Skip to main content
  • Research Letter
  • Open access
  • Published:

Orthodeoxia and its implications on awake-proning in COVID-19 pneumonia

Dear editor,

When caring for patients with respiratory failure, decubitus is a daily challenge. In the acute-respiratory-distress-syndrome (ARDS), seated and prone position increase lung volume and, consequently, oxygenation [1]. In COVID-19, however, gas-exchange is often independent of lung volume [2], and rather affected by perfusion dysregulation [3]. In similar settings, like the hepato-pulmonary syndrome (HPS), recumbency may revert hypoxemia [4]: this phenomenon goes under the name of orthodeoxia, and here we hypothesize its presence in COVID-19. Clinical implications might be relevant: recumbency is the state of lying horizontally at 0°, supine or prone. Awake-proning has already proven beneficial on oxygenation in spontaneously breathing patients with early COVID-19 pneumonia [5]. However, as a heritage from ARDS, these patients are usually seated or semi-recumbent, thereby the ventral decubitus is rarely compared to supination at 0°: the finding of orthodeoxia may lead to partially ascribe the oxygenation benefits of awake-proning [5] to recumbency rather than to the ventral decubitus itself.

At the University Hospital of Turin (Italy), following ethical approval (Città della Salute e della Scienza 00581/2020), we studied non-sedated COVID-19 patients requiring early (< 7 days) respiratory support with helmet continuous positive airway pressure (HCPAP) or high flow nasal cannula (HFNC). Concomitant pulmonary embolism and/or bacterial pneumonia represented exclusion criteria. After signing a written informed consent, participants were assigned to a random sequence of seated (trunk elevation > 60°, legs down at 45°), supine and prone position (both recumbent at 0°) during constant respiratory support as set by the attending physician. Blood gases, respiratory rate, dyspnea and discomfort, basic hemodynamics and, when available, cardiac output (CNAP®, CNSystems Medizintechnik GmbH) were assessed twenty minutes from each decubitus. A threshold of ≥ 20% increase in PaO2 defined supine responders (supine vs seated) and prone responders (prone vs supine). The primary outcome was the frequency of orthodeoxia (supine responders). R-3.5.2 was used for statistical computing: Wilcoxon test for median comparisons, Fisher exact test for contingency tables, two-sided p < 0.05 for significance.

After excluding 28 eligible patients (21 for pulmonary embolism, 7 for superimposed bacterial pneumonia), 30 were recruited in two months (February–March 2021); two declined to participate. Results and baseline characteristics of the 28 enrolled patients are summarized in Table 1. Orthodeoxia was detected in 14 (50%) of them, with a far higher PaO2 increase (31 [26–44] mmHg), than what normally required to define it (4 mmHg) [3]. Neither the starting decubitus (p = 0.33), nor the type of respiratory support (HCPAP or HFNC, p = 1.00) affected this result, and the stability of cardiac output from seated to supine minimizes the possibility that macro-hemodynamics played any significant role. A decrease in respiratory rate in the absence of dyspnea and discomfort was also associated with supination in our population. During proning, patients with and without orthodeoxia behaved similarly: respectively, 6 (46%) and 5 (36%) were prone responders (p = 0.70, median PaO2 increase 65[30–92] mmHg). This suggests that orthodeoxia cannot anticipate the response to proning, likely because of the unpredictable balance between perfusion redistribution and parenchymal reaeration in the ventral position [6]. However, the finding of orthodeoxia avoided overestimating the benefits of awake-pronation in 6 patients (22%) whose oxygenation improvement was due to lying recumbent at 0°, irrespective of prone or supine specifically (Fig. 1, green dots). Considering that the ventral decubitus was associated with discomfort, higher respiratory and heart rate, the decision to prone would be questionable in these patients.

