Comparison of Standardized Mortality Ratios in seven Dutch EDs based on presenting complaints

Abstract

Background: Comparison of emergency departments (EDs) becomes more important, but differences are difficult to interpret because of the heterogeneity of the ED population regarding reason for ED presentation. The aim of this study was two-fold: First to compare patient characteristics (including diagnoses) across 7 EDs. Secondly, to compare Standardized Mortality Ratios (SMRs) across 7 EDs and in subgroups of ED patients categorized by presenting complaints (PCs).

Methods: Observational multicenter study including all consecutive visits of 7 Dutch (two tertiary care centre and 5 teaching hospitals) EDs. Patient characteristics, including PCs as part of triage systems, and SMRs (observed divided by expected in-hospital mortality) per ED and for the most common PCs (PC-SMRs) were compared across EDs and presented as funnel plots. The expected mortality was calculated with a prediction model, which was developed using multivariable logistic regression in the overall population and for PCs separately. Demographics, disease severity, diagnoses, proxies for comorbidity and complexity, and PCs (overall population only) were incorporated as covariates.

Results: We included 693,289 ED visits from January 1, 2017 to June 31, 2023, with a median age of 56 years, of which 47.9% were women and 1.9% died. Patient characteristics varied markedly among EDs. Expected mortality was similar in prediction models with or without diagnoses as covariate. SMRs differed across EDs, ranging from 0.80 to 1.44. All EDs had SMRs within the 95%-Confidence Intervals of the funnel plot apart from one ED, which had an higher than expected SMR. However, PC-SMRs showed more variation and more EDs had SMRs falling outside the funnel, either higher or lower than expected. The ranking of SMRs across EDs was PC-dependent and differences across EDs are present only for specific PC-SMRs, such as in "dyspnea" and "feeling unwell".

Conclusion: In summary, patient characteristics and mortality varied largely across Dutch EDs, and expected mortality across EDs is well assessed in PC subgroups without adjustment for final diagnoses. Differences in SMRs across EDs are PC-dependent. Future studies should investigate reasons of the differences in PC-SMRs across EDs and whether PC-targeted quality improvement programs can improve outcomes.

Keywords: Emergency department; In-hospital mortality; Presenting complaints; Risk stratification; Standardized mortality ratio; Symptom-based; Symptom-oriented research.

Fig. 1

Patient flow through study. Study design and patient flow in study. The model uses the following potential confounders: age, gender, triage category, Glasgow Coma Scale, vitalscore- a categorical item composed of respiratory rate O2 saturation, systolic and diastolic blood pressure, heart rate,and temperature (See supplement) medication yes/no, number of consultation, addtional investigations yes/no: blood tests, radiology imaging and PCs. Models after stratification by PC do not include PCs. Abbreviations: NEED =Nederlandse Emergency department Evaluation Database,ED=emergency department,PC = presenting complaint, SMR = standardized mortality ratio

Fig. 2

Expected in-hospital mortality with and without ICD-10 codes as covariates in model in subgroups of patients by six most common PCs in five Dutch EDs The figure above is the result of the analysis in the cohort from which complete data on ICD-10 codes are available. This analysis assessed the effect of additional risk adjustment with diagnoses on the expected (predicted) mortality of PCs in participating EDs. In this cohort, data from five EDs (B, C, D, E, and G) were used, where complete diagnostic data on ED visits were available according to the International Classification of Diseases, 10th Revision (ICD-10) codes. No ICD-10 codes are known from ED A and ED F and therefore not presented in the figure. Expected mortality without adjustment for diagnosis groups (-) was calculated with multivariable binary logistic regression adjusted for: age, sex, triage category, vital score**, GCS-score, number of specialist consultations during ED stay, blood tests taken, radiology imaging performed, medication yes/no and PCs. For the expected mortality calculated including adjustment for diagnoses (+), in addition to the previously mentioned covariates for mortality, the 5 most common diagnosis groups as described in the ICD-10 coding system plus a residual group with other diagnoses were added as dummy variables for each PC. See Table 2 for most common diagnosis groups. Abbreviations: PC = presenting complaint, ED = Emergency Department, ICD-10 codes = International Classification of Diseases and health related problems 10th edition, GCS = Glasgow Coma Score. **vital score: a categorical item composed of respiratory rate, O2 saturation, systolic and diastolic blood pressure, heart rate and temperature; see figure S1, supplementary file 1

Fig. 3

Funnel plot with standardized mortality ratios of seven Dutch EDs. The figure above is the result of the analysis in which the cohort includes seven EDs over the period from January 2017 through June 2023. On the Y-axis the SMR (Observed/Expected), on the X-axis (precision) the number of cases. The funnel lines represent the 95% confidence intervals for the SMRs, based on the total population. SMRs were computed by dividing the number of observed deaths by the number of predicted deaths in the given population. An SMR value above 1 was interpreted to mean that more deaths than expected occurred in an ED; conversely, a value below 1 was interpreted to mean that there were fewer deaths than expected. The expected mortality is calculated with multivariable binary logistic regression adjusting for: age, sex, triage category, vital score**, GCS-score, number of consultations, blood tests taken, radiology imaging performed and medication yes/no and PCs. Abbreviations: PC=presenting complaint, ED=Emergency Department, SMR=standardized mortality ratio, GCS= Glasgow Coma Score. **vital score: a categorical item composed of respiratory rate, O2 saturation, systolic and diastolic blood pressure, heart rate and temperature; figure S1, supplementary file 1

Fig. 4

Funnel plot with standardized mortality ratios of in subgroups of patients by six most common presenting complaints in seven Dutch EDs. The figure above is the result of the analyses in which the cohort includes seven EDs over the period from January 2017 through June 2023. On the Y-axis the SMR (Observed/Expected), on the X-axis (precision) the number of cases. The funnel lines represent the 95% confidence intervals for the SMRs, based on the total PC populations. SMRs were computed by dividing the number of observed deaths by the number of predicted deaths in the given population. An SMR value above 1 was interpreted to mean that more deaths than expected occurred in an ED; conversely, a value below 1 was interpreted to mean that there were fewer deaths than expected. The expected mortality in EDs per PC is calculated with multivariable binary logistic regression adjusting for: age, sex, triage category, vital score**, GCS-score, number of consultations, blood tests taken, radiology imaging performed and medication yes/no. Abbreviations: PC=presenting complaint, ED=Emergency Department, SMR=standardized mortality ratio, GCS= Glasgow Coma Score. **vital score: a categorical item composed of respiratory rate, O2 saturation, systolic and diastolic blood pressure, heart rate and temperature; figure S1, supplementary file 1