EXTERNAL VALIDATION OF THE IMPROVING PARTIAL RISK ADJUSTMENT IN SURGERY (PRAIS2) MODEL FOR 30-DAY MORTALITY AFTER PEDIATRIC CARDIAC SURGERY
Authors: Cocomello Lucia , Caputo Massimo , Cornish Rosie , Lawlor Deborah A. 
Published: April 2020

Objective

Risk stratification in paediatric patients undergoing heart surgery remains a challenge. The improving partial risk adjustment in surgery (PRAIS2) is a risk model predicting 30-day mortality which has been recently developed and validated using a UK-based cohort from April 2009-March 2015. We aimed to perform an independent temporal external validation to explore its generalisability and clinical utility.

Methods

PRAIS2 validation was carried out using a single centre (Bristol, UK) cohort from April 2004 to March 2009 and April 2015 to July 2019. For each subject PRAIS2 score was calculated according to the original formula. PRAIS2 performance was assessed in terms of discrimination by means of ROC curve analysis and calibration by using the calibration belt method.

Results

A total of 1330 (2004-2009) and 1187 (2015-2019) paediatric cardiac surgical procedures were included in the first and second independent validation, respectively (median age at the procedure 6.0 and 6.9 months). PRAIS2 score showed excellent discrimination for both independent validations (AUC 0.72 (95%CI: 0.65 to 0.80) and 0.87 (95%CI: 0.82 to 0.93), respectively). While PRAIS2 was only marginally calibrated in the first validation, with a tendency to underestimate risk P-value = 0.051), the second validation showed good calibration with 95% confidence belt containing the bisector for predicted mortality (P-value = 0.15); We also observed good performance in the subgroup of patients undergoing non-elective procedures (N = 482; AUC 0.78 (95%CI 0.68 to 0.87); Calibration belt containing the bisector (P-value=0.61).

Conclusions

In a single centre UK-based cohort, PRAIS2 showed excellent discrimination and calibration in predicting 30-day mortality in paediatric cardiac surgery including in those undergoing non-elective procedures. Our results support a wider adoption of PRAIS2 score in the clinical practice.

Strengths and limitations of this study

A strength of the present study is that data were prospectively collected as part of the UK National Congenital Heart Disease Audit and as such they undergo continuous and inclusive systematic validation that includes the review of a sample of case notes by external auditors to ensure coding accuracy.

We used a recently proposed method (calibration belt) which does not require patients to be categorised according to risk percentile but rather provides a risk function across all risk value with relative uncertainty measure (95% CI)

A key limitation of this study is that the sample size is relatively small and considerably smaller than the cohort used to develop PRAIS2

Key questions

What is already known about this subject? The improving partial risk adjustment in surgery (PRAIS2) is a risk model predicting 30-day mortality which has been recently developed and validated using a UK-wide cohort.

What does this study add? The present study reported the first independent external validation of the PRAIS2 using a single centre cohort which confirmed excellent performance of the model and for the first time showed that it also accurately predicts mortality in patients undergoing non-elective procedures

How might this impact on clinical practice? Our results support a wider adoption of the PRAIS2 in the clinical practice.