Why does life-saving oxygen cause fatal damage to pneumonia patients? Scientists have discovered the key cause of the accident.

One of the signature symptoms of the transition from mild to severe after infection with the new coronavirus is shortness of breath, with significantly lower levels of oxygen in the patient's blood, known as hypoxemia.
to restore normal blood oxygen levels, oxygen absorption is a commonly used means of breathing support during treatment.
, however, a new study suggests that such treatments commonly used in patients with respiratory diseases can have unintended consequences in unexpected ways.
in a recent paper published in the scientific journal Science Translational Medicine, researchers at the University of Michigan School of Medicine found that bacteria in the lungs are rapidly affected by high levels of oxygen and play an important role in lung damage.
people often think the lungs should be relatively clean and free of bacteria, but we now know that bacteria in the lungs need to maintain an ecological balance just like gut bacteria, " he said.
," said Dr. Shanna Ashley, lead author of the study.
Although we live without oxygen, scientists have long found in animal experiments that inhaling too much oxygen can cause lung damage and is clinically associated with increased mortality, severe lung damage and pneumonia.
" oxygen is actually a very strong pulmonary toxin. Professor Robert Dickson, who led the study at
, said: "If I put healthy mice in 100 per cent oxygen, they would die within five days and suffer serious lung damage similar to those suffered by neo-corona pneumonia or other lung damage.
the respiratory and critical care medicine unit where the team is based, patients often need to continue receiving high levels of oxygen therapy.
, it is important to understand how oxygen is harmful for treatment and why some patients are more prone to misfortune.
researchers studied 1,500 critically ill patients who had been on a ventilator for more than 24 hours.
they tested the bacteria in the patient's lung samples and found significant differences in the types of bacteria in the different samples, which were related to the concentration of oxygen the patient inhaled.
specifically, patients with high levels of oxygen inhalation (FiO2-gt;55%)had significantly higher rates of Staphylococcus alobacter detected in their bacterial cultures than other bacteria.
bacteria are highly oxygen-resistant and are a common cause of lung infections in intensive care units (ICUs).
different types of bacteria are resistant to oxygen, so the researchers speculate that the oxygen given to patients may have affected the composition of bacteria in their airways.
the researchers designed a set of experiments to analyze the composition of lung bacteria in mice using 16S rRNA sequencing.
two groups of healthy mice, exposed to high-oxygen and normal-oxygen environments.
"As we predicted, when we provided high concentrations of oxygen, the lung bacterium in healthy mice changed rapidly," Dr. Ashley said.
" three days later, oxygen-resistant Staphylococcus araium became the most abundant bacteria in the lungs of mice.
, the scientists answered a "chicken first or egg first" question in the study: Does changes in lung bacterium cause lung damage, or do lung damage alter bacterial composition? The researchers first looked at the timing of the event: from the mice's reaction to high concentrations of oxygen, the composition of the lung bacteria changed after just one day, and lung damage could be detected on the third day.
relative time, lung bacteria are destroyed before lung damage occurs.
, the degree of bacterial changes in the lungs of mice was closely related to the severity of pneumonia in mice under high oxygen conditions.
to further confirm the role of lung bacteria in lung damage caused by high oxygen, the researchers conducted a key experiment using sterile mice.
high concentrations of oxygen for the same 72 hours, the sterile mice did not have lung damage.
"We think this is an unusual discovery!" Professor Dickson said: "Compared to the control group of normal bacteria mice, sterile mice had the same genetic inheritance and received the same amount of oxygen, but their lungs were protected.
" this fully demonstrates that microorganisms play an important role in the process of lung damage.
," Dr Ashley added.
that, can antibiotics protect patients receiving oxygen therapy? Critically ill patients often use antibiotics while inhaling oxygen, but the researchers point out that the problem is not that simple.
" bacteria are not all good or bad, which is why we dig out the mechanisms behind them.
the study authors note that "the interventions we use today are far from specific enough, and we need to take more targeted action against bacteria."
" Although this study strongly demonstrates in animals how different oxygen concentrations cause lung damage, the researchers caution against prematurely changing clinical practice based on these findings.
of oxygen provided to critically ill patients is a complex issue and one that requires in-depth study.
, " says Professor Dickson, "I hope that follow-up can be made through the results of randomized controlled trials."
"