Our study showed that a CP session was associated with an improvement in oxygenation and pulmonary aeration in more than half of our COVID-19 patients. However, the results did not show a significant correlation between oxygenation and lung aeration changes.
To the best of our knowledge, this study is the first to report the effects of a CP session on oxygenation and lung aeration in awake COVID-19 patients. A single-center study including 25 patients found that Rodin’s Thinker positioning was associated with a significant subsequent improvement in oxygenation of more than 40 mmHg of PaO2 measured immediately at the end of the session (11). Rodin’s Thinker positioning may be theoretically more efficient than classical CP because it reverses the gravitational gradient in a manner similar to PP. Nevertheless, the mechanism underlying this effect was not assessed in this study. Furthermore, the mean PaCO2 was not altered after a Rodin’s Thinker positioning session, suggesting an insignificant effect on lung aeration. To summarize, CP and Rodin’s Thinker positioning are feasible and may improve oxygenation in selected patients, but larger studies are needed to confirm these findings.
The pathophysiological effects of positioning in patients with acute respiratory failure are difficult to assess (27). The use of LUS allows bedside assessment of regional lung aeration. Thus, it represents a useful tool for assessing changes in patients with acute respiratory failure (12). The LUS reaeration score was recently validated in comparison to a gold-standard method—end-expiratory lung volume measured by an automated nitrogen washout/washing technique—for PP-induced lung inflation (13). In a previous study, we assessed regional aeration changes during a PP session in 51 ARDS patients (12). We found that changes in aeration and oxygenation were not correlated, suggesting that both ventilation and perfusion were critical determinants of oxygenation. Thus, the pulmonary blood flow could be diverted away from the reaerated lung regions in PP, resulting in ventilation:perfusion matching alteration (28).
Similar to the PP, CP affects the gravitational gradient, end-expiratory lung volume, and hemodynamics. However, the magnitude of these changes is poorly described. In our patients, the lack of correlation between oxygenation and lung aeration changes also suggests a ventilation:perfusion matching alteration during a CP session, as reported during PP in mechanically ventilated COVID-19 patients (29)(28).
In our study, lung involvement morphology assessed with baseline LUS scores did not predict subsequent changes in lung aeration or oxygenation. Only limited previous data have suggested that lung involvement morphology could predict oxygenation response to PP in intubated or non-intubated patients (14)(30). However, larger studies have shown that baseline lung involvement profiles, either evaluated with LUS or chest computed tomography, were not predictive of response to PP (12)(31). Thus, it seems that the complex mechanisms induced by changes in positioning are not predictable with the assessment of baseline lung involvement morphology, regardless of the imaging technique. Even if less helpful in clinical practice, changes in LUS scores during the early phase of a PP session could more accurately predict the PP response and outcome (13)(32). Future studies should determine if an early response to a CP session is predictive of oxygenation, lung aeration, or outcome improvement.
Our study has several limitations. As a retrospective analysis, we included only a convenience sample of patients who met the inclusion criteria. Due to its observational nature, we did not perform a systematic blood gas analysis at different time points. However, we used the SpO2:FiO2 ratio, which is a validated surrogate of the PaO2:FiO2 ratio (19). The number of patients was relatively small, and we did not include a control group, which precluded the analysis of clinical outcomes. However, this multicenter study reflects a global approach used by different teams. Finally, we included only non-intubated patients at the onset of their ICU stays. Therefore, as the response to PP and recruitment decreases over time due to progressive lung consolidation versus atelectasis (29), we cannot expand our results to patients previously intubated or those in a late stage of their disease progression.