Predictive Value of SpO2/RR Ratio for Short-Term Intubation and Mortality Risks in Pre-ED Patients With Acute Dyspnea Without Oxygen Therapy: A Retrospective Cohort Study.

Abstract

Background: Dyspnea is a common and complex symptom in patients presenting to the emergency department, with multiple possible underlying diseases and a high risk of tracheal intubation or even death as the condition progresses. Therefore, an easily accessible, quick, and convenient index is needed to predict patient prognosis at emergency. A single measurement of peripheral capillary oxygen saturation (SpO₂) or respiratory rate (RR) is not sufficiently accurate, while other related indices are relatively complex. This study investigated the predictive value of the SpO₂/RR ratio (SR) in patients with acute dyspnea without oxygen therapy presenting to the emergency department.

Methods: This single-center retrospective analysis was conducted in the emergency department of Jiangsu Provincial Hospital of Traditional Chinese Medicine. Patients diagnosed with acute dyspnea without oxygen therapy who were presented to the emergency triage by the 120 ambulance were included. SR was calculated from the first vital signs obtained at the 120 ambulance real-time transmission system for vehicles. Patients were divided into three groups based on terciles. Kaplan-Meier analysis, Cox regression models, and restricted cubic splines (RCS) were used to examine the associations between SR and clinical outcomes.

Results: In total, 1339 patients were included. The rates of 7-day intubation and 28-day mortality differed significantly across SR groups (22.77%, 15.28%, 15.25%; p = 0.003) and (24.55%, 15.06%, 11.88%; p < 0.001), respectively. Cox regression and Kaplan-Meier analyses showed that lower SR was significantly associated with greater intubation and mortality risk (log-rank p = 0.003, p < 0.001). Subgroup and sensitivity analyses supported these findings, with the effect more pronounced in patients with an RR of ≥ 30 breaths/min. RCS nonlinear analysis revealed L-shaped associations between SR and 7-day intubation and 28-day mortality, with inflection points identified at 4.85 and 3.53.

Conclusion: A lower SR was associated with increased 7-day intubation and 28-day mortality in emergency department patients with acute dyspnea without oxygen therapy. Inflection points of 4.85 and 3.53 suggest that SR may serve as a useful prognostic indicator for identifying high-risk patients with acute dyspnea.Yuwei Tan and Sicheng Yuan contributed equally to this work and both as co-first authors.