Advantages and limitations of the ROX index

Association between the ROX index and mortality in patients with acute hypoxemic respiratory failure: a retrospective cohort study

BACKGROUND

Although ROX index is frequently used to assess the efficacy of high-flow nasal cannula treatment in acute hypoxemic respiratory failure (AHRF) patients, the relationship between the ROX index and the mortality remains unclear. Therefore, a retrospective cohort study was conducted to evaluate the ability of the ROX index to predict mortality risk in patients with AHRF.

METHOD

Patients diagnosed with AHRF were extracted from the MIMIC-IV database and divided into four groups based on the ROX index quartiles. The primary outcome was 28-day mortality, while in-hospital mortality and follow-up mortality were secondary outcomes. To investigate the association between ROX index and mortality in AHRF patients, restricted cubic spline curve and COX proportional risk regression were utilized.

RESULT

A non-linear association (L-shaped) has been observed between the ROX index and mortality rate. When the ROX index is below 8.28, there is a notable decline in the 28-day mortality risk of patients as the ROX index increases (HR per SD, 0.858 [95%CI 0.794-0.928] P < 0.001). When the ROX index is above 8.28, no significant association was found between the ROX index and 28-day mortality. In contrast to the Q1 group, the mortality rates in the Q2, Q3, and Q4 groups had a substantial reduction (Q1 vs. Q2: HR, 0.749 [0.590-0.950] P = 0.017; Q3: HR, 0.711 [0.558-0.906] P = 0.006; Q4: HR, 0.641 [0.495-0.830] P < 0.001).

CONCLUSION

The ROX index serves as a valuable predictor of mortality risk in adult patients with AHRF, and that a lower ROX index is substantially associated with an increase in mortality.

High flow nasal oxygen vs. conventional oxygen therapy over respiratory oxygenation index after esophagectomy: an observational study

Background

Postoperative pulmonary complications after esophagectomy still represent a matter of concern. High flow nasal cannula (HFNC) early after major abdominal and thoracic surgery has demonstrated some advantages over conventional oxygen therapy. Data about respiratory effect of HFNC after esophagectomy is scarce. The primary aim of this study is to investigate if the early use of HFNC after esophagectomy could enhance patients' postoperative respiratory oxygenation (ROX) index and, ultimately, reduce postoperative pneumonia.

Methods

In this single center retrospective study all patients undergoing to esophagectomy for cancer from May 2020 to November 2022 were evaluated. Historical cohort (HC) received postoperative oxygen supplementation with Venturi mask or nasal goggles, and a cohort was put under HFNC (HFNC cohort). ROX index, blood gas analysis, radiological atelectasis score (RAS), post-operative complications' data and information on hospital stay have been collected and analyzed.

Results

Seventy-one patients were included for the final statistical analysis, 31 in the HFNC and 40 in the HC cohort. Mean age was 64±10 years and body mass index (BMI) was 26 [24-29] kg/m2. ROX index was higher in the HFNC patients than in the HC, 20.8 [16.7-25.9] vs. 14.9 [10.8-18.2] (P<0.0001). In the HFNC cohort patients, pH was higher, 7.42 [7.40-7.44] vs. 7.39 [7.37-7.43] than HC, while PaCO2 was lower in HFNC cohort compared with HC, 39 [36-41] vs. 42 [39-45] mmHg, respectively (P=0.01). RAS was similar between the two cohorts of patients, 1.5±0.98 vs. 1.4±1.04 in the HFNC and the HC cohort, respectively (P=0.611). Lower acute respiratory failure (ARF) rate was recorded among HFNC than HC cohort, 0% vs. 13% respectively, P=0.06. No difference in pneumonia frequency between two cohorts was shown.

Conclusions

HFNC improved the ROX index after esophagectomy through significant respiratory rate reduction. This tool should be considered for early respiratory support after extubation in this category of patients, not only as a rescue therapy for ARF, but also to optimize early postoperative respiratory function. Whether this will improve patients' outcomes requires further large randomized controlled trials.

