In this study, we investigated the discrimination capacity of the ROX index and the HACOR scale to predict high-flow nasal cannula failure in patients with COVID19 pneumonia. Our data suggest that the discrimination capacity of the 2 scales is similar despite the scales evaluating different variables.
In our study we found that 140 (57,14%) patients required OTI and 152 (62.04%) had the final composite outcome of HFNC failure (requirement of orotracheal intubation or death by COVID19). We believe that the differences in study populations may lead to variation in findings. Compared to the report by Roca et al., our sample analyzed had a higher median age (64 vs 53 years). Also, a higher proportion of our patients on HFNC failure had CKD (13.8% vs 4.5%). Secondly, our study found that patients with atrial fibrillation had a worse outcome. This variable was not evaluated by Roca et al. Furthermore, a later study did find that a heart rate greater than 90 beats per minute was associated with a higher risk of failure of HFNC (19).
The discriminative capacity of both is similar (ROX AUROC 0.72 vs HACOR AUROC 0.71). The discriminative capacity of the ROX index is similar to those observed in other studies (16,17,18). As for the HACOR scale, so far, we do not know that it has been evaluated in patients with COVID19 infection. In our study, the discriminative capacity of the HACOR scale was similar to that reported by Innocenti et al (AUROC of 0.68). (20) but it was lower than that found by Duan et al, (AUROC of 0.89) (9) and Carrillo et al (AUROC of 0.88) (11). We believe that these differences occurred because in the studies by Duan et al, and Carrillo et al. Patients with respiratory failure secondary to causes other than COVID19 infection, as well as patients with hypercapnic respiratory failure, were taken. These findings may also be associated because in our study the discriminative capacity of the HACOR scale was taken based on a composite result of the need for orotracheal intubation and death, similar to the study by Innocenti et al. but different from the Duan study where only the need for orotracheal intubation was taken as a result. However, more studies are needed to carefully evaluate these hypotheses.
In our study, the best cut-off point for the ROX index to determine the success of HFNC was 5.62 (sensitivity 62% specificity 65%) and not 4.88, as previously established by Roca et al. (10). On the other hand, the highest cut-off point of the HACOR scale to define the success of the HFNC was 5.5 (sensitivity 66%, specificity 65%), similar to that previously reported in the literature (16,17,18,20).
Interestingly, the HACOR scale was statistically significant in the multivariate analysis when comparing variables that are not included in the calculation of this scale, unlike the ROX index, which did not achieve statistical significance. We believe that this finding is due to the fact that the HACOR scale uses a greater number of variables that reached statistical significance such as the Glasgow scale and that are not part of the ROX index. However, the discrimination capacity of the HACOR and ROX scales is similar. Given that the outcome we seek to avoid is mortality, we suggest using both scales to define the failure of the HFNC, which would provide greater safety for the patient, although this would imply a closer monitoring of the person.
Although the predictive capacity of both scales is adequate, we believe that it was not so high that it could be used as the sole criterion to predict failure of the HFNC. Therefore, we consider it necessary to add to these tools clinical variables that were also associated with the outcome of interest, such as a history of atrial fibrillation, hypertension, and chronic kidney disease. These variables could lead to the development of new models that allow a better prediction of the failure of the HFNC. New studies will be necessary to propose and evaluate these models.
Within the strengths of the study, this is the first study to compare the ability to predict cannula failure of the ROX and HACOR scales. Furthermore, it is one of the individual studies with the largest number of patients evaluated with HFNC and is the first to describe the discriminative capacity of the HACOR scale in patients with COVID19 pneumonia. Finally, we did not have data loss and we were able to count the outcomes of all the patients. Among the limitations of the study is the fact that the criteria to define the OTI requirement depended directly on the treating physician. However, the criteria for therapeutic failure to HFNC are clearly defined in our institution and these are part of a management protocol, which is why we believe that the decision for mechanical ventilation is similar among medical personnel.