Fig. 1
figure 1

Individual Partial Pressure of Arterial Oxygen (PaO2) Variation in Supine responders (left) and Supine non-responders (right). In both groups solid lines represent prone responders, dashed lines prone non-responders (see Text for definitions). Red bars represent median PaO2 values in each decubitus, and P values (* when significant) refer to their comparisons. As shown, 14 patients (50%) were supine responders (median PaO2 increase from seated to supine: 31 [26–44] mmHg). Among these, one did not tolerate proning, six were prone responders (median PaO2 increase from supine to prone: 67 [60–92] mmHg) and seven were prone non-responders (one worsened oxygenation during proning, while the 6 patients highlighted by green dots benefit from recumbency irrespective of supine or prone position specifically). The remaining 14 patients (50%) were supine non-responders. Among these, 5 were prone responders (median PaO2 increase from supine to prone: 31 [30–68] mmHg), while in the 9 remaining subjects, PaO2 did not significantly change between supination and proning

In conclusion, orthodeoxia appears a common clinical feature of early COVID-19 pneumonia. This novel finding contributes to further distinguishing COVID-19 from other causes of ARDS [1, 2, 6], while reinforcing its advocated similarity with HPS [3, 4]. Additionally, detecting orthodeoxia may help avoid awake-pronation when oxygenation simply benefits from recumbency: in a pandemic scenario, this possibly relevant clinical implication would deserve confirmation by larger studies.

Table 1 Characteristics of Patients and Main Results

Availability of data and materials

The dataset used and analysed for this study is available from the corresponding author upon reasonable request.

References

  1. Mezidi M, Guérin C. Effects of patient positioning on respiratory mechanics in mechanically ventilated ICU patients. Ann Transl Med. 2018;6(19):384.

    Article  Google Scholar 

  2. Coppola S, Chiumello D, Busana M, Giola E, Palermo P, Pozzi T, et al. Role of total lung stress on the progression of early COVID-19 pneumonia. Intensive Care Med. 2021;47:1130–9.

    Article  CAS  Google Scholar 

  3. Reynolds AS, Lee AG, Renz J, DeSantis K, Liang J, Powell CA, Ventetuolo CE, Poor HD. Pulmonary vascular dilatation detected by automated transcranial Doppler in COVID-19 pneumonia. Am J Respir Crit Care Med. 2020;202:1037–9.

    Article  CAS  Google Scholar 

  4. Gómez FP, Martinez-Palli G, Barberà JA, Roca J, Navasa M, Rodriguez-Roisin R. Gas exchange mechanism of orthodeoxia in hepatopulmonary syndrome. Hepatology. 2004;40(3):660–6.

    Article  Google Scholar 

  5. Coppo A, Bellani G, Winterton D, Di Pierro M, Soria A, Faverio P, et al. Feasibility and physiological effects of prone positioning in non-intubated patients with acute respiratory failure due to COVID-19 (PRON-COVID): a prospective cohort study. Lancet Respir Med. 2020;8(8):765–74.

    Article  CAS  Google Scholar 

  6. Rossi S, Palumbo MM, Sverzellati N, Busana M, Malchiodi L, Bresciani P, et al. Mechanisms of oxygenation responses to proning and recruitment in COVID-19 pneumonia. Intensive Care Med. 2021. https://doi.org/10.1007/s00134-021-06562-4.

    Article  PubMed  PubMed Central  Google Scholar 

Download references

Acknowledgements

None declared.

Funding

None declared.

Author information

Authors and Affiliations

Authors

Contributions

LG, DP, MB and PC conceptualised the study. LG and AM collected the data. LG, MB and PC analysed the data. LG drafted the manuscript and PC, MB, DP and LB revised it. All authors read and approved the final version of the manuscript.

Corresponding author

Correspondence to Pietro Caironi.

Ethics declarations

Ethics approval and consent for participation

This study was approved by Città della Salute e della Scienza (00581/2020) University Hospitals’ Research Ethics Board (Turin, Italy). Every patient approved to participate by signing a written informed consent.

Patient consent for publication

Acquired (written and signed by each participant).

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Giosa, L., Payen, D., Busana, M. et al. Orthodeoxia and its implications on awake-proning in COVID-19 pneumonia. Crit Care 25, 429 (2021). https://doi.org/10.1186/s13054-021-03859-0

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1186/s13054-021-03859-0