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Paediatric Index of Mortality 3 in Sweden: Validation and Recalibration to Improve Mortality Prediction in Paediatric
Lars Engerström1,2, Shanay Daham3,4, Staffan Eksborg3,5
1Department of Anaesthesiology and Intensive Care and Department of Biomedical and Clinical Sciences, Linköping University, Norrköping, Sweden.
Insights
The Paediatric Index of Mortality 3 (PIM3) overestimated mortality in Swedish pediatric intensive care units (PICUs) and general intensive care units (ICUs). Recalibration improved PIM3 accuracy, reducing outcome differences between PICU and ICU settings.
Area of Science:
- Pediatric critical care medicine
- Health services research
- Biostatistics
Background:
- Sweden utilizes a mixed system of dedicated pediatric intensive care units (PICUs) and general intensive care units (ICUs) for critically ill children.
- The Paediatric Index of Mortality 3 (PIM3) is a global standard for risk stratification in pediatric intensive care.
Purpose of the Study:
- To validate the PIM3 model in a national Swedish cohort of critically ill children.
- To recalibrate the PIM3 model to the Swedish population if necessary.
- To compare the performance of PIM3 between PICUs and ICUs.
Main Methods:
- A retrospective cohort study utilizing prospectively collected data from the Swedish Intensive Care Registry.
- Data spanned admissions from January 1, 2016, to September 30, 2022.
- Statistical analysis included assessment of discrimination and calibration, with logistic regression used for recalibration.
Main Results:
- The study included 19,183 admissions.
- Before recalibration, PIM3 overestimated mortality: Standardized Mortality Ratios (SMRs) were 0.72 in PICUs and 0.52 in ICUs.
- After recalibration, SMRs approached 1 (0.92 in PICUs, 0.96 in ICUs), indicating improved accuracy.
Conclusions:
- The PIM3 model showed excellent discrimination but systematically overestimated mortality in Sweden.
- Recalibration effectively corrected the overestimation bias.
- The recalibrated PIM3 model reduced observed outcome disparities between PICU and ICU settings.
Aim:
In Sweden, critically ill children are admitted to one of four dedicated paediatric intensive care units (PICUs) or general intensive care units (ICUs), reflecting a partly centralised system. The Paediatric Index of Mortality 3 (PIM3) is a widely used risk stratification tool for predicting mortality in critically ill children. This study aimed to validate PIM3 in a national Swedish cohort, recalibrate the model where indicated and compare outcomes between PICUs and ICUs.
Methods:
This retrospective cohort study used prospectively collected data from the Swedish Intensive Care Registry of admissions reported between 1 January 2016 and 30 September 2022. Discrimination and calibration were assessed, and recalibration was performed using logistic regression.
Results:
19 183 admissions were included, 10 714 males and 8469 females. Prior to recalibration, PIM3 overestimated mortality in both settings, with standardised mortality rates (SMRs) of 0.72 (95% Confidence Interval (CI) 0.64-0.80) in PICUs and 0.52 (95% CI 0.42-0.63) in ICUs. Following recalibration, SMR was 0.92 (95% CI 0.70-1.20) and 0.96 (95% CI 0.59-1.49) in PICUs and ICUs, respectively.
Conclusion:
PIM3 demonstrated excellent discrimination but systematically overestimated mortality in the Swedish context. Recalibration corrected this bias and attenuated outcome differences between PICU and ICU settings.
