The relation between TISS and real paediatric ICU costs: a case study with generalizable methodology

Objective: To determine the quantitative relation between the Therapeutic Intervention Scoring System (TISS) in combination with other relevant clinical variables and the real costs of (paediatric) intensive care. Design: A prospective, observational study. Setting: A Ten-bed paediatric intensive care unit in a university children's hospital. Patients and participants: In a 17-months registration period we collected patient- and treatment-related data for all 611 consecutive admissions. A 21-day calibration period was used to collect detailed data to calculate the real costs of 33 consecutive admissions, in addition to the same data as in the registration period. Measurements and results: We used the Multi Moment Measurement method to measure time spent by nurses and physicians and medication used in the 21-day calibration period. The calibration period data set with explanatory variables including TISS was used to build a regression model to estimate nurse and physician time, which were converted to personnel costs, and to estimate medication costs. The regression models built from the calibration period were subsequently used to estimate the total costs per day and per admission in different patient groups in the registration period. Conclusion: It was feasible to calculate total direct medical costs based on a limited number of readily available clinical variables related to patient characteristics and treatment, of which TISS was the most important determinant. The proposed methods provide further tools for assessment of (paediatric) intensive care unit performance.