1 Background

Since the first report of cases from India in late 2020, the delta variant of SARS-CoV-2(DVSC-2) has become the predominant strain in much of the world [1]. Awake prone positioning has been used for non-intubated patients with COVID-19-related acute hypoxaemic respiratory failure, but the results are contradictory. We aimed to highlight the role of awake prone positioning (PP) combined with high-flow nasal oxygen therapy (HFNO) in severe COVID-19 patients infected with the Delta variant of SARS-CoV-2.

2 Case Presentation

From June 12 to December 7, 2021, 80 COVID-19 patients mainly infected with DVSC-2 were screened. Two of them had whole genome sequencing-confirmed DVSC-2 infection. They were graded as severe according to the Guidelines for the Diagnosis and Treatment of Novel Coronavirus (2019-nCoV) Infection by the National Health Commission (trial version 8). Both patients presented with bilateral opacities suggestive of pneumonia that rapidly worsened after several days of admission (Fig. 1). We successfully performed PP combined with HFNO therapy on them.

Fig. 1
figure 1

Chest computed tomographic scans in the two severe COVID-19 patients infected with the delta variant of SARS-CoV-2. Chest computed tomographic (CT) scan taken before prone position (PP) in case 1. B CT scan taken on after PP in case 1. It revealed the lung infiltrates improved significantly compared with A. C CT scan taken before PP in case 2. D CT scan taken after PP in case 2. It revealed the lung infiltrates improved significantly compared with D

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HFNO was prescribed to reach SpO2 ≥ 92%. PP was proposed to patients with PaO2/FiO2(P/F) < 150 mmHg. The PICCO was proposed for hemodynamic monitoring and volume management on their admission to intensive care unit (ICU). Arterial blood gases (ABG) and hemodynamics were monitored before and after PP sessions. The target time of PP was more than 12 h per day and could be appropriately shortened according to the patient’s tolerance. Relevant clinical data, HFNO parameters, PICCO parameters, P/F ratio and PP duration were obtained from medical records and are presented in Table 1.

Table 1 Clinical characteristics of patients
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A total of 23 PP sessions and 6 PP sessions combined with HFNO were performed in case 1 and case 2, respectively. ABG and hemodynamic were monitored before and after PP sessions during 10 PP sessions of case 1 and 4 PP sessions of case 2. The hemodynamic results showed their cardiac index (CI), systemic vascular resistance index (SVRI) and central venous pressure (CVP) were within normal range, however, global end-diastolic volume index (GEDI), intrapulmonary shunt fraction (Qs/Qt) and extravascular lung water index (ELWI)were higher than normal before PP. There was no volume responsiveness confirmed by passive leg rising test in both cases. Although their volume was limited, GEDI and ELWI were higher than normal. Compared with values before PP, GEDI, ELWI and Qs/Qt decreased significantly (GEDI: 869.50 ± 60.50 ml/m2 vs. 756.86 ± 88.25 ml/m2; ELWI: 13.64 ± 2.82 ml/kg vs. 12.43 ± 2.50 ml/kg; Qs/Qt: 15.32 ± 6.52% vs. 12.24 ± 5.39%; all p < 0.05), Meanwhile, the oxygenation improved significantly (PaO2: 84.30 ± 18.49 mmHg vs. 106.94 ± 35.12 mmHg; P/F: 184.50 ± 51.92 mmHg vs. 234.21 ± 88.84 mmHg, both p < 0.05), Nevertheless, there were no significant differences in respiratory rate (RR), heart rate (HR) and mean arterial pressure (MAP) between before and after PP (all p > 0.05). The chest CT revealed the lung infiltrates improved significantly after PP (Fig. 1). Both cases were discharged to a dedicated COVID-19 ward without requiring intubation. we used the paired t test for numerical variables to compare variables between before awake prone position and after awake prone position.

To our knowledge, this is the first description of severe COVID-19 patients infected with DVSC-2 managed effectively and improved pulmonary vascular involvement by PP combined with HFNO. Despres C et al. [2] showed similar findings in severe COVID-19 patients infected with the original version of SARS-CoV-2. People infected with DVSC-2 produce far more virus, acts on the angiotensin-converting enzyme 2 (ACE2), than do those infected with the original version of SARS-CoV-2 [1]. Alongside emerging understanding of the role of the ACE2 pathway in the pathogenic process, it has become clear that at least some COVID-19 patients, exhibit significant pulmonary vascular involvement [3, 4]. Besides volume overload and inflammation response, pulmonary vascular involvement caused by DVSC-2 might be one reason for elevated GEDI. Previous studies have confirmed that PP recruited some collapsed pulmonary microvessels through increasing central blood volume and decrease PVR and RV afterload through increasing the lung volume [5]. HFNO create a positive end expiratory pressure effect, contributing to decreasing the work of breathing and enhance oxygenation [6].

3 Conclusion

Combining PP with HFNO could be a useful treatment strategy for avoiding intubation in severe COVID-19 patients infected with the Delta variant of SARS-CoV-2 to improve pulmonary vascular involvement, improve oxygenation and avoid intubation, but further studies are needed to validate our approach.