Dear Editor,

The diagnostic value of CT for SARS-CoV-2 infection has been widely reported [1, 2]. However, performing CT is very difficult in critically ill patients in ICU, whereas mobile X-rays serve as an alternative. From Feb. 20 to Mar. 20, 542 mobile chest X-rays were performed in 229 COVID patients who were under assisted ventilation. Table 1 summarizes the main characteristics of the cohort.

Table 1 The main characteristics of 229 patients with SARS-CoV-2 pneumonia with mobile X-rays
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Among the 229, a significant underlying disease existed in 165 (72%): hypertension in 31%, chronic heart disease in 13%, chronic pulmonary disease in 12%, and malignancy in 11%. As of Mar. 30, 95 (41%) of 229 patients had died, and 134 (59%) survived. Among them, 58 were discharged and 76 still in hospital.

Table 1 shows the number of X-rays performed per patient. There were 229 initial examination and 313 were follow-ups. The image quality was diagnostic for all these X-rays.

Extensive pneumonia was seen on the initial X-rays in all patients. Other findings were pneumothorax (7%) and pleural effusion (23%). Subcutaneous emphysema, hiatal hernia, and intrapulmonary cavity were rare findings (Table 1). All patients with pneumothorax died. Compared to previous X-rays, increase of pneumonia was seen in 119 (38%) of 313 follow-up X-rays, while no changes were seen in 57 (18%), and improvement in 137 (44%).

Among non-survivors (n = 95), 61 patients did not have follow-up X-rays and died 1~4 days after the initial examination; 34 patients had 55 follow-up X-rays. Pneumonia progress was seen in 53 (96%) out of 55 follow-up X-rays when compared to previous radiograph (Fig. 1).

Fig. 1
figure 1

A 57-year-old female with laboratory-confirmed SARS-CoV-2 pneumonia had dyspnea one week after onset of symptoms of fever and diarrhea. Under high-flow oxygen inhalation, her pulse oxygen saturation (SPO2) was only 60%; thus, invasive ventilation was used with fraction of inspired oxygen 50–70% to maintain SPO2 around 95%. On Feb. 21, she underwent the first mobile X-ray, which indicated extensive pneumonia. Compared with initial X-ray, significant progress could be seen in the follow-up X-ray on Feb. 24, which was a typical “white lung.” A new intrapulmonary cavity was revealed by the second X-ray, and was significantly larger in the third X-ray on Mar. 1. The patient died of respiratory failure four days after the last X-ray

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Among survivors (n = 134), 111 patients had 258 follow-up X-rays. Pneumonia progress was seen in 66/258 radiographs (26%) of follow-up X-rays in 37 survivors; however, improvement was seen later.

We found mobile X-rays provided adequate image quality for diagnosing pneumonia, at least in this population of severely ill patients. Although obviously less informative than CT, X-rays can nevertheless detect serious complications like pneumothorax or lung cavitation, and estimate the evolution of pneumonia. Therefore, it is a simple but reliable alternative in critically ill SARS-CoV-2 patients who could not undergo chest CT.