Stratification of COVID-19 Patients with Moderate-to-Severe Hypoxemic Respiratory Failure for Response to High-Flow Nasal Cannula: A Retrospective Observational Study

Abstract

Background and Objectives: In patients with COVID-19, high-flow nasal cannula (HFNC) and continuous positive airway pressure (CPAP) are widely applied as initial treatments for moderate-to-severe acute hypoxemic respiratory failure. The aim of the study was to assess which respiratory supports improve 28-day mortality and to identify a predictive index of treatment response. Materials and Methods: This is a single-center retrospective observational study including 159 consecutive adult patients with COVID-19 and moderate-to-severe hypoxemic acute respiratory failure. Results: A total of 159 patients (82 in the CPAP group and 77 in the HFNC group) were included in the study. Mortality within 28 days was significantly lower with HFNC compared to CPAP (16.8% vs. 50%), while ICU admission and tracheal intubation within 28 days were significantly higher with CPAP compared to HFNC treatment (32% vs. 13%). We identified an index for survival in HFNC by including three variables easily available at admission (LDH, age, and respiratory rate) and the PaO₂/FiO₂ ratio at 48 h. The index showed high discrimination for survival with an AUC of 0.88, a negative predictive value of 86%, and a positive predictive value of 95%. Conclusions: Treatment with HFNC appears to be associated with greater survival and fewer ICU admission than CPAP. LDH, respiratory rate, age, and PaO₂/FiO₂ at 48 h were independently associated with survival and an index based on these variables allows for the prediction of treatment success and the assessment of patient allocation to the appropriate intensity of care after 48 h. Further research is warranted to determine effects on other outcomes and to assess the performance of the index in larger cohorts.

Keywords: COVID-19; CPAP; HFNC; NIRS; NIV; mortality.

Figure 1

Kaplan–Meier curve for study participants treated with HFNC (green line, n = 77) and CPAP (blue line, n = 82). Patients treated with HFNC have a significantly higher percent survival compared to patients treated with CPAP (p = 0.005).

Figure 2

(A,B): Receiver operating characteristic curves for age, LDH, and respiratory rate at admission (T0) for HFNC survival at admission. The area under the curve (AUC) for each variable is reported in (B). RR T0 = respiratory rate at admission.

Figure 3

(A) shows the receiver operating characteristic (ROC) curves for the performance of the HFNC survival index at admission. Sensitivity, specificity, and positive and negative predictive values according to the reference cut-off are reported in (B). The performance of this score applied in the entire HFNC population is reported in (C), categorized according to the cut-off value of the HFNC survival index. Respiratory rate, T0 = respiratory rate at admission.

Figure 4

(A) shows the receiver operating characteristic (ROC) curves for the performance of the HFNC Survival Timing index. Sensitivity, specificity, and positive and negative predictive values according to the reference cut-off are reported in (B). The performance of this index applied in the entire HFNC population is reported in (C), categorized according to the cut-off value. Respiratory rate, T0 = respiratory rate at admission.