What Does COVID-19 Pneumonia Cause?

COVID-19 pneumonia is a lung infection caused by SARS-CoV-2, the virus that causes the COVID-19 disease. It leads to fluid and inflammation in the lungs, and the most common symptom of its progression is worsening respiratory distress. Like other respiratory infections that cause pneumonia, COVID-19 can cause short-term lung damage, and in severe cases, this damage can last for a long time. Early data suggests that up to one third of patients with COVID-19 pneumonia have evidence of scarring on x-rays or lung tests one year after infection.

Generally, the virus is mainly limited to the upper and conductive respiratory tracts in around 80% of infected patients. However, in almost 20% of cases, the disease progresses to the pulmonary gas exchange units and causes hypoxia and opacification of frosted glass (GGO). The underlying cause of severe lung damage is thought to be due to the high expression of AEC2 type II epithelial cells in the lungs. These cells have been found to be more sensitive to SARS-CoV-2 infection and infected cells undergo apoptosis.

As these cells are responsible for secreting surfactants, their reduction due to viral destruction of pneumocytes leads to alveoli collapse, which in turn causes pneumonia and acute respiratory distress syndrome (ARDS) in severe cases. Older age, male gender and comorbidities increase the risk of serious illness from COVID-19 pneumonia. Among those hospitalized for COVID-19, between 15 and 30% will develop ARDS associated with the virus. Autopsy studies of patients who died from a severe SARS CoV-2 infection reveal diffuse alveolar damage consistent with ARDS, but with an increased thrombus burden in the pulmonary capillaries.

High-flow nasal cannula (HFNC) can be used to help patients with ARDS avoid intubation without increasing the risk of disease transmission. During invasive mechanical ventilation, low tidal volume ventilation and a positive adjustment of final expiratory pressure (PEEP) are recommended to optimize oxygenation. Dexamethasone treatment has been found to improve mortality for those with severe or critical COVID-19, while remdesivir may have a modest benefit in terms of recovery time for those with serious illness, but no statistically significant benefit in mortality or other clinical outcomes has been observed. COVID-19 survivors, particularly those with ARDS, are at high risk of long-term physical and mental disabilities, so an interdisciplinary approach is essential for recovery from a critical illness.

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