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Lung ultrasound can predict response to the prone position in awake non-intubated patients with COVID‑19 associated acute respiratory distress syndrome

To the Editor,

Prone positioning (PP) is a well-known therapeutic strategy used in acute respiratory distress syndrome (ARDS). Several studies demonstrated positive effects of PP on oxygenation parameters in awake non-intubated patients with COVID-19-associated ARDS [1,2,3]. However, PP is not effective in every case. The pilot study by Elharrar et al. demonstrated a significant improvement of oxygenation parameters during PP in only 25% of the patients [3]. The results of previous studies highlighted heterogeneity of COVID-19-associated ARDS, which demands further studies of the predictors of PP effectiveness and indications for its use in COVID-19 patients. The main objective of our study was to evaluate whether the changes of lung aeration assessed by lung ultrasound (LUS) can predict the oxygenation response during PP.

This prospective cohort study was conducted in COVID-19 care units of two university-affiliated hospitals (Sechenov University) between April 8 and May 10, 2020. The study included spontaneously breathing patients with confirmed or suspected diagnosis of COVID-19, and bilateral changes detected by high-resolution computed tomography and PaO2/FiO2 < 300 mmHg.

The study included 22 COVID-19 patients. Median age was 48.5 (39.8–62.8) years, 16 were male, and the median body mass index was 28.7 (27.3–31.6)kg/m2. The main co-morbidities were arterial hypertension (31.8%) and diabetes mellitus (18.2%). Sixteen patients (72.7%) received CPAP and 6 patients (27.3%) received oxygen therapy.

Sixteen of 22 patients (72.7%) responded to PP treatment with significant increase in PaO2/FiO2. At the same time, fewer patients had clinically significant improvement in dyspnea score—3 patients (13.6%) at 15 min in PP and 12 patients (54.5%) at 3 h in PP (Table 1). RR also significantly improved in responders.

Table 1 Comparison of changes over time in respiratory variables in responders and non-responders

Responders and non-responders demonstrated significant differences in disease duration (8.5 (5.0–10.8) vs. 13.0 (10.0–17.0) days of disease, p = 0.02), no other differences in baseline clinical and laboratory parameters were observed. Three patients (all from non-responder group) were transferred to intensive care unit and then intubated, two of them died.

The patients who responded to PP had more pronounced disturbances of aeration in posterior regions (8.5 (7.3–9.8) vs. 6.0 (4.3–7.3); p = 0.006) as reflected by greater LUS. The decrease of the total LUS score and LUS score of posterior regions was significantly greater in responders (5.0 (4.0–7.0) vs. 1.5 (1.0–3.0); p < 0.005 and 4.0 (3.5–5.0) vs. 1.0 (0.0–1.0); p < 0.001, respectively). The area under the receiver operating characteristic curve of posterior LUS score for the oxygenation response during PP was 0.87 (95% CI 0.64–1.0; p < 0.01). Changes of aeration score over time in posterior segments by LUS data correlated with PaO2/FiO2 changes (r = 0.53, p = 0.01), i.e. aeration improvement in posterior lung segments was associated with improved oxygenation status (Fig. 1).

Fig. 1
figure 1

a Lung ultrasound scores of the posterior regions before and after prone positioning (PP) in responders (n = 16) and non-responders (n = 6). b Before prone positioning: irregular and broken pleural lines with multiple confluent B-lines. c After prone positioning: irregular and thickened pleural lines with several B-lines, predominate separated B-lines

Previous studies examined the changes of aeration by LUS in PP in intubated patients with ARDS not-associated with COVID-19 [5, 6]. Haddam et al. found that oxygenation response to PP was not correlated with a specific LUS pattern regardless of the focal or non-focal nature of ARDS [5]. However, Wang et al. demonstrated that aeration score changes assessed by LUS were significantly higher in the PP responder and survivor groups [6]. Our study demonstrated in awake non-intubated patients with COVID-19-associated ARDS the relationship between the pattern of lung changes (presence of areas with subpleural consolidations), their localization (posterior segments) as shown by LUS, and the response to PP.

In conclusion, in patients with severe COVID-19, response to PP probably depends on the extent and localization of lung tissue changes. The aeration changes assessed by LUS may be useful in prediction of oxygenation response to PP in awake non-intubated patients with COVID‑19‑associated ARDS.

Availability of data and materials

Data and materials can be obtained from the corresponding author upon the reasonable request.



Prone position


Acute respiratory distress syndrome

PaO2 :

Partial pressure of oxygen

FiO2 :

Fraction of inspired oxygen

PaCO2 :

Arterial carbon dioxide tension

SpO2 :

Oxygen saturation


Continuous positive airway pressure


Respiratory rate


Heart rate


Lung ultrasound


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Authors and Affiliations



Concept and design of the study, and drafting of the manuscript: SNA; supervision and drafting of the manuscript: DK; performing the measurements and collection of data: GVN NVT NAT AIY. Transthoracic LUS was performed by two expert physicians (GVN, AIY) with expertise in LUS recording and interpretation. Double reading was conducted to reduce inter- and intra-observer variability and final decisions were reached by consensus. Our physicians were blinded to the individual patients´ oxygenation response. All authors were involved in data analysis and interpretation. Finally, all authors were involved in writing, reviewing and editing of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Sergey N. Avdeev.

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Ethics approval and consent to participate

The local ethics committee (LEC No. 16-2016-20) approved the study. The ethics committee of the hospitals (Sechenov First Moscow State Medical University) waived the written informed consent from patients with COVID-19, and all the procedures being performed were part of the routine care.

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Not applicable.

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The authors declare that they have no competing interests.

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Avdeev, S.N., Nekludova, G.V., Trushenko, N.V. et al. Lung ultrasound can predict response to the prone position in awake non-intubated patients with COVID‑19 associated acute respiratory distress syndrome. Crit Care 25, 35 (2021).

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