Detection of Residual Pulmonary Alterations With Lung Ultrasound and Effects on Postoperative Pulmonary Complications for Patients With Asymptomatic SARS-CoV-2 Infection Undergoing Surgeries

Susana González-Suárez; Antonio Barbara Ferreras; Melissa Caicedo Toro; Macarena Aznar de Legarra


BMC Anesthesiol. 2022;22(186) 

In This Article


In asymptomatic post-COVID-19 patients there are residual lung lesions that are related to the clinical course of SARS-CoV-2 infection. Patients with pleural thickening at the time of surgery had more symptoms of dyspnea, more days of hospitalization and noninvasive/invasive mechanical ventilation during SARS-CoV-2 infection comparted to patients who did not have pleural thickening (p= 0.003, 0.000, 0.002, 0.03 respectively). Also, patients with pleural thickening presented a clinical course with a higher incidence of pneumonia, acute respiratory syndrome distress, and a need for vasoactive drugs during SARS-CoV2 infection (p= 0.004, 0.001, 0.03 respectively). Patients with ≥ 3 B-lines needed more days in intensive care unit and needed vasoactive drugs during SARS-CoV2 infection (p= 0.04. 0.004). No signs of symptoms, days of hospitalization, or clinical course of COVID-19 were observed in patients with compliance < 50 ml/cmH2O the day of surgery.

Other authors also demonstrated the presence of residual lung wounds by SARS-CoV-2 infection. Lombardi F. et al.[17] and Frija-Masson J. et al.[18] showed that the residual respiratory impairment, including lower exercise tolerance, was correlated with the severity of respiratory failure during hospitalization. Abdulrahman et al.[19] and Myall et al.[20] showed that although most cases of COVID-19 recover completely, a small proportion of patients present pathological pulmonary findings by LUS with the appearances of pleural line abnormalities and B line artifacts, which result from inflammation and interstitial thickening that increase in number with severity. The persistence of LUS abnormalities was also seen in patients with dyspnea;[21] our study also found that dyspnea is correlated with an increase in pulmonary pathological findings by LUS.

However, we observed no correlation between the severity of the SARS-CoV-2 infection and a decrease in static pulmonary compliance. It is probable that the time between the diagnosis of the SARS-CoV-2 infection and surgery had been sufficient time to cure the infection. Thus, we observed that the pulmonary compliance values were higher as the time elapsed between COVID-19 diagnosis and surgery (Figure 2).

Some patients in our study obtained low values of pulmonary compliance (< 40 ml/cm H2O in 21.7 % patients); in some of these patients, this low compliance could be associated with the presence of pulmonary "fibrosis".[22–24] This fibrosis has been shown after isolated viral infections[25] and especially after persistent viral infections.[26] Nevertheless, Wallace et al.[27] argues that "fibrosis" should not apply to the abnormalities seen in cases of post-viral pulmonary fibrosis, since these changes could be reversed over time. Some authors argue that "fibrosis" can be considered a potentially reversible process, and the term "reversible pulmonary fibrosis" has been used in the current literature.[28] Truly, this term encompasses a non-idiopathic form of pulmonary fibrosis associated with COVID-19 infection, which is heterogeneous in many aspects and can present anytime from initial hospitalization to long term follow-up. However, there is still much uncertainty about many aspects of the COVID-19 condition.

On the other hand, we demonstrated an inverse correlation between pulmonary compliance and B-lines. Other authors also argue that the residual lung damage detected by LUS could be responsible for a decrease in pulmonary parenchyma distensibility or static compliance.[29] It is possible that both, the low static compliance values, and most of the wounds observed by ultrasonography, indicate residual pulmonary injuries that return to normal as time passes.

In our study, the use of LUS identifies certain pulmonary alterations in asymptomatic post-COVID-19 patients undergoing surgery, and some of these pulmonary findings could be attributed to the SARS-CoV-2 since the patients did not present previous pulmonary pathology; despite this, the incidence of PPC is low. Most studies determine the PPC in patients with active SARS-CoV2 infection;[30,31] in these cases, it is foreseeable that the complications will be greater than in those patients who have passed the infection or patients who have been asymptomatic. Other studies found an increase in PPC (51.2%) and mortality (23.8%) in patients who had SARS-CoV2 infection confirmed within 7 days before or 30 days after surgery.[2] However, the incidence obtained of PPC in our study was much lower, probably because our patients had an average number of days from diagnosis of SARS-CoV2 infection to surgery 108.56 ± 82.02 days, in the absence of symptoms and with negative PCR. These conditions would make surgery feasible. So, as we observed PPC in 5.8% of our patients; this incidence corresponds to values obtained in the pre-pandemic stage,[32,33] oscillating in some patients between 2 to 19%.[34] Furthermore, some authors, also, did not observe differences in their postoperative results when comparing SARS-CoV-2 positive patients with patients who had tested negative for SARS-CoV- 2.[16] These authors argue that the baseline characteristics of the patients have an important impact in the development of PPC. Similarly, we observed that the baseline characteristics of the patients, evaluated according to the ASA classification, are associated with the appearance of PPC. Therefore, most of patients with PPC presented high ASA scores. Other factors, such as a severe evolution of the SARS-CoV-2 infection (in terms of pneumonia, PTE, the need for vasoactive drugs, hospital stay) and both, pleural thickening, and B lines ≥ 3, were also observed in our patients with PPC.

Our study has some limitations. Given the low number of complications, we only studied whether the influence of the pulmonary pathological findings and the severe course of the SARS-CoV-2 infection affect the appearance of any of the PPC, and not of each of the PPC separately. Also, regarding the LUS technique, as with many areas of ultrasound imaging and interpretation, the identification and quantification of the nature of B-lines and pleural line can be somewhat subjective and subject to interpretation.[35] To resolve this possible misinterpretation of LUS findings, these examinations could be performed by more than one expert anesthesiologist. Even by taking this limitation into account, it's known that the LUS constitutes a useful predictive tool of clinical respiratory deterioration course and outcome, with the advantage that it can be easily performed bedside.[36–40] Moreover, the incidence of residual lung alterations that we observed in our study cannot be attributed completely to SARS-CoV-2 infection, since it is possible that these lesions are observed in patients without SARS-CoV-2 and without previous lung pathology.