The Validity of the ROX Index and APACHE II in Predicting Early, Late, and Non-Responses to Non-Invasive Ventilation in Patients with COVID-19 in a Low-Resource Setting

The use of the Ratio of Oxygen Saturation (ROX) index to predict the success of high-flow nasal oxygenation (HFNO) is well established. The ROX can also predict the need for intubation, mortality, and is easier to calculate compared with APACHE II. In this prospective study, the primary aim is to compare the ROX (easily administered in resource limited setting) to APACHE II for clinically relevant outcomes such as mortality and the need for intubation. Our secondary aim was to identify thresholds for the ROX index in predicting outcomes such as the length of ICU stay and failure of non-invasive respiratory support therapies and to assess the effectiveness of using the ROX (day 1 at admission, day 2, and day 3) versus Acute physiology and chronic health evaluation (APACHE) II scores (at admission) in patients with Coronavirus Disease 2019 (COVID-19) pneumonia and Acute Respiratory Distress Syndrome (ARDS) to predict early, late, and non-responders. After screening 208 intensive care unit patients, a total of 118 COVID-19 patients were enrolled, who were categorized into early (n = 38), late (n = 34), and non-responders (n = 46). Multinomial logistic regression, receiver operating characteristic (ROC), Multivariate Cox regression, and Kaplan-Meier analysis were conducted. Multinomial logistic regressions between late and early responders and between non- and early responders were associated with reduced risk of treatment failures. ROC analysis for early vs. late responders showed that APACHE II on admission had the largest area under the curve (0.847), followed by the ROX index on admission (0.843). For responders vs. non-responders, we found that the ROX index on admission had a slightly better AUC than APACHE II on admission (0.759 vs. 0.751). A higher ROX index on admission [HR (95% CI): 0.29 (0.13-0.52)] and on day 2 [HR (95% CI): 0.55 (0.34-0.89)] were associated with a reduced risk of treatment failure. The ROX index can be used as an independent predictor of early response and mortality outcomes to HFNO and NIV in COVID-19 pneumonia, especially in low-resource settings, and is non-inferior to APACHE II.

Daily ROX index can predict transitioning to mechanical ventilation within the next 24 h in COVID-19 patients on HFNC

INTRODUCTION

High flow nasal cannula (HFNC) is used to prevent invasive ventilation in COVID-19-associated hypoxemia. The respiratory rate‑oxygenation (ROX) index has been reported to predict failure of HFNC in patients with COVID-19 pneumonia during the intensive care unit stay when measured in first hours of therapy. However, the clinical course of ICU patients may change substantially in the first days of admission. The objective of this study was to investigate whether ROX index obtained in the first four days of ICU admission could predict the need for invasive respiratory support within the next 24 h of measurements.

METHODS

A retrospective cross-sectional study was performed using a database that included adult patients with COVID-19 pneumonia treated in the ICU. Patients were followed from ICU admission and ROX index was calculated daily on HFNC. Receiver operating characteristics curves (ROCs) were performed.

RESULTS

Two hundred forty-nine patients were enrolled, 48% of whom require mechanical ventilation (MV). The area under the ROC of the pooled 4-day values of the ROX index as a predictor of transition from HFNC to MV within 24 h of measurements was 0.86 (95%CI 0.83 to 0.88, P < 0.001) with a cutoff point of 4.06.

CONCLUSION

In COVID-19 patients in high flow nasal cannula, daily ROX index measurements successfully predicted transition to mechanical ventilation within the next 24 h.

The Relationship of Respiratory Rate-Oxygenation (ROX) and Modified ROX Index With High-Flow Nasal Cannula Oxygen Therapy in COVID-19 Patients: An Observational Pilot Study

Background and aim Respiratory Rate-Oxygenation (ROX) and modified ROX (mROX) indexes have been proposed to detect early high-flow nasal cannula (HFNC) therapy failure. We evaluated the utility and relationship of ROX and mROX indexes in COVID-19 patients started on HFNC oxygen therapy. Methods This pilot study collected data from adult COVID-19 patients requiring HFNC oxygenation from 29 Jan - 29 Jun 2021. The patients were divided into two cohorts based on HFNC therapy success. ROX and mROX were compared using statistical diagnostic testing, including receiver operating characteristics and area under the curve (AUC) using online Epitools (https://epitools.ausvet.com.au/) and MedCalc software (MedCalc Software Ltd, Ostend, Belgium, https://www.medcalc.org/); p<0.05 was considered significant. Results Twenty-seven patients fulfilled the inclusion criteria; 48.15% of therapy failed. The cohort's mean ± standard deviation age was 53.93 ± 10.67 years; 74.1% were male. The accuracy of predicting failure for mean ROX versus mROX at baseline and six-hour values was 59.81 versus 70.68 and 67.42 versus 74.88, respectively (all p>0.05). The AUC for ROX and mROX at baseline and at six hours were statistically indifferent. Only an mROX of 4.05 (mean value) and 3.34 (Youden's J cut-off) had a sensitivity plus specificity at 156% and 163%, respectively. Conclusion Both ROX and mROX at baseline and six hours had fair-to-good accuracies and AUC; the differences were insignificant. Both ROX and mROX had better accuracies at six hours. However, only mROX < 4.05 at six hours fulfilled the sensitivity plus specificity criteria to be a clinically valuable screener.