We were able to make accurate ED admission predictions using readily available clinical variables (age, gender, presenting complaint, comorbidities) and non-clinical variables (geographic location of ED, referral source, receiving home care services) known to paramedics prior to ED transport that highlight a plausible stratification of emergently triaged patients. The acceptable algorithm results demonstrated that prehospital characteristics have predictive validity to forecast ED visit dispositions even prior to ED arrival. In the absence of additional important clinical and non-clinical variables, we were able to compute acceptable AUC outputs of 0.77-0.78 and probabilistic accuracy scores of 0.22-0.24 across all algorithms. All machine learning algorithms performed similarly in all measures of statistical precision (sensitivity, specificity).
We found that that older age, living in a residential facility, presenting to ED with a respiratory complaint, and receiving home care were the most informative predictors of hospital admission. These findings are consistent with previous literature which analyzed admission predictors of unscheduled ED visits.(22–25) A plethora of research has been dedicated to examining variables predictive of admission in the older adult cohorts, yielding results consistent with our predictors.(26–29) Receiving home care was included less as an admission predictor in the literature, representing a plausible underreporting of this variables influence on ED visit dispositions. Our results highlight that later-stages of life and requiring support care (residential or institutional) are the driving forces of ED admission from prehospital patient characteristics.
Several characteristics such as the ED located in an urban region, presenting complaints related to environmental reasons or the skin, comorbidities of bowel disease or asthma, and referral from ambulatory care services or private practices were not informative in predicting hospital admissions. Our non-informative predictors were somewhat consistent with prior work.(4,30) Specifically, comorbidities of asthma and diabetes are reported as risk markers to hospital admission, although not consistently in the literature.(31,32) Our study determined these two predictors were not informative of forecasting admission, but this could be a result of analyzing only paramedic transported visits in our study, where paramedics could have treated asthma or diabetes conditions prior to ED arrival in the prehospital field, thereby decreasing the likelihood of need for admission.
To our knowledge, our study is the first to employ machine learning algorithms to predict ED outcomes using data known prehospital to paramedics. Thus, our study contributes novel research to the scientific literature, and showcases a framework for future machine learning studies in the prehospital and paramedic fields. Given the easy accessibility of these characteristics to paramedics, stakeholders of paramedic practices and policymakers should consider incorporating the most important predictors into any future modifications of patient distribution legislation or clinical decision rules for paramedics.
With advanced knowledge of which patient characteristics are most predictive of admission, a patient distribution protocol could be constructed to stratify a two-tier emergently triaged patient cohort. The first subgroup could be defined as emergently triaged patients with a high predicted probability of admission who must be transported to the closest ED. The second subgroup would be patients emergently triaged but with low predicted probability of admission, who could be transported to the most appropriate ED, not necessarily the closest. Future research is needed to delineate the inclusion criteria of subgroups within emergently triaged patients, but our study is hypothesis generating and supports research to further explore this concept. Integration of threshold tuning to identify an ideal cut-point in the predicted probability with an acceptable sensitivity could be beneficial in defining the subgroups. Stratification of patients assigned an emergent triage score into two subgroups could optimize patient distribution, improve ED congestion and plausibly improve patient-important outcomes
Bearing in mind that the discriminative and calibration accuracy of the LR model was similar to more advanced ML algorithms, it is worth nothing that this model may be best for pragmatic implementation and decision-making at the clinical and policy level. Relative odds and confidence interval interpretation are standard in medical education, whereas ML interpretation is not. Additionally, the simplicity of LR supports ease of implementation of study findings towards the use of clinical decision rules and uptake of study findings by medical and health policy professionals, who are mostly likely to influence direct practice change.
An overarching goal of this study was to determine if patient characteristics known prehospital could be predictive of ED visit dispositions prior to arrival. Our study demonstrated that prehospital patient characteristics have predictive utility of a forthcoming ED visit. We establish that ML has ample utility for integration into prehospital research, and can be an important methodology to optimize paramedic clinical practices and logistical effectiveness. Inclusion of paramedic medical reports, in addition to ED administrative data resources, would undoubtedly increase the probabilistic accuracy of predictive algorithms, and contribute variables that encompass a more complete prehospital patient presentation than ED resources alone.
Future research should leverage ML to analyze the utility of patient characteristics to predict ED visit dispositions in low acuity transports. Ontario paramedics may be granted authorization to transport low acuity patients to non-ED community-based care alternatives, though identification and classification of suitable patients for redirection from ED is challenging prehospital.(33) Future research on low acuity transports should utilize ML to investigate which patient characteristics are most predictive of an ED visit that is both discharged and did not require any the emergency medicine intervention.(33) Knowledge of these predictors would be beneficial to support paramedic clinical guideline development to identify patients potentially suitable for redirection, given clinical information is limited prehospital to paramedics.
Limitations
Additional administrative clinical and non-clinical variables known to paramedics prehospital could not be included in this study, as this data is not recorded in NACRS. Accessibility of paramedic administrative data resources remains a constant challenge in Ontario, all data are held within each of 52 paramedic service independently and do not regularly permit access for research.(7) Additionally, potentially influential characteristics known prehospital that are accessible through other ICES administrative databases (i.e. prescription medications, time of visit, caregiver attendance) could have been included in our study, but were excluded due to their large incompleteness. However, we do not believe these clinical factors would have made sizable impact to our results.