest does not mean normal oxygen during exercise
- Ask about exercise testing if you’re recovering from COVID pneumonia
- Breathlessness with activity after COVID may indicate real oxygen problems
- Lung ultrasound may help identify patients needing rehabilitation
- Patients who desaturate during exercise may benefit from pulmonary rehabilitation
Related Studies and Research
- Athletic performance study
- Network meta-analysis: Respiratory support during PR exercise
- Cancer Multistep Therapy variations
- Long-lasting effects of oxygen multistep therapy
FAQs
What does “desaturation” mean?
Desaturation means your blood oxygen level drops. In this study, a drop of 4% or more during the walking test was considered significant.
Why might oxygen be normal at rest but drop with exercise?
COVID can damage the lung tissue that transfers oxygen to blood. At rest, there’s enough time for this transfer. During exercise, your body needs oxygen faster, and damaged lungs can’t keep up.
What is a 6-minute walking test?
It’s a simple test where patients walk as far as they can in 6 minutes on a flat surface. It measures exercise capacity and oxygen levels during activity.
Bottom Line
Among COVID-19 pneumonia patients discharged with normal blood oxygen at rest, 43% showed significant oxygen drops during a 6-minute walking test. Normal resting blood gases cannot predict exercise-induced desaturation. Lung ultrasound scores above 8.5 were associated with a 4-fold higher risk of exercise desaturation. This suggests that exercise testing should be considered before discharge to identify patients who may need pulmonary rehabilitation.
