In Germany, more and more people from Covid-19 are recovering. However, there is a risk that the illness is not over for some of them. The Federal Ministry of Health assumes that late effects of Covid-19 can be expected. Above all, because a relatively high proportion of patients have to be treated in an intensive care unit or even need artificial ventilation. Reliable data are still missing to assess the risk. However, the first study results and reports from doctors already indicate where Sars-CoV-2 could cause long-term damage in the body.

"Patients who need to be treated on the ward often have a rather lengthy course," says pulmonologist Michael Pfeifer, President of the German Society for Pneumology and Respiratory Medicine. It is not yet known whether the patient will keep episodes for months or years, "but at least for the first time after the infection". Even after weeks, the pneumologist still sees changes in the lungs in many patients who have survived Covid-19. Often, the lung function is not dramatically restricted, but some have problems getting enough oxygen, especially under stress. 

Millions of alveoli collapse

It's no wonder, because Sars-CoV-2 attacks deep in the lungs. The viruses dock onto the cells, infiltrate and destroy them via certain binding sites. In severe cases, cell waste gradually accumulates in the depths of the lungs, mixed with immigrant inflammatory cells and fluid that escapes from the leaked blood vessels. At the same time, the surface tension of the alveoli rises, where the blood is enriched with oxygen. Millions of these alveoli collapse during the acute infection phase. In retrospect, it is difficult to distinguish which effects were caused by the virus and which were caused by the subsequent defense battle. However, radiologists see the traces, for example, in CT examinations of infected people ( European Radiology : Ye et al., 2020).

"The fear is that the lungs will be damaged to such an extent that they will not be able to completely rebuild their normal structure," says Pfeifer. For example, when inflammation replaces the actually tender connective tissue between the alveoli with scar tissue. Such fibrosis can lead to the affected sections no longer being able to participate as well in the gas exchange. Lung changes like this can currently be seen especially in patients with a severe course of Covid-19 who require long ventilation, says Pfeifer. However, it is still unclear how many patients are really affected.

At the moment, nobody knows whether the diverse changes in lung tissue that doctors see on X-ray and CT images will persist in the long term or will recede over time. From other severe pneumonia - such as pneumococci - it is known that the lungs of many patients regenerate surprisingly well over months, says Pfeifer. In many cases, it is so complete that people are not restricted to breathing in everyday life. "I am sure that many patients who we now believe based on CT images will suffer long-term damage will recover," said Pfeifer. You can really estimate the proportion that applies, however, at the earliest after half a year.

Possible damage from ventilation

In addition to the effects of virus and immune defense, some patients need artificial ventilation for weeks. The pressure conditions that normally prevail in the body are completely reversed. Air is actually sucked into the lungs by negative pressure, but now a respirator presses air towards the lungs. This is sensitive to any excess pressure and the longer someone has to be ventilated, the greater the likelihood that lung tissue will be injured ( Annals of Translational Medicine : Bates & Smith, 2018 PDF). Long-term ventilation - especially due to pressure fluctuations - can also damage other organs, especially the cardiovascular system. Damage to the kidney, stomach, liver or nervous system has also been described. Doctors are therefore debating how to gently ventilate patients with severe Covid 19 disease.

After a machine has blown air into their lungs for days, many people have to learn to breathe independently again. This weaning from the ventilator is called weaning. There are also special wards in clinics for this. After a long stay in the intensive care unit, even putting on the edge of the bed is hard work for many people. Only with the help of physiotherapists can they take a few steps again. Many Covid-19 patients who need hospital treatment may need rehab to get fit.

The weakness could continue to accompany some patients for a long time after a severe Covid course. An illness can play a role here, the symptom of which is, above all, enormous muscle weakness and the doctors did not consider it to be their own clinical picture for a long time: the Intensive Care Unit Acquired Weakness , ICUAW for short . It is a kind of neuromuscular organ failure ( Journal of Cachexia, Sarcopenia and Muscle : Schefold et al., 2010). It mainly occurs in connection with multi-organ failure after a life-threatening infection, as can also occur with Covid-19. With an ICUAW, the body breaks down muscle proteins at a rapid rate to convert them into inflammatory proteins. At the same time, nerve fibers that control the muscles are lost. Even if the patients survive the infection, many remain weakened for years. In a study of 109 patients with acute lung failure, one in two was unable to go back to work one year after discharge from the intensive care unit because he or she felt too weak and the muscles tired too quickly ( NEJM : Herridge et al., 2011 ). And even after five years, these patients were able to walk only about 75 percent of the distance of people of the same age in the six-minute walk test.

"This will also be one of the long-term consequences for Covid-19," says Steffen Weber-Carstens, senior consultant at the Department of Anaesthesiology with a focus on operative intensive medicine at the Charité. Seriously ill Covid patients regularly developed an ICUAW in the intensive care unit, which can already be said. Older people who are at higher risk of developing a severe infection are particularly affected, "but we also see young patients between the ages of 20 and 30 in the intensive care unit with the full picture of acute lung failure," says the intensive care doctor.