We are beginning to understand the long-term effects COVID-19 has on lung function. This new systematic review will help quantify the effects and assess long-term changes in lung function.
As our understanding of COVID-19 improves the list of the virus' effects on the lungs, it gets longer. Although the virus affects several body systems, we know that the lungs are the most damaged. Approximately 8% of all cases with rapidly progressive respiratory failure similar to ARDS and 6% of patients with critical illness require ventilation assistance.
It is assumed that a number of pathological events affect the lungs of patients with COVID. These include diffuse destruction of the alveolar epithelium, damage to the mucous membranes, capillary damage from bleeding, lung consolidation, and fibrous proliferation of the alveolar septum. It is this fibrous proliferation and endothelial damage that is the biggest problem given the long-term damage and resiparticular symptoms found with long-term COVID.
MDT involvement reduces risk of long-term COVID
There are various ways of measuring lung function. Most common are pulmonary function tests (i.e. spirometry), X-rays, and CT scans. These scans and examinations help to objectively determine the consequences of acute or chronic effects of COVID-19.
The first reports of changes in lung function in connection with coronavirus indicate that patients have a restrictive defect and a dysfunction of the small airways, which can be persistent and not related to the severity of the disease. This is similar to what is also known about SARS and MERS infections, with reductions in lung function occurring in patients from months to years. The scientific community has yet to definitely know what the pattern or prevalence of long-term impairment of lung function due to Covid-19 infection is. However, a number of small studies have begun to develop our understanding.
A new systematic review was conducted to summarize these studies and increase confidence in our understanding. Especially for determining the prevalence of restrictive, obstructive and altered diffusion patterns in patients after COVID-19 infection and for describing the various assessments of the respiratory function in these patients.
The results of this systematic review are important as they give us a clear understanding of what we need to do clinically to detect changes in lung function for the diagnosis and follow-up of patients after Covid-19 infection. This ensures that the risk of long-term impairment is kept as low as possible.
Methodology
One of the most important parts of a systematic review is the search strategy because without a robust search strategy you cannot be sure that you have included all relevant data in your pooled analysis. For this reason, it is advisable for authors to fully incorporate the search strategy in order to enable fair and transparent criticism and analysis by the readers. This article is a great example of a search strategy that comes complete with all the boolean operators and quotation marks for finding specific keywords. It's also refreshing to see that there are no language restrictions placed on search results either.
To maintain excellence, the review adhered to PRISMA and the protocol was registered with PROSPERO. The review process was also of high quality as three different skilled systematic reviewers were available to extract data, decide which articles to include, and the third was specifically used when one and two did not match. The methodological quality of the studies was assessed using the NHLBI tool.
Part of the challenge in performing systematic reviews is to account for publication bias. One way to combat publication bias is to find unpublished data from studies. One way to accomplish this is to look for relevant studies published on websites prior to publication / registration of studies, check if they were ever published / completed, and include the data from those studies in the SR if they are of sufficient quality. This is what the authors of the paper did and it should be commended.
A total of 7 studies were included in the review – 6 Chinese studies and 1 French study with 380 COVID-19 patients after infection.
Results & clinical significance
The results of the systematic review show that patients after Covid-19 show different degrees and severity of the altered lung function, with the diffusion capacity being the most common impairment (~ 40% of patients). Pulmonary function tests are an important tool in assessing long-term damage to the virus. However, caution should be exercised when interpreting the results in comorbidities and smokers. We're still not sure which test is best, but spirometry is a good place to start to repeat the x-ray 3 weeks after infection if it's severe enough to get approved.
Brief summary of the results
An altered diffusion capacity was found in 39% of the patients
Restrictive pattern in 15% of patients
7% of the patients had an obstructive pattern
Spirometry was the most commonly used test to assess respiratory function
Lung function should be assessed 3 months after the discharge / onset of the virus
Seriously ill patients with high indicators of inflammation are more likely to develop fibrosis
The British Thoracic Society recommends evaluating pulmonary function tests 3 months after discharge from hospital, especially for people with suspected interstitial diseases. Current evidence suggests that many tests take place only 1 month after the infection started or 1 month after discharge. The consequences of a hasty assessment can lead to diagnostic errors.
Although our understanding of the long-term effects of covid infection is limited, our knowledge moves quickly. Yes, we may be missing the specifics, but we know that the likelihood of a patient getting a long Covid is lower when a patient is involved in their recovery.
