Association of Prehospital Oxygen Saturation to Inspired Oxygen Ratio With 1-, 2-, and 7-Day Mortality

Francisco Martín-Rodríguez,Miguel A Castro Villamor,Carlos Del Pozo Vegas,Ancor Sanz-García,Juan F Delgado-Benito,Raúl López-Izquierdo,Guillermo J Ortega

doi:10.1001/jamanetworkopen.2021.5700

Abstract

The early identification of patients at high risk of clinical deterioration represents one of the greatest challenges for emergency medical services (EMS). To assess whether use of the ratio of prehospital oxygen saturation measured by pulse oximetry (Spo2) to fraction of inspired oxygen (Fio2) measured during initial contact by EMS with the patient (ie, the first Spo2 to Fio2 ratio) and 5 minutes before the patient's arrival at the hospital (ie, the second Spo2 to Fio2 ratio) can predict the risk of early in-hospital deterioration. A prospective, derivation-validation prognostic cohort study of 3606 adults with acute diseases referred to 5 tertiary care hospitals in Spain was conducted between October 26, 2018, and June 30, 2020. Eligible patients were recruited from among all telephone requests for EMS assistance for adults who were later evacuated with priority in advanced life support units to the referral hospitals during the study period. The primary outcome was hospital mortality from any cause within the first, second, third, or seventh day after EMS transport to the hospital. The main measure was the Spo2 to Fio2 ratio. A total of 3606 participants comprised 2 separate cohorts: the derivation cohort (3081 patients) and the validation cohort (525 patients). The median age was 69 years (interquartile range, 54-81 years), and 2122 patients (58.8%) were men. The overall mortality rate of the patients in the study cohort ranged from 3.6% for 1-day mortality (131 patients) to 7.1% for 7-day mortality (256 patients). The best model performance was for 2-day mortality with the second Spo2 to Fio2 ratio with an area under the curve of 0.890 (95% CI, 0.829-0.950; P < .001), although the other outcomes also presented good results. In addition, a risk-stratification model was generated. The optimal cutoff resulted in the following ranges of Spo2 to Fio2 ratios: 50 to 100 for high risk of mortality, 101 to 426 for intermediate risk, and 427 to 476 for low risk. This study suggests that use of the prehospital Spo2 to Fio2 ratio was associated with improved management of patients with acute disease because it accurately predicts short-term mortality.

Highlights

Emergency medical services (EMS) represent the initial contact between the patient and the health system, but it is usually the gateway for the patient to the emergency department.[1,2] New prehospital care procedures include different tools, such as the use of early warning scores,[3,4] which have the fundamental challenge of detecting patients at high risk of clinical deterioration
The best model performance was for 2-day mortality with the second oxygen saturation measured by pulse oximetry (SpO2) to fraction of inspired oxygen (FIO2) ratio with an area under the curve of 0.890, the other outcomes presented good results
The optimal cutoff resulted in the following ranges of SpO2 to FIO2 ratios: 50 to for high risk of mortality, to for intermediate risk, and to 476 for low risk

Summary

Introduction

Emergency medical services (EMS) represent the initial contact between the patient and the health system, but it is usually the gateway for the patient to the emergency department.[1,2] New prehospital care procedures include different tools, such as the use of early warning scores (eg, the National Early Warning Score, the VitalPAC Early Warning Score, and the Modified Early Warning Score),[3,4] which have the fundamental challenge of detecting patients at high risk of clinical deterioration. Oxygen saturation as measured by pulse oximetry (SpO2) is present in almost all the scores. The use of SpO2 is a routine, noninvasive, continuous, and safe standard procedure implemented in most multiparameter monitors in prehospital care, which, together with the use of capnography, can help to determine the patient’s ventilatory status more precisely.[5,6] In addition, as of the initial contact between EMS health care workers and the patient, the fraction of inspired oxygen (FIO2) is known precisely. The combined use of both parameters, known as the SpO2 to FIO2 ratio, has demonstrated its clinical utility in the context of hospital care, in intensive care units, for patients receiving noninvasive or invasive mechanical ventilation, even though it is not routinely used in prehospital care.[7,8]

Methods

Results

Discussion

Conclusion