Our study showed a success rate of awake SPP-HFNO in COVID-19 patients of 48%. We believe this intervention is worth trying since it is a simple technique to correct hypoxemia thus avoiding the need for intubation with few side effects. In a cohort of 56 patients with COVID-19, proning was feasible in 84% with substantial improvement of oxygenation . The addition of non-invasive ventilation (NIV), in the form of applying continuous positive airway pressure of 10 cm H2O and 60% FiO2, to prone position to COVID-19 patients outside of ICU resulted in improvement in oxygenation and respiratory rate . The early application of SPP-HFNO avoided intubation in 7 out of 20 patients with moderate ARDS and baseline SpO2 > 95% .
The main challenge in SPP-HFNO is patient fatigue and delaying invasive mechanical ventilation. In a prospective, multicenter study of COVID-19 patients receiving HFNO therapy, there were no effects of SPP on intubation rate or mortality . In our study, patients were monitored in the ICU and the average time spent on SPP-HFNO was 5.26 days in the success group versus 3.38 days in the failure group. Furthermore, the mortality rate in the SPP-HFNO success group was 3% versus 49% in those who required intubation and mechanical ventilation.
There have been several attempts to investigate predictors of failure of NIV and/or HFNO in patients with COVID-19 pneumonia such as HACOR score  and ROX index . More recently a machine learning algorithm based on vital signs, laboratory values, and demographic data outperformed the ROX index in predicting the need for intubation in COVID-19 patients . The baseline physiologic parameters (i.e. RR, HR, SpO2) in our cohort were comparable except for statistically significant lower HR in the success group (91 vs. 98 bpm, p = 0.04). Those who responded to SPP-HFNO therapy had statistically significant improvement in their SpO2 (96% vs. 93%, p < 0.001), and lower RR (HR = 1.40, CI: 1.05–1.87, p = 0.022). Similar findings showing improvements in SpO2 and RR have been reported previously [11, 12].
Multiple blood tests were shown to be associated with independent risk for poor ICU outcomes in COVID-19 patients. Elevated white blood cell count and neutrophils and low lymphocyte count are directly proportional to the severity of COVID-19 . Moreover, elevated biomarkers of inflammation in COVID-19 namely: D-dimer, CRP, LDH, and ferritin, are independently associated with higher ICU admission, invasive ventilatory support, and death . In our study, the SPP-HFNO successful group had lower WBC and is a predictor of outcome (HR = 0.88, CI: 0.80–0.95, p = 0.005). The biomarkers of inflammation, except for D-Dimer, were more elevated in the SPP-HFNO failure group but did not reach statistical significance. We found the D-dimer was more elevated in the SPP-HFNO successful group, but with a wide range, and was not statistically significant. The hazard ratio for D-Dimer was mildly elevated with a marginal p-value (HR = 1.01, CI: 1.00-1.03, p = 0.057).
The APACHE-II score was designed to measure the severity of disease in patients admitted to the ICU and to predict mortality . In our cohort of patients, APACHE-II was a significant covariate in the success group (HR = 0.91, CI: 0.82-1.0, p = 0.045), indicating an improved survival of 9% with every 1.0-point decrease in the APACHE II score. Studies have shown that the APACHE-II score accurately predicts the severity of illness in patients with COVID-19 disease admitted to ICU [20, 21].
Advanced age and obesity were previously reported as predictors of poor outcomes in COVID-19 patients, but this association was lacking in our study. A meta-analysis showed that age is an important indicator for predicting the severity and outcome of COVID-19, with a relative risk of 3.59 (95% CI: 1.87–6.90, p < 0.001) . Although an association between severity of COVID-19 disease and comorbidities has been reported , this relationship was not revealed in our cohort of patients. Diabetes and hypertension are very common comorbidities in the Saudi population . In addition, our cohort of patients was too small to detect association with other comorbidities like cancer. Regarding the treatment modalities and the predictability of successful SPP-HFNO in COVID-19 patients, treatment with convalescent plasma was associated with better outcomes in our study (HR = 2.33, CI: 1.03–5.3, p = 0.043). Initial reports on treatment with convalescent plasma for severe COVID-19 pneumonia showed promising results ; however, a recent randomized trial failed to demonstrate significant improvement in mortality .
A major limitation of this study is being retrospective with no control arm to compare. Second, the unavailability of complete data on 39 out of 110 patients. Third, measures of symptoms of dyspnea or comfort after prone positioning were not collected.