Abstract
ObjectivesTo calculate fractional inspired oxygen concentration (FiO2) thresholds in ward patients and add these to the National Early Warning Score (NEWS). To evaluate the performance of NEWS-FiO2 against NEWS when predicting in-hospital death and unplanned intensive care unit (ICU) admission. MethodsA multi-centre, retrospective, observational cohort study was carried out in five hospitals from two UK NHS Trusts. Adult admissions with at least one complete set of vital sign observations recorded electronically were eligible. The primary outcome measure was an ‘adverse event’ which comprised either in-hospital death or unplanned ICU admission. Discrimination was assessed using the Area Under the Receiver Operating Characteristic curve (AUROC). ResultsA cohort of 83,304 patients from a total of 271,363 adult admissions were prescribed oxygen. In this cohort, NEWS-FiO2 (AUROC 0.823, 95% CI 0.819–0.824) outperformed NEWS (AUORC 0.811, 95% CI 0.809–0.814) when predicting in-hospital death or unplanned ICU admission within 24 h of a complete set of vital sign observations. ConclusionsNEWS-FiO2 generates a performance gain over NEWS when studied in ward patients requiring oxygen. This warrants further study, particularly in patients with respiratory disorders.
Highlights
An Early Warning Score (EWS) identifies clinical deterioration in hospitalised patients using simple algorithms that sum integer scores assigned to values of individual vital sign observations[1] The score increases as the vital signs become more abnormal
Techniques that minimise this information loss by using the fractional inspired oxygen as an alternative or adjunct to SpO2 to construct an EWS are relatively under-developed, and are mainly used in obstetric populations[8,9] The National Early Warning Score (NEWS) is the most widely adopted in the UK and scores in a binary manner for oxygen use.[10,11]
One database contained vital signs, oxygen administration data and patient outcome data on all patients admitted to the four acute care hospitals in the Oxford University Hospitals NHS Foundation Trust (OUHNHSFT) between October 2014 and October 2016 where vital sign recordings were taken at the bedside using the System for Electronic Notification and Documentations (SEND, Sensyne Health, www.sensynehealth.com)[14] The second database contained similar data on patients admitted to the Queen Alexandra Hospital (QAH), an acute care hospital in Portsmouth, between January 2010 and May 2016 where vital sign recordings were taken using CareFlow Vitals (System C Healthcare, www.systemc.com)
Summary
An Early Warning Score (EWS) identifies clinical deterioration in hospitalised patients using simple algorithms that sum integer scores assigned to values of individual vital sign observations[1] The score increases as the vital signs become more abnormal. Patients with a low SpO2 are often treated by increasing their inspired oxygen fractional concentration (FiO2), which returns their SpO2 value to normal and makes the FiO2 the important value for detecting deterioration[5,6] Despite this, FiO2 is not part of any widely implemented EWS7 Techniques that minimise this information loss by using the fractional inspired oxygen as an alternative or adjunct to SpO2 to construct an EWS are relatively under-developed, and are mainly used in obstetric populations[8,9] The National Early Warning Score (NEWS) is the most widely adopted in the UK and scores in a binary manner for oxygen use (scoring zero for room air and two for all forms of supplementary oxygen).[10,11] As a result, it may be that important information about respiratory dysfunction in ward patients is being lost in NEWS, impairing its performance. This study was designed to test the hypothesis that adding FiO2 to NEWS would improve the predictive performance of the score when used in patients requiring oxygen.[12]
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