Forecasting ICU Census by Combining Time Series and Survival Models

Abstract

OBJECTIVES: Capacity planning of ICUs is essential for effective management of health safety, quality of patient care, and the allocation of ICU resources. Whereas ICU length of stay (LOS) may be estimated using patient information such as severity of illness scoring systems, ICU census is impacted by both patient LOS and arrival patterns. We set out to develop and evaluate an ICU census forecasting algorithm using the Multiple Organ Dysfunction Score (MODS) and the Nine Equivalents of Nursing Manpower Use Score (NEMS) for capacity planning purposes. DESIGN: Retrospective observational study. SETTING: We developed the algorithm using data from the Medical-Surgical ICU (MSICU) at University Hospital, London, Canada and validated using data from the Critical Care Trauma Centre (CCTC) at Victoria Hospital, London, Canada. PATIENTS: Adult patient admissions (7,434) to the MSICU and (9,075) to the CCTC from 2015 to 2021. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We developed an Autoregressive integrated moving average time series model that forecasts patients arriving in the ICU and a survival model using MODS, NEMS, and other factors to estimate patient LOS. The models were combined to create an algorithm that forecasts ICU census for planning horizons ranging from 1 to 7 days. We evaluated the algorithm quality using several fit metrics. The root mean squared error ranged from 2.055 to 2.890 beds/d and the mean absolute percentage error from 9.4% to 13.2%. We show that this forecasting algorithm provides a better fit when compared with a moving average or a time series model that directly forecasts ICU census. Additionally, we evaluated the performance of the algorithm using data during the global COVID-19 pandemic and found that the error of the forecasts increased proportionally with the number of COVID-19 patients in the ICU. CONCLUSIONS: It is possible to develop accurate tools to forecast ICU census. This type of algorithm may be important to clinicians and managers when planning ICU capacity as well as staffing and surgical demand planning over a short time horizon.

Modelagem Matemática para a Alocação de Leitos de UTI com Diferentes Tipos de Leitos e Taxa de Ocupação

“…Um protocolo estruturado foi proposto em conjunto com os médicos, com base na pontuac ¸ão SOFA (Avaliac ¸ão Sequencial de Falha de Órgãos). [Murray et al 2023] desenvolveram um modelo autorregressivo de série temporal de média móvel integrada, que prevê a chegada de pacientes à UTI e um modelo de sobrevivência usando MODS, NEMS e outros fatores para estimar o tempo de permanência do paciente.…”

“…Diversos modelos focam na alocac ¸ão de recursos escassos [Frej et al 2021, White et al 2021, no planejamento para diferentes cenários de COVID-19 [Schmidt et al 2021], ou na análise de decisões de admissão e alta de pacientes [de Vicuña Bilbao and de Vicuña Bilbao 2022]. Existem também pesquisas que abordam a atribuic ¸ão de leitos a pacientes com base em estimativas de sobrevivência e custos [Karboub and Tabaa 2023], na otimizac ¸ão da saída de pacientes da UTI [Valeva et al 2023], e na previsão da demanda e do tempo de permanência [Frej et al 2023, Murray et al 2023. A proposta deste trabalho se insere nesse contexto, mas se diferencia por considerar a alocac ¸ão em diferentes tipos de leitos e uma taxa de ocupac ¸ão ideal, além de realizar simulac ¸ões com diferentes níveis demandas.…”